No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
The course of bone healing is influenced by the initial shear fixation stability
Abstract
Fracture healing is influenced by fixation stability and experimental evidence suggests that the initial mechanical conditions may determine the healing outcome.
We hypothesised that mechanical conditions influence not only the healing outcome, but also the early phase of fracture healing. Additionally, it was hypothesised that decreased fixation stability characterised by an increased shear interfragmentary movement results in a delay in healing. Sixty‐four sheep underwent a mid‐shaft tibial osteotomy which was treated with either a rigid or a semirigid external fixator. Animals were sacrificed at 2, 3, 6 and 9 weeks postoperatively and the fracture callus was analysed using radiological, biomechanical and histological techniques.
The tibia treated with semi‐rigid fixation showed inferior callus stiffness and quality after 6 weeks. At 9 weeks, the calluses were no longer distinguishable in their mechanical competence. The calluses at 9 weeks produced under rigid fixation were smaller and consisted of a reduced fibrous tissue component. These results demonstrate that the callus formation over the course of healing differed both morphologically and in the rate of development.
In this study, we provide evidence that the course of healing is influenced by the initial fixation stability. The semi‐rigid fixator did not result in delayed healing, but a less optimal healing path was taken. An upper limit of stability required for successful healing remains unknown, however a limit by which healing is less optimal has been determined. © 2005 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.
... Third, mechanical conditions at the fracture are most critical immediately post-operatively, so for lower limb fixation this occurs during the toe-touch weight-bearing typically prescribed to patients for 6 weeks [ 12 , 13 , 16-18 ]. Fourth, shear interfragmentary motion (SIM) remains controversial regarding early callus formation [ 10 , 11 , 13 , 19-21 ], but some researchers recommend a ratio of SIM / AIM < 1.6 [13] . ...
... The FCL screw configurations with the 6 highest AIM FC values for promoting the earliest possible callus formation had to be excluded since they had excessive shear motion ratios of SIM FC /AIM FC and/or SIM NC /AIM NC > 1.6 [13] , which would impede early callus formation. Consequently, the optimal FCL screw configuration had 3 screws in plate holes #1, 5, and 6 ( Fig. 10 ) with the following properties ( Table 1 ). ...
... The combined average coefficient of variation caused by different FCL screw distribution at a given WL (i.e. standard deviation/average * 100) was 63.0% for plate σ MAX . and SIM NC /AIM NC ratios were < 1.6 [13] to ensure no delay in callus formation caused by shear. Von Mises σ MAX for femur shaft cortex, condylar cortex, plate, shaft FCL screws, and condylar locking screws reached various levels depending on the material and geometry, as expected [ 23 , 39 ]. ...
This finite element study optimized far cortical locking (FCL) technology for early callus formation in distal femur fracture fixation with a 9-hole plate using FCL screws proximal to, and standard locking screws distal to, the fracture. Analyses were done for 120 possible FCL screw configurations by varying FCL screw distribution and number. A hip joint force of 700 N (i.e. 100% x body weight) was used, which corresponds to a typical 140 N “toe-touch” foot-to-ground force (i.e. 20% x body weight) suggested to patients immediately after surgery. Increased FCL screw distribution (i.e. shorter plate working length) caused a decrease at the medial side and an increase at the lateral side of the axial interfragmentary motion (AIM), mildly affected shaft and condylar cortex Von Mises max stress (σMAX), increased plate σMAX, and decreased shaft FCL screw and condylar locking screw σMAX. Increased FCL screw number decreased AIM and σMAX on the shaft cortex, condylar cortex, plate, and FCL screws, but not condylar screws. The optimal FCL screw configuration had 3 FCL screws in plate holes #1, 5, and 6 (proximal to distal) for optimal AIM of 0.2 - 1 mm and reduce shear fracture motion, thereby encouraging early callus formation.
... Inadequately stiff metal implants may permit too much shear interfragmentary motion (SIM) leading to DH, but this is controversial [20][21][22] . One investigation showed that a semi-rigid external fixator that permitted more initial SIM at the time of longbone surgery eventually produced greater total callus area, mineralized bone area, and fibrous tissue area at 6 and/or 9 weeks after surgery vs. a rigid external fixator that permitted less initial SIM [21] . ...
... Inadequately stiff metal implants may permit too much shear interfragmentary motion (SIM) leading to DH, but this is controversial [20][21][22] . One investigation showed that a semi-rigid external fixator that permitted more initial SIM at the time of longbone surgery eventually produced greater total callus area, mineralized bone area, and fibrous tissue area at 6 and/or 9 weeks after surgery vs. a rigid external fixator that permitted less initial SIM [21] . Conversely, another study showed that axial callus stiffness at the longbone fracture site increased to a maximum at 4 weeks after nailing under isolated AIM, but it took 10-13 weeks for axial callus stiffness to reach a maximum under isolated translational or rotational SIM [22] . ...
... Also, prior steel vs. titanium distal femur/plate constructs under a 1200 N axial load had less SIM (medial-lateral component only) of 0.19-2.06 vs. 0.22-2.65 mm over a WL of 20-180 mm [30] ; this agrees with current results showing that steel plates allowed less SIM than titanium plates for all corresponding test cases ( Table 1 ). Another report of a distal femur fixed with a locked titanium plate under a 716 N axial load with various locations and/or materials for the screws produced a ratio of SIM/AIM at the fracture's medial side of 0.67 -1.2 [27] , which is less than the 1.6 value needed for early callus formation [21] ; similarly, 6 of 8 current SIM/AIM ratios for semi-rigid plates were below 1.6 ( Table 1 ), suggesting the healing benefits of AIM were not negated by SIM. ...
This proof-of-concept study designs distal femur fracture plates from semi-rigid materials vs. traditional metals for toe-touch weight-bearing recommended to patients immediately after surgery. The two-fold goal was to (a) reduce stress shielding (SS) by increasing cortical bone stress thereby reducing the risk of bone absorption and plate loosening, and (b) reduce delayed healing (DH) via early callus formation by optimizing axial interfragmentary motion (AIM). Finite element analysis was used to design semi-rigid plates whose elastic moduli E ensured plates permitted AIM of 0.2 - 1 mm for early callus formation. A low hip joint force of 700 N (i.e. 100% x body weight) was applied, which corresponds to a typical 140 N toe-touch foot-to-ground force (i.e. 20% x body weight) recommended to patients after surgery. Analysis was done using 2 screw materials (steel or titanium) and types (locked or non-locked). Steel and titanium plates were also analyzed. Semi-rigid plates (vs. metal plates) had lower overall femur/plate construct stiffnesses of 508 - 1482 N/mm, higher cortical bone stresses under the plate by 2.02x - 3.27x thereby reducing SS, and lower E values of 414 - 2302 MPa to permit AIM of 0.2 - 1 mm thereby reducing DH.
... 0.2-1 mm) required for early secondary-type healing by callus generation [24][25][26]. Conversely, inadequately rigid metal plates could allow excessive shear interfragmentary motion (SIM) leading to delayed healing, although a SIM/AIM ratio < 1.6 could prevent this [27]. ...
... Based on current AIM MED (Fig. 5A) and SIM MED /AIM MED (Fig. 5E) design curves, the plate material chosen should generate 172.6 ≤ E P ≤ 200 GPa (no KS screw), 79.8 ≤ E P ≤ 200 GPa (1 KS screw), and 4.9 ≤ E P ≤ 200 GPa (2 KS screws). This will fulfill the optimization criteria of 0.2 mm ≤ AIM MED ≤ 1 mm [24][25][26]30,35] and SIM MED /AIM MED < 1.6 [27,30,35] for early callus formation on the fracture's medial side. However, all SIM LAT /AIM LAT ratios (Fig. 5F) were > 1.6; thus, plate optimization cannot achieve early callus formation on the fracture's lateral side. ...
Comminuted proximal tibia fractures are an ongoing surgical challenge. This “proof of concept” study is the first step in designing a new percutaneous plate for this injury under toe-touch weight-bearing as prescribed after surgery. Finite element simulations generated design curves for overall stiffness, bone and implant stress, and interfragmentary motion using 3 fixations (no, 1, or 2 “kickstand” (KS) screws across the fracture gap) over a range of plate elastic moduli (EP = 5 to 200 GPa). Combining well-established optimization criteria to enhance callus formation (i.e. 0.2 mm ≤ axial interfragmentary motion ≤ 1 mm; shear / axial interfragmentary motion ratio < 1.6), lessen stress shielding (i.e. bone stress under the proposed plate > bone stress under a traditional titanium or steel plate), and reduce steel screw breakage (i.e. screw max stress < ultimate tensile stress of steel) resulted in plate design recommendations: 172.6 ≤ EP < 200 GPa (no KS screw), 79.8 ≤ EP < 100 GPa (1 KS screw), and 4.9 ≤ EP < 100 GPa (2 KS screws). A prototype plate could be made from materials currently used or proposed for orthopaedics, such as polymers, fiber-reinforced polymers, fiber metal laminates, metal foams, or shape memory alloys.
... Am Schafmodel konnte gezeigt werden, dass Scherkräfte im Frakturspalt ---im Vergleich zu axialen Bewegungen gleicher Stärke ---die Heilung einschränken[44]. Durch Scherkräfte proliferiert das Weichteilgewebe zusätzlich stärker, was in der Regel für eine Heilung negativ zu bewerten ist[45]. Andere Studien kommen zu dem Ergebnis dass Scherkräfte sich nicht notwendigerweise negativ auf die Heilung auswirken müssen[46,47]. ...
... Die schlechten biomechanischen Ergebnisse im Vergleich zur Kontrollgruppe und die Inhomogenität des Gewebes in der Histologie stellen keine neue Erkenntnis dar, sondern unsere Studie konnte in diesem Punkt den momentanen Stand des Wissens bestätigen[44,45].Was jedoch zunächst verwundert ist die Tatsache, dass dieFast 1 Gruppe in der biomechanischen Testung ein höheres maximales Drehmoment als die Fast 2 Gruppe erzielte. Die Fast 2 Gruppe wies nämlich nicht nur in der histologischen Untersuchung einen höheren Anteil an neuem Knochen auf, sondern besass zudem von allen Gruppen den strukturiertesten Kallus und hatte auch in der Biomechanik eine deutlich höhere Torsionssteifigkeit als die Fast 1 Gruppe. ...
... Excessive constant instability and early mechanical loading have been reported to be detrimental to vascular growth (76,80,85,86). Constant less-stable fixation has been reported to prolong the chondral phase, which has been deemed responsible for delayed bridging and increases in the time required for healing in sheep (87,88) rats (89), and mice (78). On the other hand, superior results have been shown when rigid fixation changed to more flexible fixation at 3 and 4 weeks (73) after surgery compared with at 1 week (90). ...
Delayed union and non-union of fractures continue to be a major problem in trauma and orthopedic surgery. These cases are challenging for the surgeon. In addition, these patients suffer from multiple surgeries, pain and disability. Furthermore, these cases are a major burden on healthcare systems. The scientific community widely agrees that the stability of fixation plays a crucial role in determining the outcome of osteosynthesis. The extent of stabilization affects factors like fracture gap strain and fluid flow, which, in turn, influence the regenerative processes positively or negatively. Nonetheless, a growing body of literature suggests that during the fracture healing process, there exists a critical time frame where intervention can stimulate the bone's return to its original form and function. This article provides a summary of existing evidence in the literature regarding the impact of different levels of fixation stability on the strain experienced by newly forming tissues. We will also discuss the timing and nature of this “window of opportunity” and explore how current knowledge is driving the development of new technologies with design enhancements rooted in mechanobiological principles.
... 55 In addition, the failure to apply adequate compression impacts stability and can lead to coracoid osteolysis. 30,33,44 Similarly, osteolysis with the Latarjet procedure may also be the result of the proximal screw shielding from the distal screw because of stress. 43 To avoid these complications, plates and washers have been employed to help distribute the pressure of screw fixation across the graft. ...
Background
Glenohumeral dislocations often lead to glenoid bone loss and recurrent instability, warranting bony augmentation. While numerous biomechanical studies have investigated fixation methods to secure a graft to the glenoid, a review of available constructs has yet to be performed.
Purpose
To synthesize the literature and compare the biomechanics of screw and suture button constructs for anterior glenoid bony augmentation.
Study Design
Systematic review.
Methods
A systematic review was conducted in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. There were 2 independent reviewers who performed a literature search using the PubMed, Embase, and Google Scholar databases of studies published between 1950 and 2020. Studies were included that compared the biomechanical outcomes of fixation for the treatment of anterior shoulder instability with glenoid bone loss.
Results
Overall, 13 of the 363 studies screened met the inclusion criteria. The included studies measured the biomechanical strength of screws or suture buttons on a cadaveric or synthetic Latarjet construct. Screws and suture buttons were biomechanically similar, as both constructs exhibited comparable loads at failure and final displacement. Screw type (diameter, threading, or composition) did not significantly affect construct strength, and double-screw fixation was superior to single-screw fixation. Additionally, 2 screws augmented with a small plate had a higher load at failure than screws that were not augmented. Unicortical double-screw fixation was inferior to bicortical double-screw fixation, although construct strength did not significantly decrease if 1 of these screws was unicortical. Further, 2 screws inserted at 15° off axis experienced significantly higher graft displacement and lower ultimate failure loads than those inserted at 0° parallel to the glenoid.
Conclusion
Suture buttons provided comparable strength to screws and offer an effective alternative to reduce screw-related complications. Augmentation with a small plate may clinically enhance construct strength and decrease complications through the dispersion of force loads over a greater surface area. Differences in screw type did not appear to alter construct strength, provided that screws were placed parallel to the articular surface and were bicortical.
... An industrially produced helical plate might behave differently. The results from the current study demonstrated bigger fracture gap movements for the helical plate constructs, however, whether these bigger movements support or prevent bone healing cannot be ultimately answered as there are controversial reports on the role of shear movements at the fracture gap [36][37][38]. Further studies are needed to answer this question. ...
Background
Proximal humeral shaft fractures are surgically challenging and plate osteosynthesis with a long straight plate is one operative treatment option in these patients although endangering the radial nerve distally. Helical plates potentially avoid the radial nerve by twisting around the humeral shaft. Aim of the study was to investigate in a human cadaveric model the biomechanical competence of helical plates versus straight lateral plates used for fixation of proximal third comminuted humeral shaft fractures.
Methods
Eight pairs of humeral cadaveric humeri were instrumented using either a long 90°-helical plate (Group1) or a straight long PHILOS plate (Group2). An unstable proximal humeral shaft fracture was simulated by means of a 5 cm osteotomy gap. All specimens were tested under quasi-static loading in axial compression, internal and external rotation, and bending in four directions. Subsequently, progressively increasing cyclic loading in internal rotation until failure was applied and interfragmentary movements were monitored by motion tracking.
Results
During static testing flexion/extension deformation in Group1 was significantly higher, however, varus/valgus deformation as well as shear and torsional displacement under torsional load remained statistically indifferent between both groups. During cyclic testing shear and torsional displacements were both significantly higher in Group1 compared to Group 2. However, cycles to catastrophic failure remained statistically indifferent between the groups.
Conclusions
From a biomechanical perspective, although 90°-helical plating is associated with higher initial stability against varus/valgus collapse and comparable endurance under dynamic loading, it demonstrates lower resistance to flexion/extension and internal rotation with bigger shear interfragmentary displacements versus straight lateral plating and, therefore, cannot be considered as its real alternative. Alternative helical plate designs should be investigated in the future.
... Generally, shear movements at a fracture site negatively affect healing, independently of whether they are caused by a nail that is too thin or an inadequate external fixation. Shear within the fracture gap hinders bone healing not only because it blocks vascular ingrowth but because it affects the early transition of the pro-inflammatory phase to the anti-inflammatory phase 136 . During the past few years, new techniques for fracture fixation have emerged, including the use of angle stable plate 137,138 or angle stable nail 139 fixations, which enable anchorage in weak bone and provide ideal fracture stabilization. ...
Bone has a remarkable endogenous regenerative capacity that enables scarless healing and restoration of its prior mechanical function, even under challenging conditions such as advanced age and metabolic or immunological degenerative diseases. However - despite much progress - a high number of bone injuries still heal with unsatisfactory outcomes. The mechanisms leading to impaired healing are heterogeneous, and involve exuberant and non-resolving immune reactions or overstrained mechanical conditions that affect the delicate regulation of the early initiation of scar-free healing. Every healing process begins phylogenetically with an inflammatory reaction, but its spatial and temporal intensity must be tightly controlled. Dysregulation of this inflammatory cascade directly affects the subsequent healing phases and hinders the healing progression. This Review discusses the complex processes underlying bone regeneration, focusing on the early healing phase and its highly dynamic environment, where vibrant changes in cellular and tissue composition alter the mechanical environment and thus affect the signalling pathways that orchestrate the healing process. Essential to scar-free healing is the interplay of various dynamic cascades that control timely resolution of local inflammation and tissue self-organization, while also providing sufficient local stability to initiate endogenous restoration. Various immunotherapy and mechanobiology-based therapy options are under investigation for promoting bone regeneration.
... Günümüzde bir kırığın iyileşmesi için en faydalı ortamın ne olduğu tam olarak açıklanamamıştır. Fakat büyük eksenel hareketlerin yanı sıra eğme ve büyük kayma kuvvetleri negatif parametreler olarak kabul edilmiştir (Noordeen MH, Lavy CB, Shergill NS, Tuite JD, 1995;Schell et al., 2005;Yamaji et al., 2001). Bunun aksine küçük kayma ve küçük eksenel hareketler ise faydalı parametreler olarak dikkate alınmıştır (Bishop et al., 2006;Wolf et al., 1998). ...
External stabilizers are seen as a method used in the treatment of bone and joint damage as well as the correction of skeletal deformities with an externally applied device that stabilizes damaged limbs. The aim of this research is to perform the biomechanical optimization of the circular external fixator system, which is one of the external stabilizers used in the field of orthopaedics. The study was evaluated numerically and, in the study, the effects of the changes on the system and the fracture line, taking into account the parameters determined on the DEF system, were examined with the ANSYS software using the finite element method. As a result of the optimization process, the wire diameter is 1mm, the angle between the wires is 55°, the spring coefficient is 20 N/mm and the preload is obtained as two different variables. Based on the results obtained in this study, a broader knowledge of fracture healing was obtained.
... Hence, studies often simplify their analysis by neglecting the effects of muscle loads and assuming simpler geometries. Although this simplification may be a reasonable first step toward elucidating the interactions between mechanical loading and fracture healing, the effect of muscle loading during the early stages of healing requires special attention as the fracture site is sensitive to loading at this time (Epari et al., 2006), and the early stages may be decisive in determining the tissue differentiation pathway and even the healing outcome (Epari et al., 2006;Schell et al., 2005). A better understanding of the influence of weight-bearing on early fracture healing is needed, and more specifically, an explication of the synergistic effects of muscle and joint loading on early-stage fracture healing under various weight-bearing conditions. ...
Designing weight-bearing exercises for patients with lower-limb bone fractures is challenging and requires a systematic approach that accounts for patient-specific loading conditions. However, 'trial-and-error' approaches are commonplace in clinical settings due to the lack of a fundamental understanding of the effect of weight-bearing exercises on the bone healing process. Whilst computational modelling has the potential to assist clinicians in designing effective patient-specific weight-bearing exercises, current models do not explicitly account for the effects of muscle loading, which could play an important role in mediating the mechanical microenvironment of a fracture site. We combined a fracture healing model involving a tibial fracture stabilised with a locking compression plate (LCP) with a detailed musculoskeletal model of the lower limb to determine interfragmentary strains in the vicinity of the fracture site during both full weight-bearing (100% body weight) and partial weight-bearing (50% body weight) standing. We found that muscle loading significantly altered model predictions of interfragmentary strains. For a fractured bone with a standard LCP configuration (bone-plate distance = 2 mm, working length = 30 mm) subject to full weight-bearing, the predicted strains at the near and far cortices were 23% and 11% higher when muscle loading was included compared to the case when muscle loading was omitted. The knee and ankle muscles accounted for 38% of the contact force exerted at the knee joint during quiet standing and contributed significantly to the strains calculated at the fracture site. Thus, models of bone fracture healing ought to account explicitly for the effects of muscle loading. Furthermore, the study indicated that LCP configuration parameters play a crucial role in influencing the fracture site microenvironment. The results highlighted the dominance of working length over bone-plate distance in controlling the flexibility of fracture sites stabilised with LCP devices.
... Semi-rigid fixation is associated less optimal bony healing with excessive callus formation 265 with inferior callus stiffness 35 . However, a very rigid fixation can delay healing 11 . ...
Background:
Neer Type-IIB lateral clavicle fractures are inherently unstable fractures with associated disruption of the coracoclavicular (CC) ligaments. Due to the high rate of non-union and malunion, surgical fixation is recommended, however no consensus has been reached regarding the optimal fixation method. A new plating technique using a superior lateral locking plate with antero-posterior (AP) locking screws, resulting in orthogonal fixation in the lateral fragment has been designed to enhance stability and reduce implant failure. The purpose of this study was to biomechanically compare three different clavicle plating constructs within a fresh-frozen human cadaveric shoulder model.
Methods:
24 fresh-frozen cadaveric shoulders were randomized into three groups (n=8 specimens). Group 1: lateral locking plate only (Medartis Aptus Superior Lateral Plate); Group 2: lateral locking plate with CC stabilization (No. 2 FiberWire); and Group 3: lateral locking plate with two AP locking screws stabilizing the lateral fragment. All specimens were subject to cyclic loading of 70N for 500 cycles. Data was analyzed for gap formation after cyclic loading, construct stiffness and ultimate load to failure, defined by a marked decrease in the load displacement curve.
Results:
After 500 cycles, there was no statistically significant difference between the three groups in gap-formation (p = 0.179). No specimen (0/24) failed during cyclic loading. Ultimate load to failure was significantly higher in Group 3 compared to Group 1 (286N vs. 167N; p = 0.022), but not to Group 2 (286N vs. 246N; p = 0.604). There were no statistically significant differences in stiffness (Group 1: 504N/mm; Group 2: 564N/mm; Group 3: 512N/mm; p = 0.712). Peri-implant fracture was the primary mode of failure for all three groups, with Group 3 demonstrating the lowest rate of peri-implant fractures (Group 1: 6/8; Group 2: 7/8, Group 3: 4/8; p = 0.243).
Conclusion:
Biomechanical evaluation of the clavicle plating techniques showed effective fixation across all specimens at 500 cycles. The lateral locking plate with orthogonal AP locking screw fixation in the lateral fragment demonstrated the greatest ultimate failure load, followed by the lateral locking plate with CC stabilization. This new plating technique showed compatible stiffness and gap formation when compared to conventional lateral locking plates as well as plates with CC fixation. The use of orthogonal screw fixation in the distal fragment may negate against the need for CC stabilization in these types of fractures, thus minimizing surgical dissection around the coracoid and potential complications.
... However, biomechanical research into long bone fractures has increasingly established that a small amount of controlled axial micromotion at the fracture site of 2 to 10% strain actually enhances secondarytype fracture healing via early callus formation [48]. In contrast, shear micromotion at the fracture site can have a negative influence on callus formation if the ratio of shear to axial micromotion is >1.6 [49]. Consequently, new strategies (e.g., fiber-reinforced composite materials and dynamized implants) that are more mechanically flexible than traditional metal implants are being investigated for long bone fracture repair [47,[50][51][52] and even spine fixation/fusion [47,[53][54][55]. ...
A vertebral compression fracture (VCF) is an injury to a vertebra of the spine affecting the cortical walls and/or middle cancellous section. The most common risk factor for a VCF is osteoporosis, thus predisposing the elderly and postmenopausal women to this injury. Clinical consequences include loss of vertebral height, kyphotic deformity, altered stance, back pain, reduced mobility, reduced abdominal space, and reduced thoracic space, as well as early mortality. To restore vertebral mechanical stability, overall spine function, and patient quality of life, the original percutaneous surgical intervention has been vertebroplasty, whereby bone cement is injected into the affected vertebra. Because vertebroplasty cannot fully restore vertebral height, newer surgical techniques have been developed, such as kyphoplasty, stents, jacks, coils, and cubes. But, relatively few studies have experimentally assessed the biomechanical performance of these newer procedures. This article reviews over 20 years of scientific literature that has experimentally evaluated the biomechanics of percutaneous VCF repair methods. Specifically, this article describes the basic operating principles of the repair methods, the study protocols used to experimentally assess their biomechanical performance, and the actual biomechanical data measured, as well as giving a number of recommendations for future research directions.
... In the latter stages, stiffness is increased and/or loading decreased, thus enabling the previously produced large callus to quickly mineralize and ossify. Some studies have shown that faster union with higher rates of bone stiffness and strength can be achieved (41)(42)(43). The majority of these animal studies were performed under simplified mechanical conditions, with IFM being applied in one or two directions. ...
Background and aim:
Mechanical influence on secondary fracture healing remains an incompletely understood phenomenon. This is of special importance in biological osteosynthesis, where stability is sacrificed for the sake of an optimal biological fracture environment. Under condition of relative stability, a wide range of biomechanical conditions can be achieved. Mechanobiology, which studies mechanical influences on biological systems has become a large, interdisciplinary field. The aim of this article is to present a comprehensive synthesis of the literature for the practicing clinician, with insights relevant to their practice of fracture care.
Methods:
The MEDLINE online database (Pubmed) was searched in September 2021 for relevant articles Results: The search provided 816 results, which were scanned by the first author by the title and abstract. With relevance to the research topic, 59 articles were chosen and read in detail. Another 70 articles were added by screening the references of relevant articles. A total of 129 articles were read and analysed Conclusions: Mechanical environment plays a crucial role in the fracture healing process. The definition of an optimal mechanical environment still evades us, due to the complexity of the problem. Computational models could replicate the complex mechanical environment of bone healing in humans but require detailed knowledge of mechano-transduction and material properties of healing tissues. The literature reminds us of the importance of adequate stiffness of constructs used under conditions of relative stability. Hopefully, further research in this field will result in not only empirical but more accurate and evidence-based assessments of osteosynthesis fixations.
... The amount of movement that occurs at the fracture gap is influenced by the stiffness of the bone/implant construct [12]. Construct stiffness is the mechanical rigidity, or resistance to deformation, of a reduced bone fracture with in situ hardware and this property has a significant impact on callus formation [13][14][15]. Clinically, a less rigid construct will lead to more interfragmentary motion at the fracture site. Based on the fracture type being addressed and the type of bone healing desired, the surgeon may require a less or more rigid construct to achieve their goal. ...
The mechanics of distal femur fracture fixation has been widely studied in bench tests that employ a variety of approaches for holding and constraining femurs to apply loads. No standard test methods have been adopted for these tests and the impact of test setup on inferred construct mechanics has not been reported. Accordingly, the purpose of this study was to use finite element models to compare the mechanical performance of a supracondylar osteotomy with lateral plating under conditions that replicate several common bench test methods. A literature review was used to define a parameterized virtual model of a plated distal femur osteotomy in axial compression loading with four boundary condition sets ranging from minimally to highly constrained. Axial stiffness, longitudinal motion, and shear motion at the fracture line were recorded for a range of applied loads and bridge spans. The results showed that construct mechanical performance was highly sensitive to boundary conditions imposed by the mechanical test fixtures. Increasing the degrees of constraint, for example by potting and rigidly clamping one or more ends of the specimen, caused up to a 25x increase in axial stiffness of the construct. Shear motion and longitudinal motion at the fracture line, which is an important driver of interfragmentary strain, was also largely influenced by the constraint test setup. These results suggest that caution should be used when comparing reported results between bench tests that use different fixtures and that standardization of testing methods is needed in this field.
... These results are in agreement with other ex vivo and in silico studies that reported shear to be the primary mode of motion supplied by IMNs [64,65], and that increasing the diameter of the IMN or minimizing the annular gap between the nail and endosteal surface reduces interfragmentary motion [51,64]. While some studies have demonstrated that shear strain hinders fracture healing [66,67], others have concluded that shear strain may not be detrimental [68,69]. These conflicting conclusions are likely due in part to IMNs supporting both shear and axial strain [36]. ...
Delayed long bone fracture healing and nonunion continue to be a significant socioeconomic burden. While mechanical stimulation is known to be an important determinant of the bone repair process, understanding how the magnitude, mode, and commencement of interfragmentary strain (IFS) affect fracture healing can guide new therapeutic strategies to prevent delayed healing or non-union. Mouse models provide a means to investigate the molecular and cellular aspects of fracture repair, yet there is only one commercially available, clinically-relevant, locking intramedullary nail (IMN) currently available for studying long bone fractures in rodents. Having access to alternative IMNs would allow a variety of mechanical environments at the fracture site to be evaluated, and the purpose of this proof-of-concept finite element analysis study is to identify which IMN design parameters have the largest impact on IFS in a murine transverse femoral osteotomy model. Using the dimensions of the clinically relevant IMN as a guide, the nail material, distance between interlocking screws, and clearance between the nail and endosteal surface were varied between simulations. Of these parameters, changing the nail material from stainless steel (SS) to polyetheretherketone (PEEK) had the largest impact on IFS. Reducing the distance between the proximal and distal interlocking screws substantially affected IFS only when nail modulus was low. Therefore, IMNs with low modulus (e.g., PEEK) can be used alongside commercially available SS nails to investigate the effect of initial IFS or stability on fracture healing with respect to different biological conditions of repair in rodents.
... Bone loss greater than 2 times the diameter of the long bone diaphysis is unlikely to result in union despite appropriate stabilization methods (Gugala et al. 2007). While it is well known that mechanical signals (i.e., strains/stresses) influence the bone healing process (Claes et al. 1997;Klein et al. 2003;Schell et al. 2005;Epari et al. 2006;Willie et al. 2011), their role in critical-sized bone defects remains largely unknown. In the early phases of healing, critical-sized bone defects are characterized by an altered mechanical loading environment within the fracture callus (Mehta et al. 2012). ...
Critical-sized bone defects are critical healing conditions that, if left untreated, often lead to non-unions. To reduce the risk, critical-sized bone defects are often treated with recombinant human BMP-2. Although enhanced bone tissue formation is observed when BMP-2 is administered locally to the defect, spatial and temporal distribution of callus tissue often differs from that found during regular bone healing or in defects treated differently. How this altered tissue patterning due to BMP-2 treatment is linked to mechano-biological principles at the cellular scale remains largely unknown. In this study, the mechano-biological regulation of BMP-2-treated critical-sized bone defect healing was investigated using a multiphysics multiscale in silico approach. Finite element and agent-based modeling techniques were combined to simulate healing within a critical-sized bone defect (5 mm) in a rat femur. Computer model predictions were compared to in vivo microCT data outcome of bone tissue patterning at 2, 4, and 6 weeks postoperation. In vivo, BMP-2 treatment led to complete healing through periosteal bone bridging already after 2 weeks postoperation. Computer model simulations showed that the BMP-2 specific tissue patterning can be explained by the migration of mesenchymal stromal cells to regions with a specific concentration of BMP-2 (chemotaxis). This study shows how computational modeling can help us to further understand the mechanisms behind treatment effects on compromised healing conditions as well as to optimize future treatment strategies.
... Pin diameter of 4.5mm and 5.5mm possess a high stress which will affect the stability of configuration while 6.5mm and 6.0mm have the largest area of pin diameter which then results in a slower healing process. It has been proved by clinical study where bigger size of hole will slowing the rate of healing process [23]. The 5.5mm pin diameter has the average stress distribution and pin diameter which make it the most favourable option for fixator configuration. ...
Biomechanical perspective of external fixator is one of the biggest elements that should be considered in treating fracture bone. This is due to the mechanical behavior of the structure could be analyzed and optimized in order to avoid failure, increase bone fracture healing rate and prevents preterm screw loosening. There are three significant factors that affect the stability of external fixator and those are the placement of pin at the bone, configuration and components of external fixator. All these factors contribute to a question, what is the optimum pin diameter which exerts good stress distribution? To date, the research on the above-mentioned factors are limited in the literature. Therefore, this study was conducted to evaluate the unilateral external fixator with different pin sizes in treating tibia shaft fracture via the finite element method. First and foremost, the development of the tibia shaft fracture was conducted using Mimics software. The computed tomography (CT) data image was utilized to develop three-dimensional tibia bone followed by crafting fracture on the bone. Meanwhile, the unilateral external fixator was developed using SolidWorks software. In this study, five pin diameters (4.5, 5.0, 5.5, 6.0 and 6.5 mm) were developed and analyzed. Both tibia bone and external fixator were meshed in 3-matic software. Simulation of this configuration took place in a finite element software, Marc.Mentat. From the findings, it is shown that the larger diameter of pin demonstrated the lowest stress distribution. The size of the 5.5mm pin shows optimum diameter in terms of stress distribution with the value of 21.50 MPa in bone and 143.33 MPa in fixator. Meanwhile the displacement value of 1.42mm in bone and 1.20mm in fixator. In conclusion, it is suggested that the pin diameter of 5.5 mm is the most favorable option in treating tibia shaft fracture in terms of mechanical perspective.
... Similar limitations can be found with companion animals, like cats and dogs, while minipigs, which are currently one of the most used animal models for craniomaxillofacial studies, despite similarities to humans in the biomechanics of mastication (Vapniarsky et al., 2017(Vapniarsky et al., , 2018, present high stiffness of both mandibular bone and soft tissues. In the last decades, sheep have been used to test fixation devices for fractures (Tepic et al., 1997;Hente et al., 1999;Krischak et al., 2002;Schell et al., 2005;Claes et al., 2008) and large bone defects (den Boer et al., 1999;Egermann et al., 2008;Christou et al., 2014;Pobloth et al., 2018) in long bones. In the mandible, from the surgical point of view, sheep bring important advantages in terms of soft tissue management and body weight comparable to humans. ...
Mandibular fracture fixation and reconstruction are usually performed using titanium plates and screws, however, there is a need to improve current fixation techniques. Animal models represent an important step for the testing of new designs and materials. However, the validity of those preclinical models in terms of implant biomechanics remains largely unknown. In this study, we investigate the biomechanics of the sheep mandible as a preclinical model for testing the mechanical strength of fixation devices and the biomechanical environment induced on mandibular fractures. We aimed to assess the comparability of the biomechanical conditions in the sheep mandible as a preclinical model for human applications of fracture fixation devices and empower analyses of the effect of such defined mechanical conditions on bone healing outcome. We developed 3D finite element models of the human and sheep mandibles simulating physiological muscular loads and three different clenching tasks (intercuspal, incisal, and unilateral). Furthermore, we simulated fractures in the human mandibular body, sheep mandibular body, and sheep mandibular diastema fixated with clinically used titanium miniplates and screws. We compared, at the power stroke of mastication, the biomechanical environment (1) in the healthy mandibular body and (2) at the fracture sites, and (3) the mechanical solicitation of the implants as well as the mechanical conditions for bone healing in such cases. In the healthy mandibles, the sheep mandibular body showed lower mechanical strains compared to the human mandibular body. In the fractured mandibles, strains within a fracture gap in sheep were generally not comparable to humans, while similar or lower mechanical solicitation of the fixation devices was found between the human mandibular body fracture and the sheep mandibular diastema fracture scenarios. We, therefore, conclude that the mechanical environments of mandibular fractures in humans and sheep differ and our analyses suggest that the sheep mandibular bone should be carefully re-considered as a model system to study the effect of fixation devices on the healing outcome. In our analyses, the sheep mandibular diastema showed similar mechanical conditions for fracture fixation devices to those in humans.
... According to Wolff 's law, tissue adaptations in bone in particular are due to physical or mechanical forces during its dynamic homeostatic remodeling (Wolff, 1986;Rho et al., 1998). This force-sensitivity is also remarkably relevant for healing and regeneration such as the healing of bone fractures (Lienau et al., 2005;Schell et al., 2005;Epari et al., 2007;Ghiasi et al., 2017). For example osteocytes show extraordinary mechano-sensitivity and are engaged in regulating other cells in their activity (e.g., osteoblasts and osteoclasts) according to their mechanical sensation they perceive (Bonewald and Johnson, 2008;Prideaux et al., 2016;Qin et al., 2020;Sato et al., 2020). ...
A misdirected or imbalanced local immune composition is often one of the reasons for unsuccessful regeneration resulting in scarring or fibrosis. Successful healing requires a balanced initiation and a timely down-regulation of the inflammation for the re-establishment of a biologically and mechanically homeostasis. While biomaterial-based approaches to control local immune responses are emerging as potential new treatment options, the extent to which biophysical material properties themselves play a role in modulating a local immune niche response has so far been considered only occasionally. The communication loop between extracellular matrix, non-hematopoietic cells, and immune cells seems to be specifically sensitive to mechanical cues and appears to play a role in the initiation and promotion of a local inflammatory setting. In this review, we focus on the crosstalk between ECM and its mechanical triggers and how they impact immune cells and non-hematopoietic cells and their crosstalk during tissue regeneration. We realized that especially mechanosensitive receptors such as TRPV4 and PIEZO1 and the mechanosensitive transcription factor YAP/TAZ are essential to regeneration in various organ settings. This indicates novel opportunities for therapeutic approaches to improve tissue regeneration, based on the immune-mechanical principles found in bone but also lung, heart, and skin.
... If the site is unstable, excess callus formation will occur; however, a bridging callus will not be formed [20]. Furthermore, Schell et al. [21] reported that semi-rigid fixation resulted in the formation of a larger callus than rigid fixation. Radiolucency at the osteotomy site and excess callus formation at the posterior osteotomy site indicate some instability. ...
Background
Hybrid closed-wedge high tibial osteotomy (hybrid CWHTO) is an effective surgical treatment for medial compartment osteoarthritis of the knee. Our study investigated whether the combination of a lateral locking plate and a single medial screw promoted bone union after hybrid CWHTO.
Methods
The study cohort consisted of 30 patients (15 men and 15 women) who underwent hybrid CWHTO for medial compartment osteoarthritis or spontaneous osteonecrosis of the knee. Sixteen knees were fixed with a lateral locking plate (LP group), and 17 were fixed with both a lateral locking plate and a cannulated cancellous screw on the medial side of the tibia (LPS group). The times to bone union, radiolucency, and callus formation at the osteotomy site were evaluated radiographically.
Results
The mean postoperative time to radiographic confirmation of bone union was 5.5 ± 2.6 months in the LP group and 3.4 ± 1.5 months in the LPS group. Radiolucency at the osteotomy site and excess callus formation on the posterior side of the tibia were lower in the LPS group than in the LP group.
Conclusions
This modified hybrid CWHTO combining a lateral locking plate and a cannulated cancellous screw on the medial side of the tibia improves the stability of the osteotomy site and shortens the period of bone union.
... One treatment method of interest is mechanical loading of bone. Mechanical interactions have a longestablished relationship to bone physiology, leading to earlier concepts of micromotion during bone defect healing 2 , and the significance of fracture instability in healing outcomes 3,4 . The effects of mechanical forces on bone healing have been previously reviewed 5,6 ; mechanical loading is likely to depend on frequency 7 and cycle number 8 , influences mesenchymal stem cell differentiation 9 , and has a role in guiding healing towards primary and secondary bone healing pathways 10 . ...
Methods to repair bone defects arising from trauma, resection, or disease, continue to be sought after. Cyclic mechanical loading is well established to influence bone (re)modelling activity, in which bone formation and resorption are correlated to micro-scale strain. Based on this, the application of mechanical stimulation across a bone defect could improve healing. However, if ignoring the mechanical integrity of defected bone, loading regimes have a high potential to either cause damage or be ineffective. This study explores real-time finite element (rtFE) methods that use three-dimensional structural analyses from micro-computed tomography images to estimate effective peak cyclic loads in a subject-specific and time-dependent manner. It demonstrates the concept in a cyclically loaded mouse caudal vertebral bone defect model. Using rtFE analysis combined with adaptive mechanical loading, mouse bone healing was significantly improved over non-loaded controls, with no incidence of vertebral fractures. Such rtFE-driven adaptive loading regimes demonstrated here could be relevant to clinical bone defect healing scenarios, where mechanical loading can become patient-specific and more efficacious. This is achieved by accounting for initial bone defect conditions and spatio-temporal healing, both being factors that are always unique to the patient.
... In addition to interrupted circulation, prolonged healing after single-screw osteosynthesis might arise because of an existing instability occurring during wrist loading and motion [11,25]. Wrist motion leads to torque and lever force along the longitudinal axis of the scaphoid. ...
Purpose:
We hypothesised that intercarpal K-wire fixation of adjacent carpal bones would reduce torque and lever force within a fractured scaphoid bone.
Methods:
In eight cadaver wrists, a scaphoid osteotomy was stabilised using a locking nail, which also functioned as a sensor to measure isometric torque and lever forces between the fragments. The wrist was moved through 80% of full range of motion (ROM) to generate torque and force within the scaphoid. Testing was performed with and without loading of the wrist and K-wire stabilisation of the adjacent carpal bones.
Results:
Average torque and lever force values were 49.6 ± 25.1 Nmm and 3.5 ± 0.9 N during extension and 41 ± 26.7 Nmm and 8.1 ± 2.8 N during flexion. Torque and lever force did not depend on scaphoid size, individual wrist ROM, or deviations of the sensor versus the anatomic axis. K-wire fixation did not produce significant changes in average torque and lever force values except with wrist radial abduction (P = 0.0485). Other than wrist extension, torque direction was not predictable.
Conclusion:
In unstable scaphoid fractures, we suggest securing rotational stability with selected implants for functional postoperative care. Wrist ROM within 20% extension and radial abduction to 50% flexion limit torque and lever force exacerbation between scaphoid fragments.
... For example, many animal models have been used to show how the fixation mechanics influence the healing outcome. In particular, multiple studies have shown that fixation that allows excessive torsional rotation and shear movement significantly delays the healing of diaphyseal osteotomies (Epari et al. 2007;Schell et al. 2005;Augat et al. 2003;Kaspar et al. 2005). However, the osteotomy fractures in these models do not reflect the complex and diverse morphologies of clinical fractures, which are categorized by the OTA/AO Classification System (Kellam et al. 2018) (Fig. 1). ...
In bone fracture healing, new tissue gradually forms, ossifies, and eventually remodels itself to restore mechanical stiffness and strength across injury site. Mechanical strain at the fracture site has been implicated in controlling the process of healing and numerical mechanoregulation models with strain-based fuzzy logic rules have been applied to simulate bone healing for simple fracture geometries. However, many of these simplified models cannot capture in vivo observations such as delays in healing with torsional instability or differences in healing rate between different fracture types. Accordingly, the purpose of this work was to apply a fuzzy logic mechanoregulation fracture healing simulation technique to 3D models representing a range of clinically inspired fracture geometries with intramedullary nail fixation and multiaxial loading conditions. The models predicted that the rate of healing depends on the geometry of the fracture and that all fracture types experience a small healing delay with torsional instability. The results also indicated that when realistic torsional loading and fixator mechanics are included, previously published strain-based rules for tissue destruction lead to simulated nonunions that would not be expected in vivo. This suggested that fracture healing may be more robust to distortional strain than has been previously reported and that fuzzy logic models may require parameter tuning to correctly capture clinically relevant healing. The strengths of this study are that it includes fracture morphology effects, realistic implant mechanics, and an exploratory adaptation of the upper distortional strain threshold. These findings may help future researchers extend these methods into clinical fracture healing prediction.
... inflammation, soft callus, hard callus, bone remodeling) with increasing mechanical stiffness and strength [6]. This can be enhanced by permitting axial motion at the fracture site of 0.2 to 1 mm [7,8], although the ratio of shear motion / axial motion should be <1.6 [9]. Pre-clinical studies and finite element modeling have shown that an optimal amount of axial motion at the fracture site can substantially speed up callus formation (i.e. ...
Metallic intramedullary nails are the “gold standard” implant for repairing femur shaft fractures. However, their rigidity may eliminate axial micromotion at the fracture (causing delayed healing) and they may carry too much load relative to the femur (causing “stress shielding”). Consequently, some researchers have proposed fiber-reinforced composite nails, but only one evaluated cyclic fatigue performance. Therefore, this study assessed the cyclic fatigue response of a carbon fiber/epoxy nail with a novel ply stacking sequence of [02/-45/452/-45/0/-45/452/-452/452/-45/902] previously developed by the present authors. Nails were cyclically loaded in tension-tension at 5 Hz with a stress ratio of R=0.1 from 30% - 85% of the material's ultimate tensile strength (UTS). Thermographic stress analysis, rather than conventional fatigue testing, was used to obtain high cycle fatigue strength (HCFS), below which the nail can be cyclically loaded indefinitely without damage. Also, the mechanical tester's built-in load cell and an extensometer were used to create stress-strain curves, from which the change in static EO and dynamic E* moduli were obtained. Results showed that HCFS was 70.3% of UTS (or about 283 MPa), while EO and E* remained at 42 GPa without any degradation during testing. The current nail shows potential for clinical use.
... Bone-block fixation is essential because poor bone contact is responsible for nonunion [8] [ Fig 1]. In the Latarjet-Patte-Walch procedure, the coracoid process is fixed by two 4.5mm partial threaded cancellous AO malleolar screws. ...
PurposeThis work compares the biomechanical resistance of five modes of fixation coracoid bone-block fixation during Latarjet open-air or arthroscopic procedures. The hypothesis is that these systems are equivalent.Methods
Latarjet procedures were performed on cadavers, then the samples were subjected to an increasing tension until the fixation failed. Five systems were tested: two malleolar screws, one screw with washer, two 3.5-mm self-compressive screws, one 4-mm self-compressive screw associated with one 3-mm self-compressive screw, and endobutton. The main judgment criterion was the strength necessary for the failure of the fixation. The secondary criterion was the stiffness of the assembly.ResultsThe single malleolar screw fixing has a lower breaking threshold than other fixings. There is no difference in strength concerning the other systems. The average strength is greater than the stresses of a shoulder during daily life activities. There is no difference regarding the secondary criterion.Conclusion
The use of a single screw is insufficient, but the other systems seems reliable. The use of small diameter self-compressive cannulated screws can provide a better result. This biomechanical work must be validated in clinical studies.
... Optimal fracture healing requires optimal cortical bone alignment, apposition and immobilization [10]. Some degree of subluxation of a sternal cortical edge over that of the other side may occur with continued movement which could lead to a reduction in sternal width over time. ...
Objectives:
We sought to compare the effects of conventional wire cerclage with that of the band and plate fixation of the sternum.
Methods:
A parallel randomized open-label trial with 1:1 allocation ratio compared healing after adult cardiac surgery using 'figure-of-8' stainless steel wire cerclage or a band and plate system (plates). The primary end point was maximal sternal edge displacement during active coughing of ≥2 mm in ≥2 of 4 sites measured with ultrasound by 2 assessors blinded to the other at 6 weeks postoperatively. Secondary end points at 12 weeks included ultrasound assessment, computed tomography (CT) scan and multidimensional assessment of quality of recovery using the Postoperative Quality of Recovery Scale.
Results:
Of 50 patients, 26 received plates and 24 wires. Two patients died and 1 withdrew consent leaving 25 plates and 22 wires for primary end point analysis. Operations included 37 coronary, 5 valve and 8 combined coronary and valve procedures. At 6 weeks, less sternal movement was observed in patients with plates than those with wires, 4% (1/25) vs 32% (7/22), P = 0.018. Agreement between observers was high, kappa = 0.850. At 12 weeks, less ultrasound motion was seen in patients with plates, 0% (0/23) than those with wires, 25% (5/20), P = 0.014. Recovery from pain was higher for patients with plates 92% (22/24) than those with wires 67% (14/21), P = 0.004. CT bone edge separation was less for plates 38% (9/24) than wires 71% (15/21), P = 0.036. CT mild bone synthesis or greater was similar between patients with plates 21% (5/24) and wires 14% (3/21), P = 0.71.
Conclusions:
Patients receiving the band and plate system had significantly less sternal edge motion than those receiving wires, 6 and 12 weeks after cardiac surgery and experienced less pain.
Clinical trial registration:
clinicaltrials.gov NCT03282578.
... Other studies reached a similar conclusion: that manipulation of the materials and configuration of the device can be optimized to enhance image quality, retaining the diagnostic utility of external fixation in MRI [6,[16][17][18]. On one hand, variability in the amount of stiffness applied to the fracture site influences the way the bone heals in the long term [19][20][21][22][23][24][25]. On the other hand, temporary post-trauma stability at the fracture site reduces pain, risk of infection [26], and minimizes secondary soft-tissues injuries [27,28]. ...
Introduction
Temporary external fixation has been widely utilized in the stabilization of plateau fractures while waiting for an optimization of the soft tissue conditions before subsequent permanent internal fixation. Simultaneously, MRI is beneficial in the assessment of concomitant damage to ligaments and menisci so that these injuries could be promptly identified, and surgical planning executed at the time of definitive fixation of the bony injury. Increasing numbers of side-bars and pins have been previously suggested to increase frame rigidity, but at the same time, several studies have indicated the presence of MRI artifacts which may obscure key anatomical structures, even when MRI-compatible fixation devices are used. This study aims to identify, among six potential configurations, the construct that maximizes stability while most minimizing the number of MRI artifacts generated among different configurations commonly used.
Hypothesis
There is one or more configurations among the others that maximize stability while preserving a clinically acceptable level of MRI quality.
Material and methods
Six constructs were recreated on cadaveric specimens and identified by the disposition of the bars: H, Anterior, Flash, Hashtag, Rhomboid, and Diamond. Stage one evaluated the amount of artifact produced during MRI on instrumented cadaveric legs, as well as the signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR) at five specific regions of interest. Stage two assessed the amount of compressional and torsional stiffness of the configurations on bone surrogate models.
Results
Image artifacts were not detected within the knee joint for all considered constructs. In terms of SNR The H, Anterior, Hashtag, and Diamond configurations were not significantly different from their control (p > 0.366) while the others were significantly different (p < 0.03). The values of CNR found for the H and Hashtag configurations were not significantly different from their controls (p > 0.07) while the remaining configurations were significantly different (p < 0.03). In compression, the H and Diamond configurations had similar stiffness (p = 0.468) of 35.78 N/mm and 31.44 N/mm, respectively, and were stiffer than the other configurations. In torsion, the constructs have shown different stiffness (p < 0.001) with a minimum value of 0.66 Nm/deg for the Rhomboid configuration, which was significantly less stiff than the Anterior configuration (1.20 Nm/deg [p < 0.001]). There was no difference between the Diamond and H configurations (p = 0.177) or between them and the Hashtag configuration (p = 0.215).
Discussion
An external fixator construct directly bridging the femur and tibia without interconnections is the most stable and produces MRI scans without image artifacts that would interfere with diagnostic quality.
Level of evidence
V, basic science study, diagnostic imaging and mechanical testing.
... Graft displacement was measured continuously (Fig. 5.9). Failure was set at 0.8 mm of shear displacement, based on previously published fracture healing data (Schell et al., 2005) (Augat et al., 2006). Graft displacement was recorded as the final displacement during the last cycle of each loading increment. ...
... The main questions regarding fractures of weightbearing bone segments are related to type of fixation (rigid or elastic) and implants type that is most biologically favorable based on surgical indications. 7 Every fracture has peculiar characteristics (fracture line, bone loss, fragment comminution, etc.), supporting the theory that different mechanical moments and variable mechanical stresses that occur during the healing process are necessary. Forces acting on the fracture site cause biochemical changes such as release of chemical mediators, growth factors, 8 hormones that work on a systemic level, and alteration/ deprivation of neuronal signals that negatively affect bone healing. ...
Angular stability plates are largely used for treating complex fractures, but the incidence of nonunion is high. The innovative dynamic internal fixator (DIF) system is comprised of a plate with angular stability that combines the principles of internal fixator with dynamic device. In this study, we evaluate the feasibility of surgical reconstruction using the DIF in adult patients with epiphyseal-metaphyseal femur fractures and examine complications and outcomes at long-term follow-up. We retrospectively analyze 26 patients (14 females and 12 males), with a mean age of 64 yr, who were treated for femoral fractures between 2008 and 2017. Primary fractures were stratified according to the Muller AO Classification of fractures (mostly types 33-A3 and 31-A3). One patient was treated for a periprosthetic fracture and another for the early breakage of a conventional plate. Mean overall follow-up was 4.3 yr. Fracture healing with complete bony consolidation was achieved in 25 of 26 patients (96%). Two patients experienced complete union after revision surgery. The mean time to bridging callus formation was 58 d (range, 41 d to 4 mo) and to radiographic union was 4.6 mo (range, 1.2 to 12.5 mo). Dynamization of the system was performed in 16 cases. The following major complications occurred in 15% of cases: wound dehiscence (1), nonunion (2), and deep infection (1). No implant breakdowns were observed. The DIF system merged the advantages of angular stability plates with the possibility of dynamization, increasing fracture site compression to modulate and guarantee the healing process.
... Specifically, the early phase of the healing cascade is considered to be highly mechanosensitive (Klein et al., 2003). In this regard, we and others suggested that the initial mechanical condition influence the entire subsequent inflammatory, angiogenic, and endochondral healing cascades (Goodship, Cunningham, & Kenwright, 1998;Klein et al., 2003;Schell et al., 2005). To further employ the power of mechanobiology in critical healing scenarios, an improved understanding of how mechanical stimuli influence cellular processes like migration, differentiation, and growth factor signaling is needed. ...
Mechanical boundary conditions critically influence the bone healing process. In this context, previous in vitro studies have demonstrated that cyclic mechanical compression alters migration and triggers osteogenesis of mesenchymal stromal cells (MSC), both processes being relevant to healing. However, it remains unclear whether this mechano‐sensitivity is a direct consequence of cyclic compression, an indirect effect of altered supply or a specific modulation of autocrine BMP signaling. Here, we investigate the influence of cyclic mechanical compression (ε=5% and 10%, f=1 Hz) on human bone marrow MSC (hBMSC) migration and osteogenic differentiation in a 3D biomaterial scaffold, an in vitro system mimicking the mechanical environment of the early bone healing phase. The open‐porous architecture of the scaffold ensured sufficient supply even without cyclic compression, minimizing load‐associated supply alterations. Furthermore, a large culture medium volume in relation to the cell number diminished autocrine signaling. Migration of hBMSCs was significantly down‐regulated under cyclic compression. Surprisingly, a decrease in migration was not associated with increased osteogenic differentiation of hBMSCs, as the expression of RUNX2 and osteocalcin decreased. In contrast, BMP2 expression was significantly upregulated. Enabling autocrine stimulation by increasing the cell‐to‐medium ratio in the bioreactor finally resulted in a significant upregulation of RUNX2 in response to cyclic compression, which could be reversed by rhNoggin treatment. The results indicate that osteogenesis is promoted by cyclic compression, when cells condition their environment with BMP. Our findings highlight the importance of mutual interactions between mechanical forces and BMP signaling in controlling osteogenic differentiation.
Bone fracture healing is regulated by mechanobiological cues. Both, extracellular matrix (ECM) deposition and microvascular assembly determine the dynamics of the regenerative processes. Mechanical instability as by inter‐fragmentary shear or compression is known to influence early ECM formation and wound healing. However, it remains unclear how these external cues shape subsequent ECM and microvascular network assembly. As transcriptional coactivators, the mechanotransducers yes‐associated protein 1 (YAP)/transcriptional coactivator with PDZ‐binding motif (TAZ) translate physical cues into downstream signaling events, yet their role in sprouting angiogenesis into the hematoma after injury is unknown. Using bone healing as model system for scar‐free regeneration, the role of endothelial YAP/TAZ in combination with tuning the extrinsic mechanical stability via fracture fixation is investigated. Extrinsically imposed shear across the gap delayed hematoma remodeling and shaped the morphology of early collagen fiber orientations and microvascular networks, suggesting that enhanced shear increased the nutrient exchange in the hematoma. In contrast, endothelial YAP/TAZ deletion has little impact on the overall vascularization of the fracture gap, yet slightly increases the collagen fiber deposition under semi‐rigid fixation. Together, these data provide novel insights into the respective roles of endothelial YAP/TAZ and extrinsic mechanical cues in orchestrating the process of bone regeneration.
Clinical findings, manufacturer instructions, and surgeon's preferences often dictate the implantation of distal femur locked plates (DFLPs), but healing problems and implant failures still persist. Also, most biomechanical researchers compare a particular DFLP configuration to implants like plates and nails. However, this begs the question: Is this specific DFLP configuration biomechanically optimal to encourage early callus formation, reduce bone and implant failure, and minimize bone "stress shielding"? Consequently, it is crucial to optimize, or characterize, the biomechanical performance (stiffness, strength, fracture micro-motion, bone stress, plate stress) of DFLPs influenced by plate variables (geometry, position, material) and screw variables (distribution, size, number, angle, material). Thus, this article reviews 20 years of biomechanical design optimization studies on DFLPs. As such, Google Scholar and PubMed websites were searched for articles in English published since 2000 using the terms "distal femur plates" or "supracondylar femur plates" plus "biomechanics/biomechanical" and "locked/locking," followed by searching article reference lists. Key numerical outcomes and common trends were identified, such as: (a) plate cross-sectional area moment of inertia can be enlarged to lower plate stress at the fracture; (b) plate material has a larger influence on plate stress than plate thickness, buttress screws, and inserts for empty plate holes; (c) screw distribution has a major influence on fracture micro-motion, etc. Recommendations for future work and clinical implications are then provided, such as: (a) simultaneously optimizing fracture micro-motion for early healing, reducing bone and implant stresses to prevent re-injury, lowering "stress shielding" to avoid bone resorption, and ensuring adequate fatigue life; (b) examining alternate non-metallic materials for plates and screws; (c) assessing the influence of condylar screw number, distribution, and angulation, etc. This information can benefit biomedical engineers in designing or evaluating DFLPs, as well as orthopedic surgeons in choosing the best DFLPs for their patients.
Fracture healing is stimulated by micromotion at the fracture site, whereby there exists an optimal amount of strain to promote secondary bone formation. Surgical plates used for fracture fixation are often evaluated for their biomechanical performance using benchtop studies, where success is based on overall construct stiffness and strength measures. Integration of fracture gap tracking to this assessment would provide crucial information about how plates support the various fragments present in comminuted fractures, to ensure there are appropriate levels of micromotion during early healing. The goal of this study was to configure an optical tracking system to quantify 3D interfragmentary motion to assess the stability (and corresponding healing potential) of comminuted fractures. An optical tracking system (OptiTrack, Natural Point Inc, Corvallis, OR) was mounted to a material testing machine (Instron 1567, Norwood, MA, USA), with an overall marker tracking accuracy of 0.05 mm. Marker clusters were constructed that could be affixed to individual bone fragments, and segment-fixed coordinate systems were developed. The interfragmentary motion was calculated by tracking the segments while under load and was resolved into compression-extraction and shear components. This technique was evaluated using two cadaveric distal tibia-fibula complexes with simulated intra-articular pilon fractures. Normal and shear strains were tracked during cyclic loading (for stiffness tests), and a wedge gap was also tracked to assess failure in an alternate clinically relevant mode. This technique will augment the utility of benchtop fracture studies by moving beyond total construct response and providing anatomically relevant data on interfragmentary motion, a valuable proxy for healing potential.
Three-dimensional hydroxyapatite-chitosan (HA-CS) composites loaded with ciprofloxacin antibiotic (HA–CS–CIP) were formulated using the in situ and the solid-liquid method coupled with the freeze-drying process. The interaction of the HA-CS composite powder and ciprofloxacin antibiotic (CIP) was investigated by batch adsorption essays. The kinetic and the isotherm data were fitted well to the pseudo-second-order and Freundlich models, respectively. The compressive strength of the HA-CS composite was increased by 7-fold and 10-fold when using respectively 15 wt% and 30 wt% of the polymer compared to the HA-CS5 formulation (3.6 ± 0.7 MPa) made only from HA powder and CS gel (5 wt%). However, this parameter decreased from 36.8 ± 8.5 MPa down to 20.5 ± 4.7 MPa when the antibiotic content increased from 0 up to 9 wt%, respectively. The in vitro release results showed a sustained and controlled CIP release for up to 10 days. The release data fitting and modeling indicate that the process follows a Fickian diffusion mechanism. Also, the formulated composite revealed an antibacterial effect against Staphylococcus aureus and Escherichia coli bacteria. The developed composite may be a promising candidate for bone substitution and as an antibiotic local delivery system for the treatment of orthopedic implant-associated infections.
Introduction:
In the surgical fixation of fractures, proper biomechanical stability is key in preventing clinical complications including poor fracture healing, residual deformity, loss of fixation, or implant failure. Stability is largely influenced by treatment decisions made by the surgeon. The interplay of surgeon-controlled variables and their effect on the three-dimensional (3D) biomechanics of a fracture fixation construct are often not intuitive, and current training methods do not facilitate a deep understanding of these interactions.
Methods:
A simulation software interface, FracSim, was developed. FracSim is built on a large precomputed library of finite element simulations. The software allows a surgeon to make adjustments to a virtual fracture fixation construct/weight-bearing plan and immediately visualize how these changes affect 3D biomechanics, including implant stress and fracture gap strain, important for clinical success. Twenty-one orthopaedic residents completed an instructor-led educational session with FracSim focused on bridge plating. Subjects completed pretests and posttests of knowledge of biomechanical concepts and a questionnaire.
Results:
Subjects scored a mean of 5.6/10 on the pretest of biomechanical knowledge. Senior residents scored better than junior residents (P = 0.04). After the educational session with FracSim, residents improved their test scores to a mean of 8.0/10, with a significant improvement (P < 0.001). Questionnaire scores indicated that subjects believed that FracSim had realistic implants, constructs, and motions and that training with FracSim was purposeful, desirable, efficient, fun, and useful for enhancing the understanding of fracture fixation biomechanics.
Discussion:
This new type of simulation software enables interactive visualization of 3D fracture fixation biomechanics. Limitations of this study include lack of a control group undergoing traditional education and lack of a delayed posttest to assess retention. FracSim may provide an effective and engaging way to promote a deeper understanding of biomechanical concepts in the orthopaedic learner.
The ovine critical-sized defect model provides a robust preclinical model for testing tissue-engineered constructs for use in the treatment of non-union bone fractures and severe trauma. A critical question in cell-based therapies is understanding the optimal therapeutic cell dose. Key to defining the dose and ensuring successful outcomes is understanding the fate of implanted cells, e.g., viability, bio-distribution and exogenous infiltration post-implantation. This study evaluates such parameters in an ovine critical-sized defect model 2 and 7 days post-implantation. The fate of cell dose and behaviour post-implantation when combined with nanomedicine approaches for multi-model tracking and remote control using external magnetic fields is also addressed. Autologous STRO-4 selected mesenchymal stromal cells (MSCs) were labelled with a fluorescent lipophilic dye (CM-Dil), functionalised magnetic nanoparticles (MNPs) and delivered to the site within a naturally derived bone extracellular matrix (ECM) gel. Encapsulated cells were implanted within a critical-sized defect in an ovine medial femoral condyle and exposed to dynamic gradients of external magnetic fields for 1 h per day. Sheep were sacrificed at 2 and 7 days post-initial surgery where ECM was harvested. STRO-4-positive (STRO-4+) stromal cells expressed osteocalcin and survived within the harvested gels at day 2 and day 7 with a 50% loss at day 2 and a further 45% loss at 7 days. CD45-positive leucocytes were also observed in addition to endogenous stromal cells. No elevation in serum C-reactive protein (CRP) or non-haem iron levels was observed following implantation in groups containing MNPs with or without magnetic field gradients. The current study demonstrates how numbers of therapeutic cells reduce substantially after implantation in the repair site. Cell death is accompanied by enhanced leucocyte invasion, but not by inflammatory blood marker levels. Crucially, a proportion of implanted STRO-4+ stromal cells expressed osteocalcin, which is indicative of osteogenic differentiation. Furthermore, MNP labelling did not alter cell number or result in a further deleterious impact on stromal cells following implantation.
Methods to repair bone defects arising from trauma, resection, or disease, continue to be sought after. Cyclic mechanical loading is well established to influence bone (re)modelling activity, in which bone formation and resorption are correlated to micro-scale strain. Based on this, the application of mechanical stimulation across a bone defect could improve healing. However, if ignoring the mechanical integrity of defected bone, loading regimes have a high potential to either cause damage or be ineffective. This study explores real-time finite element (rtFE) methods that use three-dimensional structural analyses from micro-computed tomography images to estimate effective peak cyclic loads in a subject-specific and time-dependent manner. It demonstrates the concept in a cyclically loaded mouse caudal vertebral bone defect model. Using rtFE analysis combined with adaptive mechanical loading, mouse bone healing was significantly improved over non-loaded controls, with no incidence of vertebral fractures. Such rtFE-driven adaptive loading regimes demonstrated here could be relevant to clinical bone defect healing scenarios, where mechanical loading can become patient-specific and more efficacious. This is achieved by accounting for initial bone defect conditions and spatio-temporal healing, both being factors that are always unique to the patient.
Objective
To compare the stiffness of constructs fixed with a type II external skeletal fixator (ESF) or a 3.5‐mm locking compression plate (LCP) in axial compression and bending with a fracture gap model.
Study design
Quasi‐static four‐point bending and axial compression tests.
Sample population
Ten LCP and 10 ESF immobilizing epoxy cylinders with a 40‐mm fracture gap.
Methods
Five constructs of each type were tested in nondestructive mediolateral (ML) four‐point bending and then rotated and tested in nondestructive craniocaudal (CC) four‐point bending. Five additional constructs of each type were tested in nondestructive axial compression. Stiffness was compared between loading modes by construct type and between construct types by loading mode.
Results
Type II ESF were stiffer than LCP in ML bending (difference, 1474 N/mm, P < .0001) and in axial compression (difference, 458 N/mm, P = .008) but not in CC bending (P = .1673). Type II ESF were stiffer in ML bending than in CC bending (difference, 999 N/m, P < .0001), while LCP were stiffer in CC bending than in ML bending (difference, 634 N/mm, P < .0001).
Conclusion
Type II ESF generated stiffer constructs compared with LCP in ML bending and in axial compression without a difference in CC bending. External skeletal fixator and LCP bending stiffness varied by loading direction.
Clinical significance
A type II ESF should be considered in a comminuted fracture requiring increased stability in ML and axial directions.
Background
Fracture site motion creates mechanical strains on the healing tissues which influences bone formation. Axial micro-motion maximizes dilatational strains, whereas shearing motions maximize deviatoric strains on the healing tissues. Dilatational strains optimize bone healing, deviatoric strains retard bone healing. Dynamization of external fixation using either an Ilizarov or Spatial Frame platform is used to increase loading on the limb which increases the mechanical stress and strain on the tissues to improve healing. The scientific literature does not address how dynamization of the spatial frame effects fracture site motion. The purpose of this study is to assess the effect of modified shoulder bolts incorporated into a spatial frame during dynamic loading.
Methods
Five identical two-ring spatial frame constructed were mounted on Sawbones tibias with an osteotomy performed distal to the tibial tubercle. Sinusoidal load was applied at a rate of 0.25 Hz. Axial force and displacement, in addition to motion of the proximal and distal tibia segments were recorded. Eight constructs were tested: 1) All struts of the Spatial Frame rigid, 2) Strut #1 loose, 3) Struts #1 and #3 loose, 4) Struts #1, #3 and #5 loose, 5) All struts loose, 6) All struts rigid with dynamization bolts on the proximal end, 7) All struts rigid with dynamization bolts on alternating sides, 8) Threaded rods between the rings with two millimeters of dynamization.
Results
No difference in vertical displacement was observed between the Ilizarov and all struts locked. No significant difference in shear values between all struts locked and modified shoulder bolt struts was observed. Increase in vertical movement with the modified shoulder bolts was an average of 1.83 mm. Significant shear forces at the fracture site were observed with unlocking single or multiple struts of the spatial frame.
Conclusion
Modified shoulder bolts can be used for spatial frame dynamization without increasing shear motion.
Adult large-bodied theropods are often found with numerous pathologies. A large, almost complete, probably adult Allosaurus specimen from the Howe Stephens Quarry, Morrison Formation (Late Kimmeridgian–Early Tithonian), Wyoming, shows multiple pathologies. Pathologic bones include the left dentary, two cervical vertebrae, one cervical and several dorsal ribs, the left scapula, the left humerus, right ischium, and two left pedal phalanges. These pathologies can be classified as follows: the fifth cervical vertebra, the scapula, several ribs and the ischium are traumatic, and a callus on the shaft of the left pedal phalanx II-2 is traumatic-infectious. Traumatically fractured elements exposed to frequent movement (e.g. the scapula and the ribs) show a tendency to develop pseudarthroses instead of callus healing. The pathologies in the lower jaw and a reduced flexor tubercle of the left pedal phalanx II-2 are most likely traumatic or developmental in origin. The pathologies on the fourth cervical are most likely developmental in origin or idiopathic, that on the left humerus is infectious or idiopathic, whereas left pedal phalanx IV-1 is classified as idiopathic. With exception of the ischium, all traumatic / traumatic-infectious pathologic elements show unambiguous evidences of healing, indicating that the respective pathologies did not cause the death of this individual. Alignment of the scapula and rib pathologies from the left side suggests that all may have been caused by a single traumatic event. The ischial fracture may have been fatal. The occurrence of multiple traumatic pathologies again underlines that large-bodied theropods experienced frequent injuries during life, indicating an active predatory lifestyle, and their survival perhaps supports a gregarious behavior for Allosaurus. Signs of infections are scarce and locally restricted, indicating a successful prevention of the spread of pathogens, as it is the case in extant reptiles (including birds).
Background:
A new locking-screw technology, the Variable Fixation Locking Screw (VFLS; Biomech Innovations), was developed with the aim of promoting secondary fracture-healing. The VFLS features a resorbable sleeve that progressively decreases its mechanical properties and mass during the fracture-healing time. In this study, we investigated whether the VFLS can provide rigid as well as progressive dynamic fixation.
Methods:
The interfragmentary stability provided by the VFLS was tested in a simulated fracture-gap model and compared with that provided by standard locking or by a combination of both technologies under compression and torsional loading. Tests were performed with an intact sleeve (initial condition) and after its chemical dissolution. An optical measurement system was used to characterize interfragmentary movements.
Results:
The axial stiffness did not differ significantly among groups in the initial condition. Sleeve resorption significantly decreased construct stiffness. The torsional stiffness of the samples instrumented with the VFLS was lower than that of the control group. The degradation of the sleeve resulted in a significant increase in axial displacement recorded at both the cis and trans cortices. In samples featuring combined technologies, this increase was about 12% to 20% at the trans cortex and about 50% to 60% at the cis cortex. In samples featuring VFLS technology only, this increase was about 20% to 37% at the trans cortex and about 70% to 125% at the cis cortex.
Conclusions:
The initial stability offered by the VFLS is equivalent to that of standard locking-screw technology. The resorption of the degradable sleeve leads to effective and reproducible fracture-gap dynamization, progressively varying the way the fracture gap is strained and the magnitude of the strain.
Clinical relevance:
The VFLS provides rigid and progressive dynamic fixation in vitro. Such variable stability might have beneficial effects in terms of triggering and boosting secondary fracture-healing.
An improved understanding of how local mechanical stimuli guide the fracture healing process has the potential to enhance clinical treatment of bone injury. Recent preclinical studies of bone defect in animal models have used cross-sectional data to examine this phenomenon indirectly. In this study, a direct time-lapsed imaging approach was used to investigate the local mechanical strains that precede the formation of mineralised tissue at the tissue scale. The goal was to test two hypotheses: 1) the local mechanical signal that precedes the onset of tissue mineralisation is higher in areas which mineralise, and 2) this local mechanical signal is independent of the magnitude of global mechanical loading of the tissue in the defect. Two groups of mice with femoral defects of length 0.85 mm (n = 10) and 1.45 mm (n = 9) were studied, allowing for distinct distributions of tissue scale strains in the defects. The regeneration and (re)modelling of mineralised tissue was observed weekly using in vivo micro-computed tomography (micro-CT), which served as a ground truth for resolving areas of mineralised tissue formation. The mechanical environment was determined using micro-finite element analysis (micro-FE) on baseline images. The formation of mineralised tissue showed strong association with areas of higher mechanical strain (area-under-the-curve: 0.91 ± 0.04, true positive rate: 0.85 ± 0.05) while surface based strains could correctly classify 43% of remodelling events. These findings support our hypotheses by showing a direct association between the local mechanical strains and the formation of mineralised tissue.
Purpose:
To compare screw insertional torque and coracoid-glenoid compression from 4 fixation techniques with different screw design parameters and cortical augmentation for the Latarjet procedure.
Methods:
Simulated Latarjet procedures were performed with 4 fixation techniques using laminated polyurethane blocks with dimensions similar to the coracoid-glenoid construct. The groups included DePuy Synthes Mitek 3.5-mm partially threaded screws with top hats, Arthrex 3.75-mm fully threaded screws with a 2-hole plate, Arthrex 3.75-mm fully threaded screws, and Smith & Nephew 4.0-mm partially threaded screws. Screws were inserted using a digital torque-measuring screwdriver to determine maximum insertional torque. Pressure-sensitive film was used to measure the maximum contact pressure and the effective pressure distribution (EPD) between the coracoid and glenoid; the EPD represents the percentage of the film's surface area that experienced pressure greater than 10 MPa. One-way analysis of variance and post hoc tests were used for statistical analysis.
Results:
Significant differences were found between the 4 fixation groups for each variable measured. The 2 cortically augmented systems produced significantly higher maximum insertional torque than the non-cortically augmented systems (P < .001 for both). The 3.75-mm screws with a 2-hole plate yielded significantly higher contact pressures than the 4.0-mm screws (P = .028). This group also had a high EPD, with a mean value more than double the values of the non-cortically augmented systems (P = .037 and P < .001).
Conclusions:
Cortically augmented fixation methods showed higher maximum insertional torque, maximum contact pressure, and EPD between the surfaces of the coracoid and glenoid in this Sawbones model.
Clinical relevance:
Various implants are available for the Latarjet procedure, but their biomechanical characteristics have not yet been fully elucidated. Graft fracture and nonunion represent 2 modes of failure that may be related to insertional torque and coracoid-glenoid compression. This study compared screw insertional torque and compression achieved using 4 fixation techniques with different screw design parameters and cortical augmentation in a Sawbones model.
Sufficient vascularization of the fracture-healing zone is a prerequisite for undisturbed bone healing. One important factor affecting the vascularization is the interfragmentary movement in the fracture-healing zone. Many studies have demonstrated that stable fixation with predominatly moderate interfragmentary compression movement can stimulate vascularization and the healing process whereas unstable fracture fixation delays the vascularization and bone healing process. Instability of fracture fixation, in particular large shearing interfragmentary movement, can cause delayed healing or non-unions.
We hypothesize that the direction of interfragmentary movement affects vascularization in the fracture-healing zone. Cyclic compressive strain stimulates greater vessel formation than tensile or shearing strain. This is due to differences in the local mechanical environment which are not delineated by the direction-independent characterization of interfragmentary movement typically reported. We propose that new vessel formations buckle under compressive loading without significant load transfer across endothelial cell junctions while both tensile and shearing deformations result in disruptive loads despite a biochemically angiogenic environment.
From a clinical perspective, this means that the optimal conditions for rapid vascularization result from fracture fixation that minimizes cyclic tensile and shearing movements in the healing zone while allowing moderate compressive movements
We examined the effect of periosteal devascularisation upon the early healing of osteotomies of sheep tibiae held in an instrumented external fixation system with an axial stiffness of 240 N/mm. At 14 days, cortical blood flow measured by the microsphere technique was 19.3 ml/min/100g in the well-vascularised osteotomies, but only 1.7 ml/min/100g in the devascularised osteotomies, despite an increase in medullary flow (p less than 0.0005). Delay in healing of the devascularised osteotomies was suggested by an in vivo monitoring system and confirmed by post-mortem mechanical testing. We suggest that the osteogenic stimulus of dynamic external fixation is dependent on the early restoration of cortical blood flow in devascularised fractures.
A computerized motion sensor was used to record the three-dimensional components of interfragmentary motion during healing in three patients with closed, low-energy fractures of the tibial diaphysis treated with functional braces. At the first measurement session 2 weeks after fracture, the patients applied approximately 15 kg to the injured limb. Although this produced 1-4 mm of translation of the fragments, this was recovered when the load was removed. The maximum rotational and angulatory displacements often occurred as the patients rose from the chair with no weight applied to the limb and frequently were reduced as the 15 kg of load was applied. Under load, the maximum axial rotation was 3 degrees and the maximum angular displacement was 1 degree. As with the translations, the initial rotational and angulatory positions of the fragments were recovered when the load was removed and the patient returned to the seated position. At 8 weeks, the patient applied full body weight, producing a maximum interfragmentary translation of 0.5 mm and maximum axial rotation or angulation of 0.5 degrees. Abundant peripheral callus formed in all three fractures, and they healed by 15 weeks through typical gradual consolidation and mineralization of the callus, accompanied by a corresponding reduction in interfragmentary motions.
Flexible fixation of fractures with minimally invasive surgical techniques has become increasingly popular. Such techniques can lead to relatively large fracture gaps (larger than 5 mm) and considerable interfragmentary movements (0.2-5 mm). We investigated the influence of the size of the fracture gap, interfragmentary movement, and interfragmentary strain on the quality of fracture healing. A simple diaphyseal long-bone fracture was modeled by means of a transverse osteotomy of the right metatarsus in sheep. In 42 sheep, the metatarsus was stabilized with a custom-made external ring fixator that was adjustable for gap size and axial interfragmentary movement. The sheep were randomly divided into six groups with three different gap sizes (1, 2, or 6 mm) and small or large interfragmentary strain (approximately 7 or 31%). The movement of the fracture gap was monitored telemetrically by a displacement transducer attached to the fixator. After 9 weeks of healing, the explanted metatarsus was evaluated mechanically in a three-point bending test to determine bending stiffness and was radiographed to measure the amount of periosteal callus formation. Increased size of the gap (from 1 to 6 mm) resulted in a significant reduction in the bending stiffness of the healed bones. Larger interfragmentary movements and strains (31 compared with 7%) stimulated larger callus formation for small gaps (1-2 mm) but not for larger gaps (approximately 6 mm). The treatment of simple diaphyseal fractures with flexible fixation can be improved by careful reduction of the fracture; this prevents large interfragmentary gaps. The experimental fracture model for the metatarsus showed that the healing process was inferior when the gap was larger than 2 mm.
The effects of interfragmentary sliding (shear) motion, axial motion, and locked external fixation on the healing of mid-tibial closed fractures were studied in fifty-six skeletally mature New Zealand White rabbits. The fractures were fixed with use of a four-pin, double-bar frame and were allowed to heal for either two or four weeks. Four experimental conditions were evaluated: transverse and oblique fractures treated with a locked external fixator (Groups 1 and 3, respectively), transverse fractures treated with an axially telescoping fixator (Group 2), and oblique fractures treated with a sliding oblique fixator (Group 4). The maximum interfragmentary motion, recorded in vivo with an electronic motion sensor that was attached to the fixator, was 0.6 millimeter in Group 2 during the first week and then declined rapidly. In contrast, the motion in Group 4 exceeded 1.5 millimeters during the first week. The circumference of the callus in Group 4 was 11 to 23 per cent greater than that in the other groups at both two and four weeks (p < or = 0.02). At two weeks, torsional stiffness, strength, and energy absorption were comparable among Groups 1, 2, and 3. The increase in healing was most rapid for Group 4; by four weeks, the torsional strength and energy to failure of the fractures in Group 4 exceeded those in the other groups (p < or = 0.025) and reached or exceeded those of intact bone. Apparently, oblique sliding (shear) motion promoted greater cartilage differentiation and expansion of the peripheral callus than did axial motion or locked external fixation.
An interdisciplinary study based on animal experiments, cell culture studies, and finite element models is presented. In a sheep model, the influence of the osteotomy gap size and interfragmentary motion on the healing success was investigated. Increasing gap sizes delayed the healing process. Increasing movement stimulated callus formation but not tissue quality. Typical distributions of intramembranous bone, endochondral ossification, and connective tissue in the fracture gap are quantified. The comparison of the mechanical data determined by a finite element model with the histologic images allowed the attribution of certain mechanical conditions to the type of tissue differentiation. Intramembranous bone formation was found for strains smaller than approximately 5% and small hydrostatic pressure (< 0.15 MPa). Strains less than 15% and hydrostatic pressure more than 0.15 MPa stimulated endochondral ossification. Larger strains led to connective tissue. Cell culture studies on the influence of strain on osteoblasts supported these findings. Proliferation and transforming growth factor beta production was increased for strains up to 5% but decreased for larger strains. Osteoblasts under larger strains (> 4%) turned away from the principal strain axis and avoided larger deformations. It is hypothesized that gap size and the amount of strain and hydrostatic pressure along the calcified surface in the fracture gap are the fundamental mechanical factors involved in bone healing.
Different external fixators demonstrated different motion patterns at the fracture site in AP bending. This indicates that fracture gap motion patterns cannot be predicted from a single value of overall frame stiffness. This type of information may be useful in examining existing theories of fracture healing in response to different types of fracture gap motion.
Different fixation systems are used for fracture and defect treatment. A prerequisite for complication free healing is sufficient mechanical stability of the osteosynthesis. In vitro investigations offer the possibility of both analysing and assessing the pre-clinical fixation stability. Due to the complex loading environment in vivo, stiffness analysis should include a complete determination of the stiffness under standardised conditions. Based on a mathematical procedure to calculate the 3-D stiffness, a mechanical testing device for the 3-D loading of fixation systems was designed and integrated in the existing test set-up. The set-up consisted of a material testing machine to produce the necessary loads and an optical measurement device to detect the resulting inter-fragmentary movements. To validate the testing device, the 3-D stiffness matrices of different Ilizarov fixator configurations were determined and compared. The good reproducibility of the test was reflected in the small intra-individual variability of the stiffness components. A distinct direction dependence of the fixator stiffness was observed. Increasing the number of rings led to a stiffness increase of up to 50 %, especially in bending. The presented testing device allows a complete standardised determination of the stiffness of different fixation systems. It considers the direction dependence of the stiffness and creates a prerequisite for a more direct implant comparison.
Measurement of ground contact forces can be used to assess the loads to which the human body is subjected in normal activities, like walking, or in more demanding situations such as in sports. With regard to clinical problems it is useful to compare the loads in the limb either between injured and non-injured or pre- and post-traumatic or -operative states. Otherwise, comparisons between patients and control groups are necessary. Measurement of the plantar pressure, i.e. the distribution of force over the sole of the foot, is useful as it provides detailed information specific to each region of contact. A wide variety of measurement systems are available on the market. These systems should be considered with respect to their technical specifications and the intended application. In general, one should distinguish between different sensor principles (resistive, capacitive, piezoelectric) and different devices (platform, insole, single transducer system). Platform systems are restricted to use in a laboratory setting (embedded in a walkway) and are used for barefoot measurements. Insole or single transducer systems can be used to record the plantar pressures within the shoe and therefore are appropriate to evaluate the effects of different shoe constructions or modifications like orthotics. Some of the precautions to be taken into account for reproducible measurements and the factors influencing pressure patterns have to be considered. Furthermore, the application of plantar pressure measurements to various clinical problems will be discussed.
Classical stable plate osteosynthesis with its anatomical repositioning, absolute stability between fragments and medial support
should only be applied to joint fractures and spongy bone. In cortical bone, the anatomical reposition connected with the
plate promotes bone necrosis along the fracture and prevents callus formation. Direct cortical synthesis, a method also known
as ``primary bone healing'', serves the bone's revascularisation and is not necessarily aimed at healing. Thus, this may also
be termed ``necrosis healing''. Along the shaft of long bones, elastic plate osteosynthesis, a biological method, is safer
than and superior to the rigid technique. This even applies to short oblique and transverse fractures insofar as nailing does
not appear feasible. Elasticity is achieved by leaving a flexible stretch of at least 2 – 4 holes, i.e. as long as possible,
without screws over the fracture and by employing a titanium plate. Thus, there is no punctate fatigue leading to plate breakage.
The fitting of third fragments is deliberately left out. The same applies to all kinds of compression with lag screws, tension
devices or DC-gliding holes – and this with the intention of allowing micromovements in the fracture's fissure. Periost and
muscle are not removed and the fracture is not examined. Healing occurs spontaneously via a fixating callus forming within
the first 3 – 6 weeks out of the periost-soft tissue combination. Histomorphological investigation dates the first woven-
bone bridges between the fragments to 3 weeks subsequent to the accident. In Göttingen University trauma centre, 87 fractures
have been attended to over 2 years using this technique. Despite considerable soft-tissue damage, no delayed bone healing,
pseudoarthrosis or bone infection has been observed. The risks of elastic plate osteosynthesis lie in unbiological and exaggerated
reposition methods, too short a flexible stretch, and insufficient anchorage of the screws.
This review is primarily concerned with those features which have direct clinical relevance and it is fortunately possible to treat fractures successfully without a complete understanding of the cellular mechanisms involved without at the same time relying entirely on empiricism. A number of factors influence the healing which can be identified from both clinical and experimental work and may be taken into consideration to put treatment on a more rational basis. It is with these observations that we shall be particularly concerned and cellular mechanisms will be discussed only if they appear to have clinical implications. Such an account must necessarily include details of the healing process as it is modified by contemporary methods of treatment but first it is necessary to consider that events that occur in the healing of a simple fracture in an unsplinted longe bone.
Based on analysis of the torque-angle curves and roentgenographic findings in fifty-three healing tibial fractures in rabbits tested in torsion to failure, four biomechanical stages of fracture healing were defined, as follows: Stage I--failure through original fracture site, with low stiffness; Stage II--failure through original fracture site, with high stiffness; Stage III--failure partially through original fracture site and partially through intact bone, with high stiffness; and Stage IV--failure entirely through intact bone, with high stiffness. These stages correlated with the progressive increases in the average torque and energy absorption to failure as healing progressed and also with the average times since the original experimental fracture. It is hoped that this system of staging will provide both a standard by which important variables related to ultimate strength of healing fractures can be correlated and an objective way to predict delayed unions and non-unions and to determine the level of activity that is safe for patients with a healing fracture.
The sequence of events occurring after fracture is now relatively well understood. Healing takes place in three phases--inflammatory, reparative and remodelling. In each phase certain cells predominate and specific histologic and biochemical events are characteristic. Factors that influence fracture healing are both local and systemic; the former include particularly the degree of local trauma and bone loss, the type of bone affected, the degree of immobilization and local pathologic conditions; the latter include age, hormones, local stress and electric currents. Natural processes of healing should be allowed to take their usual course and interference should be attempted only when there is demonstrable need or substantial advantages for the patient.
In a prospective study, since March 1989, 55 tibial shaft fractures have been treated with a new, unreamed solid tibial nail (UTN). This nail was initially designed as a temporary implant. The first 33 cases with second or third degree soft tissue damage were reviewed 6 months or more after the operation. Fractures were classified according to Müller: 6 type A (18.2%), 15 type B (45.5%), and 12 type C (36.7%). In 9 cases (27.3%), there was GII (n = 4) or GIII (n = 5) closed soft tissue damage according to Tscherne's classification. The 24 open fractures (72.7%) comprised 11 OII, 3 OIIIA and 10 OIIIB fractures (Gustilo classification). 24 patients (72.7%) were polytraumatized, the mean PTS (Hannover Polytrauma Score) was 18 points (range: 8-65 points). All fractures were stabilized without reaming. The implant diameter was 8mm (n = 14) or 9 mm (n = 19). Static locking was performed in 31 cases. Dermatofasciotomy was necessary because of compartment syndrome in 14 cases. In 1 grade IIIB open fracture soft tissue coverage was performed with a latissimus dorsi myocutaneous free flap 4 days after nailing. In 32 of the 33 cases the use of an additional cast or brace was not necessary during the follow-up treatment; 1 patient had a cast for 8 weeks for the treatment of accompanying injuries. Full weight-bearing was achieved in 5 cases within 3 weeks, in 16 cases within 12 weeks, and in 30 cases within 26 weeks. In 16 cases (48.5%) the interlocking screws were removed after 5-26 weeks (mean: 10 weeks).(ABSTRACT TRUNCATED AT 250 WORDS)
The bone healing process normally unites fractures, arthrodeses, osteotomies, and bone grafting operations. The process normally proceeds in successive stages named the fracture, granulation, and modeling/remodeling stages. A separate regional acceleratory phenomenon speeds up each of the other stages. The osteoclast and osteoblast cells that make intercellular substances of each stage do not exist in sufficient numbers to heal the bone at the moment of fracture or operation. They are made by local multicellular mediator mechanisms that contain precursor and supporting cells, capillaries, lymph, and innervation, plus local autocrine and paracrine regulation. Under the influences of local and systemic agents, these mediator mechanisms determine whether new local osteoclasts and osteoblasts will appear, in addition to when, where, how many, what kind, and for how long. Errors in those functions can then lead to several kinds of retarded or otherwise abnormal bone healing that will be discussed in Part II of this work.
The American Society of Bone and Mineral Research appointed a committee to devise a unified system of terminology for bone histomorphometry, whose report was recently published in the society's journal (Parfitt et al., 1987). In the interests of scientific communication the editors of Bone, Calcified Tissue International, and Bone and Mineral have each agreed to publish a summary of the new system, which has been adopted as part of the instructions to authors by all four journals. This summary is intended to make the system intelligible to the general readership of the journal; the complete version should be consulted by those preparing manuscripts reporting bone histomorphometric data.
Publisher Summary The origin of all cells in the body is the fertilized ovum. Studies of the mechanisms resulting in the development of different cell types, tissues, and organs from this single cell represent one of the most active fields of current research. Certain hemopoietic tissues contain cells capable of forming induced bone when exposed to a suitable environment. The bone formed from these undifferentiated mesenchymal cells is of a temporary nature; repeated acts of inductive activity are required for osteogenesis to be maintained, and if the inducing agent is removed, the bone disappears. Marrow tissues also contain cells capable of bone induction. In this case, the bone formed is of a more permanent nature. A self-perpetuating population of bone cells capable of relatively unlimited osteogenesis can be derived from these cells, and the presence of an inducing agent is not necessary. At present, there is no evidence for the transformation of undifferentiated mesenchymal cells into precursors of bone cells and eventually into the mature cells of bone in the postfetal organism in vivo in normal circumstances..
Fracture healing or bone regeneration has been described histologically, histochemically, biochemically, physiologically, biophysically, and biomechanically. However, these various descriptive analyses do not answer the following all-important questions: What is the inductor(s) that incites cells to start forming bone at the fracture site? What are the responding cells that serve as progenitor cells for the osteoblasts and chondroblasts that appear in the interfragmentary gap? Do factors exist that are required to maintain the regenerating process to its conclusion? Until answers to these questions are found in the laboratory, we will not know "how" bone heals or regenerates itself.
This experimental study examines the relative influence of five unilateral external fixators on tibial fracture stability during simulated walking. Stability during routine patient activity is important, because cyclic inter fragmentary motion, or strain, has been shown to affect fracture healing. In model stable fractures simulating early healing (six weeks), it was found that fixators do little to constrain against axial inter fragmentary strains as great as 100% at only nominal weight-bearing (6.0 kg). These strains may occur repeatably at peak amplitudes of motion during walking. Similarly, peak angular movements may lead to additional axial strains of up to 25% at the external cortex and shear movements may lead to shear strains of up to 100%. Such strains are great enough to yield and possibly refracture the intra gap fracture tissue that may be composed of a combination of granulation tissue, fibrous cartilage, cartilage and bone. It was also shown that the procedure of releasing the fixator column to telescope (dynamize) has little influence on peak cyclic axial motion and on loading at the fracture, although increases occurred in peak transverse and torsional shear strains of up to 100%. Since permanent inter fragmentary translation also arises from the consequent compaction of the intra gap tissue, it may be permanent displacement rather than any change in the amplitude of motion that is responsible for the beneficial effect on healing claimed for the dynamizing procedure. In unstable fractures that are unable to support tibial load at the fracture, the peak amplitudes of cyclic movement were as great as those reported for fractures stabilized by plaster casts, and were approximately twice the movement of the stable fractures simulating early healing. Therefore, patients with unstable fractures supported by external fixators, may be expected to have similar patterns of healing to plaster-casted patients with similar fractures.
Classical stable plate osteosynthesis with its anatomical repositioning, absolute stability between fragments and medial support should only be applied to joint fractures and spongy bone. In cortical bone, the anatomical reposition connected with the plate promotes bone necrosis along the fracture and prevents callus formation. Direct cortical synthesis, a method also known as "primary bone healing", serves the bone's revascularisation and is not necessarily aimed at healing. Thus, this may also be termed "necrosis healing". Along the shaft of long bones, elastic plate osteosynthesis, a biological method, is safer than and superior to the rigid technique. This even applies to short oblique and transverse fractures insofar as nailing does not appear feasible. Elasticity is achieved by leaving a flexible stretch of at least 2-4 holes. i.e. as long as possible, without screws over the fracture and by employing a titanium plate. Thus, there is no punctate fatigue leading to plate breakage. The fitting of third fragments is deliberately left out. The same applies to all kinds of compression with lag screws, tension devices or DC-gliding holes- and this with the intention of allowing micromovements in the fracture's fissure. Periost and muscle are not removed and the fracture is not examined. Healing occurs spontaneously via a fixating callus forming within the first 3-6 weeks out of the periost-soft tissue combination. Histomorphological investigation dates the first woven-bone bridges between the fragments to 3 weeks subsequent to the accident. In Göttingen University trauma centre, 87 fractures have been attended to over 2 years using this technique. Despite considerable soft-tissue damage, no delayed bone healing, pseudoarthrosis or bone infection has been observed. The risks of elastic plate osteosynthesis lie in unbiological and exaggerated reposition methods, too short a flexible stretch, and insufficient anchorage of the screws.
OBJECTIVE: The purpose of this study was to investigate the effect of an externally applied mechanical stimulus on fracture healing under flexible fixation. DESIGN: Stimulation of fracture healing under various conditions of interfragmentary movement in an in vivo fracture model on 41 sheep. BACKGROUND: It is generally accepted that small interfragmentary movements (IFMs) yield better bone healing results than larger IFMs (> 1 mm). However, the optimal size of IFM within the 1-mm range remains undetermined. METHODS: Standardized transverse osteotomy of 3 mm gap size in the left ovine tibia was fixed with an unilateral external fixator. The sheep were divided into four IFM groups of 0.0, 0.2, 0.4 and 0.8 mm and stimulated with this amplitude for 1200 cycles per day at 1 Hz. After a healing period of 6 weeks, bone mineral density and biomechanical stability were evaluated to determine the quality of healing. RESULTS: The amount of callus formation increased significantly with increasing IFM (P <0.05). However, highest biomechanical stability of the healed bone and mineral density of the gap tissue was achieved with an IFM of 0.4 mm, although the differences were not significant. CONCLUSIONS: These results suggest that the optimal interfragmentary movement for acceleration of delayed fracture healing is in the range of 0.5 mm. However, the enhancement of the healing of flexibly-fixed fractures by external application of interfragmentary movement is limited. RELEVANCE: In this model the external application of a mechanical stimulus in addition to the stimulation caused by normal loading and the flexibility of the fixation did not enhance the healing process significantly. It appears that the external application of interfragmentary motion is promising perhaps only for patients unable to stimulate their fracture healing by weight-bearing.
Different fixation systems are used for fracture and defect treatment. A prerequisite for complication free healing is sufficient mechanical stability of the osteosynthesis. In vitro investigations offer the possibility of both analysing and assessing the pre-clinical fixation stability. Due to the complex loading environment in vivo, stiffness analysis should include a complete determination of the stiffness under standardised conditions. Based on a mathematical procedure to calculate the 3-D stiffness, a mechanical testing device for the 3-D loading of fixation systems was designed and integrated in the existing test set-up. The set-up consisted of a material testing machine to produce the necessary loads and an optical measurement device to detect the resulting inter-fragmentary movements. To validate the testing device, the 3-D stiffness matrices of different Ilizarov fixator configurations were determined and compared. The good reproducibility of the test was reflected in the small intra-individual variability of the stiffness components. A distinct direction dependence of the fixator stiffness was observed. Increasing the number of rings led to a stiffness increase of up to 50%, especially in bending. The presented testing device allows a complete standardised determination of the stiffness of different fixation systems. It considers the direction dependence of the stiffness and creates a prerequisite for a more direct implant comparison.
We have developed a method to study the molecular basis of intramembranous fracture healing. Unlike intramedullary rods that permit rotation of the fractured bone segments, our murine model relies on an external fixation device to provide stabilization. In this study we compare stabilized fracture callus tissues with callus tissues from non‐stabilized fractures during the inflammatory, soft callus, hard callus, and remodeling stages of healing. Histological analyses indicate that stabilized fractures heal with virtually no evidence of cartilage whereas non‐stabilized fractures produce abundant cartilage at the fracture site. Expression patterns of collagen type IIa (colIIa) and osteocalcin (oc) reveal that mesenchymal cells at the fracture site commit to either a chondrogenic or an osteogenic lineage during the earliest stages of healing. The mechanical environment influences this cell fate decision, since mesenchymal cells in a stabilized fracture express oc and fail to express colIIa . Future studies will use this murine model of intramembranous fracture healing to explore, at a molecular level, how the mechanical environment exerts its influence on healing of a fracture.
© 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.
The advent of 'biological internal fixation' is an important development in the surgical management of fractures. Locked nailing has demonstrated that flexible fixation without precise reduction results in reliable healing. While external fixators are mainly used today to provide temporary fixation in fractures after severe injury, the internal fixator offers flexible fixation, maintaining the advantages of the external fixator but allowing long-term treatment. The internal fixator resembles a plate but functions differently. It is based on pure splinting rather than compression. The resulting flexible stabilisation induces the formation of callus. With the use of locked threaded bolts, the application of the internal fixator foregoes the need of adaptation of the shape of the splint to that of the bone during surgery. Thus, it is possible to apply the internal fixator as a minimally invasive percutaneous osteosynthesis (MIPO). Minimal surgical trauma and flexible fixation allow prompt healing when the blood supply to bone is maintained or can be restored early. The scientific basis of the fixation and function of these new implants has been reviewed. The biomechanical aspects principally address the degree of instability which may be tolerated by fracture healing under different biological conditions. Fractures may heal spontaneously in spite of gross instability while minimal, even non-visible, instability may be deleterious for rigidly fixed small fracture gaps. The theory of strain offers an explanation for the maximum instability which will be tolerated and the minimal degree required for induction of callus formation. The biological aspects of damage to the blood supply, necrosis and temporary porosity explain the importance of avoiding extensive contact of the implant with bone. The phenomenon of bone loss and stress protection has a biological rather than a mechanical explanation. The same mechanism of necrosis-induced internal remodelling may explain the basic process of direct healing.
Experimental analyses have demonstrated the impact of mechanical conditions on bone healing. In critical clinical cases the mechanical conditions may be even more demanding than those in experimental studies. This study set out to examine the gap movements in distraction and correction osteotomies and to determine the suitability of initial fixation.
Interfragmentary movements, ground reaction forces, and stability (ground reaction force divided by interfragmentary movement) were measured in 18 patients with tibial osteotomies stabilized by Ilizarov hybrid constructs until either bone union or conversion to internal fixation occurred (9 distraction treatments, 9 correction osteotomies). Consolidation was determined by clinical evaluation and standard radiographic techniques.
In both groups cocontraction led to gap movements comparable to level walking. Although the in vitro stiffness was slightly increased in the correction constructs, the interfragmentary movement in vivo was initially comparable between the groups. Patients undergoing distraction returned later to full weight bearing than patients undergoing correction treatment. In the correction group the stability increased with treatment time, while in the distraction group the stability remained relatively small.
The in vivo mechanical conditions in challenging clinical cases appear far more demanding than those in experimental studies. In distraction, mechanical conditions at the defect appear to be more critical than during correction osteosynthesis. According to the persistence of shear motion, even after 80 days of treatment, it may from the clinical point of view be important to maintain interfragmentary compression during the whole healing process and thereby reduce shear.
Interfragmentary movements affect the quality and quantity of callus formation. The mounting plane of monolateral external fixators may give direction to those movements. Therefore, the aim of this study was to determine the influence of the fixator mounting plane on the process of fracture healing.
Identically configured fixators were mounted either medially or anteromedially on the tibiae of sheep. Interfragmentary movements and ground reaction forces were evaluated in vivo during a nine week period. Histomorphological and biomechanical parameters described the bone healing processes.
Changing only the mounting plane led to a modification of interfragmentary movements in the initial healing phase. The difference in interfragmentary movements between the groups was only significant during the first post‐operative period. However, these initial differences in mechanical conditions influenced callus tissue formation significantly. The group with the anteromedially mounted fixator, initially showing significantly more interfragmentary movements, ended up with a significantly smaller callus diameter and a significantly higher callus stiffness as a result of advanced fracture healing. This demonstrates that the initial phase of healing is sensitive to mechanical conditions and influences the course of healing. Therefore, initial mechanical stability of an osteosynthesis should be considered an important factor in clinical fracture treatment. © 2003 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.
This study tested the hypothesis that interfragmentary axial movement of transverse diaphyseal osteotomies would result in improved fracture healing compared to interfragmentary shear movement. Ten skeletally mature merino sheep underwent a middiaphyseal osteotomy of the right tibia, stabilized by external fixation with an interfragmentary gap of 3 mm. A custom made external fixator allowed either pure axial (n=5) or pure shear movement (n=5) of 1.5 mm amplitude during locomotion by the animals. The movement of the osteotomy gap was monitored weekly in two sheep by an extensometer temporarily attached to the fixator. After 8 weeks the sheep were killed, and healing of the osteotomies was evaluated by radiography, biomechanical testing, and undecalcified histology. Shear movement considerably delayed the healing of diaphyseal osteotomies. Bridging of the osteotomy fragments occurred in all osteotomies in the axial group (100%), while in the shear group only three osteotomies (60%) were partially bridged. Peripheral callus formation in the shear group was reduced by 36% compared to the axial group (p<0.05). In the axial group bone formation was considerably larger at the peripheral callus and in between the osteotomy gaps but not in the intramedullary area. The larger peripheral callus and excess in bone tissue at the level of the gap resulted in a more than three times larger mechanical rigidity for the axial than for the shear group (p<0.05). In summary, fixation that allows excessive shear movement significantly delayed the healing of diaphyseal osteotomies compared to healing under axial movement of the same magnitude.
Bone histomorphometry: proposed system for stan-dardization of nomenclature, symbols, and units Bone histomorphometry: standardization of nomen-clature, symbols and units. Summary of proposed system
- [ I
- Pariitt
[I51 Pariitt AM. Bone histomorphometry: proposed system for stan-dardization of nomenclature, symbols, and units. Calcif Tissue Int 1988;42:2846. [I61 Parfitt AM. Bone histomorphometry: standardization of nomen-clature, symbols and units. Summary of proposed system. Bone Miner 1988;41-5.
The biology of fracture healing in long bonesB:15042. [I41 Owen M. The origin of bone cells
- [ I
- Mckibbin
[I31 McKibbin B. The biology of fracture healing in long bones. J Bone Joint Surg Br 1978;60-B:15042. [I41 Owen M. The origin of bone cells. Int Rev Cytol 1970;28:213-38.
Unreamed tibial nail in tibial shaft fractures with severe soft tissue damage. Initial clinical experiences Comparative study of fracture gap motion in external fixation
- H Schen
H. ScheN et al. I Journal of Orthopaedic Research 23 (2005) 1022-1028 [Ill Krettek C, Haas N, Schandelmaier P, Frigg R, Tscherne H. Unreamed tibial nail in tibial shaft fractures with severe soft tissue damage. Initial clinical experiences. Unfallchirurg 1991;94:579%87. [I21 Kristiansen T, Flemming B, Neale G, Reinecke S, Pope MH. Comparative study of fracture gap motion in external fixation. Clin Biomech 1987;2:191-5.
Histologie und Biomechanik der Frakturheilung unter den Bedingungen des Fixateur externe
- Km Stunner
Stunner KM. Histologie und Biomechanik der Frakturheilung unter den Bedingungen des Fixateur externe. Hefte Unfallheilkd 1988;2OO:23342.
- Yamagishi
- White