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ABSTRACT: PURPOSE: Cerclage technology is regaining interest due to the increasing number of periprosthetic fractures. Different wiring techniques have been formerly proposed and have hibernated over years. Hereby, they are compared to current cerclage technology. METHODS: Seven groups (n = 6) of different cable cerclage (Ø1.7 mm, crimp closure) configurations (one single cerclage looped once around the shells, one single cerclage looped twice, two cerclages each looped once) and solid wire cerclages (Ø1.5 mm, twist closure) (same configurations as cable cerclages, and two braided wires, twisted around each other looped once) fixed two cortical half shells of human femoral shaft mounted on a testing jig. Sinusoidal cyclic loading with constantly increasing force (0.1 N/cycle) was applied starting at 50 N peak load. Cerclage pretension (P), load leading to onset of plastic deformation (D) and load at total failure (T) were identified. Statistical differences between the groups were detected by univariate ANOVA. RESULTS: Double looped cables (P442N ± 129; D1334N ± 319; T2734N ± 330) performed significantly better (p < 0.05) than single looped cables (P292N ± 56; D646N ± 108; T1622N ± 171) and were comparable to two single cables (P392N ± 154; D1191N ± 334; T2675N ± 361). Double looped wires (P335N ± 49; D752N ± 119; T1359N ± 80) were significantly better (p < 0.05) than single looped wires (P181N ± 16; D343N ± 33; T606N ± 109) and performed similarly to single looped cables. Braided wires (P119N ± 26; D225N ± 55; T919N ± 197) exhibited early loss of pretension and plastic deformation. CONCLUSION: Double looped cerclages provided a better fixation stability compared to a single looped cerclage. Double looped wires were comparable to a single looped cable. The use of braided wires could not be recommended mechanically.
International Orthopaedics 11/2012; · 2.03 Impact Factor
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ABSTRACT: PURPOSE: Tibial nail interlocking screw failure often occurs during delayed fracture consolidation or at early weight bearing of nailed unstable fractures, in general when high implant stress could not be reduced by other means. Is there a biomechanical improvement in long-term performance of angle stable locking screws compared to conventional locking screws for distal locking of intramedullary tibial nails? METHODS: Surrogate bones of human tibiae were cut in the distal third and distal locking of the 10 mm intramedullary tibial nail was performed with either two angle stable locking screws or two conventional locking screws in the mediolateral plane. Six specimens per group were mechanically tested under quasi-static and cyclic axial loading with constantly increasing force. RESULTS: Angle stable locking screw constructs exhibited significantly higher stiffness values (7,809 N/mm ± 647, mean ± SD) than conventional locking screw constructs (6,614 N/mm ± 859, p = 0.025). Angle stable locking screw constructs provided a longer fatigue life, expressed in a significantly higher number of cycles to failure (187,200 ± 18,100) compared to conventional locking screw constructs (128,700 ± 7,000, p = 0.004). CONCLUSION: Fatigue performance of locking screws can be ameliorated by the use of angle stable locking screws, being especially important if the nail acts as load carrier and an improved stability during fracture healing is needed.
International Orthopaedics 08/2012; · 2.03 Impact Factor
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ABSTRACT: Cerclages regain interest due to a rising number of periprosthetic fractures. The contact distribution at the circumferential cerclage-bone interface is still unknown. Local interface pressure depends on the amount of contact area. Cortical damage at the interface would provoke cerclage loosening. Therefore, the contact area, the bone pressure along the interface and the cortical resistance underneath loaded cerclages were determined in an ex vivo model.
Human diaphyseal femoral bone was used with differing cross-sectional geometry. Bone contact points of fixed 1.5 mm wire and 1.7 mm cable cerclages were identified from axial radiographs. Pressure distribution at the cerclage-bone interface was recorded with a pressure-measuring film using a distraction setup with two cortical half shells. Bone shells with installed cerclages were separated with up to 400 N force and were subsequently analyzed histologically to detect cortical damage.
Both cerclage types exhibited a point contact fixation with non-loaded spanned zones in-between. Cables cover larger contact areas. Both cerclages exhibited an inhomogeneous interface pressure distribution depending on the bone surface geometry. Histology revealed intact cortical bone without cortical affection after loading of both cerclage types.
Point contact fixation of the cerclages installs non-loaded, spanned zones where the periosteum is not compressed, rendering a strangulation of the blood supply unlikely. Cortical bone withstands static concentric pressure produced by the cerclage. Cortical groove formation is attributed to instability under functional load and not to weakness of the cortex itself.
Archives of Orthopaedic and Trauma Surgery 06/2012; 132(10):1467-72. · 1.37 Impact Factor
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ABSTRACT: To improve proximal plate fixation of periprosthetic femur fractures, a prototype locking plate with proximal posterior angulated screw positioning was developed and biomechanically tested.
Twelve fresh frozen, bone mineral density matched human femora, instrumented with cemented hip endoprosthesis were osteotomized simulating a Vancouver B1 fracture. Specimens were fixed proximally with monocortical (LCP) or angulated bicortical (A-LCP) head-locking screws. Biomechanical testing comprised quasi-static axial bending and torsion and cyclic axial loading until catastrophic failure with motion tracking.
Axial bending and torsional stiffness of the A-LCP construct were (1,633 N/mm ± 548 standard deviation (SD); 0.75 Nm/deg ± 0.23 SD) at the beginning and (1,368 N/mm ± 650 SD; 0.67 Nm/deg ± 0.25 SD) after 10,000 cycles compared to the LCP construct (1,402 N/mm ± 272 SD; 0.54 Nm/deg ± 0.19 SD) at the beginning and (1,029 N/mm ± 387 SD; 0.45 Nm/deg ± 0.15) after 10,000 cycles. Relative movements for medial bending and axial translation differed significantly between the constructs after 5,000 cycles (A-LCP 2.09° ± 0.57 SD; LCP 5.02° ± 4.04 SD; p = 0.02; A-LCP 1.25 mm ± 0.33 SD; LCP 2.81 mm ± 2.32 SD; p = 0.02) and after 15,000 cycles (A-LCP 2.96° ± 0.70; LCP 6.52° ± 2.31; p = 0.01; A-LCP 1.68 mm ± 0.32; LCP 3.14 mm ± 0.68; p = 0.01). Cycles to failure (criterion 2 mm axial translation) differed significantly between A-LCP (15,500 ± 2,828 SD) and LCP construct (5,417 ± 7,236 SD), p = 0.03.
Bicortical angulated screw positioning showed less interfragmentary osteotomy movement and improves osteosynthesis in periprosthetic fractures.
Archives of Orthopaedic and Trauma Surgery 06/2012; 132(10):1437-44. · 1.37 Impact Factor
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ABSTRACT: INTRODUCTION: Insufficient primary stability is still reported for proximal humerus fractures in elderly patients. Fixation stability could be improved by aiming locking screws at bone volumes with better properties. The aims of this study were to investigate the bone regions engaged by the locking screws of a Proximal Humeral Nail (MultiLoc PHN), and to evaluate the influence of peri-screw bone quality on bone-nail construct stability. MATERIALS AND METHODS: Twelve cadaveric humeri were divided into two groups. The distal locking part of the PHN was fixed to the specimens. The nails were removed and the bones scanned using HR-pQCT. Bone properties were evaluated at the locations where the proximal locking screws would have been positioned after complete instrumentation. A three-part fracture model was used for mechanical testing of the instrumented bones, considering axial displacement and varus deformation as parameters of interest. RESULTS: The secondary locking screws targeted bone volumes in the posteromedial part of the humerus with statistically significant higher quality, thus reducing varus deformation. Significant correlation was found between axial displacement and bone properties at the primary proximal screws. Significant correlation was found between the varus deformation and apparent BMD at the secondary locking screws. CONCLUSION: The findings of this study confirmed that directing the proximal locking screws at bone regions with better properties can improve fixation stability.
Medical Engineering & Physics 06/2012; · 1.62 Impact Factor
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ABSTRACT: Mechanical properties of a locking attachment plate construct (LAP-LCP), allowing bicortical screw placement laterally to the prosthesis stem, are compared to a cerclage-LCP construct.
Eight right synthetic femora with implanted uncemented hip endoprosthesis were cut distally and fixed with LCP, monocortical locking screws and either LAP (n = 4) or cerclage (n = 4). Cyclic testing was performed with monotonically increasing sinusoidal load until failure. Relative movements at the plate-femur interface were registered by motion tracking. Statistical differences were detected by unpaired t-test and general linear model repeated measures.
Stiffness of the LAP-LCP was significantly higher at the beginning (875.4 N/mm ± 29.8) and after 5000 cycles (1213.0 N/mm ± 101.1) compared to the cerclage-LCP (644.96 N/mm ± 50.1 and 851.9 N/mm ± 81.9), with p = 0.013. Relative movements for AP-bending (B) and axial translation (T) of the LAP-LCP at the beginning (0.07° ± 0.02, 0.20 mm ± 0.08), after 500 cycles (0.16° ± 0.10, 0.26 mm ± 0.07) and after 5000 cycles (0.26° ± 0.11, 0.31 mm ± 0.07) differed significantly from the cerclage-LCP (beg.: 0.26° ± 0.04, 0.28 mm ± 0.05; 500 cyc: 0.47° ± 0.03, 0.53 mm ± 0.07; 5000 cyc.: 0.63° ± 0.18, 0.79 mm ± 0.13), with B: p = 0.02, T: p = 0.04. Relative movements for medial bending were not significantly different between the two constructs. Cycles to failure (criterion 1 mm axial translation) differed significantly between LAP-LCP (19,519 ± 1,758) and cerclage-LCP (11,265 ± 2,472), with p = 0.035.
Biomechanically, the LAP-LCP construct improves proximal fixation of periprosthetic fractures compared to the cerclage-LCP construct.
International Orthopaedics 05/2012; 36(9):1915-21. · 2.03 Impact Factor
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ABSTRACT: Patients with a femoral fracture due to osteoporosis are at high risk of sustaining a secondary fracture on the contralateral side. A prophylactic mechanical reinforcement of the contralateral side during operation of the initial fracture could be of interest for such patients. This biomechanical in vitro study investigates the potential of a limited V-shaped bone cement augmentation to prevent secondary hip fractures by targeting the areas of the proximal femur with the highest stresses during a fall. Five pairs of human cadaveric proximal femora were tested in a configuration simulating a fall on the greater trochanter. The femoral neck of one specimen of each pair was augmented with 8-14 ml polymethylmethacrylate from the lateral cortex towards inferior and superior, spanning a V-shaped cement pattern. Clinical relevant fractures were generated with a 45 kg mass in controlled free fall. Load-displacement data were recorded and energy to fracture, fracture load, yield load and stiffness were statistically evaluated. Augmented samples absorbed 124% more energy until fracture compared to their controls (p = 0.043). No significant differences were found between the two groups for fracture load (p = 0.5), yield load (p = 0.35) and stiffness (p = 0.5). Biomechanically, a limited V-shaped prophylactic cement augmentation carries potential to prevent secondary hip fractures indicated by increased energy absorption until fracture. Further investigations are necessary to minimize interference with the biology and to maximize the mechanical benefit of prophylactic augmentation.
Journal of Biomaterials Applications 04/2012; · 2.08 Impact Factor
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ABSTRACT: Previous studies have clearly demonstrated superior biomechanical behavior of augmented proximal femoral nail antirotation (PFNA) blades compared with nonaugmented ones with respect to implant cutout. Nevertheless, there is concern about thermal bone necrosis due to exothermic curing of polymethylmethacrylate (PMMA)-based bone cements. The objective of this study was to quantify the temperatures arising around perforated titanium PFNA blades when augmenting with PMMA.
Cylindrical samples from six pairs of fresh frozen human cadaveric femoral heads implanted with a PFNA blade were placed in a 37°C water bath and augmented with 3 mL and 6 mL PMMA. During augmentation, temperatures were measured using six K-type thermocouples that were placed at controlled distances around the implant. With the help of high-resolution quantitative computed tomography images, the locations of all thermocouples with respect to the cement-bone interface were reconstructed.
No temperatures higher than 45°C were measured in the interface region and the surrounding cement-free cancellous bone. In the same regions, the longest exposure time above 41°C was 8.5 minutes and was measured in a 6-mL sample. Average maximum temperature was significantly lower for the 3-mL group compared with the 6-mL group (p = 0.017).
The results of this study suggest that augmentation of titanium PFNA blades is not associated with a risk of thermal bone necrosis when using up to 6 mL of PMMA. However, larger amounts of cement lead to higher temperatures. PMMA application should therefore be kept low to minimally alter the biological system.
The journal of trauma and acute care surgery. 04/2012; 72(4):1098-101.
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ABSTRACT: Osteosynthesis of unstable proximal humerus fractures still remains challenging. The aim of this study was to investigate two intramedullary nailing techniques with different locking options in a three-part fracture model and prove whether two new fixation concepts, introducing additional locking screw-in-screws inserted through the head of the proximal screws, and a calcar screw, provide better stability.
A biomechanical testing model for three-part proximal humerus fractures including cyclic axial loading with increasing peak load and simultaneous pulling forces at the rotator cuff was used to test 12 pairs of human cadaver humeri, assigned to four groups and instrumented with either Targon PH (T1) or MultiLoc PHN in 3 different configurations (standard M1; two additional screw-in-screw M2; one additional calcar screw and two screw-in-screw M3).
Initial range of motion in internal-external rotation and mediolateral translation was smallest in M3 (1.82°; 0.11mm), biggest in T1 (3.63°; 0.51mm) and significantly different between these two groups (p=0.02 and p=0.04, respectively). M3 showed minimum head migration along the nail and varus tilting after 5000 cycles (0.31mm; 0.20°) and 10000 cycles (1.59mm; 0.34°). M2 and M3 performed better than M1 and T1 regarding varus collapse. The highest number of cycles to failure was observed for M3 (20733) and the lowest for T1 (10083) with significant difference between these two groups (p=0.04).
The configuration with two screw-in-screw and a calcar screw was superior in most aspects. The screw-in-screws were found to contribute against varus collapse. Both new fixation concepts could provide better stability in proximal humerus fractures.
Clinical biomechanics (Bristol, Avon) 03/2012; 27(7):686-91. · 1.76 Impact Factor
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ABSTRACT: Cement augmentation may improve fixation stability and reduce cut-out rate in the treatment of intertrochanteric hip fractures. The aim of this study was to compare the number of cycles to failure of polymethylmethacrylate (PMMA)-augmented helical blades with nonaugmented ones in human cadaveric femoral heads.
Six pairs of cadaveric femoral heads were instrumented with a perforated proximal femoral nail antirotation blade. Within each pair, one blade was augmented using 3 mL of PMMA. All specimens underwent cyclic axial loading under physiologic conditions.Starting at 1,000 N, the load was monotonically increased by 0.1 N/cycle until construct failure occurred. To monitor the migration of the blade, anteroposterior radiographs were taken at 250 cycle increments. Nonparametric test statistics were done to calculate correlations and identify differences between study groups.
Inducing failure required a significantly higher number of cycles in the augmented group (p = 0.028). Bone mineral density was significantly related with the number of cycles to failure in nonaugmented specimens (p 0.001, R2 = 0.97), but not in the augmented group (p = 0.91, R2 = 0.34).
Implant augmentation with small amounts of PMMA enhances the cut-out resistance in proximal femoral fractures. Especially in osteoporotic bone, the procedure may improve patient care.
The journal of trauma and acute care surgery. 02/2012; 72(2):E54-9.
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ABSTRACT: Hindfoot trauma including ankle and subtalar sprains may be followed by osteochondral lesions and persisting pain originating from posttraumatic arthritis.
"Acute severe" supination sprains and "mild supination sprains with increasing ligamentous incompetence" of the hindfoot lead to medial ankle and subtalar stress concentrations that may contribute to osteochondral lesions (OCLs) and subsequent arthritis.
Controlled laboratory study.
"Acute severe" sprains and "mild sprains with increasing ligamentous incompetence" (consecutive anterior talofibular ligament [ATFL], calcaneofibular ligament [CFL], and lateral talocalcaneal ligament [LTCL] transections) were simulated in human lower leg specimens (7 different specimens for each condition). The effect on the migration of the center of force (COF) and on the tibiotalar and subtalar pressures at 700-N (acute severe) and 150-N (mild sprain with increasing ligamentous incompetence) axial static and dynamic loads, respectively, was recorded using pressure sensors.
In the "acute severe" sprain, the peak pressure increase reached the level of significance in the ankle (P = .042) and in the subtalar medial facet (P = .046). The ankle COF migrated significantly toward the medial (P = .001) and posterior (P = .023) directions. In the "mild sprain with increasing ligamentous incompetence" condition, the ankle (P = .018) and subtalar (medial facet, P = .022) peak pressure increased significantly with intact ligaments and with all ligaments cut. The ankle COF migrated significantly toward the medial direction when the ATFL and CFL or when all 3 ligaments were severed. The anteroposterior ankle COF migration was anterior when all ligaments were intact or when only the ATFL was severed but posterior when the CFL or when the CFL and the LTCL were severed in addition.
Next to chronic inhomogeneous load distribution in the unstable hindfoot and shear stress during sprains, intra-articular pressure elevation (impact) in the ankle and subtalar joint during hindfoot supination sprains with intact ligaments or incompetent ligaments likely contributes to OCLs of the medial talar dome and the medial subtalar facet.
Intra-articular hindfoot pressure elevation (impact) in "acute severe" and in "mild hindfoot supination sprains with increasing ligamentous incompetence" is substantial for the development of OCLs at the medial midtalar dome and the medial facet of the subtalar joint.
The American journal of sports medicine 01/2012; 40(4):902-8. · 3.61 Impact Factor
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ABSTRACT: Areal bone mineral density (aBMD) at the distal tibia, measured at the epiphysis (T-EPI) and diaphysis (T-DIA), is predictive for fracture risk. Structural bone parameters evaluated at the distal tibia by high resolution peripheral quantitative computed tomography (HR-pQCT) displayed differences between healthy and fracture patients. With its simple geometry, T-DIA may allow investigating the correlation between bone structural parameter and bone strength.
Anatomical tibiae were examined ex vivo by DXA (aBMD) and HR-pQCT (volumetric BMD (vBMD) and bone microstructural parameters). Cortical thickness (CTh) and polar moment of inertia (pMOI) were derived from DXA measurements. Finally, an index combining material (BMD) and mechanical property (polar moment of inertia, pMOI) was defined and analyzed for correlation with torque at failure and stiffness values obtained by biomechanical testing.
Areal BMD predicted the vBMD at T-EPI and T-DIA. A high correlation was found between aBMD and microstructural parameters at T-EPIas well as between aBMD and CTh at T-DIA. Finally, at T-DIA both indexes combining BMD and pMOI were strongly and comparably correlated with torque at failure and bone stiffness.
Ex vivo, at the distal tibial diaphysis, a novel index combining BMD and pMOI, which can be calculated directly from a single DXA measurement, predicted bone strength and stiffness better than either parameter alone and with an order of magnitude comparable to that of HR-pQCT. Whether this index is suitable for better prediction of fracture risk in vivo deserves further investigation.
Bone 11/2011; 50(1):296-300. · 4.02 Impact Factor
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ABSTRACT: The use of polymethylmethacrylate (PMMA) cement to reinforce fragile or broken vertebral bodies (vertebroplasty) leads to extensive bone stiffening. This might be one reason for fractures at the adjacent vertebrae following this procedure. PMMA with a reduced Young's modulus may be more suitable. The goal of this study was to produce and characterize PMMA bone cements with a reduced Young's modulus by adding bone marrow. Bone cements were produced by combining PMMA with various volume fractions of freshly harvested bone marrow from sheep. Porosity, Young's modulus, yield strength, polymerization temperature, setting time and cement viscosity of different cement modifications were investigated. The samples generated comprised pores with diameters in the range of 30-250 μm leading to porosity up to 51%. Compared to the control cement, Young's modulus and yield strength decreased from 1830 to 740 MPa and from 58 to 23 MPa respectively by adding 7.5 ml bone marrow to 23 ml premixed cement. The polymerization temperature decreased from 61 to 38 ∘C for cement modification with 7.5 ml of bone marrow. Setting times of the modified cements were lower in comparison to the regular cement (28 min). Setting times increased with higher amounts of added bone marrow from around 16-25 min. The initial viscosities of the modified cements were higher in comparison to the control cement leading to a lower risk of extravasation. The hardening times followed the same trend as the setting times. In conclusion, blending bone marrow with acrylic bone cement seems to be a promising method to increase the compliance of PMMA cement for use in cancellous bone augmentation in osteoporotic patients due to its modified mechanical properties, lower polymerization temperature and elevated initial viscosity.
Journal of the mechanical behavior of biomedical materials. 11/2011; 4(8):2081-9.
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ABSTRACT: BACKGROUND:: Cement augmentation may improve fixation stability and reduce cut-out rate in the treatment of intertrochanteric hip fractures. The aim of this study was to compare the number of cycles to failure of polymethylmethacrylate (PMMA)-augmented helical blades with nonaugmented ones in human cadaveric femoral heads. METHODS:: Six pairs of cadaveric femoral heads were instrumented with a perforated proximal femoral nail antirotation blade. Within each pair, one blade was augmented using 3 mL of PMMA. All specimens underwent cyclic axial loading under physiologic conditions. Starting at 1,000 N, the load was monotonically increased by 0.1 N/cycle until construct failure occurred. To monitor the migration of the blade, anteroposterior radiographs were taken at 250 cycle increments. Nonparametric test statistics were done to calculate correlations and identify differences between study groups. RESULTS:: Inducing failure required a significantly higher number of cycles in the augmented group (p = 0.028). Bone mineral density was significantly related with the number of cycles to failure in nonaugmented specimens (p < 0.001, R = 0.97), but not in the augmented group (p = 0.91, R = 0.34). CONCLUSION:: Implant augmentation with small amounts of PMMA enhances the cut-out resistance in proximal femoral fractures. Especially in osteoporotic bone, the procedure may improve patient care.
The Journal of trauma 07/2011; · 2.48 Impact Factor
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ABSTRACT: To compare mechanical stability of angle-stable locking construct with four screws with conventional five screw locking in intramedullary nailed distal tibia fractures under cyclic loading.
Ten pairs of fresh-frozen human cadaveric tibiae were intramedullary nailed and assigned to either an angle-stable locking construct consisting of four screws or conventional five-screw locking. After simulating an unstable distal two-fragmental 42-A3.1 fracture, the specimens were mechanically tested under quasistatic and cyclic sinusoidal axial and torsional loading.
Bending stiffness of the angle-stable and the conventional fixation was 644.3 N/° and 416.5 N/°, respectively (P = 0.075, power 0.434). Torsional stiffness of the angle-stable locking (1.91 Nm/°) was significantly higher compared with the conventional one (1.13 Nm/°; P = 0.001, power 0.981). Torsional play of the angle-stable fixation (0.08°) was significantly smaller compared with the conventional one (0.46°; P = 0.002, power 0.965). The angle-stable locking revealed significantly less torsional deformation in the fracture gap after one cycle (0.74°) than the conventional one (1.75°; P = 0.005, power 0.915) and also after 1000 cycles (angle-stable: 1.56°; conventional: 2.51°; P = 0.042, power 0.562). Modes of failure were fracture of the distal fragment, loosening of distal locking screws, nail breakage, and their combination, equally distributed between the groups (P = 0.325).
Both the angle-stable locking technique using four screws and conventional locking consisting of five screws showed high biomechanical properties. Hence, angle-stable locking reflects a potential to maintain fixation stability while reducing the number of locking screws compared with conventional locking in intramedullary nailed unstable distal tibia fractures.
Journal of orthopaedic trauma 06/2011; 25(6):340-6. · 1.78 Impact Factor
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ABSTRACT: Major modifications in the design and techniques of total ankle replacement have challenged the perception that ankle arthrodesis is the treatment of choice for end-stage ankle arthritis. High complication and revision rates have been reported after both procedures.
We performed radiographic evaluations at a mean of thirty-nine months following 114 total ankle replacements done with use of commonly used implants and at a mean of thirty-seven months following forty-seven ankle arthrodeses. The mean age was sixty-four years for the patients (fifty-one female and sixty-three male) who underwent total ankle replacement and fifty-nine years in the patients (fifteen female and thirty-two male) who underwent ankle arthrodesis. The impact of complications was analyzed with use of the Ankle Osteoarthritis Scale (AOS), a validated outcome instrument.
Both groups had significant improvement in the mean AOS score (p < 0.001). There was no significant difference in the mean improvement between the two groups (p = 0.96). The complication rate was 54% following total ankle replacement and 26% following ankle arthrodesis, which was a significant difference (p = 0.003). The impact of major complications on the AOS outcome score was significant in both the total ankle replacement group (p = 0.031) and the ankle arthrodesis group (p = 0.02).
At the time of follow-up, at a minimum of two years postoperatively, the outcomes of total ankle replacement and ankle arthrodesis, with regard to pain relief and function, were comparable. While the rate of complications was significantly higher following total ankle replacement, the impact of complications on outcome was clinically relevant in both groups.
The Journal of Bone and Joint Surgery 05/2011; 93(9):830-9. · 3.27 Impact Factor
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ABSTRACT: Unstable distal tibia fractures are challenging injuries that require surgery. Increasingly, intramedullary nails are being used. However, fracture site anatomy may cause distal-fragment stabilization and fixation problems and lead to malunion/nonunion. We studied the influence of angle-stable nail locking on fracture gap movement and other biomechanical parameters.
Eight pairs of fresh human cadaver tibiae were used. The bone mineral density (BMD) was determined. All tibiae were nailed with a Synthes Expert tibial nail. Within each pair, one tibia was randomized to receive conventional locking screws; the other, angle-stable screws with sleeves. A 7-mm osteotomy was created 10 mm above the upper distal locking screw, to simulate an AO 42-A3 fracture. Biomechanical testing involved nondestructive mediolateral and anteroposterior pure bending, followed by cyclic combined axial and torsional loading to catastrophic failure. The neutral zone was determined. Fracture gap movement was monitored with 3-D motion tracking.
The angle-stable locked constructs had a significantly smaller mediolateral neutral zone (mean: 0.04 degree; p=0.039) and significantly smaller fracture gap angulation (p=0.043). The number of cycles to failure did not differ significantly between the locking configurations. BMD was a significant covariate affecting the number of cycles to failure (p=0.008). However, over the first 20,000 cycles, there was no significant correlation in the angle-stable construct.
Angle-stable locking of the Expert tibial nail was associated with a significant reduction in the mediolateral neutral zone and in fracture gap movement. Angle-stable fixation also reduced the influence of BMD over the first 20,000 cycles.
The Journal of trauma 02/2011; 70(2):358-65. · 2.48 Impact Factor
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ABSTRACT: Polyaxial angle-stable plating is thought to be particularly beneficial in the management of complex intra-articular fractures of the distal radius. The purpose of the present study was to investigate whether the technique provides stability to match that of conventional (fixed-angle) angle-stable constructs.
In seven pairs of human cadaver radii, an Arbeitsgemeinschaft für Osteosynthese (AO) 23 C2.1 intra-articular fracture was created. One radius of each pair received a juxta-articular 2.4-mm locking compression plate (LCP) Volar Distal Radius Plate, whilst the contralateral one received a 2.4-mm Variable Angle Locking Compression Plate (LCP) Two-Column Volar Distal Radius Plate (both plates: Synthes, Oberdorf, Switzerland). Parameters tested were construct stiffness (static axial loading with 150 N), range of motion and secondary loss of reduction (dynamic 150 N axial loading over 5000 cycles). Stiffness and range of motion were measured both pre- and post-cycling.
The polyaxial constructs were significantly stiffer, both before and after cyclic testing. However, the two-column plates showed a significant loss of stiffness during cyclic testing. The range of motion was significantly greater, both initially and at the end of cyclic testing, in the fixed-angle constructs. The conventional constructs had significantly greater secondary loss of reduction.
The polyaxial two-column plate tested in this study provides a biomechanically sound construct for the management of intra-articular fractures of the distal radius.
Injury 02/2011; 42(11):1248-52. · 1.98 Impact Factor
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ABSTRACT: For the treatment of hip fractures helically shaped implants, like the Dynamic Hip Screw (DHS) Blade, are often used. One consequence of blade implantation, the compaction of cancellous bone, is still believed to increase cut-out resistance. This in vitro study investigates implant anchorage of Dynamic Hip Screw Blades in femoral heads due to insertion with or without predrilling under cyclic physiological loading conditions.
Six pairs of fresh frozen (-20°C) human cadaveric proximal femora were instrumented with DHS Blades. Bone pairs were randomly assigned to two study groups: 1) predrilled; 2) non-predrilled. Prior instrumentation, bone mineral density was determined in the center of the femoral head by Xtreme-CT measurement. After instrumentation biomechanical testing was performed under cyclic loading. The bone-implant interface was monitored by means of fluoroscopic imaging throughout the experiment. Paired t-tests were performed to identify differences regarding bone mineral density, stiffness and cycles to failure.
No significant differences were found between study groups with regard to axial stiffness (P=0.626) and number of cycles to failure (P=0.961).
This in vitro study did not show differences in biomechanical stability of proximal femora instrumented with a helical blade implant with or without predrilling. Clinically, the findings suggest that predrilling may be performed to ease the surgical procedure without compromising the implant anchorage.
Clinical biomechanics (Bristol, Avon) 12/2010; 25(10):1053-7. · 1.76 Impact Factor
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ABSTRACT: The optimal surgical treatment for displaced proximal humeral fractures is still controversial. A new implant for the treatment of three-part fractures has been recently designed. It supplements the existing Expert Humeral Nail with a locking plate. We developed a novel humeral cadaveric model and the existing implant and the prototype were biomechanically compared to determine their ability in maintaining interfragmentary stability.
The bone mineral density of eight pairs of cadaveric humeri was assessed and a three-part proximal humeral fracture was simulated with a Greater Tuberosity osteotomy and a surgical neck wedge ostectomy. The specimens were randomly assigned to either treatment. A bone anchor simulated part of a rotator cuff tendon pulling on the Greater Tuberosity. Specimens were initially tested in axial compression and afterward with a compound cyclic load to failure. An optical 3D motion tracking system continuously monitored the relative interfragmentary movements.
The specimen stabilized with the prototype demonstrated higher stiffness (P=0.036) and better interfragmentary stability (P values<0.028) than the contralateral treated with the existing implant. There was no correlation between the bone mineral density and any of the investigated variables.
The convenience of this new IM-nail and locking plate assembly must be confirmed in vivo but the current study provides a biomechanical rationale for its use in the treatment of three-part proximal humeral fractures. The improved stability could be advantageous in particular when medial buttress is missing, even in osteoporotic bone.
Clinical biomechanics (Bristol, Avon) 11/2010; 25(9):886-92. · 1.76 Impact Factor
