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POSTEROMEDIAL MENISCAL AND ANTERIOR CRUCIATE LIGAMENT STRAINS DURING DYNAMIC ACTIVITIES FOLLOWING ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION
Abstract
Background: Meniscal strain patterns are not well understood during dynamic activities. Furthermore, the impact of ACL reconstruction on meniscal strain has not been thoroughly investigated. The purpose of this study was to characterize ACL and meniscal strain during dynamic activities and investigate the strain difference between ACL-intact and ACL-reconstructed ligament conditions. Methods: ACL and medial meniscal strain were measured in-vitro during gait, a double leg squat, and a single leg squat. For each activity kinematics and muscle forces were applied to seven cadaveric specimens using a dynamic knee simulator. Testing was performed in the ACL-intact and ACL-reconstructed ligament conditions. Results: Both the ACL and meniscus had distinct strain patterns that were found to have a significant interaction with knee angle during gait and double leg squat ([Formula: see text]). During gait, both tissues experienced lower strain during swing than stance (ACL: 3.0% swing, 9.1% stance; meniscus: 0.2% swing, 1.3% stance). Meniscal strain was not found to be different between ACL-intact and ACL-reconstructed conditions ([Formula: see text]). Conclusions: During dynamic activities, the strain in the meniscus was not altered between ACL ligament conditions. This indicates that meniscal mechanics after ACL reconstruction are similar to a healthy knee. These results help further the understanding of osteoarthritis risk after ACL reconstruction.
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Purpose: This prospective case series is designed to determine the 2-year clinical and radiological outcomes of patients undergoing an ACL reconstruction using the ligament augmentation reconstruction system (LARS) 133 prosthesis as an augmentation device for a 4-tunnel autologous hamstrings graft, in the context of accelerated rehabilitation. Methods: A total of 91 patients were assessed at 2 years post-operatively after undergoing an anterior cruciate ligament reconstruction (ACLR) with a doubled semitendinosis and LARS 133 prosthesis for the anteromedial bundle (AMB) and gracilis for the posterolateral bundle. Assessment included clinical review, KT-1000 arthrometry, IKDC, Tegner, Lysholm, Cincinnati and ACL QOL knee scoring, graft failure and re-operation rates. Tunnel positions and synovitis were assessed using gadolinium magnetic resonance imaging (MRI) scans and X-rays. Results: This technique in the context of accelerated rehabilitation is not associated with increased knee laxity and failure. There was no increase in knee laxity, with a mean side-to-side difference in KT-1000 arthrometer testing of 0.5mm (+/− 1.7). Two-year outcomes were satisfactory with 98% of all patients having an IKDC rating of A or B, and mean values of IKDC subjective 86.5 (+/− 11.6), Tegner 6.5 (+/− 2.0), Lysholm 87.1 (+/− 8.9), Cincinnati 378.8 (+/− 41.5) and ACL Quality of Life 81.5 (+/− 19.3). There was no evidence of synovitis and all tunnels were positioned satisfactorily. The graft failure rate was 1.1% and there was a re-operation rate of 15.4%. Conclusion: We conclude that LARS 133 augmentation of autologous hamstrings ACLR provides a graft construct allowing accelerated rehabilitation without increased knee laxity. It is not associated with significant synovitis within the first two years. Re-operation rates however are higher. The rates at which patients recover and return to life and sports activity following different ACLR graft types appears as a topic of future research interest.
Background:
Reconstruction of anterior cruciate ligament (ACL) tears may potentially prevent the development of secondary meniscal injuries and arthritis.
Purpose/hypothesis:
The purpose of this study was to (1) evaluate the protective benefit of ACL reconstruction (ACLR) in preventing subsequent meniscal tears or arthritis, (2) determine if earlier ACLR (<1 year after injury) offers greater protective benefits than delayed reconstruction (≥1 year after injury), and (3) evaluate factors predictive of long-term sequelae after ACLR. The hypothesis was that the incidence of secondary meniscal tears, arthritis, and total knee arthroplasty (TKA) would be higher in patients treated nonoperatively after ACL tears than patients treated with surgical reconstruction.
Study design:
Cohort study; Level of evidence, 3.
Methods:
This retrospective study included a population-based incidence cohort of 964 patients with new-onset, isolated ACL tears between 1990 and 2000 as well as an age- and sex-matched cohort of 964 patients without ACL tears. A chart review was performed to collect information related to the initial injury, treatment, and outcomes. A total of 509 patients were treated with early ACLR, 91 with delayed ACLR, and 364 nonoperatively. All patients were retrospectively followed (range, 2 months to 25 years) to determine the development of subsequent meniscal tears, arthritis, or TKA.
Results:
At a mean follow-up of 13.7 years, patients treated nonoperatively after ACL tears had a significantly higher likelihood of developing a secondary meniscal tear (hazard ratio [HR], 5.4; 95% CI, 3.8-7.6), being diagnosed with arthritis (HR, 6.0; 95% CI, 4.3-8.4), and undergoing TKA (HR, 16.7; 95% CI, 5.0-55.2) compared with patients treated with ACLR. Similarly, patients treated with delayed ACLR had a higher likelihood of developing a secondary meniscal tear (HR, 3.9; 95% CI, 2.2-6.9) and being diagnosed with arthritis (HR, 6.2; 95% CI, 3.4-11.4) compared with patients treated with early ACLR. Age >21 years at the time of injury, articular cartilage damage, and medial/lateral meniscal tears were predictive of arthritis after ACLR.
Conclusion:
Patients treated with ACLR have a significantly lower risk of secondary meniscal tears, symptomatic arthritis, and TKA when compared with patients treated nonoperatively after ACL tears. Similarly, early ACLR significantly reduces the risk of subsequent meniscal tears and arthritis compared with delayed ACLR.
Background
Functional exercises are important in the rehabilitation of anterior cruciate ligament deficient and reconstructed individuals but movement compensations and incomplete recovery persist. This study aimed to identify how tasks pose different challenges; and evaluate if different activities challenge patient groups differently compared to controls.
Methods
Motion and force data were collected during distance hop, squatting and gait for 20 anterior cruciate ligament deficient, 21 reconstructed and 21 controls.
Findings
Knee range of motion was greatest during squatting, intermediate during hopping and smallest during gait (P < 0.01). Peak internal knee extensor moments were greatest during distance hop (P < 0.01). The mean value of peak knee moments was reduced in squatting and gait (P < 0.01) compared to hop. Peak internal extensor moments were significantly larger during squatting than gait and peak external adductor moments during gait compared to squatting (P < 0.01). Fluency was highest during squatting (P < 0.01). All patients demonstrated good recovery of gait but anterior cruciate ligament deficient adopted a strategy of increased fluency (P < 0.01). During squatting knee range of motion and peak internal knee extensor moment were reduced in all patients (P < 0.01). Both anterior cruciate ligament groups hopped a shorter distance (P < 0.01) and had reduced knee range of motion (P < 0.025). Anterior cruciate ligament reconstructed had reduced fluency (P < 0.01).
Interpretation
Distance hop was most challenging; squatting and gait were of similar difficulty but challenged patients in different ways. Despite squatting being an early, less challenging exercise, numerous compensation strategies were identified, indicating that this may be more challenging than gait.
Running is a bouncing gait in which the body mass center slows and lowers during the first half of the stance phase; the mass center is then accelerated forward and upward into flight during the second half of the stance phase. Muscle-driven simulations can be analyzed to determine how muscle forces accelerate the body mass center. However, muscle-driven simulations of running at different speeds have not been previously developed, and it remains unclear how muscle forces modulate mass center accelerations at different running speeds. Thus, to examine how muscles generate accelerations of the body mass center, we created three-dimensional muscle-driven simulations of ten subjects running at 2.0, 3.0, 4.0, and 5.0m/s. An induced acceleration analysis determined the contribution of each muscle to mass center accelerations. Our simulations included arms, allowing us to investigate the contributions of arm motion to running dynamics. Analysis of the simulations revealed that soleus provides the greatest upward mass center acceleration at all running speeds; soleus generates a peak upward acceleration of 19.8m/s(2) (i.e., the equivalent of approximately 2.0 bodyweights of ground reaction force) at 5.0m/s. Soleus also provided the greatest contribution to forward mass center acceleration, which increased from 2.5m/s(2) at 2.0m/s to 4.0m/s(2) at 5.0m/s. At faster running speeds, greater velocity of the legs produced larger angular momentum about the vertical axis passing through the body mass center; angular momentum about this vertical axis from arm swing simultaneously increased to counterbalance the legs. We provide open-access to data and simulations from this study for further analysis in OpenSim at simtk.org/home/nmbl_running, enabling muscle actions during running to be studied in unprecedented detail.
The popliteus tendon has important dynamic and static stabilizing functions at the knee. Evaluation of its static role as the "fifth ligament" of the knee and a subsequent analysis of a popliteus tendon reconstruction has not been performed.
In vitro knee stability can be restored to a popliteus tendon-deficient knee with an anatomic popliteus tendon reconstruction.
Controlled laboratory study.
Eleven nonpaired cadaveric knees were tested under the following popliteus tendon states: intact, sectioned, and reconstructed using an autogenous semitendinosus graft. Each knee was subjected to 10-N.m varus moments, 5-N.m external and internal torques, and 88-N anterior and posterior loads at flexion angles of 0 degrees , 20 degrees , 30 degrees , 60 degrees , and 90 degrees . A 6 degrees of freedom electromagnetic motion tracking system was used to assess motion changes of the tibia with respect to the femur.
Significant increases in external rotation and small but significant increases in internal rotation, varus angulation, and anterior translation motion were found after sectioning the popliteus tendon compared to the intact state. Significant decreases in external rotation were found in the reconstructed state compared with the sectioned state at knee flexion angles of 20 degrees , 30 degrees , 60 degrees , and 90 degrees . Comparing the reconstructed state to the intact state, there were no significant differences at knee flexion angles of 0 degrees and 20 degrees , but significant decreases of external rotation were found at knee flexion angles of 30 degrees , 60 degrees , and 90 degrees . Additionally, there were small but significant differences between the reconstructed and intact state with respect to varus angulation at knee flexion angles of 20 degrees , 30 degrees , and 60 degrees ; anterior translation at 20 degrees and 30 degrees ; and internal rotation at all flexion angles.
The popliteus tendon has important primary stabilization roles at the knee. The authors also found that an anatomic popliteus tendon reconstruction significantly reduced the increase in external rotation that occurred with sectioning the popliteus tendon; however, differences seen with respect to internal rotation, varus angulation, and anterior translation were not restored.
The popliteus tendon functions essentially as the fifth major ligament of the knee. An anatomic popliteus tendon reconstruction can restore external rotation stability to knees with popliteus tendon injury.
Muscles actuate walking by providing vertical support and forward progression of the mass center. To quantify muscle contributions to vertical support and forward progression (i.e., vertical and fore-aft accelerations of the mass center) over a range of walking speeds, three-dimensional muscle-actuated simulations of gait were generated and analyzed for eight subjects walking overground at very slow, slow, free, and fast speeds. We found that gluteus maximus, gluteus medius, vasti, hamstrings, gastrocnemius, and soleus were the primary contributors to support and progression at all speeds. With the exception of gluteus medius, contributions from these muscles generally increased with walking speed. During very slow and slow walking speeds, vertical support in early stance was primarily provided by a straighter limb, such that skeletal alignment, rather than muscles, provided resistance to gravity. When walking speed increased from slow to free, contributions to support from vasti and soleus increased dramatically. Greater stance-phase knee flexion during free and fast walking speeds caused increased vasti force, which provided support but also slowed progression, while contralateral soleus simultaneously provided increased propulsion. This study provides reference data for muscle contributions to support and progression over a wide range of walking speeds and highlights the importance of walking speed when evaluating muscle function.
The objective of this study was to develop an efficient methodology for generating muscle-actuated simulations of human walking that closely reproduce experimental measures of kinematics and ground reaction forces. We first introduce a residual elimination algorithm (REA) to compute pelvis and low back kinematic trajectories that ensure consistency between whole-body dynamics and measured ground reactions. We then use a computed muscle control (CMC) algorithm to vary muscle excitations to track experimental joint kinematics within a forward dynamic simulation. CMC explicitly accounts for delays in muscle force production resulting from activation and contraction dynamics while using a general static optimization framework to resolve muscle redundancy. CMC was used to compute muscle excitation patterns that drove a 21-degrees-of-freedom, 92 muscle model to track experimental gait data of 10 healthy young adults. Simulated joint kinematics closely tracked experimental quantities (mean root-mean-squared errors generally less than 1 degrees), and the time histories of muscle activations were similar to electromyographic recordings. A simulation of a half-cycle of gait could be generated using approximately 30 min of computer processing time. The speed and accuracy of REA and CMC make it practical to generate subject-specific simulations of gait.
Dynamic simulations of movement allow one to study neuromuscular coordination, analyze athletic performance, and estimate internal loading of the musculoskeletal system. Simulations can also be used to identify the sources of pathological movement and establish a scientific basis for treatment planning. We have developed a freely available, open-source software system (OpenSim) that lets users develop models of musculoskeletal structures and create dynamic simulations of a wide variety of movements. We are using this system to simulate the dynamics of individuals with pathological gait and to explore the biomechanical effects of treatments. OpenSim provides a platform on which the biomechanics community can build a library of simulations that can be exchanged, tested, analyzed, and improved through a multi-institutional collaboration. Developing software that enables a concerted effort from many investigators poses technical and sociological challenges. Meeting those challenges will accelerate the discovery of principles that govern movement control and improve treatments for individuals with movement pathologies.
Background:
A medial meniscal tear is a common knee injury, especially following an anterior cruciate ligament injury. Decreasing the compressive force on the medial meniscus during dynamic activities using an unloader knee brace could reduce meniscal strain, effectively reducing injury risk and/or severity.
Objectives:
To investigate the efficacy of two unloader knee braces on medial meniscus strain during dynamic activities in intact & deficient anterior cruciate ligament states.
Study design:
Combined in vivo/in vitro study.
Methods:
In vivo knee kinematics and muscle force profiles from a healthy individual performing single/doubleleg squats and walking motions were simulated on 10 cadaveric specimens using a dynamic knee simulator system. Simulations were performed on knees in unbraced and braced scenarios, with and without the anterior cruciate ligament. Anterior and posterior medial meniscal strains were measured.
Results:
Two different braces each showed a significant reduction in the posteromedial meniscal strain ( p ⩽ 0.01) in an intact anterior cruciate ligament state. Neither brace mirrored this result for the anteromedial strain ( p > 0.05). In the deficient anterior cruciate ligament state, the braces had no significant effect on strain ( p > 0.05).
Conclusion:
Two unloader knee braces effectively reduced strain in the medial meniscus with an intact anterior cruciate ligament during dynamic activities. Neither brace made a significant reduction in strain for anterior cruciate ligament-deficient knees. Clinical relevance Unloader knee braces could be used to reduce the medial meniscus strain following meniscal surgery and during rehabilitation in patients with an isolated medial meniscus injury. However, these braces cannot be recommended for this purpose in patients with an anterior cruciate ligament deficiency.
PurposeInjury or degeneration of the meniscus has been associated with the development of osteoarthritis of the knee joint. Meniscal allograft transplant (MAT) has been shown to reduce pain and restore function in patients who remain symptomatic following meniscectomy. The purpose of this study is to evaluate and compare the three-dimensional (3D) strain in native medial menisci compared to allograft-transplanted medial menisci in both the loaded and unloaded states. Methods
Ten human cadaveric knees underwent medial MAT, utilizing soft-tissue anterior and posterior root fixation via transosseous sutures tied over an anterolateral proximal tibial cortical bone bridge. The joint was imaged first in the non-loaded state, then was positioned at 5° of flexion and loaded to 1× body weight (650 ± 160 N) during MR image acquisition. Anatomical landmarks were chosen from each image to create a tibial coordinate system, which were then input into a custom-written program (Matlab R2014a) to calculate the 3D strain from the unloaded and loaded marker positions. Six independent strains were obtained: three principal strains and three shearing strains. ResultsNo statistically significant difference was found between the middle and posterior strains in the native knee compared to the meniscus allograft. This would suggest that soft-tissue fixation of meniscal allografts results in similar time zero principal and shear strains in comparison to the native meniscus. Conclusion
These results suggest that time zero MAT performs in a similar manner to the native meniscus. Optimizing MAT strain behavior may lead to potential improvements in its chondroprotective effect.
Estimation of muscle forces through musculoskeletal simulation is important in understanding human movement and injury. Unmatched filter frequencies used to low-pass filter marker and force platform data can create artifacts during inverse dynamics analysis, but their effects on muscle force calculations are unknown. The objective of this study was to determine the effects of filter cutoff frequency on simulation parameters and magnitudes of lower extremity muscle and resultant joint contact forces during a high-impact maneuver. Eight participants performed a single leg jump-landing. Kinematics were captured with a 3D motion capture system and ground reaction forces were recorded with a force platform. The marker and force platform data were filtered using two matched filter frequencies (10-10Hz, 15-15Hz) and two unmatched frequencies (10-50Hz, 15-50Hz). Musculoskeletal simulations using Computed Muscle Control were performed in OpenSim. The results revealed significantly higher peak quadriceps (13%), hamstrings (48%), and gastrocnemius forces (69%) in the unmatched (10-50Hz, 15-50Hz) conditions than in the matched (10-10Hz, 15-15Hz) conditions (p<0.05). Resultant joint contact forces and reserve (non-physiologic) moments were similarly larger in the unmatched filter categories (p<0.05). This study demonstrated that artifacts created from filtering with unmatched filter cutoffs result in altered muscle forces and dynamics which are not physiologic.
Purpose:
The effectiveness of ACL functional knee braces to reduce meniscal and ACL strain after ACL injury or reconstruction is not well understood. A new dynamic knee tensioning brace system has been designed to apply an active stabilizing force to the knee. The ability of this system to reduce tissue strains is unknown. The purpose of this study was to test the ability of the dynamically tensioned brace to reduce strain in both the ACL and meniscus during rehabilitation activities.
Methods:
A combined in vivo/in silico/in vitro method was used to study three activities: gait, double leg squat, and single leg squat. Muscle forces and kinematics for each activity were derived through in vivo motion capture and applied to seven cadaveric knee specimens fitted with custom braces. Medial meniscal strain and ACL strain were measured in ACL intact, deficient and reconstructed conditions.
Results:
The brace lowered peak and average meniscal strain in ACL deficient knees (P < 0.05) by an average of 1.7%. The brace was also found to lower meniscal strain in reconstructed knees (1.1%) and lower ACL strain in ACL intact (1.3%) and reconstructed knees (1.4%) (P < 0.05).
Conclusions:
This study supports the use of a brace equipped with a dynamic tensioning system to lower meniscal strain in ACL-deficient knees. Its use may help decrease the risk of subsequent meniscal tears in chronic ACL deficiency or delayed reconstruction. In ACL-intact and reconstructed knees, the brace may be beneficial in injury prophylaxis or in protecting the ACL graft following reconstruction. These results will aid clinicians make informed recommendations for functional brace use in patients with unstable knees.
Level of evidence:
II.
We thank the authors of the letter (1) for their comments regarding our paper "Effect of Sagittal Plane Mechanics on ACL Strain during Jump Landing"(2) . Breaking apart the fundamental influencers of ACL strain and injury is difficult, in part due to the multitude of variables involved. Research studying these interconnected variables increases the experimental complexity required for biofidelic experimental setups. This article is protected by copyright. All rights reserved.
Linear and angular measurements were made on thirty-two cadaveric femora with respect to the mechanical (functional) axes of the bone. The long axis was defined as a line from the center of the femoral head to the anterolateral attachment of the posterior cruciate ligament. The transverse axis was defined as a line through the posterior cruciate ligament parallel to the line connecting each epicondyle. The condylar width, the length of each interepicondylar line, correlated well with depth, but the projections of the condyles from the transverse plane revealed significant variations from specimen to specimen. Considerable variation also was found between femora in terms of angular dimensions (that is, the angle of anteversion and the neck-shaft angle proximally, and the valgus angle of the femoral shaft distally). Considerable interspecimen variation in the angles between the transcondylar plane and the femoral center, in accord with the valgus angle of the femoral shaft distally, was also noted. The mean transcondylar valgus angle (described as the tangent of the condyles to the perpendicular of the long axis) was 3.8 degrees. In contrast, little variation among specimens was noted for the angle made by the shaft and the long axis.
This study presents a method to evaluate three-dimensional strain in meniscal tissue using medical imaging. Strain is calculated by tracking small teflon markers implanted within the meniscal tissue using computed tomography imaging. The results are presented for strains in the middle and posterior third of the medial menisci of 10 human cadaveric knees, under simulated physiologically relevant loading. In the middle position, an average compressive strain of 3.4% was found in the medial lateral direction, and average tensile strains of 1.4% and 3.5% were found in the anterior posterior and superior inferior directions respectively at 5° of knee flexion with an applied load of 1×body weight. In the posterior position, under the same conditions, average compressive strains of 2.2% and 6.3% were found in the medial lateral and superior inferior directions respectively, and an average tensile strain of 3.8% was found in the anterior posterior direction. No statistically significant difference between strain in the middle or posterior of the meniscus or between the global strains is uncovered.
The relationships between non-contact anterior cruciate ligament injuries and the underlying biomechanics are still unclear, despite large quantities of academic research. The purpose of this research was to study anterior cruciate ligament strain during jump landing by investigating its correlation with sagittal plane kinetic/kinematic parameters and by creating an empirical model to estimate the maximum strain. Whole-body kinematics and ground reaction forces were measured from seven subjects performing single leg jump landing and were used to drive a musculoskeletal model that estimated lower limb muscle forces. These muscle forces and kinematics were then applied on five instrumented cadaver knees using a dynamic knee simulator system. Correlation analysis revealed that higher ground reaction force, lower hip flexion angle and higher hip extension moment among others were correlated with higher peak strain (p <.05). Multivariate regression analyses revealed that intrinsic anatomic factors account for most of the variance in strain. Among the extrinsic variables, hip and trunk flexion angles significantly contributed to the strain. The empirical relationship developed in this study could be used to predict the relative strain between jumps of a participant and may be beneficial in developing training programs designed to reduce an athlete's risk of injury. This article is protected by copyright. All rights reserved
Computational modeling and simulation of neuromusculoskeletal (NMS) systems enables researchers and clinicians to study the complex dynamics underlying human and animal movement. NMS models use equations derived from physical laws and biology to help solve challenging real-world problems, from designing prosthetics that maximize running speed to developing exoskeletal devices that enable walking after a stroke. NMS modeling and simulation has proliferated in the biomechanics research community over the past 25 years, but the lack of verification and validation standards remains a major barrier to wider adoption and impact. The goal of this paper is to establish practical guidelines for verification and validation of NMS models and simulations that researchers, clinicians, reviewers, and others can adopt to evaluate the accuracy and credibility of modeling studies. In particular, we review a general process for verification and validation applied to NMS models and simulations, including careful formulation of a research question and methods, traditional verification and validation steps, and documentation and sharing of results for use and testing by other researchers. Modeling the NMS system and simulating its motion involves methods to represent neural control, musculoskeletal geometry, muscle-tendon dynamics, contact forces, and multibody dynamics. For each of these components, we review modeling choices and software verification guidelines; discuss variability, errors, uncertainty, and sensitivity relationships; and provide recommendations for verification and validation by comparing experimental data and testing robustness. We present a series of case studies to illustrate key principles. In closing, we discuss challenges the community must overcome to ensure that modeling and simulation are successfully used to solve the broad spectrum of problems that limit human mobility.
The mechanism of noncontact anterior cruciate ligament (ACL) injury is not well understood. It is partly because previous studies have been unable to relate dynamic knee muscle forces during sports activities such as landing from a jump to the strain in the ACL. We present a combined in vivo/in vitro method to relate the muscle group forces to ACL strain during jump-landing using a newly developed dynamic knee simulator. A dynamic knee simulator system was designed and developed to study the sagittal plane biomechanics of the knee. The simulator is computer controlled and uses six powerful electromechanical actuators to move a cadaver knee in the sagittal plane and to apply dynamic muscle forces at the insertion sites of the quadriceps, hamstring, and gastrocnemius muscle groups and the net moment at the hip joint. In order to demonstrate the capability of the simulator to simulate dynamic sports activities on cadaver knees, motion capture of a live subject landing from a jump on a force plate was performed. The kinematics and ground reaction force data obtained from the motion capture were input into a computer based musculoskeletal lower extremity model. From the model, the force-time profile of each muscle group across the knee during the movement was extracted, along with the motion profiles of the hip and ankle joints. This data was then programmed into the dynamic knee simulator system. Jump-landing was simulated on a cadaver knee successfully. Resulting strain in the ACL was measured using a differential variable reluctance transducer (DVRT). Our results show that the simulator has the capability to accurately simulate the dynamic sagittal plane motion and the dynamic muscle forces during jump-landing. The simulator has high repeatability. The ACL strain values agreed with the values reported in the literature. This combined in vivo/in vitro approach using this dynamic knee simulator system can be effectively used to study the relationship between sagittal plane muscle forces and ACL strain during dynamic activities.
Today, energy efficiency in production systems has partially been achieved on the component level, but methods are missing for the energy optimal operation of plants, machines and components. We therefore, propose a novel generic method to model the energy consumption behaviour of machines and plants based on a statistical discrete event formulation. It is lean, integrative and scalable and can be used directly in planning processes to make predictions of the energy consumption of different configurations in different scenarios based on any amount of available information. Using the modelling framework, we introduce applications in real-time, tactical and strategic decision making processes that make it possible to exploit the potential for energy consumption minimisation of any given machine or production system while obeying conflicting general conditions.
This paper reviews the functional anatomy of the anterior cruciate ligament (ACL), which has a parallel array of collagen fascicles that have usually been divided into two 'fibre bundles': anteromedial (AM) and posterolateral (PL), according to their tibial attachment sites. The PL bundle has shorter fibres, and so it is subjected to greater tensile strains than the AM bundle when the whole ACL is stretched; its oblique orientation in the coronal plane imbues it with greater ability to resist tibial rotation than the more vertical AM fibre bundle. Most studies have found that the AM bundle is close to isometric when the knee flexes, while the PL bundle slackens approximately 6 mm. There is little evidence of significant fibre bundle elongation in response to tibial rotation. Selective bundle cutting studies have been performed, allowing both the bundle tensions and their contributions to resisting tibial anterior translation and tibial rotation to be calculated. These show that the function of the PL bundle was dominant near knee extension in some studies, particularly when resisting anterior drawer and that its contribution reduced rapidly with knee flexion through 30 degrees. There has been little study of the contributions of the fibre bundles in control of tibial internal-external rotation or the pivot shift: one study found that the AM bundle had larger tensions than the PL bundle during a simulated pivot shift, but another study found that cutting the PL bundle allowed a larger increase in coupled tibial anterior translation than cutting the AM bundle. It was concluded that the AM bundle is most important for resisting tibial anterior drawer-the primary function of the ACL-while the PL bundle is tight near knee extension, when it has a role in control of tibial rotational laxity. There is a clear need for further study of dynamic knee instability, to gain better understanding of how best to reconstruct the ACL and associated tissues.
The aim of this systematic review was to evaluate studies published on anatomic double-bundle anterior cruciate ligament (ACL) reconstruction.
A systematic electronic search was performed by use of the Medline and Embase databases. Studies that were published from January 1995 to April 2009 were included. The selection criteria were studies that reported on a surgical technique for "anatomic double-bundle ACL reconstruction" on skeletally mature living human subjects and were written in English. Data collected and analyzed included a variety of surgical data. Tables were created to provide an overview of surgical techniques for anatomic ACL reconstruction.
Seventy-four studies were included in this review. Some surgical factors were adequately reported in the majority of the articles: visualizing the native ACL insertion sites, placing the tunnels in the footprint, graft type, and fixation method. However; ACL insertion site measurement, femoral intercondylar notch measurement, individualization of surgery, and intraoperative/postoperative imaging were poorly reported. The most variety was seen in knee flexion angle during femoral tunnel drilling and tensioning pattern of the grafts.
For most surgical data, there was a gross under-reporting of specific operative technique data. We believe that the details of an "anatomic" operative technique are crucial for the valid interpretations of the outcomes. Thus we encourage authors to report their surgical technique in a specific and standardized fashion.
The anterior cruciate ligament has been and is of great interest to scientists and orthopaedic surgeons worldwide. Anterior cruciate ligament reconstruction was initially performed using an open approach. When the approach changed from open to arthroscopic reconstruction, a 2- and, later, 1-incision technique was applied. With time, researchers found that traditional arthroscopic single-bundle reconstruction did not fully restore rotational stability of the knee joint and a more anatomic approach to reconstruct the anterior cruciate ligament has been proposed. Anatomic anterior cruciate ligament reconstruction intends to replicate normal anatomy, restore normal kinematics, and protect long-term knee health. Although double-bundle anterior cruciate ligament reconstruction has been shown to result in better rotational stability in both biomechanical and clinical studies, it is vital to differentiate between anatomic and double-bundle anterior cruciate ligament reconstruction. The latter is merely a step closer to reproducing the native anatomy of the anterior cruciate ligament; however, it can still be done nonanatomically. To evaluate the potential benefits of reconstructing the anterior cruciate ligament in an anatomic fashion, accurate, precise, and reliable outcome measures are needed. These include, for example, T2 magnetic resonance imaging mapping of cartilage and quantification of graft healing on magnetic resonance imaging. Furthermore, there is a need for a consensus on which patient-reported outcome measures should be used to facilitate homogeneous reporting of outcomes.
The menisci play an important role in load distribution, load bearing, joint stability, lubrication, and proprioception. Partial meniscectomy has been shown to result in changes in the kinematics and kinetics at the knee during gait that can lead to progressive meniscal degeneration. This study examined changes in the strains within the menisci associated with kinematic and kinetic changes during the gait cycle. The gait changes considered were a 5 deg shift toward external rotation of the tibia with respect to the femur and an increased medial-lateral load ratio representing an increased adduction moment. A finite element model of the knee was developed and tested using a cadaveric specimen. The cadaver was placed in positions representing heel-strike and midstance of the normal gait, and magnetic resonance images were taken. Comparisons of the model predictions to boundaries digitized from images acquired in the loaded states were within the errors produced by a 1 pixel shift of either meniscus. The finite element model predicted that an increased adduction moment caused increased strains of both the anterior and posterior horns of the medial meniscus. The lateral meniscus exhibited much lower strains and had minimal changes under the various loading conditions. The external tibial rotational change resulted in a 20% decrease in the strains in the posterior medial horn and increased strains in the anterior medial horn. The results of this study suggest that the shift toward external tibial rotation seen clinically after partial medial meniscectomy is not likely to cause subsequent degenerative medial meniscal damage, but the consequence of this kinematic shift on the pathogenesis of osteoarthritis following meniscectomy requires further consideration.
To evaluate the influence of tibial and femoral tunnel position in ACL reconstruction on knee kinematics, we compared ACL reconstruction with a tibial and femoral tunnel in anteromedial (AM-AM reconstruction) and in posterolateral footprint (PL-PL reconstruction) with a reconstruction technique with tibial posterolateral and femoral anteromedial tunnel placement (PL-AM reconstruction). In 9 fresh-frozen human cadaveric knees, the knee kinematics under simulated Lachman (134 N anterior tibial load) and a simulated pivot shift test (10 N/m valgus and 4 N/m internal tibial torque) were determined at 0°, 30°, 60°, and 90° of flexion. Kinematics were recorded for intact, ACL-deficient, and single-bundle ACL reconstructed knees using three different reconstruction strategies in randomized order: (1) PL-AM, (2) AM-AM and (3) PL-PL reconstructions. Under simulated Lachman test, single-bundle PL-AM reconstruction and PL-PL reconstructions both showed significantly increased anterior tibial translation (ATT) at 60° and 90° when compared to the intact knee. At all flexion angles, AM-AM reconstruction did not show any statistical significant differences in ATT compared to the intact knee. Under simulated pivot shift, PL-AM reconstruction resulted in significantly higher ATT at 0°, 30°, and 60° knee flexion and AM-AM reconstructions showed significantly higher ATT at 30° compared to the intact knee. PL-PL reconstructions did not show any significant differences to the intact knee. AM-AM reconstructions restore the intact knee kinematics more closely when compared to a PL-AM technique resembling a transtibial approach. PL-PL reconstructions showed increased ATT at higher flexion angles, however, secured the rotational stability at all flexion angles. Due to the independent tibial and femoral tunnel location, a medial portal technique may be superior to a transtibial approach.
The function of the anteromedial (AM) and posterolateral (PL) bundles of the anterior cruciate ligament (ACL) during gait has not been reported.
The AM and PL bundles have distinct functional behavior during the stance phase of treadmill gait.
Descriptive laboratory study.
Three-dimensional models of the knee were created by magnetic resonance images from 8 healthy subjects. The contour of the 2 bundle attachments were constructed on each model. Each bundle was represented by a straight line connecting its tibial and femoral attachment centroids. Next, the knee kinematics during the stance phase of gait was determined with a dual fluoroscopic imaging system. The relative elongation, sagittal plane elevation, coronal plane elevation, and transverse plane deviation of the 2 bundles were measured directly from heel strike to toe-off.
At heel strike, the AM and PL bundles had first peak elongation of 9% +/- 7% and 9% +/- 13%, respectively. At 50% progress of the stance phase, both bundles were maximally elongated, 12% +/- 7% for the AM bundle and 13% +/- 15% for the PL bundle. No significant difference was found for each bundle between 40% and 60% of the stance phase (P > .05). With increasing knee flexion, the sagittal plane and coronal plane elevations of the 2 bundles decreased, whereas the deviation angles increased.
Both bundles are anisometric and function in a similar manner during the stance phase of gait. They were maximally elongated throughout the midstance where they were stretched maximally to resist anterior tibial translation.
This information can be useful for further improving anatomical ACL reconstructions to better reproduce the 2 bundle functions. It may also be useful for designing postoperative rehabilitation regimens to prevent overstretch of the grafts.
This article describes the use of the Hall Effect strain transducer (HEST) in a new arthroscopic technique to study the normal anterior cruciate ligament (ACL) in-vivo. Study participants were patient volunteers with normal ACLs undergoing diagnostic arthroscopic or meniscal surgery under local anaesthesia. The HEST was implanted into the Anterior Medial Band (AMB) of the ACL. Anterior shear loading of the tibia in relation to the fixed femur at 30° of knee flexion (Lachman test), produced significantly greater strain values in comparison to anterior shear loading at 90° (Anterior Drawer test). During isometric quadriceps contraction a significant increase in AMB strain was measured with the knee flexed to 30°, while no significant change was measured at 90°. For quadriceps contraction there were significantly higher values of AMB strain measured at 30° of knee flexion in comparison to that observed at 90°. For active range of motion (AROM) the AMB was strained between 10° and 48°, and unstrained between 48° and 110°. During passive range of motion (PROM) the AMB remained unstrained until the joint was brought into extension. There were significant differences in strain values found between AROM and PROM at the flexion angles 10°, 20°, 30° and 40°, while between 50° and 110° there were no significant differences. These results confirm previous studies that the Lachman test is a superior technique in comparison to the classic anterior drawer test for evaluating the AMB. They suggest that isometric quadriceps activity at 90° of knee flexion can be prescribed for rehabilitation immediately after ACL reconstruction. These data indicate that AROM (between the limits of 50° and 110°) and PROM may also be performed with minimal risk of strain to a reconstructive replacement. The PROM data may also serve as an important standard for the reconstruction of the ACL.
This article reviews our research studies on the anterior cruciate ligament (ACL). The human ACL was found to be a primary restraint to anterior tibial displacement at both 90 degrees and 30 degrees of flexion. Geometric measurements of the ligament showed it to have a complex macrostructure, consisting of bundles of different lengths, curvatures, and orientations. Similar material properties were measured for subunits from the human anterior and posterior cruciate and lateral collateral ligaments. However, the linear modulus, maximum stress, and strain energy density to maximum stress of the ACL were significantly less than similar properties for patellar tendons. These tissue subunits exhibited nonuniform axial strain during tensile loading, which was partially attributed to differences in bundle crimp period and crimp angle. The structural mechanical properties (stiffness, strength, and energies and elongations to maximum force and failure) of nine commonly used human ACL substitutes were also compared. Only the bone-patellar tendon-bone unit had maximum force and stiffness greater than that of the ACL. The patellar tendon, when used as an ACL replacement in the dog and primate, exhibited significant loss in structural mechanical and material properties early after implantation. These properties showed only a gradual improvement up to 1 year after surgery. Maintaining a vascular supply to these grafts or using intermittent passive motion immediately after surgery produced no significant improvement in graft properties in the primate model.
Decreased range of knee motion during gait is often treated by surgically releasing the rectus femoris from the patella and transferring it to one of four sites: semitendinosus, gracilis, sartorius, or the iliotibial tract. This study was conducted to determine if there are differences between these four tendon transfer sites in terms of post-surgical moment arms about the knee and hip. A graphics-based model of the lower extremity was used to simulate the origin-to-insertion path of the rectus femoris after transfer. Anatomical studies were conducted to evaluate the accuracy of the simulated tendon transfers by comparing knee flexion moment arms calculated with the computer model to moment arms measured in two anatomical specimens. The computer simulations and anatomical studies revealed substantial differences in the knee moment arms between the four sites. We found that the rectus femoris has the largest peak knee flexion moment arm (4-5 cm) after transfer to the semitendinosus. In contrast, after transfer to the iliotibial tract the rectus femoris has a slight (0-5 mm) knee extension moment arm. None of the transfers to muscle-tendon complexes on the medial side of the knee (semitendinosus, gracilis, sartorius) substantially affect the hip rotation moment arm of the rectus femoris. Transferring to the iliotibial tract increases hip internal rotation moment arm of the rectus femoris, but only when the hip is externally rotated.
Disruption of the anterior cruciate ligament (ACL), a primary stabilizer of the knee, can produce disability. The purpose of our work has been to study the normal ACL in humans, in the presence of normal muscle function and body weight, and develop clinical criteria for reconstruction, establish a basis for rehabilitation programs, and evaluate how knee braces protect this important ligament. The strain behavior of the ACL has been measured by arthroscopic implantation of the Differential Variable Reluctance Transducer while subjects are under local anesthesia. Movement of the knee from a flexed to an extended position, either passively or through contraction of the leg muscles, produces an increase in ACL strain values. Isolated contraction of the dominant quadriceps with the knee between 50 degrees and extension creates substantial increases in strain. In contrast, isolated contraction of the hamstrings at any knee position does not increase strain. With the knee un-weighted, the protective strain shielding effect of a functional knee brace decreases as the magnitude of anterior shear load applied to the tibia increases. A different behavior occurs during weight bearing, the strain shielding effect of the brace remains constant as the magnitude of anterior load increases. Our approach is novel in that it can be used to measure on important portion of the ACLs strain distribution while clinically relevant loads are applied to the knee, subjects perform rehabilitation exercises, or in the presence of different orthoses such as functional knee braces.
Meniscal injury has been well documented in association with injury to the anterior cruciate ligament. The purpose of this study was to evaluate the effect of anterior cruciate ligament transection and reconstruction on meniscal strain. Four differential variable reluctance transducer strain gauges were placed in the medial and lateral menisci of nine cadaveric knees. Each specimen was mounted to a six-degree-of-freedom knee testing device. Testing was conducted with the knee fully extended and at 45 degrees and 90 degrees of flexion, both with and without applied axial load. At each angle of flexion, an anterior and posterior tibial load was applied. Next, the anterior cruciate ligament was transected and the testing sequence was repeated. Finally, the ligament was reconstructed using a central one-third patellar tendon graft and the testing sequence was repeated. The results demonstrated statistically significant increases in meniscal strain in ligament-transected knees compared with intact specimens. A reduction in meniscal strain to a level similar to that detected in the ligament-intact knees was observed after anterior cruciate ligament reconstruction. These results have important clinical implications regarding the potentially deleterious effect of the anterior cruciate ligament-deficient knee on meniscal strain and the potential benefit of anterior cruciate ligament reconstruction.
OBJECTIVE: To measure the circumferential or hoop strains generated in the medial meniscus during loading of the knee joint and to examine the effect of longitudinal and radial tears in the meniscus on these strain values. DESIGN: An in vitro investigation measuring the circumferential strains in the medial menisci of cadaveric human knees as they were loaded in a materials testing machine. BACKGROUND: The menisci transmit approximately 50% of the load through the knee, the rest being transmitted by direct contact of the articular cartilage. Damage to the menisci will alter the pattern of load transmission as will meniscectomy. This study examined the changes in the mechanics of the meniscus in situ as a result of simulated tears to assess the effect of its load carrying capacity and the implications of surgery to remove part or all of a damaged meniscus. METHODS: Nineteen human cadaveric knees were tested. Windows were made in the joint capsule and strain gauges inserted into the anterior, middle and posterior sections of the medial meniscus. The knees were then loaded to three times body weight at speeds of 50 and 500 mm/min, with the knee joint at 0 degrees and 30 degrees of flexion. The tests were repeated following the creation of a longitudinal or a radial tear in the meniscus. RESULTS: The intact menisci showed significantly less strain in the posterior section compared to the anterior and middle sections (P < 0.003, with strains of 1.54%, 2.86% and 2.65% respectively). With a longitudinal tear this pattern changed with strains decreasing anteriorly and increasing posteriorly. There were also significant differences at different angles of knee joint flexion not seen in the intact meniscus. 50% radial tears reduced the strains anteriorly whilst a complete radial tear completely defunctioned the meniscus. CONCLUSIONS: This study has shown that there are significantly different hoop strains produced in different sections of the medial meniscus under load and the patterns of strain distribution are disturbed by meniscal tears. RELEVANCE: These results provide important data for mathematical models which must include non-uniform behaviour. They also have implications for the surgical management of torn menisci. Undamaged portions should be preserved and the integrity of the circumferential fibres maintained to ensure the menisci retain a load bearing capability.
The objective of this study is to determine how kinematical parameters and electromyography data of selected muscles may change as a result of anterior cruciate ligament (ACL) deficiency and following ACL reconstruction. The study was conducted on 25 anterior cruciate ligament deficient subjects prior to and 6 weeks, 4 months, 8 months and 12 months following ACL reconstructive surgery using the bone-patellar tendon-bone technique. Gait analysis was performed by applying the zebris three-dimensional ultrasound-based system with surface electromyograph (zebris). Kinematic data were recorded for the lower limb. The muscles surveyed include vastus lateralis and medialis, biceps femoris and adductor longus. The results obtained from the injured subjects were compared with those of 51 individuals without any ACL damage whatsoever. Acute ACL deficient patients exhibited a quadriceps avoidance pattern prior to and 6 weeks following surgery. No quadriceps avoidance phenomenon develops in chronic ACL deficient patients. In operated individuals, tempo-spatial parameters and the knee angle regained a normal pattern for the ACL-deficient limb during gait as early as 4 months following surgery. However, the relative ACL movement parameter, which describes the tibial translation into the direction of ACL, and the EMG traces show no significant statistical difference compared with the same values of the healthy control group just 8 months following surgery. The analysis of spatial-temporal parameters and EMG traces show that the development of a quadriceps avoidance pattern is less common than previously reported. These data suggest that anterior cruciate ligament deficiency and reconstruction produce considerable changes in the lower extremity gait pattern. The results suggest that gait parameters tend to shift towards a normal value pattern; and the re-establishment of pre-injury gait patterns-including the normal biphase of muscles-takes at least 8 months to occur.
The relationship between posterior cruciate ligament insufficiency and meniscal injury is unclear.
Posterior cruciate ligament insufficiency results in increased medial and lateral meniscal strain.
Descriptive anatomic study.
Eight cadaveric specimens were evaluated with a 6-axis load cell and differential variable reluctance transducer strain gauges placed in both menisci. Data were recorded in the posterior cruciate ligament-intact state after posterior cruciate ligament transection and after posterior cruciate ligament reconstruction.
The effect of posterior cruciate ligament state on meniscal strain was more pronounced at higher flexion angles. At 60 degrees and 90 degrees of flexion, there was a significant effect of posterior cruciate ligament sectioning and reconstruction on meniscal strain (P < .026). Average meniscal strain for both medial and lateral menisci increased between the intact and the posterior cruciate ligament-cut states. Posterior cruciate ligament reconstruction decreased strain values to that of the intact knee.
Meniscal strain increases with complete posterior cruciate ligament injury and is returned to posterior cruciate ligament-intact levels after posterior cruciate ligament reconstruction. Clinical Relevance: Posterior cruciate ligament reconstruction may play an important role in reducing meniscal strain and subsequent degeneration within the posterior cruciate ligament-injured knee.
An instrumented cadaveric knee construct was used to quantify the association between impact force, quadriceps force, knee flexion angle, and anterior cruciate ligament relative strain in simulated unipedal jump landings.
Anterior cruciate ligament strain will correlate with impact force, quadriceps force, and knee flexion angle.
Descriptive laboratory study.
Eleven cadaveric knees (age, 70.8 [19.3] years; 5 male; 6 female) were mounted in a custom fixture with the tibia and femur secured to a triaxial load cell. Quadriceps, hamstring, and gastrocnemius muscle forces were simulated using pretensioned steel cables (stiffness, 7 kN/cm), and the quadriceps tendon force was measured using a load cell. Mean strain on the anteromedial bundle of the anterior cruciate ligament was measured using a DVRT. With the knee in 25 degrees of flexion, the construct was vertically loaded by an impact force initially directed 4 cm posterior to the knee joint center. Tibiofemoral kinematics was measured using a 3D optoelectronic tracking system.
The increase in anterior cruciate ligament relative strain was proportional to the increase in quadriceps force (r(2) = 0.74; P < .00001) and knee flexion angle (r(2) = 0.88; P < .00001) but was not correlated with the impact force (r(2) = 0.009; P = .08).
The increase in knee flexion and quadriceps force during this simulated 1-footed landing strongly influenced the relative strain on the anteromedial bundle of the anterior cruciate ligament.
These results suggest that even in the presence of knee flexor muscle forces, the increase in quadriceps force required to prevent the knee from flexing during landing can place the anterior cruciate ligament at risk for large strains.