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Background: Anterior cruciate ligament injuries are commonly treated with ligament reconstruction surgery, but post-operative joint contracture is a major complication. The optimal timing for anterior cruciate ligament reconstruction remains controversial, with some clinical studies suggesting that early surgery may increase the risk of joint contractures, while others have found no such association. To clarify this, we investigated the effects of the timing of reconstruction surgery on contracture formation using a rat model., Methods: Anterior cruciate ligament-transected rats were divided into groups based on the timing of reconstruction: immediate, early, and delayed (1, 14, and 28 days after transection, respectively). Some anterior cruciate ligament-transected rats did not receive reconstruction surgery. Untreated rats served as controls. At 56 days after ligament transection, we assessed knee extension range of motion before (including both myogenic and arthrogenic factors) and after myotomy (arthrogenic factor only), as well as fibrotic changes in the joint capsule., Finding: Anterior cruciate ligament transection alone significantly decreased range of motion before myotomy, but not after myotomy. In all reconstructed groups, both range of motions before and after myotomy were significantly reduced compared to the control, indicating the induction of arthrogenic contracture by reconstruction surgery. Fibrotic changes in the joint capsule were observed in all reconstructed groups, contributing to arthrogenic contracture formation. However, the timing of reconstruction had no effect on range of motions and fibrotic changes in the joint capsule., Interpretation: Our findings may help guide clinical decision-making regarding the timing of anterior cruciate ligament reconstruction surgery., Competing Interests: Declaration of competing interest The authors report no conflict of interest., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Background: Strength and neuromuscular decrements following knee musculoskeletal injury may accelerate knee osteoarthritis development. This study assessed isometric knee extensor and flexor strength and steadiness between individuals with knee injury, i.e., ligament reconstruction, and knee osteoarthritis to healthy age-matched controls., Methods: Four cohorts (1: knee injury and 2: age-matched controls, and 3: radiographic knee osteoarthritis and 4: age-matched controls) were recruited. Participants performed maximal voluntary isometric knee extensor and flexor contractions. Then, strength (e.g., peak and rate of torque development) and steadiness (e.g., peak power, mean, and median frequency) were derived from each raw torque-time curve and associated power spectral density. A Kruskal-Wallis H test and Spearman's rho correlation analysis assessed cohort differences and association between knee extensor and flexor strength and steadiness., Findings: The young adult control and knee injury cohorts exhibited greater knee extensor and flexor strength than the older, knee osteoarthritis cohort (p < 0.043). The knee injury cohort, despite being as strong as their healthy counterparts, were significantly less steady with a 92% increase in peak power frequency (p = 0.046). The osteoarthritis cohort exhibited 157% less total power compared to the knee injury and young control cohorts (p < 0.019). Knee extensor and flexor peak torque, rate of torque development, and mean torque exhibit a significant, positive relation with total power (p < 0.018)., Interpretation: Individuals with knee injury and disease may exhibit weaker or less steady knee musculature, predisposing them to degenerative joint disease. Clinicians may need to restore knee extensor and flexor steadiness to facilitate better joint neuromuscular control., Competing Interests: Declaration of competing interest None of the authors demonstrate any conflict of interest regarding this submission., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Background: Those who undergo ACL reconstruction are at an increased risk of suffering a second ACL injury. A suggested rationale for the increased injury risk is sensory reweighting to the visual system to compensate for a lack of somatosensory information from the knee. Understanding this proposed visual reliance may help clinicians improve return to sport outcomes and reduce the risk of a subsequent ACL injury., Methods: Thirteen ACL reconstructed individuals and thirteen matched controls completed two common static postural control assessments under three different visual conditions; eyes open, low visual disruption, and high visual disruption. Center of pressure data was collected for 30 s using force plates. Static postural stability was evaluated using the following: 1) root mean square distance, 2) mean velocity, 3) sway area, and 4) mean frequency., Findings: No significant interactions between group and vision were observed. Significant differences between groups were observed for mean frequency in the double-limb stance (p < .05). Additionally, significant differences were observed for visual conditions in both double-limb (mean velocity; p < .05) and single-limb stances (root mean square distance, mean velocity, sway area, and mean frequency; p < .05)., Interpretation: The findings of the current study suggest that ACL reconstructed individuals, who are at least two years removed from surgery, do not rely on visual information to a greater extent than controls during static postural stability assessments. Stroboscopic glasses may be a cost-effective alternative for rehabilitation purposes compared to the traditional binary eyes open vs. eyes closed methods., Competing Interests: Declaration of competing interest Nathan Robey reports financial support was provided by University of Northern Colorado. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Published by Elsevier Ltd.)

Background: Rupturing the anterior cruciate ligament is an orthopedic injury that results in neuromuscular impairments affecting sensory input to the central nervous system. Traditional physical therapy after anterior cruciate ligament reconstruction aims to rehabilitate orthopedic impairments but fails to address asymmetric gait mechanics that are present post-operatively and are linked to the development of post-traumatic osteoarthritis. A first step towards developing gait interventions is understanding if individuals after anterior cruciate ligament reconstruction have the capacity to learn new walking mechanics., Methods: The split-belt treadmill offers a task-specific approach to examine neuromuscular adaptations in patients after injury. The potential for changing spatiotemporal gait mechanics via split-belt treadmill adaptation has not been tested early after anterior cruciate ligament reconstruction; nor has the ability to retain and transfer newly learned gait mechanics. Therefore, we used a split-belt treadmill paradigm to compare gait adaptation, retention, and transfer to overground walking between 15 individuals 3-9 months after anterior cruciate ligament reconstruction and 15 matched control individuals., Findings: Results suggested individuals after anterior cruciate ligament reconstruction were able to adapt and retain step length symmetry changes as well as controls. There was also evidence of partial transfer to overground walking, similar to controls., Interpretation: Despite disruption in afferent feedback from the joint, individuals early after anterior cruciate ligament reconstruction can learn a new gait pattern using sensorimotor adaptation, retain, and partially transfer the learned gait pattern. This may be a critical time to intervene with gait-specific interventions targeting post-operative gait asymmetries., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Elanna K. Arhos reports financial support was provided by National Institutes of Health. Elanna K. Arhos reports financial support was provided by Foundation for Physical Therapy. Karin G Silbernagel reports financial support was provided by National Institutes of Health. Susanne M. Morton reports financial support was provided by National Institutes of Health. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Background: Individuals with a recent anterior cruciate ligament reconstruction may demonstrate an altered movement strategy for protecting the knee and maintaining stability. Altered knee movement might lead to abnormal intra-articular load, potentially contributing to early knee osteoarthritis onset. A protective strategy may be particularly evident during active tasks that induce a pivot-shift manoeuvre, such as a step-down and cross-over task. In this study, we investigated whether knee joint mechanics and muscle activity differed between participants early (∼3 months) following reconstruction (n = 35) to uninjured controls (n = 35) during a step-down and cross-over task with a 45° change-of-direction., Methods: We used motion capture, force plates and surface electromyography to compare time-normalised curves of sagittal and transverse-plane knee mechanics and muscle activity during the cross-over phase between groups using functional t-tests. We also compared knee mechanics between sides within the injured group and compared discrete outcomes describing the cross-over phase between groups., Findings: Compared to controls, the injured participants had greater knee flexion angle and moment, lower internal rotation moment, more preparatory foot rotation of the pivoting leg, a smaller cross-over angle, and a longer cross-over phase for both the injured and uninjured sides. The injured leg also had greater biceps femoris and vastus medialis muscle activity compared to controls and different knee mechanics than the uninjured leg., Interpretation: Individuals with anterior cruciate ligament reconstruction showed a knee-stabilising and pivot-shift avoidance strategy for both legs early in rehabilitation. These results may reflect an altered motor representation and motivate considerations early in rehabilitation., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Charlotte K Häger reports financial support was provided by Swedish Research Council (2017–00892; 2022–00774). Charlotte K Häger reports financial support was provided by Region Västerbotten (Cutting Edge funding Grant No RV966109; ALF funding RV 967112; VLL838421; Strategic funding VLL358901, Project No. 7002795; ALF funding 2022–2024; Cutting Edge Funding 2022–2024). Charlotte K Häger reports financial support was provided by The Swedish Research Council for Sports Science (P2020–0035; P2021–0061; 2022/10 P2023–0030). Charlotte K Häger reports financial support was provided by Umeå University Foundation for Medical Research 2019–2023. Charlotte K Häger reports financial support was provided by King Gustaf V and Queen Victoria's Foundation of Freemasons. Charlotte K Häger reports financial support was provided by Umeå university Strategic research area health care science, SFOV. All authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

Background: Although knee immobilization may deteriorate the mechanical parameters of the anterior cruciate ligament, such as stiffness and failure strength, it is unknown whether it induces laxity in the whole joint. We examined the effects of immobilization on anterior-posterior joint laxity and mechanical properties of the anterior cruciate ligament, as well as histological and gene expression profiles of the joint capsule in rat knee joints., Methods: Unilateral rat knees were immobilized using an external fixator. Non-immobilized contralateral knees were used as controls. After 3 weeks, anterior-posterior laxity in the whole joint (i.e., a complex of bones, ligaments, and capsule) and stiffness and failure strength in the anterior cruciate ligament were examined using a universal testing machine. Moreover, the knee joint capsule was histologically analyzed, and the expression levels of genes related to collagen turnover in the posterior joint capsule were examined., Findings: Joint immobilization slightly but significantly increased anterior-posterior laxity compared with the contralateral side. Unexpectedly, the stiffness and failure strength of the anterior cruciate ligament were not altered by immobilization. There was no correlation found between anterior cruciate ligament stiffness and anterior-posterior joint laxity. In the posterior joint capsule, thinning of the collagen fiber bundles accompanied by a decrease in COL3A1 gene expression was observed after immobilization., Interpretation: These results suggest that 3 weeks of joint immobilization alters the biomechanical integrity in the knee joint without altering the mechanical properties of the anterior cruciate ligament. Changes in the joint capsule may contribute to the immobilization-induced increase in anterior-posterior laxity., Competing Interests: Declaration of competing interest None., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Background: There is currently no consensus among orthopaedic surgeons as to when patients with anterior cruciate ligament reconstruction are ready to return to sport or whether or not patients should wear a functional knee brace during athletic activity. The purpose of the present study was to determine the effects of time since return to sport and of a functional knee brace on hop distance and loading symmetry during hop testing in patients with anterior cruciate ligament reconstruction., Methods: Twenty-eight patients with anterior cruciate ligament reconstruction completed hop testing after being released to return to sport and again 3 months later, both with and without wearing a custom fit extension constraint functional knee brace. The loadsol® captured plantar loading data (100 Hz) to quantify peak impact force, loading rate, and impulse during the final landing of every hop test. A limb symmetry index was calculated between surgical and non-surgical limbs for hop distance and loading measures., Findings: Wearing a knee brace increased hop distance symmetry during the single and crossover hop tests and peak impact force symmetry on each test (all p < 0.05). While single (p = 0.022) and triple (p = 0.002) hop distance symmetry increased with time, there was no effect of time on any loading symmetry outcomes., Interpretation: These results support using a functional knee brace during athletic activities for improving symmetry in the early return to sport period. These results also support previous findings that while hop distance symmetry improves with time, asymmetrical landing mechanics do not and should be addressed clinically., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Background: The aim of the present study was to evaluate the relationship between tibial slope angle and ligament strain during in vitro landing simulations that induce ACL failure through the application of variable external loading at the knee. The hypothesis tested was that steeper posterior tibial slope angle would be associated with higher ACL strain during a simulated landing task across all external loading conditions., Methods: Kinetics previously derived from an in vivo cohort performing drop landings were reproduced on 45 cadaveric knees via the mechanical impact simulator. MRIs were taken of each specimen and used to calculate medial compartment posterior tibial slope, lateral compartment posterior tibial slope, and coronal plane tibial slope. Linear regression analyses were performed between these angles and ACL strain to determine whether tibial slope was a predictive factor for ACL strain., Findings: Medial and lateral posterior tibial slope were predictive factors for ACL strain during some landings with higher combined loads. Medial posterior slope was more predictive of ACL strain in most landings for male specimens, while lateral posterior and coronal slope were more predictive in female specimens, but primarily when high abduction moments were applied., Interpretation: Tibial slope has the potential to influence ACL strain during landing, especially when large abduction moments are present at the knee. Deleterious external loads to the ACL increase the correlation between tibial slope and ACL strain, which indicates that tibial slope angles are an additive factor for athletes apt to generate large out-of-plane knee moments during landing tasks., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Background: Sex-related neuromuscular differences have been linked to greater risk of anterior cruciate ligament injuries in females. Despite this, it remains unclear if sex-related differences are present after injury. This study sought to determine if sex differences are present in the functional roles of knee joint muscles in an anterior cruciate ligament deficient population., Methods: An isometric, weight-bearing, force-generation protocol required injured and healthy males and females to modulate ground reaction forces. Electromyography was used to classify the functional role of 10 lower limb muscles in their contribution to knee joint stability during various loading directions. These roles were compared between the four groups at 12 loading directions using a directional analysis., Findings: Functional muscle roles were different between groups, except for injured males and healthy females. Healthy males had either joint actuators or specific joint stabilisers, but no general stabilisers; the vastus medialis and lateralis of injured males and healthy females were classified as general stabilisers while injured females added the gluteus medialis and medial gastrocnemius as general stabilisers., Interpretation: A population-based hierarchy in functional muscle roles was discovered. Healthy males demonstrated the most specific muscle roles, which can be viewed as more adaptive to variable loading conditions. The more generalised stabilisation strategies seen in injured males and females would alter joint loading which may be detrimental to the knee joint health over time. In summary, (1) these injuries alter muscle roles; (2) these alterations are sex-specific; (3) rehabilitation might be optimised if sex-differences are considered., (Copyright © 2018. Published by Elsevier Ltd.)

Background: Following anterior cruciate ligament injury and subsequent reconstruction transverse plane tibiofemoral rotation becomes underconstrained and overconstrained, respectively. Conflicting reports exist on how rotations influence loading at the knee. This investigation aimed to determine the mechanical effects of internal and external tibial rotation offsets on knee kinematics and ligament strains during in vitro simulations of in vivo recorded kinematics., Method: A 6-degree-of-freedom robotic manipulator arm was used to articulate 11 cadaveric tibiofemoral joint specimens through simulations of four athletic tasks produced from in vivo recorded kinematics. These simulations were then repeated with 4° tibial rotation offsets applied to the baseline joint orientation., Findings: Rotational offsets had a significant effect on peak posterior force for female motion simulations (P < 0.01), peak lateral force for most simulated tasks (P < 0.01), and peak anterior force, internal torque, and flexion torque for sidestep cutting tasks (P ≤ 0.01). Rotational offsets did not exhibit statistically significant effects on peak anterior cruciate ligament strain (P > 0.05) or medial collateral ligament strain (P > 0.05) for any task., Interpretation: Transverse plane rotational offsets comparable to those observed in anterior cruciate ligament deficient and reconstructed patients alter knee kinetics without significantly altering anterior cruciate ligament strain. As knee degeneration is attributed to abnormal knee loading profiles, altered transverse plane kinematics may contribute to this. However, altered transverse plane rotations likely play a limited role in anterior cruciate ligament injury risk as physiologic offsets failed to significantly influence anterior cruciate ligament strain during athletic tasks., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Background: Malpositioning of an anterior cruciate ligament graft during reconstruction can occur during screw fixation. The purpose of this study is to compare the fixation biomechanics of a conventional interference screw with a novel Twist Lock Screw, a rectangular shaped locking screw that is designed to address limitations of graft positioning and tensioning., Methods: Synthetic bone (10, 15, 20lb per cubic foot) were used simulating soft, moderate, and dense cancellous bone. Screw push-out and graft push-out tests were performed using conventional and twist lock screws. Maximum load and torque of insertion were measured., Findings: Max load measured in screw push out with twist lock screw was 64%, 60%, 57% of that measured with conventional screw in soft, moderate and dense material, respectively. Twist lock max load was 78% and 82% of that with conventional screw in soft and moderate densities. In the highest bone density, max loads were comparable in the two systems. Torque of insertion with twist lock was significantly lower than with conventional interference screw., Interpretation: Based on geometric consideration, the twist lock screw is expected to have 35% the holding power of a cylindrical screw. Yet, results indicate that holding power was greater than theoretical consideration, possibly due to lower friction and lower preloaded force. During graft push out in the densest material, comparable max loads were achieved with both systems, suggesting that fixation of higher density bone, which is observed in young athletes that require reconstruction, can be achieved with the twist lock screw., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Background: The purpose of this study was to determine associations between self-reported function (International Knee Documentation Committee Index), isometric quadriceps strength and rate of torque development in individuals with a unilateral anterior cruciate ligament reconstruction., Methods: Forty-one individuals [31% male, BMI mean 25 (SD 4) kg/m 2 , months post anterior cruciate ligament reconstruction mean 49 (SD 40)] completed the self-reported function and isometric quadriceps function testing. Rate of torque development was assessed at 0-100ms (early), 100-200ms (late) ms, and peak following the onset of contraction. Associations were examined between rate of torque development, strength, and self-reported function. Linear regression was used to determine the unique amount of variance explained by the combination of rate of torque development and strength., Findings: Higher rate of torque development 100-200ms is weakly associated with higher self-reported function in individuals with a unilateral anterior cruciate ligament reconstruction (r=0.274, p=0.091); however, rate of torque development 100-200ms does not predict a significant amount of variance in self-reported function after accounting for strength (ΔR 2 =0.003, P=0.721)., Interpretation: Quadriceps strength has a greater influence on self-reported function compared to rate of torque development in individuals with an anterior cruciate ligament reconstruction with time from surgery., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Background: Over 250,000 anterior cruciate ligament ruptures occur each year; therefore, it is important to understand the underlying mechanisms of these injuries. The objective of the current investigation was to develop and analyze an impact test device that consistently produces anterior cruciate ligament failure in a clinically relevant manner., Method: A mechanical impact simulator was developed to simulate the ground reaction force impulse generated from landing in a physiologic and clinically relevant manner. External knee abduction moment, anterior shear, and internal tibial rotation loads were applied to the specimen via pneumatic actuators. The magnitudes of applied loads were determined in vivo from a cohort of healthy athletes. Loads were systematically increased until specimen failure was induced. Three cadaveric lower extremity specimens were tested and clinically assessed for failure. Knee specimens were physically and arthroscopically examined at baseline and at post-injury by a board certified orthopedic surgeon., Findings: All three specimens experienced failure at either the midsubstance or the femoral insertion site. The mean peak strain prior to failure was 18.8 (6.2)%, while the mean peak medial collateral ligament strain was 7.9 (5.9)%., Interpretation: A board certified orthopedic surgeon confirmed observed rupture patterns were representative of clinical cases. Peak strains were consistent with literature. The novel mechanical impact simulator will allow researchers to assess clinically relevant patterns of rupture and the data generated will inform clinician decisions. This novel machine presents the ability to assess healthy specimens as well as differences in the function of deficient and reconstructed knees., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Background: Gait analysis is a useful tool to evaluate the functional status of patients with anterior cruciate ligament injury. Pattern recognition methods can be used to automatically assess walking patterns and objectively support clinical decisions. This study aimed to test a pattern recognition system for analyzing kinematic gait patterns of recently anterior cruciate ligament injured patients and for evaluating the effects of a therapeutic treatment., Methods: Gait kinematics of seven male patients with an acute unilateral anterior cruciate ligament rupture and seven healthy males were recorded. A support vector machine was trained to distinguish the groups. Principal component analysis and recursive feature elimination were used to extract features from 3D marker trajectories. A Classifier Oriented Gait Score was defined as a measure of gait quality. Visualizations were used to allow functional interpretations of characteristic group differences. The injured group was evaluated by the system after a therapeutic treatment. The results were compared against a clinical rating of the patients' gait., Findings: Cross validation yielded 100% accuracy. After the treatment the score improved significantly (P<0.01) as well as the clinical rating (P<0.05). The visualizations revealed characteristic kinematic features, which differentiated between the groups., Interpretation: The results show that gait alterations in the early phase after anterior cruciate ligament injury can be detected automatically. The results of the automatic analysis are comparable with the clinical rating and support the validity of the system. The visualizations allow interpretations on discriminatory features and can facilitate the integration of the results into the diagnostic process., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Background: The knowledge of muscle activation patterns when doing a certain task in subjects with anterior cruciate ligament deficiency could help to improve their rehabilitation treatment. The goal of this study is to identify differences in such patterns between anterior cruciate ligament-deficient and healthy subjects during walking., Methods: Electromyographic data for eight muscles were measured in a sample of eighteen subjects with anterior cruciate ligament deficiency, in both injured (ipsilateral group) and non-injured (contralateral group) legs, and a sample of ten healthy subjects (control group). The analysis was carried out at two levels: activation-deactivation patterns and muscle synergies. Muscle synergy components were calculated using a non-negative matrix factorization algorithm., Findings: The results showed that there was a higher co-contraction in injured than in healthy subjects. Although all muscles were activated similarly since all subjects developed the same task (walking), some differences could be observed among the analyzed groups., Interpretation: The observed differences in the synergy components of injured subjects suggested that those individuals alter muscle activation patterns to stabilize the knee joint. This analysis could provide valuable information for the physiotherapist to identify alterations in muscle activation patterns during the follow-up of the subject's rehabilitation., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Background: Clinical outcome studies showed a high incidence of knee osteoarthritis after anterior cruciate ligament reconstruction. Abnormal joint kinematics and loading conditions were assumed as risking factors. However, little is known on cartilage contact forces after the surgery., Methods: A validated computational model was used to simulate anatomic and transtibial single-bundle anterior cruciate ligament reconstructions. Two graft fixation angles (0° and 30°) were simulated for each reconstruction. Biomechanics of the knee was investigated in intact, anterior cruciate ligament deficient and reconstructed conditions when the knee was subjected to 134 N anterior load and 400 N quadriceps load at 0°, 30°, 60° and 90° of flexion. The tibial translation and rotation, graft forces, medial and lateral contact forces were calculated., Findings: When the graft was fixed at 0°, the anatomic reconstruction resulted in slightly larger lateral contact force at 0° compared to the intact knee while the transtibial technique led to higher contact force at both 0° and 30° under the muscle load. When graft was fixed at 30°, the anatomic reconstruction overstrained the knee at 0° with larger contact forces, while the transtibial technique resulted in slightly larger contact forces at 30°., Interpretation: This study suggests that neither the anatomic nor the transtibial reconstruction can consistently restore normal knee biomechanics at different flexion angles. The anatomic reconstruction may better restore anteroposterior stability and contact force with the graft fixed at 0°. The transtibial technique may better restore knee anteroposterior stability and articular contact force with the graft fixed at 30° of flexion., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Background: Despite interventions, anterior cruciate ligament ruptures can cause long-term deficits. To assist in identifying and treating deficiencies, 3D-motion analysis is used for objectivizing data. Conventional statistics are commonly employed to analyze kinematics, reducing continuous data series to discrete variables. Conversely, functional data analysis considers the entire data series., Methods: Here, we employ functional data analysis to examine and compare the entire time-domain of knee-kinematic curves from one-leg hops between and within three groups. All subjects (n=95) were part of a long-term follow-up study involving anterior cruciate ligament ruptures treated ~20 years ago conservatively with physiotherapy only or with reconstructive surgery and physiotherapy, and matched knee-healthy controls., Findings: Between-group differences (injured leg, treated groups; non-dominant leg, controls) were identified during the take-off and landing phases, and in the sagittal (flexion/extension) rather than coronal (abduction/adduction) and transverse (internal/external) planes. Overall, surgical and control groups demonstrated comparable knee-kinematic curves. However, compared to controls, the physiotherapy-only group exhibited less flexion during the take-off (0-55% of the normalized phase) and landing (44-73%) phase. Between-leg differences were absent in controls and the surgically treated group, but observed during the flight (4-22%, injured leg>flexion) and the landing (57-85%, injured leg

Background: An anterior cruciate ligament injury may lead to deteriorations in postural stability. The goal of this study was to evaluate postural stability during the transition from double-leg stance to single-leg stance of both legs in anterior cruciate ligament injured subjects and non-injured control subjects with a standardized methodology., Methods: Fifteen control subjects and 15 anterior cruciate ligament injured subjects (time after injury: mean (SD)=1.4 (0.7) months) participated in the study. Both groups were similar for age, gender, height, weight and body mass index. Spatiotemporal center of pressure outcomes of both legs of each subject were measured during the transition from double-leg stance to single-leg stance in eyes open and eyes closed conditions. Movement speed was standardized., Findings: The center of pressure displacement after a new stability point was reached during the single-leg stance phase was significantly increased in the anterior cruciate ligament injured group compared to the control group in the eyes closed condition (P<.001). No significant different postural stability outcomes were found between both legs within both groups (P>.05). No significant differences were found during the transition itself (P>.05)., Interpretation: The anterior cruciate ligament injured group showed postural stability deficits during the single-leg stance phase compared to the non-injured control group in the eyes closed condition. Using the non-injured leg as a normal reference when evaluating postural stability of the injured leg may lead to misinterpretations, as no significant differences were found between the injured and non-injured leg of the anterior cruciate ligament injured group., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Investigators use in vitro joint simulations to invasively study the biomechanical behaviors of the anterior cruciate ligament. The aims of these simulations are to replicate physiologic conditions, but multiple mechanisms can be used to drive in vitro motions, which may influence biomechanical outcomes. The objective of this review was to examine, summarize, and compare biomechanical evidence related to anterior cruciate ligament function from in vitro simulations of knee motion. A systematic review was conducted (2004 to 2013) in Scopus, PubMed/Medline, and SPORTDiscus to identify peer-reviewed studies that reported kinematic and kinetic outcomes from in vitro simulations of physiologic or clinical tasks at the knee. Inclusion criteria for relevant studies were articles published in English that reported on whole-ligament anterior cruciate ligament mechanics during the in vitro simulation of physiologic or clinical motions on cadaveric knees that were unaltered outside of the anterior-cruciate-ligament-intact, -deficient, and -reconstructed conditions. A meta-analysis was performed to synthesize biomechanical differences between the anterior-cruciate-ligament-intact and reconstructed conditions. 77 studies met our inclusion/exclusion criteria and were reviewed. Combined joint rotations have the greatest impact on anterior cruciate ligament loads, but the magnitude by which individual kinematic degrees of freedom contribute to ligament loading during in vitro simulations is technique-dependent. Biomechanical data collected in prospective, longitudinal studies corresponds better with robotic-manipulator simulations than mechanical-impact simulations. Robotic simulation indicated that the ability to restore intact anterior cruciate ligament mechanics with anterior cruciate ligament reconstructions was dependent on loading condition and degree of freedom examined., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Background: Alterations in sagittal plane landing biomechanics in the lower extremity have been observed within the chronic ankle instability (CAI) population. Interestingly, a potential link between the risk of anterior cruciate ligament (ACL) injury and ankle sprain history has been proposed. However, it is not known if the observed biomechanical changes associated with CAI could mimic factors related to the mechanism of ACL injury. We investigated the influence of CAI on anterior tibial shear force (ATSF), lower extremity sagittal plane kinematics, and posterior ground reaction force (GRF) in a jump landing task., Methods: Nineteen participants with CAI and 19 healthy control participants performed a vertical stop jump. Peak ATSF was calculated during the first landing of the stop jump, with sagittal-plane kinematics and posterior GRF measured at peak ATSF. Independent t-tests, multiple linear regression, and Pearson bivariate correlation were used for statistical analysis., Findings: Participants with CAI demonstrated less knee flexion at peak ATSF compared to the controls (P=.026). No group-differences were found for peak ATSF or the other biomechanical variables. Knee flexion was moderately correlated with peak ATSF (r=-0.544, P=.008); however, the contributing factor that most explained the variance in ATSF was posterior GRF (R2=0.449; P=.002) in the CAI group., Interpretation: Our findings indicate that the CAI group may be exhibiting altered knee function during functional movement. Screening knee movement patterns in individuals with CAI may help develop preventative measures for future joint injury throughout the kinetic chain., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Background: Semitendinosus and gracilis muscles whose tendons are used in surgical reconstruction of the anterior cruciate ligament maintain their contractile ability, and a limited decrease of hamstring muscles force is observed postoperatively despite important changes. The goal was to quantify the influence of the myofascial structures on excursions and moment arms of knee muscles to attempt explaining the above-mentioned post-surgical observations., Methods: Hamstring harvesting procedures were performed by a senior orthopaedic surgeon on seven lower limbs from fresh-frozen specimens. Femoro-tibial kinematics and tendons excursion were simultaneously recorded at each steps of the surgery., Findings: No significant difference was demonstrated for excursions and moment arms after tenotomies and gracilis tendon harvesting (P≥0.05). The first significant semitendinosus excursion (P<1.17×10(-4)) and moment arm (P<6.88×10(-5)) decrease was observed after semitendinosus tendon harvesting (46% of the initial excursion)., Interpretation: Gracilis and semitendinosus myofascial pathway is crucial for force transmission towards the knee joint., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Background: It has been hypothesized that arthrogenic muscle inhibition is responsible for altering physical function following knee injury. The association between the onset of arthrogenic muscle inhibition, measured using voluntary quadriceps activation, and changes in muscle strength and gait biomechanics are unknown., Methods: Outcomes were collected before and following a 60 ml experimental knee effusion in eighteen healthy participants. Voluntary quadriceps activation was the predictor variable, while the criterion variable included, maximal voluntary isometric strength, peak knee flexion angle, peak internal knee extension moment, and peak vertical ground reaction forces during the first half of stance phase upon stair descent. Percent change scores (Δ) were imputed into linear regression equations to determine associations between predictor and criterion variables., Findings: The variance in Δ voluntary quadriceps activation significantly predicted 87% the variance in the Δ strength (R(2)=0.87, P<0.001; Δ strength=-2.15+1.77Δ voluntary quadriceps activation) and 25% of the Δ vertical ground reaction force following effusion (R(2)=0.25, P=0.04; Δ vertical ground reaction force=-6.1+0.57 Δ voluntary quadriceps activation). After accounting for Δ knee flexion angle, Δ voluntary quadriceps activation predicted an additional 29% (Δ R(2)=0.29, P=0.007) of the variance in the Δ knee extension moment (R(2)=0.54, P=0.003, Δ knee extension moment=-10.79+0.74Δ knee flexion angle+1.64Δ voluntary quadriceps activation) following knee effusion., Interpretation: Immediate quadriceps activation deficits following joint effusion result in immediate alterations in muscle strength, knee extensor moment and vertical ground reaction force during gait., (Published by Elsevier Ltd.)

Background: Patients with a history of anterior cruciate ligament rupture are at elevated risk of developing knee osteoarthritis. Altered knee kinematics and kinetics during functional activities have been viewed as risk factors for cartilage breakdown and, therefore, one of the primary goals of anterior cruciate ligament reconstruction is to restore knee joint function., Methods: Patients' (n=18) knee mechanics while performing a single leg hop for distance were calculated for both legs using a soft-tissue artifact optimized rigid lower-body model at the pre-reconstruction state and six and twelve months after anterior cruciate ligament reconstruction., Findings: Independent of the analyzed time point the involved leg showed a lower external flexion and adduction moment at the knee, and an increased anterior translation and external rotational offset of the shank with respect to the thigh compared to the uninvolved leg. There were no differences for any of the analyzed knee kinematic and kinetic parameters within the control subject group., Interpretation: The identified kinematic changes can cause a shift in the normal load-bearing regions of the knee and may support the view that the risk of developing knee osteoarthritis in an anterior cruciate ligament ruptured joint while performing activities involving frequent landing and stopping actions is less likely to be associated with the knee adduction moment and is rather due to kinematic changes. Anterior cruciate ligament reconstruction surgery failed to restore normal knee kinematics during landing, potentially explaining the persistent risk for the development of knee osteoarthritis in patients who have returned to sports following reconstruction surgery., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Background: Recent work has shown that anterior cruciate ligament reconstructed patients exhibit an increased peak knee adduction moment during walking gait compared to healthy controls. An increased peak knee adduction moment has been suggested to be a potential mechanism of degeneration for knee osteoarthritis. The few studies in this area have not considered an exclusively female anterior cruciate ligament reconstructed group. This study tested the hypothesis that female anterior cruciate ligament-reconstructed patients would have higher peak knee adduction moments than controls., Methods: Peak knee adduction moment during walking was compared between a group of anterior cruciate ligament reconstructed females and a group of female activity matched controls over ten 15m walking trials in a laboratory at a self-selected pace., Findings: Peak knee adduction moment was lower for the anterior cruciate ligament reconstructed group (N = 17, M = 0.31 Nm/kg · m, SD = 0.08) than for the control group (N = 17, M = 0.41 Nm/kg · m, SD = 0.12; t(32) = 2.483, p = 0.010, one-tailed, eta squared effect size = 0.16)., Interpretation: A group of female anterior cruciate ligament reconstructed subjects did not exhibit a gait characteristic which has been suggested to be associated with knee osteoarthritis development and has been shown to be present in male and mixed sex anterior cruciate ligament reconstructed populations previously., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

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., (Copyright © 2013 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Background: Challenges in accurate, in vivo quantification of multi-planar knee kinematics and relevant timing sequence during high-risk injurious tasks pose challenges in understanding the relative contributions of joint loads in non-contact injury mechanisms. Biomechanical testing on human cadaveric tissue, if properly designed, offers a practical means to evaluate joint biomechanics and injury mechanisms. This study seeks to investigate the detailed interactions between tibiofemoral joint multi-planar kinematics and anterior cruciate ligament strain in a cadaveric model of landing using a validated physiologic drop-stand apparatus., Methods: Sixteen instrumented cadaveric legs, mean 45(SD 7) years (8 female and 8 male) were tested. Event timing sequence, change in tibiofemoral kinematics (position, angular velocity and linear acceleration) and change in anterior cruciate ligament strain were quantified., Findings: The proposed cadaveric model demonstrated similar tibiofemoral kinematics/kinetics as reported measurements obtained from in vivo studies. While knee flexion, anterior tibial translation, knee abduction and increased anterior cruciate ligament strain initiated and reached maximum values almost simultaneously, internal tibial rotation initiated and peaked significantly later (P<0.015 for all comparisons). Further, internal tibial rotation reached mean 1.8(SD 2.5)°, almost 63% of its maximum value, at the time that peak anterior cruciate ligament strain occurred, while both anterior tibial translation and knee abduction had already reached their peaks., Interpretation: Together, these findings indicate that although internal tibial rotation contributes to increased anterior cruciate ligament strain, it is secondary to knee abduction and anterior tibial translation in its effect on anterior cruciate ligament strain and potential risk of injury., (© 2013. Published by Elsevier Ltd on behalf of American Society of Biomechanics. All rights reserved.)

Background: A novel tibial baseplate design (Transversal Support Tibial Plateau) as a new treatment concept for bi-cruciate retaining total knee arthroplasty is evaluated for mechanical stability and compared to other tibial baseplate designs. This concept should provide better primary stability and thus, less subsidence, than implantation of two separate unicondylar tibial baseplates., Methods: Different baseplates were implanted into synthetic bone specimens (Sawbones® Pacific Research Laboratories, Inc., Washington, USA), all uncemented. Using a standardized experimental setup, subsidence was achieved, enabling comparison of the models regarding primary stability., Findings: Overall implant subsidence was significantly increased for the two separate unicondylar tibial baseplates versus the new Transversal Support Tibial Plateau concept, which showed comparable levels to a conventional tibial baseplate. Reduced subsidence results in better primary stability., Interpretation: Linking of two separate baseplates appears to provide increased primary stability in terms of bony fixation, comparable to that of a conventional single tibial baseplate., (© 2013. Published by Elsevier Ltd. All rights reserved.)

Background: Pain that accompanies anterior cruciate ligament deficiency during dynamic knee extension exercises is usually caused by excessive anterior tibial translation, which can be restricted if the anterior cruciate ligament was intact., Methods: A functional electrical stimulator is incorporated with a training device to induce hamstring contractions during certain degrees of knee extension to replicate effects similar to those generated by an intact anterior cruciate ligament and to reduce anterior tibial translation. By using a camera that tracks markers placed on bony prominences of the femur and tibia, the anterior tibial translations corresponding to various settings were determined by customized image processing procedures., Findings: In the electrical stimulation sessions, the knee extensions with electrical stimulation feedback induced significantly (n=6, P<.05) less anterior tibial translation over the range of 20 to 50° when compared to those using the standard isokinetic shank restraint. Likewise, the knee extensions with an anti-shear device that blocks tibia displacement mechanically also induced significantly (n=6, P<.05) less anterior tibial translation, but over a different range of knee extension (30 to 70°)., Interpretation: Despite the fact that both the electrical stimulator and the anti-shear device assisted in reducing anterior tibial translation, the tendency of the curves generated with the functional electrical stimulation was generally more similar to those generated when using the standard isokinetic shank restraint., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Background: Instability associated with anterior cruciate ligament injury is commonly evaluated against the patient's contralateral knee. The objectives of this study were, therefore, to assess symmetry of rotational knee laxity in vivo under passive torsional loading in uninjured subjects, and to compare mean rotation of this control group with the contralateral, intact knees of anterior cruciate ligament deficient patients., Methods: Axial knee rotation was measured in 29 patients with unilateral anterior cruciate ligament injury and 15 uninjured age and gender-matched control subjects using an imaging-compatible torsional loading device. Side-to-side differences in internal, external, and range of knee rotation were assessed in the control group and mean bilateral knee rotation was compared to the patients' contralateral knee data at both full extension and 30° of flexion., Findings: Statistically significant differences in symmetry were found in three of the six measures of transverse plane rotation in the uninjured knees; a mean side-to-side difference of 2.2° in range of rotation was detected in the flexed position. No significant differences were observed between the mean values of the healthy control group and the contralateral knees of the anterior cruciate ligament deficient patients., Interpretation: Bilateral asymmetry of rotational laxity occurs in healthy individuals. Nevertheless, comparability of rotational knee laxity between the contralateral limbs of patients and the uninjured population was evidence that rotational laxity was not inherent or developed in the contralateral knees of the anterior cruciate ligament deficient participants., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Background: Alterations in knee joint kinematics have been suggested as a potential mechanism that influences the development of osteoarthritis of the knee after anterior cruciate ligament reconstruction. Whilst previous work has shown changes in internal-external tibial rotation during level walking, many patients aim to return to high impact activities following surgery. This study examined tibial rotation during single limb hop and drop landings in anterior cruciate ligament reconstructed knees compared to a control group, and also evaluated the influence of graft type (hamstring or patellar tendon)., Methods: In 48 participants (17 patellar tendon graft, 18 hamstring graft and 13 controls) internal-external rotation was measured during single limb hop and drop landings in a gait laboratory at mean of 10 months after surgery., Findings: There was no difference between the two graft types and both patient groups had less internal rotation when compared to the control group. For 60% of patients, internal rotation values were at least 5° less than the control group mean., Interpretation: Anterior cruciate ligament reconstructed knees with both hamstring tendon and patellar tendon grafts show altered rotational kinematic patterns during high impact dynamic load activities., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Background: Anterior cruciate ligament reconstruction does not necessarily restore normal knee movement. Increased tibial rotation has previously been noted during pivoting activities and may be due to the orientation of the anterior cruciate ligament graft associated with traditional single bundle reconstruction techniques. Recent research has shown that it is possible to limit rotation during level walking using a single bundle anterior cruciate ligament reconstruction. This study evaluated rotational knee kinematics during a pivot task in a group of patients who had undergone anterior cruciate ligament reconstruction using a single bundle technique and compared the findings to a normal control group., Methods: In 27 anterior cruciate ligament reconstruction and 25 control participants, internal-external rotation was measured during a descend stairs and pivot task in a gait laboratory., Findings: Results showed that the anterior cruciate ligament reconstruction patients had less internal tibial rotation (for both range of rotation and maximum rotation) than the control participants (effect size=0.7)., Interpretation: These results suggest that it is possible to limit rotation after anterior cruciate ligament reconstruction using a single bundle technique, even during a pivoting movement that places a high rotational load at the knee joint. The positioning of the femoral tunnel in a more anatomical position may be responsible for the reduced tibial rotation., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Background: Anterior cruciate ligament rupture is the most common knee ligament injury sustained by active individuals, and the relative injury risk is sex-specific. Women not only demonstrate an increased risk for injury, but also a poorer response following ligament rupture. Perturbation training has shown positive results in healthy females, but gender-specific responses to training after injury have not been evaluated. The purpose of this investigation was to describe the effects of perturbation training on the gait characteristics of male and female non-copers., Methods: Biomechanical data were collected before and after training on 12 male and nine female non-copers using standard motion analysis techniques. Subjects walked at a consistent, self-selected speed over an embedded force plate. Data from both limbs were post-processed and analyzed using a mixed model analysis of variance and minimal clinically important differences to compare the limb behaviors of men and women., Findings: Prior to training, only women demonstrated significant hip joint excursion asymmetry (ES=1.03; P=0.009). Minimal clinically important difference values showed that the involved limb of the women had reduced hip and knee flexion angles and moments, truncated knee excursions, and increased hip excursions when compared to their own uninvolved limb and the limbs of the male non-copers. Following training, only knee extensor moment values exceeded the minimal clinically important differences in women., Interpretation: Female non-copers demonstrated unique movement strategies following injury and perturbation training. Women may be a meaningful subgroup of non-copers, and future investigations should consider the effects of gender in the outcomes of non-copers., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Background: Normal ambulatory kinematics of the knee joint is often not fully restored after anterior cruciate ligament reconstruction, which may increase the risk for cartilage degeneration and premature osteoarthritis in the involved knees. Lower limb dominance may have impacts on knee joint kinematics after anterior cruciate ligament reconstruction, which may lead to a different prevalence of cartilage degeneration. This study aimed to evaluate the knee joint kinematics among patients with reconstruction on the dominant and non-dominant side., Methods: Forty-one subjects with unilateral anterior cruciate ligament reconstruction (19 dominant, 22 non-dominant) were recruited after being discharged from rehabilitation programs. Twenty healthy subjects were recruited as the control group. Six degrees-of-freedom tibiofemoral motion during level walking was determined using a redundant point cluster-based marker set. Tibiofemoral joint motion and its bilateral differences were compared within each group and between groups., Findings: The non-dominant reconstructed knees had less extension compared to their contralateral knees at heel strike and during middle stance phase (P=0.02); whereas, the dominant reconstructed knees exhibited significantly reduced varus rotation (-2.1° on mean, P=0.027) and internal tibial rotation (P=0.034) compared to their contralateral knees during both stance and swing phases., Interpretation: The results show that different kinematics has been developed between the involved dominant and non-dominant knees after anterior cruciate ligament reconstruction, especially the secondary rotations. The differences are consistent with the unequal prevalence of cartilage degeneration in the knee joint. The findings demonstrated that the lower limb dominance had a significant effect on post-surgery knee kinematics., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Background: Reconstruction of the anterior cruciate ligament is a standard surgical procedure in sports traumatology. The widespread replacement method using hamstring tendons has an important shortcoming namely delayed or missing bony healing in contrast to patellar tendon grafts where implant-free fixation is established by using the adjacent bone blocks. The purpose of this study was to describe a new implant-free surgical procedure using hamstring tendon grafts and to analyse the influence on tibiofemoral kinematics in vitro., Methods: Nine human knee specimens with arthroscopically transected anterior cruciate ligaments were mounted on a dynamic knee simulator and weight-bearing muscle-loaded knee flexions were simulated while a robotic universal force sensor system was used to provide external tibial loads. Three different loading conditions were simulated including partial body weight only, an additional 50 N anterior tibial force or an additional Five Nm of internal rotational torque. After reconstruction of the anterior cruciate ligament using a tibial bone block hybrid technique these three trials were repeated. The kinematics was measured with an ultrasonic measuring system and different loading and ligament conditions were examined. Graft tunnel placement was verified by computed tomography., Findings: Our fixation method achieved stability to anterior tibial drawer force whereas internal tibial rotation did not change before and after the reconstruction. Computed tomography confirmed anatomical graft and tunnel placement., Interpretation: The presented operative procedure is technically feasible and leads to reproducible results concerning knee joint kinematics and graft placement., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Background: Deep fresh freezing is the most commonly used preservation method for allografts, which is followed by a routine procedure before application-the thawing of the grafts. This work was to explore the biomechanics effects of repetitive freezing-thawing on human tendons., Methods: Thirty tendons (flexor digitorum superficialis and flexor pollicis longus tendons) were taken from three fresh cadavers. We assigned these tendons into six groups randomly. After the preparation and measurement of cross-sectional area, Fresh Group was tested immediately. The remaining five groups, before biomechanical testing, underwent multiple cycles (1, 2, 3, 5 or 10 cycles) of freezing (-80°C for 4 days) and thawing (room temperature for 6h). Using a material-testing machine, we performed a stress-relaxation test, a creep test and a load to failure test to estimate structural and mechanical properties as well as viscoelastic changes of each group., Findings: The results of fewer cycles (<3) of freezing-thawing groups were similar to Fresh Group. The tendons that underwent more than five freezing-thawing cycles demonstrated a significantly smaller ultimate load, stiffness, ultimate stress and Young's modulus. Moreover, the 5 and 10 Cycle Groups showed a significant increase of elongation in creep test and a decrease of load in stress-relaxation test compared with other groups., Interpretation: Repetitive freezing-thawing (>5 cycles) declines the structural, mechanical and viscoelastic properties of human tendons. From our results, it is recommended that for deep-frozen preservation of tendon allografts the cycles of freezing-thawing should be less than five times with caution., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Background: Previous research has shown that patients with anterior cruciate ligament reconstruction have altered movement patterns in the reconstructed knee during walking. In the sagittal plane, graft specific changes in knee joint motion have been reported between hamstring and patellar tendon anterior cruciate ligament reconstruction grafts. This study examined the secondary planes of movement during walking in anterior cruciate ligament reconstructed knees to evaluate the influences of graft type (hamstring or patellar tendon) and control condition (control group or contralateral knee)., Methods: In 54 participants (18 patellar tendon graft, 18 hamstring graft and 18 controls) varus-valgus and internal-external rotation was measured during level walking in a gait laboratory at mean of 10 months after surgery. All patients had undergone primary unilateral anterior cruciate ligament reconstruction within 12 months of injury., Findings: For internal-external rotation there was no difference between the graft types and both patient groups had reduced internal rotation (an external rotation offset) and reduced internal rotation range when compared to the control group and contralateral knee. For 31 of 36 patients, internal rotation values were less than the control group mean. The hamstring group had reduced varus rotation compared to both the patellar tendon and control groups, but not when compared to the contralateral knee., Interpretation: The results show that there are differences in tibial rotation during walking in anterior cruciate ligament reconstructed knees compared to both the contralateral knee and uninjured control group. These kinematic alterations may relate to the high incidence of knee osteoarthritis observed in this population over time. Reduced varus in the hamstring group may relate to the graft harvest., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Background: Recently backward walking is used by physical therapists to strengthen the hamstring muscles and thus improve the function of the knee joint of anterior cruciate ligament deficient patients. The aim of this study was to examine the stride-to-stride variability of anterior cruciate ligament deficient patients during backward walking. The variation of how a motor behavior emerges in time is best captured by tools derived from nonlinear dynamics, for which the temporal sequence in a series of values is the facet of interest., Methods: Fifteen patients with unilateral anterior cruciate ligament deficiency and eleven healthy controls walked backwards at their self-selected speed on a treadmill while three-dimensional knee kinematics were collected (100 Hz). A nonlinear measure, the largest Lyapunov Exponent was calculated from the resulted knee joint flexion-extension data of both groups to assess the stride-to-stride variability., Findings: Both knees of the deficient patients exhibited significantly lower Lyapunov Exponent values as compared to the healthy control group revealing more rigid movement pattern. The intact knee of the deficient patients showed significantly lower Lyapunov Exponent values as compared to the deficient knee., Interpretation: Anterior cruciate ligament (ACL) deficiency leads to loss of optimal variability regardless of the walking direction (forwards in previous studies or backwards here) as compared to healthy individuals. This could imply diminished functional responsiveness to the environmental demands for both knees of ACL deficient patients which could result in the knees being more susceptible to injury., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Background: Prospective measures of high knee abduction moment during landing identify female athletes at high risk for non-contact anterior cruciate ligament injury. Biomechanical laboratory measurements predict high knee abduction moment landing mechanics with high sensitivity (85%) and specificity (93%). The purpose of this study was to identify correlates to laboratory-based predictors of high knee abduction moment for use in a clinic-based anterior cruciate ligament injury risk prediction algorithm. The hypothesis was that clinically obtainable correlates derived from the highly predictive laboratory-based models would demonstrate high accuracy to determine high knee abduction moment status., Methods: Female basketball and soccer players (N=744) were tested for anthropometrics, strength and landing biomechanics. Pearson correlation was used to identify clinically feasible correlates and logistic regression to obtain optimal models for high knee abduction moment prediction., Findings: Clinical correlates to laboratory-based measures were identified and predicted high knee abduction moment status with 73% sensitivity and 70% specificity. The clinic-based prediction algorithm, including (Odds Ratio: 95% confidence interval) knee valgus motion (1.43:1.30-1.59 cm), knee flexion range of motion (0.98:0.96-1.01 degrees ), body mass (1.04:1.02-1.06 kg), tibia length (1.38:1.25-1.52 cm) and quadriceps to hamstring ratio (1.70:1.06-2.70) predicted high knee abduction moment status with C statistic 0.81., Interpretation: The combined correlates of increased knee valgus motion, knee flexion range of motion, body mass, tibia length and quadriceps to hamstrings ratio predict high knee abduction moment status in female athletes with high sensitivity and specificity., Clinical Relevance: Utilization of clinically obtainable correlates with the prediction algorithm facilitates high non-contact anterior cruciate ligament injury risk athletes' entry into appropriate interventions with the greatest potential to prevent injury., (Copyright (c) 2010 Elsevier Ltd. All rights reserved.)

Background: Gait adaptations in persons with anterior cruciate ligament (ACL) injuries have been debated. Many studies examine high speed, 3-dimensional video gait analysis to compare knee joint torques during simulated activities of daily living., Methods: We performed a systematic review of the literature for published clinical papers that reported sagittal plane knee joint kinetics in ACL deficient or reconstructed individuals. We calculated weighted effect sizes (Cohen's d) to evaluate the magnitude of differences between the injured limb and the contralateral limb and healthy, uninjured limbs in control subjects., Findings: Ten published papers reported kinetic data in ACL deficient subjects while walking for comparisons to the contralateral side (weighted average d=-0.83, range: -3.21, 1.07), and to healthy control knees (weighted average d=-1.0, range: -3.36, 0.17); four papers reported data during jogging compared to the contralateral side (weighted average d=-0.94, range: -4.15, 0.17), and to controls (weighted average d=-1.42, range: -3.83,-0.2). Four papers reported data for ACL-reconstructed patients compared to healthy controls during walking (weighted average d=-0.94, range: -0.4, -1.77) and jogging (weighted average d=-1.18)., Interpretation: Effect sizes comparing knee joint moments in injured vs. healthy control subjects appear to be slightly higher while jogging than walking, and higher in ACL-deficient patients compared to reconstructions. However, magnitudes are all large. Few studies report stair climbing. Consequently, it is difficult to make inferences with confidence during these tasks., (Copyright 2009 Elsevier Ltd. All rights reserved.)

Background: High risk of cartilage degeneration and premature osteoarthritis development has been clinically observed in anterior cruciate ligament (ACL) deficient knees. The risk has not been significantly reduced even after ACL reconstructive surgery. It was hypothesized that three-dimensional knee joint kinematics has been altered after ACL injury, and the biomechanical alteration has not been fully restored to a normal level after reconstructive surgery., Methods: Spatiotemporal parameters and three-dimensional knee joint rotations and translations were measured in ACL-deficient, ACL-reconstructed, and ACL-intact knees during level walking. The variables were compared between the ACL-deficient and ACL-intact knees, as well as between the ACL-reconstructed and ACL-intact knees., Findings: Altered spatiotemporal variables and key event timings in a gait cycle were observed in both ACL-deficient and ACL-reconstructed subjects. Significant reduction of extension was observed in the ACL-deficient knees during midstance and in the ACL-reconstructed knees during swing phase. Greater varus and internal tibial rotation were identified in the ACL-deficient knees. Although being small in magnitude, these secondary kinematic alterations were consistent throughout the whole gait cycle, and such trends were not eliminated in the ACL-reconstructed knees., Interpretation: Significant abnormalities of spatiotemporal performance and three-dimensional joint kinematics during walking were identified in the ACL-deficient knees. The ACL-reconstructed knees exhibited some improvement in joint kinematics, but not being fully restored to a normal level. Identification of biomechanical alterations during daily activities in ACL-deficient and ACL-reconstructed knees could help better understand clinical outcomes and seek improvement in surgical technique and rehabilitation regimen for ACL injury treatment.

Background: Posterior-cruciate ligament retaining total knee arthroplasty designs have long been used with excellent clinical success, but often have shown kinematics and flexion performance that are significantly different from the natural knee. The purpose of this study was to compare deep-flexion knee kinematics in patients with two types of posterior-cruciate ligament retaining total knee arthroplasty., Methods: One group received a traditional curved symmetric articular configuration, and one group received a design incorporating a lateral compartment which constrains the lateral condyle to the antero-posterior center of the tibial plateau in extension, but allows translation in flexion--roughly approximating the role of the anterior cruciate ligament. In vivo kinematics were analyzed using three-dimensional model registration and plain radiographs of kneeling and squatting activities in 20 knees in 18 patients., Findings: Knees with the anterior cruciate ligament substituting design exhibited greater flexion, femoral antero-posterior translation and tibial internal rotation., Interpretation: Geometric features intended to improve knee flexion, including greater antero-posterior stability, a more posterior tibial sulcus, and reshaped femoral condyles, do provide measurable and significant differences in deep-flexion knee kinematics.

Background: Despite partial meniscectomies and ligament reconstructions as treatments of choice for meniscal and ligament injuries, respectively, the knee joint osteoarthritis persists., Methods: A detailed nonlinear finite element model of the knee joint was developed to evaluate biomechanics of the tibiofemoral joint under 200 N drawer load with and without 1500 N compression preload. The model incorporated composite structure of cartilage and meniscus. The effects on joint response and articular contact pressure of unilateral partial meniscectomy, of changes in prestrain or material properties of the anterior cruciate ligament and of their combination were investigated., Findings: Compressive preload further increases anterior cruciate ligament strains/forces in drawer loading. Partial meniscectomy and perturbations in anterior cruciate ligament prestrain/material properties, alone or combined, substantially alter the load transfer via covered and uncovered areas of cartilage as well as contact pressure distribution on cartilage. Partial meniscectomy especially when combined with a slacker anterior cruciate ligament diminish the load via affected meniscus generating unloaded regions on the cartilage., Interpretation: Partial meniscectomy concurrent with a slack anterior cruciate ligament substantially alter cartilage contact pressures. These alterations further intensify in the event of greater external forces, larger meniscal resections and total anterior cruciate ligament rupture, thus suggesting a higher risk of joint degeneration.

Background: Knee kinematics during pivoting activities are not well studied, but might provide insight critical to understanding the pathology of the anterior cruciate ligament deficient knee. The purpose of this study was to compare in vivo kinematics during weight bearing pivot and squat activities in patients with unilateral anterior cruciate ligament deficient knees, and to contrast those kinematics with the uninjured contralateral knees., Methods: Eight unilateral anterior cruciate ligament deficient patients with a mean age of 41 (SD 7) years were enrolled. Anterior cruciate injury was confirmed by positive Lachman test and MRI. Lateral fluoroscopic images of pivot and squat activities were recorded for both anterior cruciate ligament deficient and contralateral knees. Three-dimensional tibiofemoral kinematics and centers of rotation for each knee were determined using 3D-2D model registration techniques., Findings: During pivoting, the tibia of the anterior cruciate ligament deficient knee was significantly more anterior than the contralateral knee during tibial neutral to internal rotation. The pivot activity showed lateral centers of rotation in both anterior cruciate ligament deficient and contralateral knees while squatting showed medial centers of rotation., Interpretation: This dynamic method might be useful to objectively characterize restoration of dynamic function in knees with various types of anterior cruciate ligament reconstructions. These results also indicate kinematics during squatting type activities cannot be extrapolated to predict knee kinematics during pivoting types of activities.

Background: Despite the ongoing evolution of anterior cruciate ligament injury prevention methods, injury rates and the associated sex-disparity remain. Strategies capable of successfully countering key control parameters existent within the injury mechanism thus remain elusive. Forward dynamics model simulations afford an expedited means to study realistic injury causing scenarios, while controlling all facets of the movement control strategy. Utilizing these methods, the current study examined the potential for perturbations in key initial contact neuromuscular parameters to injure the anterior cruciate ligament during the stance phase of sidestep cutting maneuvers., Methods: Controlled experiments were performed on optimized and validated subject-specific forward dynamic musculoskeletal sidestep models generated from 10 male and 10 female data sets. Random perturbations (n=5000) were applied to initial contact kinematic and muscle activation parameters in these baseline models and then to those with prescribed systematic modifications in initial hip and knee flexion, hip internal rotation and hip internal rotation velocity postures. The number of injuries via an isolated anterior tibial shear (>2000 N) or knee valgus load (>125 Nm) mechanism was determined for each of the seven model conditions and subsequently compared., Findings: Neuromuscular control perturbations produced peak stance phase (0-100 ms) knee valgus loads large enough to induce anterior cruciate ligament injury. Decreases and increases in combined initial contact hip and knee flexion postures and hip internal rotation velocity produced significant increases and decreases in these valgus-induced ACL injury rates respectively., Interpretation: Anterior cruciate ligament injury via a valgus load mechanism is more likely during sidestepping when landing in a more extended posture, or with increased hip external rotation velocity. The fact that injury rates are reduced when these control parameters are reversed suggests they should be central to ongoing prevention strategy developments.

Background: Although the linear elastic (high-load) properties of patellar tendon graft used for anterior cruciate ligament (ACL) reconstruction are studied extensively, the low-load properties of the graft, associated with the toe region of its load-deformation curve, are largely neglected. The objectives of this study were to (i) determine the properties of the patellar tendon in the low-load region and compare to that of the intact ACL, (ii) assess the extent of variability in these properties and relate them to donor factors, and (iii) establish the theoretical importance of low-load properties to the function of the reconstructed knee., Methods: The patellar tendons of 20 unpaired fresh frozen human knees (10 males and 10 females) were harvested. The central portions were trimmed, measured, and tested in tension to failure. The stress-strain curves were fitted with a bi-linear model and the graft properties were measured., Findings: The low-load region modulus of elasticity, E 0, of the patellar tendon, ranged from 49 MPa to 276 MPa in males and 63 MPa to 279 MPa in females. The strain at which the graft transitions from its low-load region to its linear elastic region (epsilon* approximately 4.6%) is on average above the strain levels experienced by the ACL during daily activities (epsilon approximately 4%). Donor sex, height and body mass were found to significantly affect some of the mechanical properties of the low-load region., Interpretation: The results suggest that the low-load region properties of the patellar tendon, not the linear elastic properties, govern the biomechanics of the tibiofemoral joint during the early healing period. Also, a wide variability of graft properties in the low-load region exists partly due to certain donor factors. Clinicians should be aware of the low-load region behaviour of the graft and its influence on time=0 behaviour of the reconstructed knee.

Background: After an anterior cruciate ligament injury, the contra-lateral non-injured leg has been found to adapt towards the injured leg. Accordingly, in order to study changes in knee motion pattern after an anterior cruciate ligament injury, the ideal is to compare the same leg prior to and after the injury. However, this is very seldom possible. The purpose of the present study was to describe changes in static and dynamic sagittal tibial translation, electromyographic activity and muscle torque relevant to an anterior cruciate ligament tear in one patient evaluated both before and after the injury., Methods: A male soccer player was examined 11 weeks before and eight weeks after an anterior cruciate ligament injury. Sagittal tibial translation was measured with the CA-4000 electrogoniometer; statically during Lachman's test, and dynamically during isokinetic muscle testing, one-legged squat and level walking. The electromyographic activity of mm. quadriceps and hamstrings, was registered simultaneously during the one-legged squat test., Findings: Static tibial translation was increased by approximately 2 mm, while dynamic tibial translation was decreased by 0.4 mm at isokinetic testing, 0.9 mm at one-legged squat and 2.4 mm during level walking compared to before the injury. Muscle torque decreased 30% and 35% for the quadriceps and the hamstrings muscle, respectively. The electromyographic activity revealed similar activation levels in quadriceps and a doubled level of activation in hamstring compared to before the injury., Interpretation: In spite of an increase in static tibial translation eight weeks after an anterior cruciate ligament injury, the tibial translation decreased during activity, thus indicating that the patient could stiffen the knee in order to protect it against increased shear forces.

Background: The purpose of this study was to determine whether current post-operative rehabilitation protocols return the strength of the contralateral uninjured limb knee flexors and extensors after an anterior cruciate ligament (ACL) reconstruction to those of an uninjured control group., Methods: Subjects with a hamstring tendon ACL reconstruction (n=12) were compared to an active control group (n=30). Comprehensive bilateral knee flexor and extensor isovelocity strength testing was performed (five speeds, 5-95 degrees , concentric and eccentric contractions)., Findings: After hamstring tendon ACL reconstruction and rehabilitation, bilateral strength normalization (within 10% of the contralateral limb) is achieved by the knee extensors but not the knee flexors. When compared to the uninjured control group, large and statistically significant strength deficits were demonstrated in the knee extensors and knee flexors of both the anterior cruciate ligament reconstructed (extensors 24.8%; flexors 26.8%) and the contralateral uninjured (extensors 21%; flexors 13.5%) limbs., Interpretation: These findings suggest that improvement can be made in knee flexor rehabilitation after ACL reconstruction and limit the validity of the use of a contralateral leg as a rehabilitation endpoint or as a control in the ACL reconstructed population.

Background: Intra-articular techniques (single and double bundles) are the most widely used procedures for the anterior cruciate ligament reconstruction. Lemaire introduced in 1967 the extra-articular techniques, and combined intra-articular and extra-articular reconstruction, to better restore the stability of the knee. However, the effectiveness of these procedures (intra-articular, extra-articular combined or not with intra-articular) seems to be controversial., Methods: In the present study, we developed numerical models of a knee joint to evaluate the effects of these different procedures on the kinematics and biomechanics of the knee during an internal rotation test. Six cases were simulated: intact anterior cruciate ligament, intra-articular reconstructed anterior cruciate ligament (single and double bundles), extra-articular reconstructed anterior cruciate ligament alone, and combination of extra- and intra-articular reconstructions. The loading condition was an internal tibial torque of 2 N m at 0 degrees, 15 degrees, 30 degrees and 45 degrees of knee flexion. Internal rotation of the tibia and forces within the grafts and the ligaments were calculated., Findings: This study showed that both single and double bundles intra-articular reconstructions restore similar internal rotation control and biomechanics of the soft structures as the intact anterior cruciate ligament situation. On the other hand, our results indicate that extra-articular reconstruction reduces appreciably the internal rotation and modifies the charges distribution in the soft structures when compared to the intact anterior cruciate ligament., Interpretation: The extra-articular procedure alters the kinematics of the knee, which might overconstraint the ligaments and the femorotibial joints, leading to the failure of the anterior cruciate ligament reconstruction.

Background: Researchers have theorized that the disproportionate number of anterior cruciate ligament injuries in females, as compared to males, may be related to knee laxity, which in turn may be influenced by hormones. The purpose of this study was to investigate the collective effects of gender, estrogen and exercise on knee laxity., Methods: Subjects consisted of 12 females and 12 males with no history of lower extremity injury. Serum estrogen levels and knee laxity were measured for the female subjects at specific times to represent three menstrual cycle phases while knee laxity of the male subjects was measured on three different days. For each data collection session, knee laxity was measured just prior to and immediately following an exercise protocol. Separate repeated measures ANOVAs were used to compare estrogen levels across the phases and analyze the laxity data., Findings: Females exhibited greater knee laxity than males both pre- and post-exercise across all phases of the menstrual cycle. Estrogen fluctuations across the menstrual cycle did not modify knee laxity in females. Prior exercise induced equivalent increases in knee laxity in males and females across the data collection periods and irrespective of estrogen concentration., Interpretation: If the anterior cruciate ligament is more distensible during athletic activities, it may be less capable of providing the necessary stability in order to prevent injury. This decreased stability may be contributing to the female athlete's increased incidence of anterior cruciate ligament injury. Overall, if females experience greater knee laxity during athletic activities, specific training strategies to compensate for these differences are warranted.

Background: Knee stability following an anterior cruciate ligament lesion has been widely studied. Only recent studies focused on the contribution of the soleus muscle. Our purpose was to characterize the dynamic and muscular activity of balance recovery in healthy subjects and patients with an anterior cruciate ligament rupture. The role of the soleus was investigated in the ipsilateral compensation developed to stabilize the knee and in the contralateral compensation to recover balance., Methods: Twelve anterior cruciate ligament deficient patients, ten anterior cruciate ligament repaired patients and 14 control subjects were recorded during a forward fall involving stepping to recover balance., Findings: The dynamic of the centre of gravity remained normal when compared to the control group regardless of the treatment, suggesting an adapted compensation to knee instability in this situation. A bilateral increase in soleus activity was related to an increased duration in the balance recovery process in all patients. Patients used one of two strategies to recover balance regardless of the treatment: reducing the step length, involving an early recruitment of the soleus before heel contact, or anticipating braking with a similar step length requiring a predominant activity of the hamstrings., Interpretations: These results suggest that bilateral activity of the soleus is involved to compensate for instability and highlight the contribution of the soleus to rehabilitation after an anterior cruciate ligament lesion, not only as a compensatory muscle acting at the knee level but also at a higher level in the bilateral control of stance.