Preferential loading of the ACL compared with the MCL during landing: a novel in sim approach yields the multiplanar mechanism of dynamic valgus during ACL injuries

The early peak knee abduction moment waveform is a novel risk factor predicting anterior cruciate ligament injury in young athletes: A prospective study

PURPOSE

In this study, prospective data were used to evaluate whether the early peak knee abduction moment waveform is associated with the risk of anterior cruciate ligament (ACL) injury.

METHODS

Biomechanical data from 84 athletes who participated in the study as adolescents were analysed after cross-referencing national health registry data to confirm ACL reconstruction in the subsequent years. The knee abduction moment waveform shape was obtained with cluster analysis for the first 100 ms of a cutting manoeuvre (1776 trials in total) and classified as either containing an early peak knee abduction moment or not, and the odds ratio for later ACL injury was then calculated. Additionally, discrete kinematic and kinetic variables were extracted, and tested against the risk of ACL injury using mixed model logistic regression.

RESULTS

Of 84 athletes, 8 (all female) sustained a total of 13 ACL injuries in the years after motion analysis data collection. Six clusters of knee abduction moment waveform shapes were identified. Two clusters containing 446 trials were classified as an early peak knee abduction waveform. This waveform was associated with a 7.2-fold increase in the risk of ACL injury (95% confidence interval: 2.4-24.6; p < 0.001). Of the kinematic and kinetic variables tested, only the knee abduction angle at initial contact was associated with an increased risk of ACL injury (p < 0.001).

CONCLUSION

This is the first study to confirm the association between the early peak knee abduction moment waveform and the risk of ACL injury. Using waveforms, instead of discrete peak values of the knee abduction moment, may better represent risky movement patterns. Replicating these findings in a larger cohort will support the use of this method to screen athletes for risk and guide targeted preventive interventions and their efficacy.

LEVEL OF EVIDENCE

Level II.

Shear wave elastography demonstrates different material properties between the medial collateral ligament and anterolateral ligament

BACKGROUND

Anterolateral ligament and medial collateral ligament injuries could happen concomitantly with anterior cruciate ligament ruptures. The anterolateral ligament is injured more often than the medial collateral ligament during concomitant anterior cruciate ligament ruptures although it offers less restraint to knee movement. Comparing the material properties of the medial collateral ligament and anterolateral ligament helps improve our understanding of their structure-function relationship and injury risk before the onset of injury.

METHODS

Eight cadaveric lower extremity specimens were prepared and mechanically tested to failure in a laboratory setting using a hydraulic platform. Measurements of surface strains of superficial surface of each medial collateral ligament and anterolateral ligament specimen were found using three-dimensional digital image correlation. Ligament stiffness was found using ultrasound shear-wave elastography. t-tests were used to assess for significant differences in strain, stress, Young's modulus, and stiffness in the two ligaments.

FINDINGS

The medial collateral ligament exhibited greater ultimate failure strain along its longitudinal axis (p = 0.03) and Young's modulus (p < 0.0018) than the anterolateral ligament. Conversely, the anterolateral ligament exhibited greater ultimate failure stress than the medial collateral ligament (p < 0.0001). Medial collateral ligament failure occurred mostly in the proximal aspect of the ligament, while most anterolateral ligament failure occurred in the distal or midsubstance aspect (P = 0.04).

INTERPRETATION

Despite both being ligamentous structures, the medial collateral ligament and anterolateral ligament exhibited separate material properties during ultimate failure testing. The weaker material properties of the anterolateral ligament likely contribute to higher rates of concomitant injury with anterior cruciate ligament ruptures.

ACL Reconstruction in a Poliotic Limb with Peroneus Longus Graft

Introduction

Prevalence of polio was very high in India before its eradication, with a number of people living with its residual effects. Anterior cruciate ligament (ACL) injury is the most common knee injury. To the best of our knowledge, this is the first report in literature presenting ACL injury in a poliotic limb and its management.

Case Report

A 30-year-old male with poliotic limb and equinovarus deformity presented with ACL injury to the same limb. ACL reconstruction was done using Peroneus longus graft. Postoperatively patient was gradually returned to preinjury activity levels.

Conclusion

ACL tears in a poliotic limb can be a challenging case. Proper preoperative planning and anticipation of problems can help in managing the case with a good outcome.

Strain evaluation of axially loaded collateral ligaments: a comparison of digital image correlation and strain gauges

The response of soft tissue to loading can be obtained by strain assessment. Typically, strain can be measured using electrical resistance with strain gauges (SG), or optical sensors based on the digital image correlation (DIC), among others. These sensor systems are already established in other areas of technology. However, sensors have a limited range of applications in medical technology due to various challenges in handling human soft materials. The aim of this study was to compare directly attached foil-type SG and 3D-DIC to determine the strain of axially loaded human ligament structures. Therefore, the medial (MCL) and lateral (LCL) collateral ligaments of 18 human knee joints underwent cyclic displacement-controlled loading at a rate of 20 mm/min in two test trials. In the first trial, strain was recorded with the 3D-DIC system and the reference strain of the testing machine. In the second trial, strain was additionally measured with a directly attached SG. The results of the strain measurement with the 3D-DIC system did not differ significantly from the reference strain in the first trial. The strains assessed in the second trial between reference and SG, as well as between reference and 3D-DIC showed significant differences. This suggests that using an optical system based on the DIC with a given unrestricted view is an effective method to measure the superficial strain of human ligaments. In contrast, directly attached SGs provide only qualitative comparable results. Therefore, their scope on human ligaments is limited to the evaluation of changes under different conditions.

The relationship between kinesiophobia and biomechanics in anterior cruciate ligament reconstructed females

OBJECTIVE

Kinesiophobia has been associated with deleterious biomechanical alterations during dual-limb landing tasks in anterior cruciate ligament (ACL) reconstructed females, however, no research has yet investigated single-limb tasks related to ACL injury. The aim of this investigation was to examine the relationship between kinesiophobia and biomechanics during a series of dual and single-limb functional tasks associated with ACL injury risk.

DESIGN

Cross-sectional study.

PARTICIPANTS

Fifteen females (age = 22.67 ± 2.58yrs, height = 1.65 ±0 .05m, mass = 65.28 ± 10.36 kg) with a history of ACL reconstruction (time post surgery = 3.40 ±0 .74yrs) were recruited for this investigation.

MAIN OUTCOME MEASURES

Kinesiophobia, measured via the Tampa Scale of Kinesiophobia (TSK-11). Kinematics and muscle activation were measured during three functional tasks: the drop jump (DJ), single-limb hop (SLH), and single-limb landing (SLL).

RESULTS

For the DJ task, there was a strong negative correlation between kinesiophobia and knee flexion (r = -.592, p = .20) and between kinesiophobia and trunk flexion (r = -0.724, p = .002). For the SLH task, there was a strong positive correlation between kinesiophobia and hip flexion (r = 0.560, p = .03).

CONCLUSIONS

These findings indicate that kinesiophobia is associated with movement alterations years after completion of ACL reconstruction and rehabilitation.

The association of bone bruising and grade of MCL injury in patients sustaining isolated MCL injuries

OBJECTIVES

To investigate the incidence of bone bruising with isolated medial collateral ligament injury and to assess whether the presence of bone bruising is related to the injury grade.

MATERIALS AND METHODS

Patients who sustained an acute isolated medial collateral ligament injury demonstrated on knee MRI between 2016 and 2020 were included in this study. Patient's characteristics and injury classification (clinical and radiological) were reviewed from clinical notes and imaging. The patients were divided into two groups, based on the presence of bone bruising. Fisher's exact test was used for dichotomous variables and odds ratios were computed in areas of clinical significance.

RESULTS

Sixty patients with a median age of 37.6 ± 13.8 were included. Twenty-eight (46.7%) had bone bruising demonstrated on MRI scan. The bone bruising group were 7 times (95% CI [1.4;36.5]) more likely to have a complete disruption of the superficial medial collateral ligament and MRI grade III injury. Injury to the deep medial collateral ligament was more often observed in this group (p < 0.05). The most common location of bone bruising was the lateral femoral condyle (57.1%, 16/28) and/or the medial femoral condyle (57.1%, 16/28).

CONCLUSIONS

The incidence of bone bruising with isolated medial collateral ligament injury is significant and is more common with radiologically higher grade injuries. There was no statistically significant difference between the anatomical location of bone bruise and the grade of MCL injury. Bone bruising patterns can help determine the mechanism of injury, with a valgus impact or avulsion type injury most commonly seen.

Contemporary Principles for Postoperative Rehabilitation and Return to Sport for Athletes Undergoing Anterior Cruciate Ligament Reconstruction

Despite advancements in our understanding of anterior cruciate ligament (ACL) injury prevention and nonsurgical management, ACL reconstruction continues to occur at an alarming rate. Among athletic patients, individuals participating in basketball, soccer, and football have the highest incidence of ACL injury, often requiring surgical intervention. To ensure the optimal treatment strategy for return to sport and prevention of secondary graft re-tear, it is important to tailor to the specific demands of the injured athlete and apply evidence-based best practices and rehabilitation principles. The purpose of this review is to provide readers with a brief background regarding ACL injuries, a focused review of clinical outcome studies after ACL reconstruction, and an updated framework with expert-guided recommendations for postoperative rehabilitation and return to sporting activity. Currently, there is no gold standard for rehabilitation after ACL reconstruction, highlighting the need for robust studies evaluating the best modalities for athlete rehabilitation, as well as determining the efficacy of new tools for improving therapy including blood flow restriction therapy and neuromuscular electrical stimulation. Based on clinical experience, a renewed focus on objective, criteria-based milestones may maximize the ability of return to preinjury levels of athletic function.

Sex differences in muscle activation patterns associated with anterior cruciate ligament injury during landing and cutting tasks: A systematic review

Neuromuscular control is critical for maintaining dynamic joint stability and mitigating the risk of anterior cruciate ligament (ACL) injury. Given the increased risk of ACL injury in females, sex-based differential muscle activation strategies are often associated with this risk. For example, the quadriceps-dominant muscle activation strategy sometimes observed in females has been discussed as a cause of their increased risk of ACL injury. However, there has been no synthesised knowledge on sex differences in muscle activation patterns associated with ACL injuries. Therefore, the purpose of this review was to synthesise sex differences in muscle activation patterns in movements associated with ACL injuries in both adult and adolescent populations. A systematic electronic database search was conducted. Thirty studies were included in the review. Females demonstrated higher pre- and post-landing activation of the quadriceps and lower activation of the hamstrings in 15 studies. Females also had higher quadriceps-to-hamstring co-contraction ratios during pre- and post-landing phases compared to their male counterparts in 4 of 9 studies that considered co-contraction. While some studies supported the quadriceps-dominant activation strategies in females, no consensus can be drawn due to methodological inconsistencies and limitations. Also, despite the importance of ACL injury prevention in children and adolescents, the evidence on sex difference in muscle activation patterns in this population is insufficient to draw meaningful conclusions.

Estimation of forces on anterior cruciate ligament in dynamic activities

In this work, a nonlinear strain rate dependent plugin developed for the OpenSim® platform was used to estimate the instantaneous strain rate (ISR) and the forces on the ACL's anteromedial (aACL) and posterolateral (pACL) bundles during walking and sudden change of direction of running termed as 'plant-and-cut' (PC). The authors obtained the kinematics data for walking via optical motion capture. PC movements, along with running kinematics, were obtained from the literature. A nonlinear plugin developed for ligaments was interfaced with OpenSim® platform to simulate walking and PC motions with a flexed knee and an extended knee. PC phase is sandwiched between an approach phase and take-off phase and was studied at various event velocities (1.8, 3, and 4.2 m s^-1), and angles of PC (23°, 34°, and 45°) as encountered in adult ball games. In both cases of PC-with-extended knee and PC-with-flexed-knee, the maximum forces on both the ACL bundles were observed after the take-off phase. A maximum force of ~ 35 N kg^-1 of body weight (BW) was observed on aACL after the take-off phase for an event velocity of 4.2 m s^-1. In the posterolateral bundle (pACL), the maximum forces (~ 40 N kg^-1 of BW) were observed towards the end of the mid-swing phase (after the take-off phase) for the various combinations of the parameters studied. The forces observed in the simulation of PC-with-flexed-knee and PC-with-extended-knee has resulted in magnitude higher than sustainable by the adults. This study is novel in attempting to incorporate differing rates-of-strain that have been shown to alter soft tissue properties into the OpenSim® musculoskeletal model. The proposed model can be used by researchers to predict the forces during various kinematic activities for other soft tissues.

ACL deficiency influences medio-lateral tibial alignment and knee varus-valgus during in vivo activities

PURPOSE

The role of the anterior cruciate ligament (ACL) in knee biomechanics in vivo and under weight-bearing is still unclear. The purpose of this study was to compare the tibiofemoral kinematics of ACL-deficient knees to healthy contralateral ones during the execution of weight-bearing activities.

METHODS

Eight patients with isolated ACL injury and healthy contralateral knees were included in the study. Patients were asked to perform a single step forward and a single leg squat first with the injured knee and then with the contralateral one. Knee motion was determined using a validated model-based tracking process that matched subject-specific MRI bone models to dynamic biplane radiographic images, under the principles of Roentgen stereophotogrammetric analysis (RSA). Data processing was performed in a specific software developed in Matlab.

RESULTS

Statistically significant differences (p < 0.05) were found for single leg squat along the frontal plane: ACL-deficient knees showed a more varus angle, especially at the highest knee flexion angles (40°-50° on average), compared to the contralateral knees. Furthermore, ACL-deficient knees showed tibial medialization along the entire task, while contralateral knees were always laterally aligned. This difference became statistically relevant (p < 0.05) for knee flexion angles included between 0° and about 30°.

CONCLUSION

ACL-deficient knees showed an abnormal tibial medialization and increased varus angle during single leg squat when compared to the contralateral knees. These biomechanical anomalies could cause a different force distribution on tibial plateau, explaining the higher risk of early osteoarthritis in ACL deficiency. The clinical relevance of this study is that also safe activities used in ACL rehabilitation protocols are significantly altered in ACL deficiency.

LEVEL OF EVIDENCE

III.

Association between ankle angle at initial contact and biomechanical ACL injury risk factors in male during self-selected single-leg landing

BACKGROUND

Increasing the ankle plantar-flexion angle at initial contact (IC) during landing reduces the impact features associated with landing, such as the vertical ground reaction force and loading rate, potentially affecting the risk of anterior cruciate ligament (ACL) injury. However, the relationships between the ankle plantar-flexion angle at IC and the previously identified biomechanical factors related to noncontact ACL injury have not been studied.

RESEARCH QUESTION

Thus, the purpose of this study was to determine whether significant relationships exist between the ankle plantar-flexion angle at IC and the biomechanical factors related to noncontact ACL injury.

METHODS

The peak anterior tibial shear force, peak external knee valgus moment, peak knee valgus angle, and combined peak external knee valgus plus tibial internal rotation moments were measured in 26 individuals while performing self-selected, single-leg landing. Pearson correlation analyses were performed to assess the relationships between the ankle plantar-flexion angle at IC and the biomechanical factors mentioned above.

RESULTS

The greater ankle plantar-flexion angle at IC was related to smaller the peak knee valgus moment (r = -0.5, p = 0.009) and the combined peak knee valgus plus internal rotation moments (r = -0.58, p = 0.001).

SIGNIFICANCE

These results suggest that large ankle plantar-flexion angle at IC might be associated with lesser loading of the knee frontal plane and altering the self-selective ankle angle may result in biomechanical changes associated with ACL injury risk.

Prospective Frontal Plane Angles Used to Predict ACL Strain and Identify Those at High Risk for Sports-Related ACL Injury

Background:

Knee abduction moment during landing has been associated with anterior cruciate ligament (ACL) injury. However, accurately capturing this measurement is expensive and technically rigorous. Less complex variables that lend themselves to easier clinical integration are desirable.

Purpose:

To corroborate in vitro cadaveric simulation and in vivo knee abduction angles from landing tasks to allow for estimation of ACL strain in live participants during a landing task.

Study Design:

Descriptive laboratory study.

Methods:

A total of 205 female high school athletes previously underwent prospective 3-dimensional motion analysis and subsequent injury tracking. Differences in knee abduction angle between those who went on to develop ACL injury and healthy controls were assessed using Student t tests and receiver operating characteristic analysis. A total of 11 cadaveric specimens underwent mechanical impact simulation while instrumented to record ACL strain and knee abduction angle. Pearson correlation coefficients were calculated between these variables. The resultant linear regression model was used to estimate ACL strain in the 205 high school athletes based on their knee abduction angles.

Results:

Knee abduction angle was greater for athletes who went on to develop injury than for healthy controls (P < .01). Knee abduction angle at initial contact predicted ACL injury status with 78% sensitivity and 83% specificity, with a threshold of 4.6° of knee abduction. ACL strain was significantly correlated with knee abduction angle during cadaveric simulation (P < .01). Subsequent estimates of peak ACL strain in the high school athletes were greater for those who went on to injury (7.7-8.1% ± 1.5%) than for healthy controls (4.1-4.5% ± 3.6%) (P < .01).

Conclusion:

Knee abduction angle exhibited comparable reliability with knee abduction moment for ACL injury risk identification. Cadaveric simulation data can be extrapolated to estimate in vivo ACL strain. Athletes who went on to ACL injury exhibited greater knee abduction and greater ACL strain than did healthy controls during landing.

Clinical Relevance:

These important associations between the in vivo and cadaveric environments allow clinicians to estimate peak ACL strain from observed knee abduction angles. Neuromuscular control of knee abduction angle during dynamic tasks is imperative for knee joint health. The present associations are an important step toward the establishment of a minimal clinically important difference value for ACL strain during landing.

Linear Discriminant Analysis Successfully Predicts Knee Injury Outcome From Biomechanical Variables

BACKGROUND

The most commonly damaged structures of the knee are the anterior cruciate ligament (ACL), medial collateral ligament (MCL), and menisci. Given that these injuries present as either isolated or concomitant, it follows that these events are driven by specific mechanics versus coincidence. This study was designed to investigate the multiplanar mechanisms and determine the important biomechanical and demographic factors that contribute to classification of the injury outcome.

HYPOTHESIS

Linear discriminant analysis (LDA) would accurately classify each injury type generated by the mechanical impact simulator based on biomechanical input variables (ie, ligament strain and knee kinetics).

STUDY DESIGN

Controlled laboratory study.

METHODS

In vivo kinetics and kinematics of 42 healthy, athletic participants were measured to determine stratification of injury risk (ie, low, medium, and high) in 3 degrees of knee forces/moments (knee abduction moment, anterior tibial shear, and internal tibial rotation). These stratified kinetic values were input into a cadaveric impact simulator to assess ligamentous strain and knee kinetics during a simulated landing task. Uniaxial and multiaxial load cells and implanted strain sensors were used to collect mechanical data for analysis. LDA was used to determine the ability to classify injury outcome by demographic and biomechanical input variables.

RESULTS

From LDA, a 5-factor model (Entropy R2 = 0.26) demonstrated an area under the receiver operating characteristic curve (AUC) for all 5 injury outcomes (ACL, MCL, ACL+MCL, ACL+MCL+meniscus, ACL+meniscus) of 0.74 or higher, with "good" prediction for 4 of 5 injury classifications. A 10-factor model (Entropy R2 = 0.66) improved the AUC to 0.86 or higher, with "excellent" prediction for 5 injury classifications. The 15-factor model (Entropy R2 = 0.85), produced 94.1% accuracy with the AUC 0.98 or higher for all 5 injury classifications.

CONCLUSION

Use of LDA accurately predicted the outcome of knee injury from kinetic data from cadaveric simulations with the use of a mechanical impact simulator at 25° of knee flexion. Thus, with clinically relevant kinetics, it is possible to determine clinical risk of injury and also the likely presentation of singular or concomitant knee injury.

CLINICAL RELEVANCE

LDA demonstrates that injury outcomes are largely characterized by specific mechanics that can distinguish ACL, MCL, and medial meniscal injury. Furthermore, as the mechanics of injury are better understood, improved interventional prehabilitation can be designed to reduce these injuries.

Sex Differences in Anatomic Features Linked to Anterior Cruciate Ligament Injuries During Skeletal Growth and Maturation

BACKGROUND

Several anatomic features of the knee have been shown to affect joint and anterior cruciate ligament (ACL) loading and the risk of subsequent injuries. While several studies have highlighted sex differences between these anatomic features, little is known on how these differences develop during skeletal growth and maturation.

HYPOTHESES

(A) Anatomic features linked to an ACL injury will significantly change during skeletal growth and maturation. (B) The age-related changes in anatomic features linked to an ACL injury are different between male and female patients.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

After institutional review board approval, magnetic resonance imaging data from 269 unique knees (patient age 3-18 years; 51% female), free from any injuries, were used to measure femoral notch width, posterior slope of the lateral tibial plateau (lateral tibial slope), medial tibial depth, tibial spine height, and posterior lateral meniscal bone angle. Linear regression was used to test the associations between age and quantified anatomic indices. Patients were then divided into 4 age groups: preschool (3-6 years), prepubertal (7-10 years), early adolescent (11-14 years), and late adolescent (15-18 years). Also, 2-way analysis of variance with the Holm-Sidak post hoc test was used to compare morphology between male and female patients in each age group.

RESULTS

The femoral notch width, medial tibial depth, and tibial spine height significantly increased with age (P < .001). The lateral tibial slope decreased with age only in male patients (P < .001). Except for the posterior lateral meniscal bone angle, the age-related changes in anatomy were different between male and female patients (P < .05). On average, early and late adolescent female patients had smaller femoral notches, steeper lateral tibial slopes, flatter medial tibial plateaus, and shorter tibial spines compared with age-matched male patients (P < .01).

CONCLUSION

Overall, the findings supported our hypotheses, showing sex-specific changes in anatomic features linked to an ACL injury during skeletal growth and maturation. These observations help to better explain the reported age and sex differences in the prevalence of ACL injuries. The fact that most of these anatomic features undergo substantial changes during skeletal growth and maturation introduces the hypothesis that prophylactic interventions (ie, activity modification) would have the potential to reshape a maturing knee in a manner that lowers the risk of noncontact ACL injuries.

Timing of Strain Response of the ACL and MCL Relative to Impulse Delivery During Simulated Landings Leading up to ACL Failure

Anterior cruciate ligament (ACL) injury videos estimate that rupture occurs within 50 milliseconds of initial contact, but are limited by imprecise timing and nondirect data acquisition. The objective of this study was to precisely quantify the timing associated with ligament strain during simulated landing and injury events. The hypotheses tested were that the timing of peak strain following initial contact would differ between ligaments and that peak strain timing would be independent of the injury-risk profile emulated during simulated landing. A mechanical impact simulator was used to perform landing simulations based on various injury-risk profiles that were applied to each specimen in a block-randomized order. The ACL and medial collateral ligament were instrumented with strain gauges that recorded continuously. The data from 35 lower-extremity specimens were included for analysis. Analysis of variance and Kruskal-Wallis tests were used to determine the differences between timing and profiles. The mean time to peak strain was 53 (24) milliseconds for the ACL and 58 (35) milliseconds for the medial collateral ligament. The time to peak ACL strain ranged from 48 to 61 milliseconds, but the timing differences were not significant between profiles. Strain timing was independent of injury-risk profile. Noncontact ACL injuries are expected to occur between 0 and 61 milliseconds after initial contact. Both ligaments reached peak strain within the same time frame.

Analysis of Internal Knee Forces Allows for the Prediction of Rupture Events in a Clinically Relevant Model of Anterior Cruciate Ligament Injuries

Background:

A recently developed mechanical impact simulator induced an anterior cruciate ligament (ACL) rupture via the application of a combination of inverse dynamics–based knee abduction moment (KAM), anterior tibial shear force (ATS), and internal tibial rotation moment with impulsive compression in a cohort of cadaveric limbs. However, there remains an opportunity to further define the interaction of internal forces and moments at the knee and their respective influence on injury events.

Purpose:

To identify the influence of internal knee loads on an ACL injury event using a cadaveric impact simulator.

Study Design:

Controlled laboratory study.

Methods:

Drop-landing simulations were performed and analyzed on 30 fresh-frozen cadaveric knees with a validated mechanical impact simulator. Internal forces and moments at the knee joint center were calculated using data from a 6-axis load cell recorded on the femur during testing. Kinetic data from a total of 1083 trials that included 30 ACL injury trials were used as inputs for principal component (PC) analysis to identify the most critical features of loading waveforms. Logistic regression analysis with a stepwise selection was used to select the PCs that predicted an ACL injury. Injurious waveforms were reconstructed with selected PCs in logistic regression analysis.

Results:

A total of 3 PCs were selected in logistic regression analysis that developed a significant model (P < .001). The external loading of KAM was highly correlated with PC1 (ρ < –0.8; P < .001), which explained the majority (>69%) of the injurious waveforms reconstructed with the 3 selected PCs. The injurious waveforms demonstrated a larger internal knee adduction moment and lateral tibial force. After the ACL was ruptured, decreased posterior tibial force was observed in injury trials.

Conclusion:

These findings give us a better understanding of ACL injury mechanisms using 6-axis kinetics from an in vitro simulator. An ACL rupture was correlated with an internal knee adduction moment (external KAM) and was augmented by ATS and lateral tibial force induced by an impact, which distorted the ACL insertion orientation.

Clinical Relevance:

The ACL injury mechanism explained in this study may help target injury prevention programs to decrease injurious knee loading (KAM, ATS, and lateral tibial force) during landing tasks.

Variation in ACL and MCL Strain Before Initial Contact Is Dependent on Injury Risk Level During Simulated Landings

Background

The existent literature has well explored knee ligament kinetics and strain at and after initial contact (IC) during landing tasks. However, little is known about knee ligament biomechanics in flight before IC.

Purpose

To quantify and compare change in anterior cruciate ligament (ACL) and medial collateral ligament (MCL) strain before IC relative to after IC.

Study Design

Descriptive laboratory study.

Methods

A total of 40 cadaveric specimens were analyzed after being subjected to simulated landings in a mechanical impact simulator. External joint loads of varying magnitudes were applied to mimic relative injury risk load levels from an in vivo cohort and were coupled with an impulse force to represent initial ground contact. Implanted strain gauges continually recorded ligament strain. Kruskal-Wallis tests evaluated the significance of risk level and pre- and post-IC factors, while Wilcoxon each-pair tests evaluated differences within both factors.

Results

Strain responses during simulated landing tasks for the ACL (P ≥ .545) and MCL (P ≥ .489) were consistent after IC regardless of the level of relative injury risk simulated in each trial. Before IC, the level of injury risk kinetics applied to a specimen differentiated strain response in the ACL (P < .001) and MCL (P < .001), as higher risk profiles produced greater changes in ligament strain. Mean baseline strain was 4.0% in the ACL and 1.0% in the MCL. Mean change in strain from the ACL ranged from 0.1% to 3.9% pre-IC and from 2.9% to 5.7% post-IC, while the MCL ranged from 0.0% to 3.0% pre-IC and from 0.9% to 1.3% post-IC.

Conclusion

Within each ligament, post-IC strain response lacked statistical differences among simulated risk profiles, while pre-IC response was dependent on the risk profile simulated. Individually, neither pre- nor poststrain changes were enough to induce ACL failure, but when combined over the course of a full landing task, they could lead to rupture.

Clinical Relevance

Prevention and rehabilitation techniques should aim to limit the presence of increased risk biomechanics in flight before landing, as impulse delivery at IC is inevitable.

Influence of relative injury risk profiles on anterior cruciate ligament and medial collateral ligament strain during simulated landing leading to a noncontact injury event

BACKGROUND

Athletes have traditionally been subdivided into risk classifications for ACL injury relative to the biomechanical traits they display during landing. This investigation aimed to discern whether these separate risk classifications elicit strain differences on the ACL and MCL during landing. It was hypothesized that the higher risk simulation profiles would exhibit greater ACL strain and that the ACL would exhibit greater strain than the MCL under all conditions.

METHOD

The mechanical impact simulator was used to simulate landing on a cohort of 46 cadaveric specimens. The simulator applied external joint loads to the knee prior to impulse delivery. These loads were organized into a series of profiles derived from in vivo motion capture previously performed on a cohort of 44 athletes and represented various risk classifications. Strain gauges were implanted on the ACL and MCL and simulations performed until a structural failure was elicited. Differences were assessed with Kruskal-Wallis tests.

FINDINGS

The highest-risk profiles tended to exhibit greater peak ACL strain and change in ACL strain than the baseline- and moderate-risk profiles. Specimens that failed during lower-risk simulations expressed greater strain at these loads than specimens that completed higher-risk simulations. The ACL recorded greater strain than the MCL throughout all simulation profiles.

INTERPRETATION

This behavior justifies why neuromuscular interventions have greater impact on higher-risk athletes and supports the continued screening and targeted training of those athletes that express greater injury risk. The loading disparity between ACL and MCL justifies their limited concomitant injury rate.

Frontal Plane Loading Characteristics of Medial Collateral Ligament Strain Concurrent With Anterior Cruciate Ligament Failure

BACKGROUND

Both the anterior cruciate ligament (ACL) and the medial collateral ligament (MCL) bear load during athletic tasks of landing, cutting, pivoting, and twisting. As dynamic knee valgus is a purported mechanism for ACL injury, the MCL should bear significant strain load with valgus force.

HYPOTHESIS

The intact MCL will demonstrate a significant increase in strain upon failure of the ACL at 25° of knee flexion.

STUDY DESIGN

Controlled laboratory study.

METHODS

In vivo kinetics/kinematics of 44 healthy athletic participants were measured to determine stratification of injury risk (ie, low, medium, and high) in 3 degrees of knee forces/moments (knee abduction moment, anterior tibial shear, and internal tibial rotation). These stratified kinetic values were input into a cadaveric impact simulator to assess ligamentous strain during a simulated landing task. Uniaxial and multiaxial load cells and differential variable reluctance transducer strain sensors were utilized to collect mechanical data for analysis. Conditions of external loads applied to the cadaveric limbs were varied and randomized.

RESULTS

ACL strain increased with increased dynamic knee abduction moment (χ²_[5] = 14.123, P = .0148). The most extreme dynamic knee abduction moment condition demonstrated significantly higher ACL strain compared with lower loaded trials (P≤ .0203). Similarly, MCL strain increased with dynamic knee abduction moment (χ²_[5] = 36.578, P < .0001). Matched-pairs analysis compared ACL strain with MCL strain (maximum ACL strain - maximum MCL strain) and demonstrated high strain for the ACL versus the MCL (S₁₇₇ = 6223.5, P < .0001).

CONCLUSION

Although significant, MCL strain had minimal increase with increased dynamic knee abduction moment, and the event of ACL failure did not significantly increase MCL strain when compared with high dynamic knee abduction moment conditions in the cadaveric model. The ACL bears more strain than the MCL at increasing amounts of dynamic knee abduction moment at 25° of knee flexion, which may explain the limited concomitant MCL injury rate that can occur during a dynamic valgus collapse of the knee.

CLINICAL RELEVANCE

These characteristics of ACL and MCL strain are important to understand the mechanisms that drive these injuries at the knee and will improve rehabilitation and injury prevention techniques.

Multiplanar Loading of the Knee and Its Influence on Anterior Cruciate Ligament and Medial Collateral Ligament Strain During Simulated Landings and Noncontact Tears

BACKGROUND

Anterior cruciate ligament (ACL) tears and concomitant medial collateral ligament (MCL) injuries are known to occur during dynamic athletic tasks that place combinatorial frontal and transverse plane loads on the knee. A mechanical impact simulator that produces clinical presentation of ACL injury allows for the quantification of individual loading contributors leading to ACL failure.

PURPOSE/HYPOTHESIS

The objective was to delineate the relationship between knee abduction moment, anterior tibial shear, and internal tibial rotation applied at the knee and ACL strain during physiologically defined simulations of impact at a knee flexion angle representative of initial contact landing from a jump. The hypothesis tested was that before ACL failure, abduction moment would induce greater change in ACL strain during landing than either anterior shear or internal rotation.

STUDY DESIGN

Controlled laboratory study.

METHODS

Nineteen cadaveric specimens were subjected to simulated landings in the mechanical impact simulator. During simulations, external knee abduction moment, internal tibial rotation moment, and anterior tibial shear loads were derived from a previously analyzed in vivo cohort and applied to the knee in varying magnitudes with respect to injury risk classification. Implanted strain gauges were used to track knee ligament displacement throughout simulation. Kruskal-Wallis tests were used to assess strain differences among loading factors, with Wilcoxon each pair post hoc tests used to assess differences of magnitude within each loading.

RESULTS

Each loading factor significantly increased ACL strain (P < .005). Within factors, the high-risk magnitude of each factor significantly increased ACL strain relative to the baseline condition (P≤ .002). However, relative to knee abduction moment specifically, ACL strain increased with each increased risk magnitude (P≤ .015).

CONCLUSION

Increased risk levels of each load factor contributed to increased levels of ACL strain during a simulated jump landing. The behavior of increased strain between levels of increased risk loading was most prevalent for changes in knee abduction moment. This behavior was observed in the ACL and MCL.

CLINICAL RELEVANCE

Knee abduction moment may be the predominant precursor to ACL injury and concomitant MCL injury. As knee abduction occurs within the frontal plane, primary preventative focus should incorporate reduction of frontal plane knee loading in landing and cutting tasks, but secondary reduction of transverse plane loading could further increase intervention efficacy. Constraint of motion in these planes should restrict peak ACL strain magnitudes during athletic performance.

Anatomic Features of the Tibial Plateau Predict Outcomes of ACL Reconstruction Within 7 Years After Surgery

BACKGROUND

Multiple anatomic features of the femoral condyles and tibial plateau have been shown to influence knee biomechanics and risk of anterior cruciate ligament (ACL) injury. However, it remains unclear how these anatomic factors affect the midterm outcomes of ACL reconstruction.

HYPOTHESIS

Decreased femoral notch width, increased posterior and coronal slopes, and decreased concavity of the tibial plateau are associated with inferior clinical, patient-reported, and osteoarthritis-related outcomes 7 years after ACL reconstruction.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

Prospectively collected data from 44 patients who did not have a subsequent graft or contralateral ACL failure within 7 years after unilateral ACL reconstruction were reviewed (mean ± SD age, 23.7 ± 9.2 years; 64% women). Notch width (after notchplasty), posterior slopes of the medial and lateral tibial plateau, maximum depth of the medial tibial plateau, and coronal tibial slope were measured from magnetic resonance images. Anatomic predictors of side-to-side differences in anterior-posterior knee laxity, Knee injury and Osteoarthritis Outcome Score (KOOS), medial joint space width, and side-to-side differences in Osteoarthritis Research Society International (OARSI) x-ray score, measured at 7 years, were identified with linear regression (bivariate) and stepwise regression (multivariate).

RESULTS

Increased posterior slope of the lateral tibial plateau was associated with increased side-to-side difference in knee laxity (bivariate model only), increased side-to-side difference in the OARSI score, and decreased KOOS subscores ( R² > .10, P < .05). Increased posterior slope of the medial tibial plateau was associated with a higher side-to-side difference in the OARSI x-ray score (bivariate model only) and lower KOOS subscores ( R² > .11, P < .03). Increased coronal tibial slope was associated with lower KOOS subscores ( R² > .11, P < .03). Decreased medial tibial depth was associated with increased knee laxity as well as decreased KOOS subscores (ie, quality of life and symptoms; R² > .12, P < .03). Postoperative notch width was not a significant predictor for any surgical outcome. None of the anatomic features were predictive of medial joint space width narrowing.

CONCLUSION

Results partially support the hypothesis and highlight the importance of knee anatomy on several outcomes of ACL reconstruction among patients without subsequent graft or contralateral ACL injures. Increasing slopes in the coronal and sagittal planes with decreasing concavity of the medial tibial plateau lead to less favorable outcomes 7 years after surgery.

External loads associated with anterior cruciate ligament injuries increase the correlation between tibial slope and ligament strain during in vitro simulations of in vivo landings

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.

Medial collateral ligament injuries of the knee in male professional football players: a prospective three-season study of 130 cases from the UEFA Elite Club Injury Study

PURPOSE

Medial collateral ligament (MCL) injury is the single most common traumatic knee injury in football. The purpose of this study was to study the epidemiology and mechanisms of MCL injury in men's professional football and to evaluate the diagnostic and treatment methods used.

METHODS

Fifty-one teams were followed prospectively between one and three full seasons (2013/2014-2015/2016). Individual player exposure and time-loss injuries were recorded by the teams' medical staffs. Moreover, details on clinical grading, imaging findings and specific treatments were recorded for all injuries with MCL injury of the knee as the main diagnosis. Agreement between magnetic resonance imaging (MRI) and clinical grading (grades I-III) was described by weighted kappa.

RESULTS

One hundred and thirty of 4364 registered injuries (3%) were MCL injuries. Most MCL injuries (98 injuries, 75%) occurred with a contact mechanism, where the two most common playing situations were being tackled (38 injuries, 29%) and tackling (15 injuries, 12%). MRI was used in 88 (68%) of the injuries, while 33 (25%) were diagnosed by clinical examination alone. In the 88 cases in which both MRI and clinical examination were used to evaluate the grading of MCL injury, 80 (92% agreement) were equally evaluated with a weighted kappa of 0.87 (95% CI 0.77-0.96). Using a stabilising knee brace in players who sustained a grade II MCL injury was associated with a longer lay-off period compared with players who did not use a brace (41.5 (SD 13.2) vs. 31.5 (SD 20.3) days, p = 0.010).

CONCLUSION

Three-quarter of the MCL injuries occurred with a contact mechanism. The clinical grading of MCL injuries showed almost perfect agreement with MRI grading, in cases where the MCL injury is the primary diagnosis. Not all grade II MCL injuries were treated with a brace and may thus indicate that routine bracing should not be necessary in milder cases.

LEVEL OF EVIDENCE

Prospective cohort study, II.

Validation of Noncontact Anterior Cruciate Ligament Tears Produced by a Mechanical Impact Simulator Against the Clinical Presentation of Injury

BACKGROUND

Anterior cruciate ligament (ACL) injuries are catastrophic events that affect athletic careers and lead to long-term degenerative knee changes. As injuries are believed to occur within the first 50 milliseconds after initial contact during a rapid deceleration task, impact simulators that rapidly deliver impulse loads to cadaveric specimens have been developed. However, no impactor has reproducibly and reliably created ACL injures in a distribution that mimics clinical observation.

PURPOSE

To better understand ACL injury patterns through a cadaveric investigation that applied in vivo-measured external loads to the knee during simulated landings.

STUDY DESIGN

Controlled laboratory study.

METHODS

A novel mechanical impact simulator reproduced kinetics from in vivo-recorded drop landing tasks on 45 cadaveric knees. Specimens were exposed to a randomized order of variable knee abduction moment, anterior tibial shear, and internal tibial rotation loads before the introduction of an impulse load at the foot. This process was repeated until a hard or soft tissue injury was induced on the joint. Injuries were assessed by an orthopaedic surgeon, and ligament strain was recorded by implanted strain gauges.

RESULTS

The mechanical impact simulator induced ACL injuries in 87% of specimens, with medial collateral ligament (MCL) injuries in 31%. ACL tear locations were 71% femoral side, 21% midsubstance, and 9% tibial side. Peak strain before failure for ACL-injured specimens was 15.3% ± 8.7% for the ACL and 5.1% ± 5.6% for the MCL ( P < .001).

CONCLUSION

The ACL injuries induced by the mechanical impact simulator in the present study have provided clinically relevant in vitro representations of in vivo ACL injury patterns as cited in the literature. Additionally, current ligament strains corroborate the literature to support disproportionate loading of the ACL relative to the MCL during athletic tasks.

CLINICAL RELEVANCE

These findings indicate that the mechanical impact simulator is an appropriate model for examining independent mechanical variables, treatment techniques, and preventive interventions during athletic tasks leading up to and including an ACL injury. Accordingly, this system can be utilized to further parse out contributing factors to an ACL injury as well as assess the shortcomings of ACL reconstruction techniques in a dynamic, simulated environment that is better representative of in vivo injury scenarios.

Low 1-Year Return-to-Sport Rate After Anterior Cruciate Ligament Reconstruction Regardless of Patient and Surgical Factors: A Prospective Cohort Study of 272 Patients

BACKGROUND

There is insufficient knowledge about the way that concomitant injuries affect the short-term likelihood of a return to a knee-strenuous sport after anterior cruciate ligament (ACL) reconstruction. Hypotheses/Purpose: The purpose was to study whether patient characteristics, concomitant injuries, and graft choice at primary ACL reconstruction can predict return to sport (RTS) 1 year after surgery. The hypotheses were that younger age at the time of ACL reconstruction would positively affect RTS, while the presence of concomitant injuries would negatively affect RTS 1 year after surgery.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

Data were extracted from a rehabilitation-specific register and the Swedish National Knee Ligament Register. Twelve months after surgery, all patients were evaluated for RTS via the Tegner Activity Scale. The primary outcome was a return to knee-strenuous sport, defined as a Tegner Activity Scale ≥6. Univariable and multivariable logistic regression analyses were performed with patient characteristics, concomitant knee injuries, and graft choice as independent variables.

RESULTS

A total of 272 patients (51% female) with a mean ± SD age of 25.0 ± 9.2 years were included. In the multivariable analysis, a favorable odds ratio (OR) for returning to sport was found for patients of male sex (OR, 2.58; 95% CI, 1.43-4.65; P = .0016), younger age at the time of ACL reconstruction (OR, 2.32; 95% CI, 1.59-3.33; P < .0001), a higher preinjury score on the Tegner Activity Scale (OR, 1.45; 95% CI, 1.13-1.87; P = .0038), and an absence of injury to the meniscus (OR, 1.92; 95% CI, 1.10-3.36; P = .023) and medial collateral ligament (OR, 7.61; 95% CI, 1.42-40.87; P = .018). In addition, the absence of cartilage injury was favorable in terms of RTS in the univariable analysis (OR, 2.48; 95% CI, 1.40-4.39; P = .0018).

CONCLUSION

Positive predictors of a return to knee-strenuous sport 1 year after ACL reconstruction were male sex, younger age, a high preinjury level of physical activity, and the absence of concomitant injuries to the medial collateral ligament and meniscus.

Sex-Based Differences of Medial Collateral Ligament and Anterior Cruciate Ligament Strains With Cadaveric Impact Simulations

Background:

Female patients sustain noncontact knee ligament injuries at a greater rate compared with their male counterparts. The cause of these differences in the injury rate and the movements that load the ligaments until failure are still under dispute in the literature.

Purpose/Hypotheses:

This study was designed to determine differences in anterior cruciate ligament (ACL) and medial collateral ligament (MCL) strains between male and female cadaveric specimens during a simulated athletic task. The primary hypothesis tested was that female limbs would demonstrate significantly greater ACL strain compared with male limbs under similar loading conditions. A secondary hypothesis was that MCL strain would not differ between sexes.

Study Design:

Controlled laboratory study.

Methods:

Motion analysis of 67 athletes performing a drop vertical jump was conducted. Kinetic data were used to categorize injury risk according to tertiles, and these values were input into a cadaveric impact simulator to assess ligamentous strain during a simulated landing task. Uniaxial and multiaxial load cells and differential variable reluctance transducer strain sensors were utilized to collect mechanical data for analysis. Conditions of external loads applied to the cadaveric limbs (knee abduction moment, anterior tibial shear, and internal tibial rotation) were varied and randomized. Data were analyzed using 1-way analysis of variance (ANOVA), 2-way repeated-measures ANOVA, and the Fisher exact test.

Results:

There were no significant differences (P = .184) in maximum ACL strain between male (13.2% ± 8.1%) and female (16.7% ± 8.3%) specimens. Two-way ANOVA demonstrated that across all controlled external load conditions, female specimens consistently attained at least 3.5% increased maximum ACL strain compared with male specimens (F_1,100 = 4.188, P = .043); however, when normalized to initial contact, no significant difference was found. There were no significant differences in MCL strain between sexes for similar parameters.

Conclusion:

When compared with baseline, female specimens exhibited greater values of ACL strain at maximum, initial contact, and after impact (33, 66, and 100 milliseconds, respectively) than male specimens during similar loading conditions, with a maximum strain difference of at least 3.5%. During these same loading conditions, there were no differences in MCL loading between sexes, and only a minimal increase of MCL loading occurred during the impact forces. Our results indicate that female patients are at an increased risk for ACL strain across all similar conditions compared with male patients.

Clinical Relevance:

These data demonstrate that female specimens, when loaded similarly to male specimens, experience additional strain on the ACL. As the mechanical environment was similar for both sexes with these simulations, the greater ACL strain of female specimens must be attributed to ligament biology, anatomic differences, or muscular stiffness.

Ligament Strain Response Between Lower Extremity Contralateral Pairs During In Vitro Landing Simulation

Background:

Limb asymmetries, as determined through in vivo biomechanical measures, are known risk factors for anterior cruciate ligament (ACL) injury. Previous cadaveric studies have shown a lack of significant differences in ligament strain between contralateral lower extremities when identical kinematics were simulated on specimens. Recent methodological developments have applied in vivo knee kinetics to exert landing forces on cadaveric lower extremities to mimic ACL injury events, but it is unknown whether contralateral limbs fail in a consistent manner during impact simulator testing.

Hypothesis:

It was hypothesized that contralateral lower extremities would not exhibit side-to-side differences in ligament strains. Furthermore, it was hypothesized that failure loads and failure locations would be independent of limb dominance.

Study Design:

Controlled laboratory study.

Methods:

Fourteen pairs of cadaveric lower extremities were obtained from an anatomic donations program (8 female, 6 male; mean ± SD: age, 41.7 ± 8.1 years; mass, 86.8 ± 27.0 kg; body mass index, 29.4 ± 9.0 kg/m²). A mechanical impact simulator was used to re-create the impulse ground-reaction force generated during an in vivo landing task. Ligament strains were recorded by differential variable force transducers implanted on the ACL and medial collateral ligament (MCL).

Results:

No significant differences were observed in peak ACL or peak MCL strain for 5 loading conditions. Fisher exact tests of independence revealed that limb dominance was independent of both load at failure and failure location.

Conclusion:

There were no significant differences in ACL and MCL strain values between limb sides during in vitro impact simulation testing. This finding indicates that limb dominance does not influence the failure threshold of the ACL, since there was no significant difference in failure strains. The functional mechanics of the ACL are comparable between contralateral pairs from the same healthy specimen.

Clinical Relevance:

Injury mechanisms and intra-articular mechanics cannot be ethically studied in an in vivo setting. The current study provides additional insight into limb asymmetry that is observed among athletes in clinical sports medicine settings.

Sex-Based Differences in Knee Kinetics With Anterior Cruciate Ligament Strain on Cadaveric Impact Simulations

Background:

Females are at an increased risk of sustaining noncontact knee ligament injuries as compared with their male counterparts. The kinetics that load the anterior cruciate ligament (ACL) are still under dispute in the literature.

Purpose/Hypothesis:

The purpose of this study was to determine whether there are differences in knee kinetics between the sexes that lead to greater ACL strain in females when similar external loads are applied during a simulated drop vertical jump landing task. It was hypothesized that female limbs would demonstrate significant differences in knee abduction moment that predispose females to ACL injury when compared with males.

Study Design:

Controlled laboratory study.

Methods:

Motion analysis data of 67 athletes who performed a drop vertical jump were collected. The kinematic and kinetic data were used to categorize tertiles of relative risk, and these values were input into a cadaveric impact simulator to assess ligamentous loads during the simulated landing task. Uni- and multiaxial load cells and differential variable reluctance transducer strain sensors were utilized to collect kinetic data and maximum ACL strain for analysis. Conditions of external loads applied to the cadaveric limbs were systematically varied and randomized. Data were analyzed with 2-way repeated-measures analysis of variance and the Fisher exact test.

Results:

Five kinetic parameters were evaluated. Of the 5 kinetic variables, only knee abduction moment (KAM) demonstrated significant differences in females as compared with males (F_1,136 = 4.398, P = .038). When normalized to height and weight, this difference between males and females increased in significance (F_1,136 = 7.155, P = .008). Compared with males, females exhibited a 10.3-N·m increased knee abduction torque at 66 milliseconds postimpact and a 22.3-N·m increased abduction torque at 100 milliseconds postimpact. For loading condition, the condition of “maximum ACL strain” demonstrated a maximum difference of 54.3-N·m increased abduction torque and 74.5-N·m increased abduction torque at 66 milliseconds postimpact.

Conclusion:

Under the tested conditions, increased external loads led to increased medial knee translation force, knee abduction moment, and external knee moment. Females exhibited greater forces and moments at the knee, especially at KAM, when loaded in similar conditions. As these KAM loads are associated with increased load and strain on the ACL, the sex-based differences observed in the present study may account for a portion of the underlying mechanics that predispose females to ACL injury as compared with males in a controlled simulated athletic task.

Clinical Relevance:

KAM increases strain to the ACL under clinically representative loading. Additionally, this work establishes the biomechanical characteristics of knee loading between sexes.

Anterior Cruciate Ligament Injury: Return to Play, Function and Long-Term Considerations

Anterior cruciate ligament tears are common and affect young individuals who participate in jumping and pivoting sports. After injury many individuals undergo ligament reconstruction (ACLR) but do not return to play, suffer recurrent injury and osteoarthritis. Outcome studies show that after ACLR, 81% of individuals return to sports, 65% return to their preinjury level and 55% return to competitive sports. Systematic reviews place the risk of ipsilateral retears at 5.8% and contralateral injuries at 11.8%, with recent reports of over 20% failure rate. Approximately 20% to 50% of patients will have evidence of OA within 10 to 20 yr. Factors important in reducing complications include timing of surgery, individualized return to play protocols, and prevention programs for injury. Further understanding of the factors that increase return to play percentages, reduce the risk of recurrent injury and improve long-term outcomes after ACL injury is needed to reduce the burden of these injuries on society.

The influence of internal and external tibial rotation offsets on knee joint and ligament biomechanics during simulated athletic tasks

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.

Timing, not magnitude, of force may explain sex-dependent risk of ACL injury

PURPOSE

The anterior cruciate ligament is loaded through valgus moment, vertical ground reaction force, and internal rotation moment. The aim of this study was to compare the timing of force peaks during early stance between youth girls and boys.

METHODS

One-hundred and twenty-nine team sport athletes aged 9-12 completed a total of 2540 cutting maneuvers captured with an 8-camera motion capture system. Timing of early force peaks was analyzed within 100 ms after ground contact.

RESULTS

Genders showed different mean (95% CI) time to peak valgus-(32 ms (30-33 ms) vs 37 ms (36-38 ms), P < 0.001) and time to peak internal rotation moments (36 ms (35-37 ms) vs 38 ms (37-39 ms), P = 0.029) but not time to peak vertical ground reaction force [38 ms (37-40 ms) vs 37 ms (36-38 ms, n.s.)]. Girls showed a smaller time between vertical ground reaction force and valgus moment peaks (mean (95% CI) of 1 ms (1-2 ms) vs 7 ms (5-9 ms), P < 0.001), and valgus- and internal rotation moment peaks (0 ms (- 2 to 1.0 ms) vs - 5 ms (- 6 to - 3 ms), P = 0.0003) but not between internal rotation moment and vertical ground reaction force.

CONCLUSIONS

Concurrent force peaks are more common for girls compared with boys, leading to more frequent multi-planar loading of the knee. Timing may explain sex-dependent risk of ACL injuries. Exposure to repeated cutting movements may result in greater ACL injury risk due to timing of knee forces as well as magnitude. Such exposure should be minimized for at-risk athletes.

LEVEL OF EVIDENCE

III.

Quadriceps force and anterior tibial force occur obviously later than vertical ground reaction force: a simulation study

BACKGROUND

Although it is well known that quadriceps force generates anterior tibial force, it has been unclear whether quadriceps force causes great anterior tibial force during the early phase of a landing task. The purpose of the present study was to examine whether the quadriceps force induced great anterior tibial force during the early phase of a landing task.

METHODS

Fourteen young, healthy, female subjects performed a single-leg landing task. Muscle force and anterior tibial force were estimated from motion capture data and synchronized force data from the force plate. One-way repeated measures analysis of variance and the post hoc Bonferroni test were conducted to compare the peak time of the vertical ground reaction force, quadriceps force and anterior tibial force during the single-leg landing. In addition, we examined the contribution of vertical and posterior ground reaction force, knee flexion angle and moment to peak quadriceps force using multiple linear regression.

RESULTS

The peak times of the estimated quadriceps force (96.0 ± 23.0 ms) and anterior tibial force (111.9 ± 18.9 ms) were significantly later than that of the vertical ground reaction force (63.5 ± 6.8 ms) during the single-leg landing. The peak quadriceps force was positively correlated with the peak anterior tibial force (R = 0.953, P < 0.001). Multiple linear regression analysis showed that the peak knee flexion moment contributed significantly to the peak quadriceps force (R ² = 0.778, P < 0.001).

CONCLUSION

The peak times of the quadriceps force and the anterior tibial force were obviously later than that of the vertical ground reaction force for the female athletes during successful single-leg landings. Studies have reported that the peak time of the vertical ground reaction force was close to the time of anterior cruciate ligament (ACL) disruption in ACL injury cases. It is possible that early contraction of the quadriceps during landing might induce ACL disruption as a result of excessive anterior tibial force in unanticipated situations in ACL injury cases.

Knee Abduction Affects Greater Magnitude of Change in ACL and MCL Strains Than Matched Internal Tibial Rotation In Vitro

BACKGROUND

Anterior cruciate ligament (ACL) injures incur over USD 2 billion in annual medical costs and prevention has become a topic of interest in biomechanics. However, literature conflicts persist over how knee rotations contribute to ACL strain and ligament injury. To maximize the efficacy of ACL injury prevention, the effects of underlying mechanics need to be better understood.

QUESTIONS/PURPOSES

We applied robotically controlled, in vivo-derived kinematic stimuli to the knee to assess ligament biomechanics in a cadaver model. We asked: (1) Does the application of abduction rotation increase ACL and medial collateral ligament (MCL) strain relative to the normal condition? (2) Does the application of internal tibial rotation impact ACL strain relative to the neutral condition? (3) Does combined abduction and internal tibial rotation increase ligament strain more than either individual contribution?

METHODS

A six-degree-of-freedom robotic manipulator was used to position 17 cadaveric specimens free from knee pathology outside of low-grade osteoarthritis (age, 47 ± 8 years; 13 males, four females) into orientations that mimic initial contact recorded from in vivo male and female drop vertical jump and sidestep cutting activities. Four-degree rotational perturbations were applied in both directions from the neutral alignment position (creating an 8° range) for each frontal, transverse, and combined planes while ACL and MCL strains were continuously recorded with DVRT strain gauges implanted directly on each ligament. Analysis of variance models with least significant difference post hoc analysis were used to assess differences in ligament strain and joint loading between sex, ligament condition, or motion task and rotation type.

RESULTS

For the female drop vertical jump simulation in the intact knee, isolated abduction and combined abduction/internal rotational stimuli produced the greatest change in strain from the neutral position as compared with all other stimuli within the ACL (1.5% ± 1.0%, p ≤ 0.035; 1.8% ± 1.3%, p ≤ 0.005) and MCL (1.8% ± 1.0%, p < 0.001; 1.6% ± 1.3%, p < 0.001) compared with all other applied stimuli. There were no differences in mean peak ACL strain between any rotational stimuli (largest mean difference = 2.0%; 95% confidence interval [CI], -0.9% to 5.0%; p = 0.070). These trends were consistent for all four simulated tasks. Peak ACL strain in the intact knee was larger than peak MCL strain for all applied rotational stimuli in the drop vertical jump simulations (smallest mean difference = 2.1%; 95% CI, -0.4% to 4.5%; p = 0.047).

CONCLUSIONS

Kinematically constrained cadaveric knee models using peak strain as an outcome variable require greater than 4° rotational perturbations to elicit changes in intraarticular ligaments.

CLINICAL RELEVANCE

Because combined rotations and isolated abduction produced greater change in strain relative to the neutral position for the ACL and MCL than any other rotational stimuli in this cadaver study, hypotheses for in vivo investigations aimed toward injury prevention that focuses on the reduction of frontal plane knee motion should be considered. Furthermore, reduced strain in the MCL versus the ACL may help explain why only 30% of ACL ruptures exhibit concomitant MCL injuries.

Structural and Anatomic Restoration of the Anterior Cruciate Ligament Is Associated With Less Cartilage Damage 1 Year After Surgery: Healing Ligament Properties Affect Cartilage Damage

BACKGROUND

Abnormal joint motion has been linked to joint arthrosis after anterior cruciate ligament (ACL) reconstruction. However, the relationships between the graft properties (ie, structural and anatomic) and extent of posttraumatic osteoarthritis are not well defined.

HYPOTHESES

(1) The structural (tensile) and anatomic (area and alignment) properties of the reconstructed graft or repaired ACL correlate with the total cartilage lesion area 1 year after ACL surgery, and (2) side-to-side differences in anterior-posterior (AP) knee laxity correlate with the total cartilage lesion area 1 year postoperatively.

STUDY DESIGN

Controlled laboratory study.

METHODS

Sixteen minipigs underwent unilateral ACL transection and were randomly treated with ACL reconstruction or bridge-enhanced ACL repair. The tensile properties, cross-sectional area, and multiplanar alignment of the healing ACL or graft, AP knee laxity, and cartilage lesion areas were assessed 1 year after surgery.

RESULTS

In the reconstructed group, the normalized graft yield and maximum failure loads, cross-sectional area, sagittal and coronal elevation angles, and side-to-side differences in AP knee laxity at 60° of flexion were associated with the total cartilage lesion area 1 year after surgery (R² > 0.5, P < .04). In the repaired group, normalized ACL yield load, linear stiffness, cross-sectional area, and the sagittal and coronal elevation angles were associated with the total cartilage lesion area (R² > 0.5, P < .05). Smaller cartilage lesion areas were observed in the surgically treated knees when the structural and anatomic properties of the ligament or graft and AP laxity values were closer to those of the contralateral ACL-intact knee. Reconstructed grafts had a significantly larger normalized cross-sectional area and sagittal elevation angle (more vertical) when compared with repaired ACLs (P < .02).

CONCLUSION

The tensile properties, cross-sectional area, and multiplanar alignment of the healing ACLs or grafts and AP knee laxity in reconstructed knees were associated with the extent of tibiofemoral cartilage damage after ACL surgery.

CLINICAL RELEVANCE

These data highlight the need for novel ACL injury treatments that can restore the structural and anatomic properties of the torn ACL to those of the native ACL in an effort to minimize the risk of early-onset posttraumatic osteoarthritis.

The influence of connective tissue growth factor on rabbit ligament injury repair

Objectives

The injured anterior cruciate ligament (ACL) is thought to exhibit an impaired healing response, and attempts at surgical repair have not been successful. Connective tissue growth factor (CTGF) is reported to be associated with wound healing, probably through transforming growth factor beta 1 (TGF-β1).

Methods

A rabbit ACL injury model was used to study the effect of CTGF on ligament recovery. Quantitative real-time PCR (qRT-PCR) was performed for detection of changes in RNA levels of TGF-β1, type 1 collagen (COL1), type 2 collagen (COL2), SRY-related high mobility group-box gene9 (SOX9), tissue inhibitor of metalloproteinase-1 (TIMP-1) and matrix metallopeptidase 13 (MMP-13). Expression of related proteins was detected by Western blotting.

Results

The current study showed that CTGF could promote the recovery of an injured anterior cruciate ligament. It can upregulate mRNA and expression of TGF-β1, COL1, COL2, SOX9, and tissue inhibitor of TIMP-1, and downregulate mRNA and expression of MMP-13, suggesting that the curative effect of CTGF on injured rabbit ligaments is through regulation of these cellular factors.

Conclusions

This finding revealed the healing role of CTGF in injured tissues and provides new possibilities of treating injured tissues and wound healing by using CTGF.

Cite this article: X. Sun, W. Liu, G. Cheng, X. Qu, H. Bi, Z. Cao, Q. Yu. The influence of connective tissue growth factor on rabbit ligament injury repair. Bone Joint Res 2017;6:399–404. DOI: 10.1302/2046-3758.67.BJR.2016-0255.R1.

Effect of sagittal plane mechanics on ACL strain during jump landing

We read with great interest the article entitled, “Effect of Sagittal Plane Mechanics on ACL Strain During Jump Landing” by Bakker et al. We congratulate the authors for their complex study design that utilized the in sim approach that is designed to cross-correlate the complex results of in vivo, in vitro, and in silico research approaches. The published study adds information in regards to potential models of the mechanisms of ACL injury to the body of literature.

Novel mechanical impact simulator designed to generate clinically relevant anterior cruciate ligament ruptures

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.

The influence of connective tissue growth factor on rabbit ligament injury repair

Objectives

The injured anterior cruciate ligament (ACL) is deemed to exhibit an impaired healing response and attempts at surgical repair have not been successful. Connective tissue growth factor (CTGF) is reported to be associated with wound healing, probably through transforming growth factor beta1 (TGF-β1).

Methods

A rabbit ACL injury model was used to study the effect of CTGF on ligament recovery. Quantitative real-time PCR was performed for detection of changes in RNA levels of TGF-β1, type 1 collagen (COL-I), type 2 collagen (COL-II), SRY-related high mobility group-box gene9 (Sox9), metalloproteinase-1 (TIMP-1) as well as matrix metallopeptidase 13 (MMP-13). And expression of related proteins was detected by western blotting.

Results

The current study showed that CTGF could promote the recovery of inured anterior cruciate ligament. It can up-regulate the mRNA and expression of TGF-β1, COL-I, COL-II, Sox9, as well as the tissue inhibitor of TIMP-1, and down-regulated the mRNA and expression of MMP-13, suggesting the curative effect of CTGF on injured rabbit ligament is through regulating these cellular factors.

Conclusion

This finding revealed the mechanism of CTFG’s healing role in injured tissues and provided new possibilities of treating injured tissues and wound healing by using CTFG.

Comparison of ACL Strain in the MCL-Deficient and MCL-Reconstructed Knee During Simulated Landing in a Cadaveric Model

BACKGROUND

Noncontact anterior cruciate ligament (ACL) injury after valgus landing has been reported and studied biomechanically. However, the role of the medial collateral ligament (MCL) in dissipating these forces has not been fully elucidated. Purpose/Hypothesis: The purpose of this study was to investigate the role that the MCL plays in ACL strain during simulated landing. The hypothesis was that ACL strain would increase significantly in MCL-incompetent knees compared with the native knee and that reconstructing the MCL would return the values to those of the intact knee.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight fresh-frozen human cadaveric knees were used in this study. A materials testing machine applied a force of 2× body weight over 60 milliseconds to simulate landing after a jump. The knees were tested in 12 loading conditions, consisting of full extension or 15° of flexion combined with 7° of valgus or neutral alignment while the tibia was in external rotation, neutral rotation, or internal rotation. This test procedure was repeated on each specimen with the MCL transected and reconstructed. The superficial and deep MCL was transected along with the posterior oblique ligament, which was thought to simulate a worst case scenario. The MCL was reconstructed by use of semitendinosus and gracilis tendon grafts.

RESULTS

During internal rotation at 0° of flexion and 0° of valgus, both the intact ( P = .005) and the reconstructed ( P = .004) MCL states placed significantly lower strain on the ACL than did the transected MCL. The reconstructed MCL state at 0° of flexion and 7° of valgus ( P = .049) along with 15° of flexion and 0° of valgus ( P = .020) also placed significantly lower strain on the ACL than did the transected MCL. For external rotation testing at 0° of flexion and 7° of valgus, the reconstructed MCL state placed significantly lower strain on the ACL than did the transected MCL ( P = .039). Finally, during neutral rotation, the ACL strain at 0° of valgus and 0° of flexion, and at 7° of valgus and 0° of flexion was significantly lower for the MCL-intact groups ( P < .028) and MCL-reconstructed groups ( P < .016) than the MCL-transected groups.

CONCLUSION

The current findings demonstrate that during valgus landing, a knee with an incompetent MCL puts the ACL under increased strain. These values are highest in full extension with the tibia in internal and neutral rotation. This increased strain can be reduced to baseline levels with reconstruction.

CLINICAL RELEVANCE

A knee with an incompetent MCL puts the ACL under increased strain. Once the MCL has healed in an elongated manner, MCL reconstruction should be considered.

How Anterior Cruciate Ligament Injury was averted during Knee Collapse in a NBA Point Guard

Non-contact anterior cruciate ligament (ACL) injuries occur with rapid decelerations and pivoting. A recent injury to a high-level National Basketball Association (NBA) player demonstrated neuromuscular control and injury-sparing mechanisms that resulted in only minor ligament injury to the medial collateral ligament. We analyzed biomechanical mechanisms via publically available orthogonal 2-D video to demonstrate how this potential ACL injury was averted. Analysis of the knee injury mechanism demonstrated that the NBA player experienced low ground reaction force, high sagittal plane flexion, and maintenance of frontal plane stability with neuromuscular control. The outcome of these factors inhibited dynamic valgus collapse of the knee throughout the fall, avoiding ACL injury - a potentially career-altering injury. Many athletes, professional and recreational, will be subjected to similar mechanisms of injury and will have improved outcomes if they can successfully utilize preventive strategies of neuromuscular control to limit injury mechanisms.

Robotic simulation of identical athletic-task kinematics on cadaveric limbs exhibits a lack of differences in knee mechanics between contralateral pairs

Limb asymmetry is a known factor for increased ACL injury risk. These asymmetries are normally observed during in vivo testing. Prior studies have developed in vitro testing methodologies driven by in vivo kinematics to investigate knee mechanics relative to ACL injury. The objective of this study was to determine if mechanical side-to-side asymmetries persist in contralateral pairs during in vitro simulation testing. In vivo kinematics were recorded for male and female drop vertical jump and sidestep cutting tasks. The recorded kinematics were used to robotically simulate the motions on 7 contralateral pairs of cadaveric lower extremities specimens. ACL and MCL force, torque, and strains were recorded and analyzed for differences between contralateral pairs. There was a general lack of mechanical differences between limb sides. Adduction peak torque for the male sidestep cut movement was significantly different between limb sides (p=0.04). However, this is consistent with ACL injury mechanics in that movement in the frontal plane (abduction/adduction) increases injury risk and it is possible loading differences in this plane may have resulted from tolerances within the setup process. The findings of this study indicate that contralateral knee joints were representative of each other during biomechanical in vitro tests. In future cadaveric robotic simulations, contralateral limbs can be used interchangeably. In addition, direct comparisons of the structural behaviors of isolated conditions for contralateral knee joints can be performed.

Restricted Hip Rotation Is Correlated With an Increased Risk for Anterior Cruciate Ligament Injury

PURPOSE

The primary purpose was to compare ipsilateral hip internal rotation (IR) in male and female athletes with or without an anterior cruciate ligament (ACL) tear. A secondary purpose was to compare radiographic markers of femoroacetabular impingement (FAI) in patients with or without an ACL tear.

METHODS

In this prospective case-control study, based on a power analysis, a convenience sample of 25 ACL-injured and 25 control patients matched by age and gender were examined over 14 months. The ACL injury group included preoperative patients 12-40 years old with an ACL rupture within the previous 3 months with no prior lower extremity injuries, ligamentous laxity, or arthralgias. Controls included patients presenting with an upper extremity complaint with no history of knee injury. In the outpatient clinic, hip axial rotation range of motion was measured with a goniometer on physical examination and hip radiographs were evaluated for morphologic variations consistent with FAI. Univariate analysis of variance was used to examine differences between groups.

RESULTS

Each group had 13 males and 12 females, average ages of 22.8 ± 7.2 years (ACL group) versus 24.5 ± 7.9 years (controls; P = .439). The average sum of hip rotation (internal plus external) in patients with an ACL tear was 60.3 ± 12.4° compared with 72.6 ± 17.2° in controls (P = .006). ACL-injured patients had decreased hip IR compared with controls, with respective mean measurements of 23.4 ± 7.6° versus 30.4 ± 10.4° (P = .009). For every 10° increase in hip IR, the odds of having an ACL tear decreased by a factor of 0.419 (P = .015).

CONCLUSIONS

Risk of ACL injury is associated with restricted hip IR, and as hip IR increases, the odds of having an ACL tear decreases. In addition, ACL injury is associated with FAI in a generalized population of male and female athletes, although causality cannot be determined and most ACL-injured patients do not exhibit hip complaints.

LEVEL OF EVIDENCE

Level II, prognostic, prospective cohort study.

The influence of muscle-tendon forces on ACL loading during jump landing: a systematic review

BACKGROUND

The goal of this review is to summarise and discuss the reported influence of muscle-tendon forces on anterior cruciate ligament (ACL) loading during the jump-landing task by means of biomechanical analyses of the healthy knee.

METHODS

A systematic review of the literature was conducted using different combinations of the terms "knee", "ligament", "load", "tension ", "length", "strain", "elongation" and "lengthening". 26 original articles (n=16 in vitro studies; n=10 in situ studies) were identified which complied with all inclusion/exclusion criteria.

RESULTS

No apparent trend was found between ACL loading and the ratio between hamstrings and quadriceps muscle-tendon forces prior to or during landing. Four in vitro studies reported reduced peak ACL strain if the quadriceps force was increased; while one in vitro study and one in situ study reported reduced ACL loading if the hamstrings force was increased. A meta-analysis of the reported results was not possible because of the heterogeneity of the confounding factors.

CONCLUSION

The reported results suggest that increased hip flexion during landing may help in reducing ACL strain by lengthening the hamstrings, and thus increasing its passive resistance to stretch. Furthermore, it appears that increased tensile stiffness of the quadriceps may help in stabilising the knee joint during landing, and thus protecting the passive soft-tissue structures from overloading.

LEVEL OF EVIDENCE

Ib.

Effect of sagittal plane mechanics on ACL strain during jump landing

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 < 0.05). 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. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1636-1644, 2016.

Strain Response of the Anterior Cruciate Ligament to Uniplanar and Multiplanar Loads During Simulated Landings: Implications for Injury Mechanism

BACKGROUND

Despite basic characterization of the loading factors that strain the anterior cruciate ligament (ACL), the interrelationship(s) and additive nature of these loads that occur during noncontact ACL injuries remain incompletely characterized.

HYPOTHESIS

In the presence of an impulsive axial compression, simulating vertical ground-reaction force during landing (1) both knee abduction and internal tibial rotation moments would result in increased peak ACL strain, and (2) a combined multiplanar loading condition, including both knee abduction and internal tibial rotation moments, would increase the peak ACL strain to levels greater than those under uniplanar loading modes alone.

STUDY DESIGN

Controlled laboratory study.

METHODS

A cadaveric model of landing was used to simulate dynamic landings during a jump in 17 cadaveric lower extremities (age, 45 ± 7 years; 9 female and 8 male). Peak ACL strain was measured in situ and characterized under impulsive axial compression and simulated muscle forces (baseline) followed by addition of anterior tibial shear, knee abduction, and internal tibial rotation loads in both uni- and multiplanar modes, simulating a broad range of landing conditions. The associations between knee rotational kinematics and peak ACL strain levels were further investigated to determine the potential noncontact injury mechanism.

RESULTS

Externally applied loads, under both uni- and multiplanar conditions, resulted in consistent increases in peak ACL strain compared with the baseline during simulated landings (by up to 3.5-fold; P ≤ .032). Combined multiplanar loading resulted in the greatest increases in peak ACL strain (P < .001). Degrees of knee abduction rotation (R(2) = 0.45; β = 0.42) and internal tibial rotation (R(2) = 0.32; β = 0.23) were both significantly correlated with peak ACL strain (P < .001). However, changes in knee abduction rotation had a significantly greater effect size on peak ACL strain levels than did internal tibial rotation (by ~2-fold; P < .001).

CONCLUSION

In the presence of impulsive axial compression, the combination of anterior tibial shear force, knee abduction, and internal tibial rotation moments significantly increases ACL strain, which could result in ACL failure. These findings support multiplanar knee valgus collapse as one the primary mechanisms of noncontact ACL injuries during landing.

CLINICAL RELEVANCE

Intervention programs that address multiple planes of loading may decrease the risk of ACL injury and the devastating consequences of posttraumatic knee osteoarthritis.