Anterior cruciate ligament (ACL) tears are regularly accompanied by damage to the meniscus, a known secondary stabilizer of the knee. Although it is well established that ACL deficiency leads to excessive anterior and rotational tibial movement, the in vivo effects of concomitant meniscal injuries on knee kinematics and kinetics are not yet clearly elucidated, particularly during dynamic activities, as prior publications have largely focused on isolated ACL tears. The purpose of this study is to systematically review the available literature on the effects of meniscal tears in ACL-deficient knees compared to isolated ACL tears on in vivo knee biomechanics.
Databases were queried for level I-IV studies reporting cross-sectional data meeting the following criteria: in vivo studies of gait or motion analysis; both isolated ACL tear cohorts and cohorts with concomitant meniscal tears; kinematics and/or kinetics outcome measures. Demographic data, method of motion analysis employed, tasks performed, and measured outcomes were extracted. Qualitative differences between concomitant meniscus tear and isolated ACL cohorts versus healthy control were summarized. Standardized mean differences between the pooled results of meniscus and isolated ACL cohorts using a random effects model were calculated whenever common outcomes were reported.
Seven studies were included, with 14 meniscus tear cohorts and a total sample of 141 knees. Five studies assessed gait, while stair ascent was the focus of two studies. Two studies used dynamic fluoroscopy and five studies used a combination of infra-red cameras and reflective markers for their analyses. There was considerable variability in the outcomes reported across studies, precluding metanalysis of most variables. All studies reported biomechanical alterations of meniscus cohorts and isolated ACL cohorts versus healthy control groups. There was qualitative evidence (4 studies) that relative to isolated ACL tears, concomitant meniscus damage results in altered knee rotation angles and moments. Standardized mean differences showed no statistical significance for range of flexion-extension (7 cohorts), internal-external rotation (4 cohorts) or adduction-abduction (4 cohorts), and for peak flexion moment (4 cohorts) or peak internal rotation moment (4 cohorts) during gait.
Qualitative evidence suggests that concomitant meniscus tears in the ACL-deficient knee result in an alteration of knee axial plane kinematics beyond that of an isolated ACL tear. However, upon meta-analysis, no statistically significant standard mean differences from the pooled sample were observed, suggesting that analyses of more demanding tasks beyond simple gait might be needed to accurately reflect the biomechanical impairment caused by a concomitant meniscus tear.