Journal of Orthopaedic Surgery

Christina R. Allen, Eric K. Wong, Glen A. Livesay, Masataka Sakane, Freddie H. Fu, S. L-Y. Woo


There is am increased incidence of meniscal tears in the chronically ACL-deficient knee, particularly in the medial meniscus, as it performs an important function in limiting anterior tibial translation. In this study, we evaluated the role which the medial meniscus plays in stabilizing the ACL-deficient knee. We hypothesized that the resultant force in the medial meniscus is significantly elevated in the ACL-deficient knee. To test this hypothesis, we employed a robotic/universal force-moment sensor (UFS) testing system to determine the increases in the resultant force in the human medial meniscus following ACL transection in response to an anterior tibial load. We also measured changes in kinematics of the knee in multiple-DOF following medial menisecectomy in the ACL-deficient knee.

In response to an isolated 134 N anterior tibial load, there were significant increases in the resultant force in the medial meniscus of the ACL-deficient knee, when compared to those in the intact knee, at all degrees of knee flexion tested. The average resultant force in the medial meniscus increased by a minimum of 10.1 N (52%) at full knee extension, to a maximum of 50.2 N (197%) at 60° of knee flexion. Medial meniscectomy in the ACL-deficient knee also caused a significant increase in anterior tibial translation, ranging from an increase of 2.2 mm at full knee extension, to 5.8 mm at 60° of knee flexion. Conversely, coupled internal tibial rotation in response to an 134 N anterior tibial load decreased significantly, ranging from a decrease of 2.5° at 15° of knee flexion, to 4.7° at 60° flexion.

Our data confirm the hypothesis that the resultant force in the medial meniscus is significantly greater in the ACL-deficient knee compared to the ACL-intact knee when the knee is subjected to anterior tibial loads. This indicates an increased demand on the medial meniscus in the ACL-deficient knee relative to the intact knee resisting anterior tibial loads, suggesting a mechanism for the increased incidence of medial meniscal tears observed in chronically ACL-deficient patients. The large changes in knee kinematics due to medial meniscectomy in the ACL-deficient knee confirm the important role which the medial meniscus plays in controlling knee stability. These finding suggest that a further indication for performing ACL reconstruction may be the reduction of resultant force in the meniscus with the goal of preserving meniscal integrity.