Knee Ligament Moment Arms Scale with Epicondylar Width and might Contribute to Ligament Injuries in Females.

Introduction: Females are prone to knee ligament injuries compared to males. Moment arms describe the mechanical advantage of ligaments to stabilise the knee from injurious moments. Compared to males of the same stature, females have a smaller femoral epicondylar width, which we hypothesised would reduce their knee joint ligament moment arms in the frontal plane.

Methods: To calculate varus-valgus ligament moment arms, we created 26 patient-specific finite element models (17F; 9 M) and simulated an axial load of half body weight. Tibial cartilage contact pressures were obtained and used to define the medial and lateral peak contact pressure, which were assumed to be the point of rotation in the frontal plane. The varus and valgus moment arms of the anterior cruciate (ACL) and the medial (MCL) and lateral collateral ligaments (LCL) were calculated as the perpendicular distance between the point of peak contact pressure and the centroid of each ligament. Multiple linear regression models with sex, height, and epicondylar width as independent variables were produced.

Results: Females had smaller varus-valgus ligament moment arms compared to males, with a mean difference of 7 to 9 mm observed by the MCL and LCL about the lateral and medial contact points, respectively (~12% smaller, p < 0.001). The female cohort exhibited ACL moment arms about the medial and lateral contact points that were ~ 4 mm less than the male cohort (p < 0.05). Correlations between varus-valgus ligament moment arm and epicondylar width were found for all three ligaments using either the medial or lateral points of peak contact pressure.

Conclusions: These findings support our hypothesis that females have smaller varus-valgus ligament moment arms compared to males, which could contribute to the higher rate of female ligament injuries compared to males.