Extrusion of medial and lateral meniscus before and after posterior root detachment

Despite contemporary surgical treatments of posterior meniscus root tears, there is a low rate of healing and an incidence of residual meniscus extrusion approaching 30%. Here, we characterized and compared the behavior of the medial and lateral meniscus in response to axial compression load and real-time dynamic motion using a cadaveric model. There were no differences in the amount of meniscus extrusion between the medial and lateral meniscus with a competent posterior root (0.338mm vs. 0.235mm; p-value = 0.181). However, posterior root detachment resulted in a consistently increased amount of meniscus extrusion for the medial meniscus compared to the lateral meniscus (2.233mm vs. 0.4705mm; p-value < 0.0001). Moreover, the medial and lateral menisci responded differently to the effects of knee flexion angle. Detachment of the posterior root of the medial meniscus resulted in an increase in extrusion at all angles of knee flexion, but was most pronounced (4.00mm ± 1.26mm) at 30-degrees of knee flexion. In contrast, the lateral meniscus only extruded (1.65mm ± 0.97mm) in full extension. Furthermore, only the medial meniscus extruded during dynamic flexion after posterior root detachment. These findings suggest that while meniscus extrusion occurs in both the medial and lateral meniscus, the functional consequences of extrusion are more significant for the medial meniscus than that of the lateral meniscus. Limiting the amount of meniscus extrusion after posterior root tear in response to static compressive forces and dynamic motion is necessary to recapitulate native meniscus function.