Biomechanical Effects of Peripheral Stabilization for the Extruded Medial Meniscus and its Effect on Tibiofemoral Contact Biomechanics

Abstract

Objectives: To quantitatively evaluate the biomechanical effects of a novel peripheral stabilization technique for the treatment of posterior medial meniscus root (PMMR) avulsions and to identify an optimal diagnostic position to assess for the presence of meniscal extrusion. Methods: Meniscal extrusion and tibiofemoral contact mechanics were measured using 3D digitization and pressure sensors, respectively, in ten nonpaired, human cadaver knees. The PMMR of each knee was tested under 6 states: (1) intact; (2) complete root detachment; (3) anatomic transtibial pull-out root repair; (4) anatomic transtibial pull-out repair with peripheral stabilization; (5) nonanatomic transtibial pull-out repair; and (6) nonanatomic transtibial pull-out repair with peripheral stabilization, with randomization of the order of conditions 3 & 4, and 5 & 6. The testing protocol loaded knees with a 1000 N axial compressive force at four flexion angles (0°, 30°, 60°, 90°) in each state. Meniscal extrusion was recorded at 0° and 90° in both loaded and unloaded states at three locations along the peripheral rim of the medial tibial plateau. Degree of meniscal extrusion was defined as the radial displacement of the medial meniscus from three corresponding points on the posteromedial edge of the tibial plateau: (1) posterior border of MCL; (2) posteromedial capsule midway between the MCL and posterior root; and (3) the direct posterior capsule. Peak contact pressure, contact area, and total contact pressure were also recorded for all states at all flexion angles. Results: Statistical analysis investigated the independent effects of flexion, state, and loading using three, distinct two-factor models. In unloaded knees in full extension, the highest degree of meniscal extrusion was observed at the posterior border of the MCL across all repair testing states (p < 0.001). At full extension, loaded knees exhibited significantly higher extrusion in comparison to unloaded across all knee states at the MCL position (mean 1.1 mm, 95% CI [0.8, 1.4], p <0.001). Significantly more extrusion was observed at 90° of flexion (mean 0.7 mm, 95% CI [0.36, 1.1], p < 0.001). In loaded knees at 90° of flexion, all repair states had significantly lower extrusion than the root tear state (all p <0.05). Only anatomic repair with peripheral stabilization had significantly lower extrusion than both nonanatomic repairs with or without peripheral stabilization (both p < 0.01). Differences in the contact mechanics between repair techniques were most notable at higher flexion angles, demonstrating significantly higher average and peak contact pressures for non-anatomic repair variations when compared to anatomic repairs with and without peripheral stabilization (all p <0.05). Root tear states were significantly higher than intact states for all comparisons except for peak pressure at 0° of flexion (all p < 0.01). Conclusion: Anatomic and anatomic with peripheral suture repair techniques best restore contact mechanics of the knee. In current clinical scenarios where knees are unloaded and imaged in full extension, extrusion is best measured in the coronal plane at the posterior border of the MCL. However, this is likely a “best-case” scenario, as this study has shown that the degree of extrusion increases as the knee is loaded and flexed to 90°. When only a non-anatomic repair can be performed the addition of this peripheral stabilization technique may be beneficial for patients in reducing pathologic extrusion of the meniscus. [Table: see text]