Biomechanical Consequences of Lateral Meniscal Posterior Root Avulsions: Influence of the Meniscofemoral Ligaments and Anterior Cruciate Ligament on Tibiofemoral Contact Mechanics

OBJECTIVES: Lateral meniscal posterior root avulsions are commonly found with anterior cruciate ligament (ACL) tears. The purpose of this study was to investigate the biomechanical effects of lateral meniscal posterior root avulsions with and without intact meniscofemoral ligaments (MFLs), and with concurrent ACL tears, on lateral compartment contact mechanics. METHODS: A controlled laboratory study was performed using ten nonpaired fresh-frozen cadaveric knees. Tekscan sensors were used to simultaneously measure contact area and pressure (Figure) in the lateral and medial compartments. Specimens were tested with 6 conditions (1: Intact; 2: Lateral meniscal posterior root avulsion; 3: Root avulsion and torn MFL; 4: Condition 3 with ACL tear; 5: Condition 4 with ACL reconstruction; 6: ACL reconstruction with root repair) at 5 flexion angles (0, 30, 45, 60, and 90 degrees), under a 1000 N axial load. RESULTS: Compared to the intact state, condition 2 did not significantly alter lateral compartment contact area or pressure (p < 0.05). A significant decrease in contact area and increase in mean contact pressure occurred in condition 3. Conditions 4 and 5 (ACL tear and reconstruction of the ACL, respectively, both with deficient MFLs and lateral meniscal posterior root avulsion) also produced significantly lower contact areas than the intact condition (p < 0.05), and were not substantially different than Condition 3 (Figure). Changes in contact mechanics tended to be greater at increased flexion angles; for condition 3 at 0 and 90 degrees, contact area decreased 37% and 52% (95% CI [21,53] and [39,66], respectively) and mean contact pressure increased 55% and 87% (95% CI [33,76] and [59,114], respectively). Condition 6 (root repair with ACL reconstruction) was not significantly different from the intact state (p < 0.05). CONCLUSION: The meniscofemoral ligaments protect the lateral compartment from changes in contact mechanics in the setting of a lateral meniscal posterior root avulsion, whereas combined lateral meniscal root avulsion and deficient meniscofemoral ligaments leads to substantial changes. Concurrent ACL reconstruction and root repair restores contact area and mean contact pressure to the intact state.