Combined Ramp Lesion and Lateral Meniscus Root Tear Increase Rotational and Translational Instability in an Anterior Cruciate Ligament‐Deficient Knee: A Cadaveric Study

PURPOSE: To evaluate knee instability associated with combined ramp lesion and lateral meniscus posterior root tear (LMRT) in an anterior cruciate ligament (ACL)-deficient knee (the new terrible triad). METHODS: Ten cadaveric knees were tested biomechanically. Internal rotation (IR), external rotation, and anterior tibial translation (ATT) were measured across 5 experimental conditions: intact, ACL-deficient, ACL-deficient with LMRT, ACL-deficient with ramp lesion, and ACL-deficient with combined LMRT and ramp lesion. Measurements were taken at knee flexion angles of 0°, 15°, 30°, 60°, and 90° under 2 Nm rotational torque and 88 N anterior tibial load. IR and ATT were also measured during a simulated pivot-shift maneuver at 0°, 15°, and 30° flexion. RESULTS: In ACL-deficient knee with combined ramp lesion and LMRT, IR was significantly increased compared with the intact, ACL-deficient, and ACL-deficient + LMRT at 0°, 15°, and 30° flexion. External rotation was significantly greater in ACL-deficient + LMRT + ramp lesion across all flexion angles. ATT was significantly higher in ACL-deficient + LMRT + ramp lesion at 30°, 60°, and 90° flexion. During the pivot-shift test, IR in ACL-deficient + LMRT + ramp lesion was significantly greater than in intact and ACL-deficient at full extension and greater than in the ACL-deficient + LMRT and ACL-deficient + ramp lesion at 30°. Similarly, pivot-shift ATT in ACL-deficient + LMRT + ramp lesion was significantly greater than in intact and ACL-deficient at full extension and greater than in intact at 30°. CONCLUSIONS: In this time-zero cadaveric study, an ACL-deficient knee with combined LMRT and ramp lesion showed significantly greater anterior and rotational instability than ACL deficiency alone or ACL deficiency with either an isolated ramp lesion or an isolated LMRT. CLINICAL RELEVANCE: These findings provide biomechanical insight into how combined ramp lesion and LMRT can exacerbate rotational instability in ACL-deficient knees at time zero (cadaveric study).