Effect of Lateral Meniscal Root Tear on the Stability of the Anterior Cruciate Ligament–Deficient Knee

Background: Meniscal root tears are an increasingly recognized subset of meniscal injury. The menisci are critical secondary stabilizers of the anterior cruciate ligament (ACL). The kinematic effect of lateral meniscus posterior root tear in the setting of ACL injury is not known. Purpose/Hypothesis: The purpose of this study was to determine the effect of tear of the lateral meniscal root on stability of the ACL-deficient knee. The hypothesis was that disruption of the lateral meniscal root will further destabilize the ACL-deficient knee during a simulated pivot shift. Study Design: Controlled laboratory study. Methods: Pivot-shift testing of 8 fresh-frozen cadaveric knees was performed after attachment of photoreflective flags and preparation of CT scans. Each knee was mounted in a custom activity simulator and dynamically loaded from 15° to 90° of flexion with all the permutations of the following: iliotibial band force (50, 75, 100, 125, 150, and 175 N), internal rotation moments (1, 2, and 3 N·m), and valgus moments (5 and 7 N·m). In addition, anterior stability tests were performed by applying a 90-N anterior force to the tibia at flexion angles of 15°, 30°, 45°, 60°, and 90°. During each test, the anterior tibial translation and rotation of the tibia were measured with a high-resolution multiple infrared camera motion analysis system for the following 3 conditions: ACL-intact (ACL-I), ACL-deficient (ACL-D), and ACL-deficient/lateral meniscal posterior root avulsion (ACL-D/LMR-A). Results: A pivot-shift phenomenon was observed in the ACL-D and ACL-D/LMR-A conditions. The mean tibial translation of the lateral tibial condyle during the pivot-shift maneuver was 2.62 ± 0.53 mm for the ACL-I knees, 6.01 ± 0.51 mm for the ACL-D knees (P value vs intact: .0005), and 8.13 ± 0.75 mm for the ACL-D/LMR-A knees (P value vs intact: