Medial collateral ligament injuries and subsequent load on the anterior cruciate ligament: A biomechanical evaluation in a cadaveric model

Background: Numerous studies have documented the effect of complete medial collateral ligament injury on anterior cruciate ligament loads; few have addressed how partial medial collateral ligament disruption affects knee kinematics. Purpose: To determine knee kinematics and subsequent change in anterior cruciate ligament load in a partial and complete medial collateral ligament injury model. Study Design: Controlled laboratory study. Methods: Ten human cadaveric knees were sequentially tested by a robot with the medial collateral ligament intact, in a partial injury model, and in a complete injury model with a universal force-moment sensor measuring system. Tibial translation, rotation, and anterior cruciate ligament load were measured under 3 conditions: anterior load (125 N), valgus load (10 N'm), and internal-external rotation torque (4 N'm; all at 0° and 30° of flexion). Results: Anterior and posterior translation did not statistically increase with a partial or complete medial collateral ligament injury at 0° and 30° of flexion. In response to a 125 N anterior load, at 0°, the anterior cruciate ligament load increased 8.7% (from 99.5 to 108.2 N; P = .006) in the partial injury and 18.3% (117.7 N; P < .001) in the complete injury; at 30°, anterior cruciate ligament load was increased 12.3% (from 101.7 to 114.2 N; P = .001) in the partial injury and 20.6% (122.7 N; P < .001) in the complete injury. In response to valgus torque (10 N'm) at 30°, anterior cruciate ligament load was increased 55.3% (30.4 to 47.2 N; P = .044) in the partial injury model and 185% (86.8 N; P = .001) in the complete injury model. In response to internal rotation torque (4 N'm) at 30°, anterior cruciate ligament load was increased 29.3% (27.6 to 35.7 N; P = .001) in the partial injury model and 65.2% (45.6 N; P < .001) in the complete injury model. The amount of internal rotation at 30° of flexion was significantly increased in the complete injury model 22.8°) versus the intact state (19.5°; P < .001). Conclusion: Partial and complete medial collateral ligament tears significantly increased the load on the anterior cruciate ligament. In a partial tear, the resultant load on the anterior cruciate ligament was increased at 30° of flexion and with valgus load and internal rotation torque. Clinical Relevance: Patients may need to be protected from valgus and internal rotation forces after anterior cruciate ligament reconstruction in the setting of a concomitant partial medial collateral ligament tear. This information may help clinicians understand the importance of partial injuries of the medial collateral ligament with a combined anterior cruciate ligament injury complex.