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 x m), and internal-external rotation torque (4 N x m; all at 0 degrees and 30 degrees of flexion).

RESULTS

Anterior and posterior translation did not statistically increase with a partial or complete medial collateral ligament injury at 0 degrees and 30 degrees of flexion. In response to a 125 N anterior load, at 0 degrees , 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 degrees , 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 x m) at 30 degrees , 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 degrees , 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 degrees of flexion was significantly increased in the complete injury model (22.8 degrees ) versus the intact state (19.5 degrees ; 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 degrees 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.