Force measurements on the posterior oblique ligament and superficial medial collateral ligament proximal and distal divisions to applied loads.

BACKGROUND:
There is limited information regarding load responses of the posterior oblique and superficial medial collateral ligaments to applied loads.

HYPOTHESES:
The degree of knee flexion affects loads experienced by the posterior oblique ligament and both divisions of the superficial medial collateral ligament. The posterior oblique ligament provides significant resistance to valgus and internal rotation forces near knee extension. Different load responses are experienced by proximal and distal divisions of the superficial medial collateral ligament.

STUDY DESIGN:
Descriptive laboratory study.

METHODS:
Twenty-four nonpaired, fresh-frozen cadaveric knees were tested. Buckle transducers were applied to the proximal and distal divisions of the superficial medial collateral and posterior oblique ligaments. Applied loads at 0 degrees, 20 degrees, 30 degrees, 60 degrees, and 90 degrees of knee flexion consisted of 10 N m valgus loads, 5 N.m internal and external rotation torques, and 88 N anterior and posterior drawer loads.

RESULTS:
External rotation torques produced a significantly higher load response on the distal superficial medial collateral ligament than did internal rotation torques at all flexion angles with the largest difference at 90 degrees (96.6 vs 22.5 N). For an applied valgus load at 60 degrees of knee flexion, loads on the superficial medial collateral ligament were significantly higher in the distal division (103.5 N) than the proximal division (71.9 N). The valgus load response of the posterior oblique ligament at 0 degrees of flexion (19.1 N) was significantly higher than at 30 degrees (10.6 N), 60 degrees (7.8 N), and 90 degrees (6.8 N) of flexion. At 0 degrees of knee flexion, the load response to internal rotation on the posterior oblique ligament (45.8 N) was significantly larger than was the response on both divisions of the superficial medial collateral ligament (20 N for both divisions). At 90 degrees of flexion, the load response to internal rotation torques reciprocated between these structures with a significantly higher response in the distal superficial medial collateral ligament division (22.5 N) than the posterior oblique ligament (9.1 N).

CONCLUSION:
The superficial medial collateral ligament experienced the largest load response to applied valgus and external rotation torques; the posterior oblique ligament observed the highest load response to internal rotation near extension.

CLINICAL RELEVANCE:
This study provides new knowledge of the individual biomechanical function of the main medial knee structures in an intact knee and will assist in the interpretation of clinical knee motion testing and provide evidence for techniques involving repair or reconstruction of the posterior oblique ligament and both divisions of the superficial medial collateral ligament.