Structural properties of the primary medial knee ligaments.

BACKGROUND The structural properties of the individual components of the superficial medial collateral ligament (MCL), deep MCL, and posterior oblique ligament (POL) have not been studied in isolation. To define the necessary strength requirements for an anatomical medial knee reconstruction, knowledge of these structural properties is necessary. HYPOTHESIS The components of the superficial MCL, POL, and deep MCL have significantly different structural properties. STUDY DESIGN Controlled laboratory study. METHODS This study used 20 fresh-frozen nonpaired cadaveric knee specimens with a mean age of 54 years (range, 27 to 68 years). These knees provided 8 samples for each tested medial knee structure, which was individually isolated and loaded to failure at 20 mm per minute. Specifically tested were the superficial MCL with intact femoral and detached proximal tibial attachments, the superficial MCL with intact femoral and detached distal tibial attachments, the central arm of the POL, and the isolated deep MCL. Load was recorded as a function of displacement. Stiffness of the ligament at failure was calculated from these measurements. RESULTS The mean load at failure for the superficial MCL with the intact femoral and distal tibial attachments was 557 N. Mean load at failure was 88 N for the intact femoral and proximal tibial divisions of the superficial MCL, 256 N for the POL, and 101 N for the deep MCL. Stiffness of the ligaments just before failure was 63, 17, 38, and 27 N/mm, in the same order as above. CONCLUSION The proximal and distal tibial divisions of the superficial MCL, POL, and deep MCL produced loads of clinical importance. CLINICAL RELEVANCE Knowledge of the structural properties of these attachment sites will assist in reconstruction graft choices, fixation method choices, and overall operative treatment of medial knee injury.