The effects of increased tension on healing medial collateral ligaments

Abstract

The effects of motion and increased levels of stress on the biomechanical, biochemical, and morphological properties of healing medial collateral ligaments were assessed in a rabbit model. In one group, the medial collateral ligament of the left hindlimb was transected and allowed to heal with cage activity for either 6 or 12 weeks. In another group, the transected ligaments were permitted to heal for 4 weeks and then were placed under increased stress by inserting a stainless steel pin perpendicularly underneath the healing medial collateral ligament. The animals were allowed cage activity for an additional 2 or 8 weeks. The varus-valgus joint laxity and the stress-strain properties of the medial collateral ligament substance were obtained. Further, the quan tity of total collagen, amount and ratio of the collagen cross-links, dihydroxylysinonorleucine and hydroxyly sinonorleucine, and the histologic appearance of the healing medial collateral ligaments were evaluated for all groups. At 6 weeks, knees with a transected medial collateral ligament were twice as lax as the controls. However, joints with the stainless steel tension pin had varus-valgus values approximately 1.5 times those of the controls. At 12 weeks, joints with increased stress were not statistically different from the controls. The group that had healing with increased stress for 12 weeks produced the highest stress for a given strain compared to any other group. Also, the total collagen levels and the ratio of dihydroxylysinonorleucine/hy droxylysinonorleucine were the closest to normal of any transected group. Finally, qualitative histologic improve ments were seen, including a more longitudinal arrange ment of collagen fibers and decreased cellularity.