Injury location affects ligament healing: A morphologic and mechanical study of the healing rabbit medial collateral ligament

Based on the heterogeneity of the rabbit medial collateral ligament (MCL) along its length, we tested the hypothesis that injury location would affect its healing response. The right MCL of 80 skeletally mature New Zealand white rabbits was sectioned adjacent to bone at the femoral end (40 rabbits) or the tibial end (40 rabbits) and reapposed with sutures. Animals were killed after 3, 6, 14, or 40 weeks of healing to examine wounds histologically (2 rabbits per healing interval) and mechanically (8 rabbits per healing interval). Results of the mechanical tests were compared to midsubstance MCL repairs (24 rabbits) and to uninjured normal MCLs (20 rabbits). The morphology of the near-insertion repairs was characterized by abnormal callus-like formation and patchy bone resorption, particularly at the tibial insertion. Mechanically, insertional injuries remodeled towards normal MCL low-load, viscoelastic and failure properties more slowly than midsubstance injuries at the early healing intervals. After 40 weeks of healing, few injury-specific differences persisted. All injured ligaments had ultimate strengths 15-35 percent short of normal at 40 weeks and the femo-rally-injured ligaments were weaker than normal at this time. These results suggest that rabbit MCLs, injured near either end, heal more slowly that those injured in their midsubstance and develop abnormal insertion morphology.