Medial collateral knee ligament healing. Combined medial collateral and anterior cruciate ligament injuries studied in rabbits

We examined the histological appearance and biochemical properties of the healing medial collateral ligament (MCL) of a rabbit knee after combined MCL and anterior cruciate ligament (ACL) injury treated with ACL reconstruction and with or without MCL repair. By so doing, we hoped to understand better our previous biomechanical observations and possibly learn where to focus future investigation into improving the quality of the healing MCL. Ligaments were examined at 6 and 12 weeks of healing. We found healing of all ligaments with hypercellularity and fibroblast elongation along the axis of loading, as expected. Unexpected, however, was the finding of multiple osteophytes in both the repaired and nonrepaired specimens at the medial borders of the joint and at the MCL insertions. These were felt to affect possibly the biomechanics of the MCL by causing stress risers at the point where they undermine the ligament. Biochemically, we demonstrated a correlation between collagen content and hydroxypyridinium crosslinks and modulus of elasticity. While this implies that the modulus is dependent on collagen content and hydroxypyridinium crosslink density, modulus is also probably dependent on other factors such as collagen organization, type and internal structure. Overall, the detailed characterization and correlation between the histological, biochemical, and biomechanical properties of the healing MCL in the severe knee injury model provide insight into the functional behavior of the healing MCL.