Transplantation of the rabbit medial collateral ligament. I. Biomechanical evaluation of fresh autografts.

This investigation was designed to study the biomechanical recovery of a free bone-ligament-bone graft that was returned to its normal extra-articular position, with as little disturbance to its mechanical and biological environments as possible. Twenty-five adult New Zealand white rabbits had their right bone-medial collateral ligament (MCL)-bone complex removed completely and replaced immediately using internal fixation. Animals were allowed unrestricted cage activity before sacrifice in groups of five at intervals of 3, 6, 12, 24, and 48 weeks posttransplantation. Contralateral legs served as internal controls and a separate series of normal animals served as external controls. All MCLs were tested biomechanically using a detailed testing protocol. Results showed early deterioration of 20-35% in autograft complex structural behavior, with weakening of both ligament substance and insertions. Viscoelastic behavior of these ligaments was also affected, showing increases in the amount of both cyclic load-relaxation and static load-relaxation at early healing intervals. These properties were statistically indistinguishable, however, from controls at 48 weeks. Failure behavior of autografts was even better preserved, reaching a low of 65% of control values at 24 weeks and recovering to within 10% of controls at 48 weeks. These results, plus the major changes in failure modes that occurred over that duration, suggest that autograft incorporation is a slow but dynamic process. These results further suggest that at least some connective tissue autografts, when placed under, as yet undefined, "proper biological and mechanical conditions," can retain and recover a number of biomechanical properties over a period of 1 year. The longer-term fate of these autografts and the exact nature of their similarities or differences from other graft alternatives (e.g., tendon for ligament), however, is unknown.