Effect of gamma irradiation on remodeling process of tendon allograft

Freeze-dried tendon allograft sterilized with gamma irradiation could be a reasonable option for ligament substitute. In the current study, the effects of freezing or freeze-drying followed by gamma irradiation on remodeling were analyzed biomechanically in a rat patellar tendon transplantation model at the time of harvest and during a 24-week healing period. The grafts were divided into four groups: fresh-freezing, freeze-drying, fresh-freezing followed by gamma irradiation, and freeze-drying followed by gamma irradiation. Before transplantation, the fresh-frozen grafts and the freeze-dried grafts showed significantly greater tensile strength than the gamma-irradiated grafts. However, at 4 weeks, the tensile strength of each group decreased to the equivalent level, which was approximately 20% of the tensile strength at Time 0, then increased gradually with time. At 24 weeks, the mean tensile strength of each transplanted graft achieved as much as 50% of the tensile strength at Time 0. The change in the tangent modulus with time followed a similar pattern as changes in the tensile strength. This study assumed that the extraarticular tendon transfer model was suitable for evaluating anterior cruciate ligament graft healing. These data suggest that the freeze-dried tendon allografts sterilized by gamma radiation could be a suitable substitute for anterior cruciate ligament reconstruction, if care is taken to protect the graft during the early stage after transplantation (< 4 weeks).