This renewal is designed to test our governing hypothesis that gamma irradiation produces dose-dependent reductions in ligament allograft biomechanics, but that these reductions are more significant before surgery than 6 months after surgery. While allografts have certain advantages, surgeons remain concerned about how effectively methods like gamma irradiation sterlize the graft against viral contaminants such as HIV-1 and hepatitis. Several authors have estimated, for example, that dosage levels of 4 MRad or more might be needed to satisfactorily inactivate the HIV-1 virus in these grafts. Unfortunately, such high levels of gamma irradiation can compromise initial biomechanical properties of frozen allograft tissues and may have deleterious effects on the structures after surgery as well. Furthermore the treatment may also reduce the concentration of permanent, covalent hydroxypyridinium crosslinks [HP] which likely transmit tissue forces. In this grant, we test four hypotheses related to these potential structural and material alterations using goat patellar tendon-bone (PTB) allografts. HYPOTHESIS 1. Goat PTB allografts undergo significant, dose-dependent reductions in initial mechanical and material properties up to 8 Mirads of gamma irradiation. The reductions in material properties are associated with decreases in [HP]. HYPOTHESIS 2. Increasing gamma irradiation level significantly increases the knee's anterior motion limits by decreasing graft stiffness immediately after surgery. These changes are caused, in part, by unfolding of the irradiated tissue substance and by increased motion at the graft's fixation sites. HYPOTHESIS 3. Four megarads of gamma irradiation produces no significant reductions in ACL allograft biomechanics 6 months postop. These studies should permit the mechanical dose-dependent curve for irradiation of ligament allograft tissues to be established and forum the basis for immunological, ultrastructural, and biochemical studies of grafted knees at various time intervals post surgery.