A biomechanical analysis of bone-patellar tendon-bone grafts after repeat freeze-thaw cycles in a cyclic loading model.

The purpose of this study was to examine the biomechanical effects of bone-patellar tendon-bone (BPTB) grafts subject to repeat freeze-thaw cycles in a cyclic loading model. We hypothesized that repeat freeze-thaw cycles have deleterious effects on the tensile properties of BPTB grafts. Thirty BPTB composite grafts were harvested from porcine knee specimens. Tendons were randomized into 3 groups: fresh, 1 freeze-thaw cycle (-80 degrees C), or 2 freeze-thaw cycles. The grafts were cyclically loaded to simulate the forces on the anterior cruciate ligament during walking and running, prior to single cycle load-to-failure testing. All tendon failures were mid-substance and occurred during the single cycle load-to-failure testing. There was no statistically significant difference in ultimate stress or strain between the groups. Repeat freeze-thaw cycles do not have deleterious effects on the tensile properties of BPTB grafts in a cyclic loading model. Potential influence on biologic graft healing or integration remains unknown.