Sterilization of tendon allografts: A method to improve strength and stability after exposure to 50 kGy gamma radiation

Terminal sterilization of tendon allografts with high dose gamma irradiation has deleterious effects on tendon mechanical properties and stability after implantation. Our goal is to minimize these effects with radio protective methods. We previously showed that radio protection via combined crosslinking and free radical scavenging maintained initial mechanical properties of tendon allografts after irradiation at 50 kGy. This study further evaluates the tissue response and simulated mechanical degradation of tendons processed with radio protective treatment, which involves crosslinking in 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide followed by soaking in an ascorbate/riboflavin-5-phosphate solution. Control untreated and treated tendons were irradiated at 50 kGy and implanted in New Zealand White rabbit knees within the joint capsule for four and 8 weeks. Tendons were also exposed to cyclic loading to 20 N at one cycle per 12 s in a collagenase solution for 150 cycles, followed by tension to failure. Control irradiated tendons displayed increased degradation in vivo, and failed prematurely during cyclic processing at an average of 25 cycles. In contrast, radio protected irradiated tendons displayed greater stability following implantation over 8 weeks, and possessed strength at 59 % of native tendons and modulus equivalent to that of native tendons after cyclic loading in collagenase. These results suggest that radio protective treatment improves the strength and the stability of tendon allografts.