Gamma Irradiated Soft Tissue Allografts are Biomechanically Equivalent to Aseptic, Non-Sterilized Tissues

Allograft safety is contingent on effective sterilization methods such as gamma irradiation. However, recent clinical studies have associated gamma irradiation with decreased graft strength and increased allograft failure rates, despite data that shows no deleterious effects to soft tissue biomechanics at gamma doses between 1.46 and 2.18 mRad. The objective of this study was to compare the biomechanical properties of anterior and posterior tibialis tendons and bone-patellar ligament-bone (BTB) allografts sterilized with gamma irradiation at a dose of 1.7-2.1 mRad to aseptically processed, non-irradiated tendons. Our hypothesis was that gamma irradiated tendons would be biomechanically equivalent to aseptic controls. Pairs of fresh-frozen tibialis tendons and bisected BTBs were either gamma sterilized or left untreated to serve as aseptically processed, non-sterilized controls. Each graft was cyclically loaded in tension for 2000 cycles at a rate of 2 Hz, allowed to relax for five minutes and then tested in tension to failure at 100% strain rate. Gamma irradiated BTBs exhibited structural (maximum load, maximum displacement, stiffness) and material (failure stress, failure strain, and elastic moduli and cyclic tendon elongation) properties that were not significantly different from non-sterilized controls. Gamma sterilized tibialis tendons were not significantly different from aseptic controls for the three structural properties and three of the four material properties, but did have lower cyclic elongation compared to controls. This difference suggests that gamma-treated tibialis tendons may be less susceptible to laxity than aseptic grafts. This study reinforces that tendon sterilization via gamma irradiation yields a safe allograft without comprising biomechanical function. The purpose of this study was to compare the biomechanical properties of tibialis tendons and BTBs sterilized with gamma irradiation to aseptic tendons. Introduction Gamma irradiation has an extensive history of use for sterilizing soft tissue allografts. Early research showing dose-dependent reductions in musculoskeletal tissue biomechanics at high gamma doses (≥ 3.0 mRad)1-3 has prompted tissue banks to employ lower doses that remain extremely efficient in deactivating microorganisms while minimizing tissue damage. Recent studies have shown that low dose gamma irradiation, loosely defined as approximately 1.5-2.0 mRad, does not alter the biomechanical properties of bone-patellar tendon-bone (BTB), tibialis, and semitendinosus tendon allografts4-5. Still, clinical studies reporting higher failure rates in ACL reconstructions using allografts, especially in younger patients6-8, have implicated gamma irradiation as a primary cause for failure without a full understanding of potential failure mechanisms9-10. This negative perception has spurred increased use of aseptic grafts to safeguard biomechanical integrity, but it comes at the risk of implanting a nonsterile graft. Further research is needed to support gamma irradiation use at appropriate doses that do not affect the graft’s biomechanical integrity.