The Biomechanical Effects of 1.0 to 1.2 Mrad of Gamma Irradiation on Human Bone–Patellar Tendon–Bone Allografts

Background: Recent data suggest that anterior cruciate ligament (ACL) reconstruction with irradiated allograft tissue may lead to increased failure rates. Hypothesis: Low-dose (1.0-1.2 Mrad) gamma irradiation does not significantly alter the preimplantation biomechanical properties of bone–patellar tendon–bone (BTB) allografts. Study Design: Controlled laboratory study. Methods: Cyclic and failure mechanical properties were evaluated for 20 paired central-third human BTB allografts, with and without 1.0 to 1.2 Mrad of gamma irradiation. Testing included cyclic loading at 0.5 Hz for 100 cycles from 50 to 200 N and failure testing at a strain rate of 10% per second. Results: Cyclic elongation did not change significantly (P = .151) with irradiation, increasing from a mean ± SD of 9.4 ± 2.1 mm to 11.3 ± 3.4 mm. Cyclic creep strain approached a significant increase with irradiation (1.3% ± 0.8% to 2.6% ± 1.5%; P = .076). Failure testing was not affected with irradiation with regard to maximum load (1680 ± 417 mm to 1494 ± 435 mm), maximum stress (40.8 ± 10.6 MPa to 37.5 ± 15.7 MPa), elongation (7.85 ± 1.35 mm to 8.67 ± 2.05 mm), or strain at maximum stress (0.158 ± 0.03 to 0.175 ± 0.03). Graft stiffness significantly decreased by 20% with irradiation (278 ± 67 N/mm to 221 ± 50 N/mm; P = .035). Conclusion: Low-dose (1.0-1.2 Mrad) gamma irradiation decreases BTB graft stiffness by 20%, but it does not affect other failure or cyclic parameters. Clinical Relevance: Aside from graft stiffness during load to failure testing, low-dose (1.0-1.2 Mrad) gamma irradiation of central-third human BTB allografts is not deleterious to preimplantation biomechanical properties.