The biomechanical effects of low-dose irradiation on bone-patellar tendon-bone allografts

Background: Despite evidence that low-dose irradiation of 2 Mrad (20 kGy) is not virucidal for patellar tendon allografts and reduces tissue strength, many tissue bank protocols include low-dose irradiation. Hypothesis: Maintaining tissue mechanical integrity may be particularly relevant toward accelerated rehabilitation of the injured knee, where the cyclic function of patellar tendon allografts is critical. Study Design: Controlled laboratory study. Methods: The cyclic and failure mechanical properties of paired bone-patellar tendon-bone allografts, with and without current low-dose irradiation of 20 kGy, were evaluated. Specimens were loaded from 50 N to 250 N for 1000 cycles at 0.5 Hz and subsequently loaded to failure at a strain rate of 100% per second. Results: After 1000 cycles, grafts elongated 27% more when irradiated than when not (4.4 +/- 1.5 mm vs; 3.4 +/- 1.0 mm; P = .03). Failure load averaged 1965 +/- 512 N for irradiated grafts and 2457 +/- 647 N for nonirradiated grafts (P = .007). Conclusions: The diminished strength of irradiated grafts may contribute to overt anterior cruciate ligament graft failure, and the increase in cyclic elongation may also be detrimental to graft function. Clinical Relevance: These results suggest that one should consider the use of nonirradiated allografts as an alternative to irradiated grafts in anterior cruciate ligament reconstruction.