The Biomechanical Effects of Low-Dose Irradiation on Bone-Patellar Tendon-Bone Allografts

Abstract

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.