DOSE-DEPENDENT RESPONSE OF GAMMA-IRRADIATION ON MECHANICAL-PROPERTIESAND RELATED BIOCHEMICAL-COMPOSITION OF COAT BONE-PATELLAR TENDON-BONEALLOGRAFTS

We studied the effects of gamma irradiation on the dimensions, mechani cal and material properties, and mature hydroxypyridinium crosslink de nsity of collagen in goat patellar tendon-bone specimens. Left and rig ht patellar tendon-bone units were removed from 10 adult female goats and were bisected longitudinally. Each tendon half was frozen, and the n the left halves were exposed to 4, 6, or 8 Mrad (40,000, 60,000, or 80,000 Gy) of gamma irradiation. The contralateral tendon halves serve d as controls (no irradiation). Each specimen then was loaded to failu re in tension, and its soft-tissue midsubstance was processed to measu re collagen content and hydroxypyridinium crosslink density. Dose-depe ndent reductions in the mechanical properties were found, including 46 % (p < 0.01) and 18% (p < 0.05) reductions in maximum force and stiffn ess, respectively, at 4 Mrad. Similar reductions were noted in materia l properties, including 37% (p < 0.005) and 8% (p > 0.05) reductions i n maximum stress and modulus, respectively, at 4 Mrad. These results a re consistent with our previous report involving 2 and 3 Mrad (20,000 and 30,000 Gy) of exposure. We also found significant decreases in hyd roxypyridinium crosslink density with 6 Mrad of irradiation (p < 0.05) . However, since only one biomechanical parameter (modulus) correlated significantly with only one biochemical measure (hydroxypyridinium cr osslink density) (p < 0.05), other possible mechanisms also are being explored to more fully explain these dose-dependent changes.