THE EFFECTS OF 4 MRAD OF GAMMA-IRRADIATION ON THE INITIAL MECHANICAL-PROPERTIES OF BONE PATELLAR TENDON BONE-GRAFTS

Pairs of frozen human patellar tendon-bone (PTB) ligament allografts w ere exposed to either 0 or 4 Mrad of gamma irradiation sterilization, the latter value based on recent reports suggesting higher dosage leve ls for adequate sterilization against the human immunodeficiency virus . All specimens were subjected to three levels of loading: lower funct ional loads, higher functional loads, and failure. Lower functional lo ads were simulated by performing in vitro static and cyclic creep test s, similar to loads that the surgeon and patient would apply before an d after implantation, respectively. Higher functional loads, simulatin g moderate activities of daily living, were represented by the slope o f the linear portion of the force-elongation curve or linear stiffness . Failure or trauma was then simulated by failing the grafts in tensio n at a high strain rate. We found that the irradiation treatment short ened the tendon by only 0.6 mm, which was nevertheless statistically s ignificant (p < 0.01). By contrast, 4 Mrad did not significantly alter either static or cyclic creep (p > 0.05) at lower functional loads. I nstead, irradiation produced the greatest changes during failure testi ng, reducing both the graft's linear stiffness by 12% (p < 0.025) and maximum force by 26% (p < 0.001). Although our data do not describe ho w an allograft might perform during the early healing and later collag en-remodelling phases, such in vitro studies remain important if we ar e to optimize allograft properties before arthroscopic anterior and po sterior cruciate ligament reconstruction.