Some effects of gamma irradiation on patellar tendon allografts

The purpose of this study was to investigate possible causes for altered mechanical properties of patellar tendon allografts, used for reconstructive surgery, after sterilization with 2.0 Mrads gamma irradiation. The tissues were analyzed using a Hydrothermal Isometric Tension (HIT) device in conjunction with biochemical assays of soluble collagen and electron microscopy to understand the action of this processing. Gamma irradiation was found to significantly lower the shrinkage temperature and tended to increase the rate of isometric tension development. While no significant alteration in the acetic acid solubility was noted, the processing doubled the solubility of collagen to pepsin. This could mean that the predominant effect of the gamma irradiation at this dose level is polypeptide chain scission. The stiffening of the HIT curve may suggest some minor cross linking also occurred. The damaging effect of gamma irradiation, however, was not significant enough to cause any major disruption of the normal banding pattern in collagen. These data support earlier biomechanical data showing that using current processing methods, 2.0 Mrads of gamma irradiation sterilization significantly decreases the tensile strength and modulus of human patellar tendon graft tissues.