THE PERSISTENCE OF ELECTRON SPIN RESONANCE IN BONE GRAFTS STERILIZED BY IONIZING RADIATION.

An adequate supply of sterile bone is essential for many orthopedic procedures. Since arteries and bone used for grafting do not survive in the recipient's body, they need not be viable. Hence, tissue from suitable cadavers can be removed under nonsterile conditions and be sterilized subsequently by procedures that may kill the tissue. Ionizing radiation has been advocated as a sterilizing agent for arterial (1) and bone grafts (2). It is an excellent sterilizing agent, and, since 1951, the method has gained widespread acceptance. Originally, the expense and limited availability of the necessary equipment restricted this means of sterilizing tissue grafts to large research centers. Recently, this procedure has become more widely available (3-5). Unfortunately, information on the fate of such bone grafts is still limited. It has been shown that such grafts have no radioactivity (4) and that they heal very well in experimental animals, where they show no histologic abnormality 3 months postoperatively (2). Since 1956, 3051 patients have received such grafts. Of these, 1000 have now been followed for more than 5 years. They have shown a very low (0.6 %) rate of wound infection and good clinical results.' Biopsies obtained in 38 cases on the 15th to 504th day postoperatively have shown good healing (6). Recently, irradiated banked bone grafts have been reported to show electron spin resonance signals as long as 12 weeks after irradiation (7). Although the exact identity of this resonance center still awaits identification, it is most probably either a trapped electron or an organic free radical.