Ethylene oxide sterilisation of allogenic bone implants.

We have evaluated the ability of ethylene oxide gas to penetrate bone matrices and subsequently kill a defined microbiological load. These experiments demonstrated that freeze-dried cancellous and cortical bone did not pose a barrier to the rapid diffusion of the gas. A normal cycle on a commercial ethylene oxide steriliser provided a sixfold overkill. Minor differences in the rate at which the microbiological load was killed (D-value) were seen between cortical and cancellous bone, processed and unprocessed bone, and bone of different thickness. These differences were negligible in comparison to the degree of overkill observed. Spore indicators placed freely in the steriliser chamber were shown to act as excellent monitors for the bone sterilisation process. Preliminary studies of ethylene oxide residuals indicated that processed, freeze-dried bone could be sterilised without leaving leachable toxic residuals in the matrix.