Biomechanical properties of canine cortical bone allografts: Effects of preparation and storage

SUMMARY The effects of various preparation and storage procedures and of different storage times on structural properties of canine cortical bone allografts were determined by evaluation of the compressive load to failure of a whole diaphyseal segment, the ability of a screw to resist being pulled from a cortical segment, and the torque required to strip the threads of a screw hole in a cortical segment. Preparation and storage procedures evaluated were sterile collection and storage at −20 C; ethylene oxide sterilization and storage at room temperature (22 C); chemical sterilization (methanol and chloroform, then iodoacetic acid) and storage at −20 C; and chemical sterilization, partial decalcification, and storage at − 20 C. Storage times were 1, 16, and 32 weeks for each procedure. After 1 week of storage, aseptically collected frozen bone and ethylene oxide-sterilized bone had an increase, compared with matched controls, in load to failure in compression, but pullout load or screw-stripping torque did not change. Chemically sterilized bone had not changed after 1 week of storage, whereas chemically sterilized and partially decalcified bone had a 40% to 60% decrease in compressive load to failure, pullout load, and screw-stripping torque. Chemically sterilized and partially decalcified bone remained weak after 16 and 32 weeks of storage. Significant structural alterations were not detected in aseptically collected bone after 16 or 32 weeks of storage. Ethylene oxide-sterilized bone had a reduced pullout load after 32 weeks of storage. Chemically sterilized bone had significantly reduced compressive load to failure and pullout load after 16 and 32 weeks of storage. The use of aseptically collected, ethylene oxide-sterilized, or chemically sterilized bone within 1 week of preparation would be acceptable for grafts used for diaphyseal replacement, whereas chemically sterilized and partially decalcified bone would be unacceptable, regardless of storage time. Aseptically collected bone still would be acceptable for use after 32 weeks of storage. Ethylene oxide sterilized bone and chemically sterilized bone developed structural alterations during storage, making it questionable whether their use for diaphyseal replacement after lengthy storage of the graft would be successful.