Influence of different sterilization procedures and partial demineralization of screws made of bone on their mechanical properties.

Since 1992, screws made of allogenic, autoclaved human cortical bone have been employed as osteosynthesis materials. Autoclaving at 134 degrees C for 5 min makes them microbiologically safe, but on the other hand it reduces both their mechanical properties and osteoconductive capacity. The aim of this in vitro study was to determine if the mechanical properties of these screws could be improved after receiving different autoclaving procedures and partial inner demineralization, the latter additionally tending to increase their osteoconductive potential. 132 screws made of bovine cortical bone were employed. Some of them were partially demineralized with 0.6 N HCl from an inner canal performed following their longitudinal axis. All the specimens were autoclaved at 134 degrees C but under different vacuum conditions and sterilization time (A1-A2). They were then subjected to tension, shear and torque tests. A difference between both sterilization procedures was observed. Samples sterilized at 134 degrees C, 2-2.4 mbars for 5 min (A1) showed better mechanical properties than those autoclaved for longer time and higher vacuum conditions (A2). Demineralization also influenced their mechanical properties, being less resistant with increasing time. Based on these results, a standard screw made of bone and autoclaved at 134 degrees C, 2-2.4 mbars, 5 min seems to be the most appropriate, from a biomechanical point of view, to be used as osteosynthesis material.