Tissue Reactions to Metals—The Influence of Surface Finish

Screws of chromium-cobalt alloy and of identical dimensions but with three different surface finishes were inserted into various substances and into the bones of dogs. The torque needed to insert and remove them was measured. In vivo, and also in one in vitro setup, the highest removal torque occurred with the coarsest surface finish. Histological examination of the bone revealed the same tissue reaction to all three surface finishes. Small amounts of a black granular powder of unknown composition were found in all the sections. Weight losses were recorded for all the screws implanted. The factors influencing the torque of insertion and that of removal of a screw were discussed.