[Studies of explanted shot-peened osteosynthesis plates]

Shot peening is a cold-working process to increase the fatigue life of osteosynthesis plates. Using ceramic particles for this process we observed no change in the corrosive properties of the plates. Up to now we implanted 37 shot peened osteosynthesis plates for fixation of intertrochanteric osteotomies. 13 plates were explanted after an average time of 14,2 months. We investigated the plates as well as the tissue surrounding the implants. Metallurgic specimens showed not so many pittings at the shot peened plates in the region of the screw hole as were seen at the polished plates after the same period of implantation. By histological investigation corrosive products or fretting particles were detected mostly in the region of the screws. Only a few metal particles were found in the region between the screw holes. Analysing the elements which were black or red-brown coloured in histological specimens by scanning electron microscopy we identified these particles as metal components. But there was a great difference in the relation of the particles found in the tissue compared to the components forming the plates alloy. This is due to the difference of distribution of the metal components at the surface of the implant in comparison with the central part of the plate. These austenitic stainless steels are protected by an enrichment of Cr in the surface layer. This could be shown in the shot peened plates as well as in the polished plates. The results of our investigations show a corrosive behaviour which is at least equal at both plates types in laboratory investigations as well as after implantations in men.(ABSTRACT TRUNCATED AT 250 WORDS)