SummaryThe cobalt-based alloy containing approximately 30% chromium and 57, molybdenum is widely used for the fabrication of internal fixation appliances. This alloy exhibits superior corrosion resistance in the presence of body fluid because of a durable and rapidly formed surface layer of chromium oxide.Although biocompatible, clinical use of this alloy appears to have been complicated by relatively great adhesion of tissue and bone to the metal. The adhesion engenders considerable difficulty when removal of an appliance should become necessary.It was hypothezied that this adhesion derives from the ceullular growth proceeding within the microporosity of the metal surface; the growth proceeds efficiently because of relatively low levels of cytotoxic metal ions released at the metal surface. I n order to limit adhesion, polytetrafluoroethylene polymer (PTFE) was used to virtually eliminate surface microporosity and to substantially reduce metal surface free energy.' One of the efficient techniques was to lap the metal surface with a solid piece of PTFE.A series of eighteen 12-to 22-kg dogs were used to evaluate the above thesis. Control and treated cobalt alloy plates and screws were used to fix induced longbone fractures in the same animal. Also, five animals received implants on decorticated iliac crests. The histological data for control (untreated) plates showed that in nine of the eleven experiments bone was demonstrated closely adjacent to the surface of the appliance. However, in seven of these cases fibrous tissue was also present to a substantial degree. The presence of bone correlated with generally increased difficulty in removal of the plate. On the other hand, the results with treated implants showed that in ten of eleven cases the appliances were grossly encapsulated with fibrous tissue and were relatively easy to remove. The results of this study were r i o t definit,ivc but. tended t.0 confirm the premise that. eliminaLioxi of surfacc roughness arid decrease of surface wetstability of cast cobalt, alloy appliances with perfluorinat,ed polymers reduces the tendency for intimat,e adhesion of t,he tissue environment, to the appliance.