Biomechanical implant fixation of CoCrMo coating inferior to titanium coating in a canine implant model

Abstract

The use of CoCrMo in orthopedic surgery is not new, and CoCrMo (cobalt-chromium-molybdenum) is well tolerated. Nevertheless, the alloy is still considered less biocompatible than titanium. We therefore wanted to explore the biocompatibility of CoCrMo by investigating the biomechanical implant fixation and implant osseointegration of CoCrMo (ASTM F-75) porous bead-coated and titanium (ASTM F-136) porous bead-coated implants. In 10 dogs, the two implant types were inserted into the proximal part of the humerus. Implant sites were overdrilled, leaving an empty 0.75-mm gap between implant and surrounding bone. The implants were observed for 6 weeks and were evaluated by biomechanical push-out test and histomorphometry. We found a statistically significant 40% decrease in the biomechanical fixation of CoCrMo porous bead-coated implants compared with titanium porous bead-coated implants. Implant osseointegration was comparable between the two implants; however, a slight decrease in bone volume density around CoCrMo implants was observed. Insertions of CoCrMo implants are associated with a disturbance of the delicate peri-implant milieu. Even from implants not subjected to any mechanical forces, metal ions are liberated and result in intra- and extracellular accumulation in the immediate implant vicinity, presenting a likely explanation for our findings. A 40% reduction of initial implant fixation could prove to be serious because initial implant fixation is critical for long-term performance. The choice between titanium alloy and CoCrMo should, however, ultimately be governed by a comprehensive review of all factors influencing clinical implant survival. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.