SURFACE DAMAGE TO COBALT-CHROME FEMORAL-HEAD PROSTHESES

Fifty-four cobalt-chrome alloy femoral heads were retrieved at revisio n surgery or at post-mortem; 23 came from uncemented, eight from hybri d and 23 from cemented hip arthroplasties. The uncemented and hybrid i mplants had porous coating, metal backing and modular femoral heads; w ith one exception none of the cemented implants had any of these. Twen ty-five of the 31 heads from uncemented and hybrid arthroplasties, and 11 of the 23 heads from cemented arthroplasties showed surface damage involving more than 25% of the surface. Scanning electron microscopy revealed multidirectional fine scratches 1 mu m to 10 mu m in depth an d width which appeared to have been made by fine, hard particles. Ther e was a higher rate of such damage in the uncemented and hybrid arthro plasties than in the cemented implants, suggesting that the abrasive p articles were mainly released from the metal, rather than from the cem ent or polyethylene components of the implants.