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PERIPROSTHETIC TISSUES FROM FAILED METAL ON METAL TOTAL HIP REPLACEMENTS SHOW AN UNUSUAL LYMPHOCYTIC INFITRATION

Bristol Implant Research Centre, Bristol BS10 5NB

Metal-on-metal bearing surfaces have been reintroduced for use in total hip replacement, despite concerns regarding the potential risks posed by metallic by-products. We have compared periprosthetic tissues from metal-on-metal and metal-on-polyethylene hip replacements at revision surgery with control tissues at primary arthroplasty.

Tissues were obtained from 9 control, 25 contemporary metal-on-metal, 9 CoCr-on-polyethylene and 10 titanium-on-polyethylene hip replacement arthroplasties. Each was processed for routine histology with Haematoxylin and Eosin. Quantitative stereological analysis was performed at the light microscopic level.

Metal-on-metal sections showed more surface ulceration and this was correlated with the density of inflammation in the deeper tissues layers. Metal-on-metal tissues displayed a pattern of well-demarcated tissue layers, which were rarely seen in metal-on-polyethylene cases. In metal-on-polyethylene cases, the inflammation was predominantly histiocytic. Metal-on-metal cases by contrast showed a lymphocytic infiltrate with abundant plasma cells. Metal-on-metal tissues showed a striking pattern of peri-vascular inflammation with prominent lymphocytic cuffs especially deep to areas of surface ulceration. Levels of inflammation were higher in cases revised for failure than in those retrieved at autopsy or exploratory surgery. Total replacement and surface replacement designs of metal-on-metal arthroplasty showed similar histological changes. Plasma cells were not seen in any of the metal-on-polyethylene cases. The differences between the patterns of inflammation and cellular infiltration seen in metal-on-metal and metal-on-polyethylene tissues were highly statistically significant.

The pattern and type of inflammation in periprosthetic tissues from metal-on-metal and metal-on-poly-ethylene arthroplasties is very different. Our findings support the conclusion that metal-on-metal articulations are capable of generating a form of immunological response to metallic wear debris that has not been described previously. The incidence and clinical implications of these immunological responses in failed metal-on-metal joints are unknown.

The abstracts were prepared by Mr Tim Briggs. (Editoral Secretary 2003/4) Correspondence should be addressed to him at Lane Farm, Chapel Lane, Totternhoe, Dunstable, Bedfordshire LU6 2BZ, United Kingdom