Dr. Harris' response to Dr. Cameron

Abstract

capsule surrounding a metal-polyethylene bearing is thick and stiff and that there is a p rominent synovitis resembling that found in rheumatoid arthritis. Particles do play a role, therefore, but the role of polyethylene particles, as opposed to metal particles, is the production of a synovitis that leads to capsular scarring. The synovitis overproduces the fluid and the tight scarred capsule gives rise to high pressure. This means that polyethylene particles are important, but not in the way that has been thought previously. The treatment of osteolysis therefore has to be rethought. Perhaps a capsulectomy and synovectomy should be carried out when osteolysis is first seen, and perhaps a bleeding valve should be sewn into the residual capsule. Polyethylene wear should, of course, be minimized. The thick necks of the original European 14/16 trunions have now been waisted to prevent impingement, and the t runion size in common use in the United States is 10/12, which is only liable to impinge if significant component malposition occurs at the time of surgery. Should metallic particles from t runion fretting enter the bearing, then theoretically third-body wear will occur. The evidence that this is important in the hip is scanty, as metallic particles are forced into the soft plastic. With 15 years of experience with modular heads, I have failed to notice any runaway wear in the plastic acetabular component, a Third-body wear may be a much greater problem in metal-metal bearings if the congruence is kept too tight to allow particle escape. With respect to the issue of t runion damage, having revised a large number of hips, I have yet to see a t runion that had sustained sufficient damage that it was believed unsafe to replace a new head on an old trunion. In most ithe t runion appears normal or with very minimal damage to the naked eye. It is, of course, a personal choice, but it seems unreasonable that most surgeons should be asked to give up the proven benefits of modulari ty for the theoretical drawbacks.