HISTOLOGIC AND BIOCHEMICAL DIFFERENCES BETWEEN OSTEOLYTIC AND NONOSTEOLYTIC MEMBRANES AROUND FEMORAL COMPONENTS OF AN UNCEMENTED TOTAL HIP-ARTHROPLASTY

The unique design characteristics of an uncemented femoral component w ere used to study differences in the periprosthetic membranes in the p resence and absence of osteolysis. A component (Omniflex, Osteonics, A llendale, NJ) that has a large midportion of the stem that does not co ntact bone was studied. A membrane forms, even in the absence of bone resorption, in Gruen zones 3 and 5 of this component. Analysis of this membrane showed noninflammatory fibrous tissue, no or minimal particu late debris, and few macrophages. In contrast, analysis of membranes f rom osteolytic regions around the same prosthesis demonstrated typical inflammatory characteristics. Collagenase, gelatinase, and stromelysi n expression was high in osteolytic membranes but was low in tissues f rom noninflammatory regions without osteolysis. The data suggest a seq uence of events in periprosthetic membrane formation. A noninflammator y membrane initially forms between the bone and the prosthesis. This m embrane is transformed into an inflammatory membrane by the influx of particulate debris. Matrix metalloproteinases are selectively expresse d in regions of osteolysis, implicating these enzymes in periprostheti c bone loss and suggesting a possible level for pharmaceutical interve ntion to prevent or treat osteolysis. Formation of the noninflammatory membrane around the distal part of the prosthesis of this or similar designs in the absence of bone resorption implies that these tissue sa mples could serve as useful negative control tissues to identify facto rs present in osteolytic periprosthetic membranes.