SUMMARY

A pseudomembranous structure invariably develops at the cement-bone interface of implanted prostheses in association with aseptic loosening. The tissue has histological characteristics of a foreign body reaction presumably initiated by repeti-tive microtrauma-associated release of methacrylate cement and polyethylene wear debris. Explant cultures of pseudo-membrane and synovial tissue derived from osteoarthritic patients undergoing revision for cemented hip implant failure have been shown to produce interleukin-1, tumour necrosis factor and prostaglandin E2, recognized mediators of bone resorption. Further, the conditioned media obtained from pseudomembrane cultures could directly effect bone resorption by inducing 4iCa release from prelabelled limb bone rudiments. Results implicate the prosthesis-associated pseudomem-brane in the pathogenesis of the bone resorptive process responsible for prosthesis failure. KEY WORDS: Bone resorption, Interleukin-1, Polymethylmethacrylate, Prostaglandins, Prosthesis failure, Tumour nec-rosis factor. ASEPTIC failure of cemented prostheses is invariably associated with formation of a pseudomembranous structure at the bone-cement interface adjacent to regions of bone resorption [1—5]. The tissue is rich in palisading vacuolated histiocytes and macrophages