Histological patterns of the tissue reaction to polymers in orthopaedic surgery

Unless coated with calcium hydroxyapatite, a layer of fibrous tissue, referred to as the interface membrane, separates polymeric devices from bone into or onto which they have been implanted. Though bone may directly contact certain polymers, e.g. polysulfone, the bulk of implanted prostheses is separated from the bony bed by such an interface membrane. Polymers in current use, e.g. polymethylmethacrylate, polyethylene and polyacetal, when subject to micromotion at the interface, release breakdown products, which induce a giant cell granulomatous reaction. An exuberant granulomatous response, accompanied by chronic inflammatory infiltration and cicatrization, characterizes the ‘pathological’ interface membrane, which is the hallmark of the aseptically loosened prosthetic component. Diverse polymers comprising different prostheses excite a stereotyped granulomatous reaction. Expectedly, when implanted into soft tissue, polymeric devices elicit the formation of an essentially similar granulomatous-cicatrizing response.