Tissue reactions around loosened hip prostheses. Histologic study of pseudocapsules and interface membranes

Pseudocapsules and interface membranes from 142 consecutive revision surger ies of hip prostheses were histomorphologically analyzed including a semiqu antitative grading of the wear particles from the prostheses and bone cemen t as well as the cell infiltrates. The implant duration varied between 3 mo nths and 19.5 years. In 37% of the cases up to 6 months in situ, inflammatory cell infiltrates c haracteristic for early infection were seen. In 22% of the cases with longe r implant duration, signs of late infection were found. In the tissues of t he predominantly cemented prostheses, bone cement wear prevailed, which cou ld be regularly detected after about 1 year. Polyethylene wear appeared to be the second most common foreign material. Metallic wear was found in only 18% of the cases. Ceramic wear was only seen in tissues around loosened pr ostheses with ceramic-ceramic couples. Due to the material abrasion,a forei gn body reaction rich in macrophages developed with minimal lymphocytic inf iltration. The degree of these tissue alterations and the amount of wear pa rticles showed a statistically significant increase with increasing implant duration. In contrast, Win exudates, hemorrhages, and metaplastic ossifica tions were not dependent on the length of time in situ. Differences in respect to the amount of wear particles were found between p rostheses with ceramic and metallic heads. Prostheses with metal-polyethyle ne combinations generated approximately twice as many polyethylene wear par ticles as prostheses with ceramic heads. Among the metal-polyethylene coupl es the bipolar prostheses showed a markedly increased polyethylene wear, so me of them with extensive osteolyses. Deposits of calcium pyrophosphate wer e twice as common in pseudocapsules as in capsules from joints with degener ative arthrosis. Because of the increasing frequency of revision surgery, k nowledge of the histologic changes around joint prostheses seems to be impo rtant as these changes may indicate complications and give information in r espect to the biocompatibility of implant materials.