[Tissue reactions around loosened hip joint endoprostheses. A histological study of secondary capsules and interface membranes].

Pseudocapsules and interface membranes from 142 consecutive revision surgeries of hip prostheses were histomorphologically analyzed including a semiquantitative grading of the wear particles from the prostheses and bone cement as well as the cell infiltrates. The implant duration varied between 3 months and 19.5 years. In 37% of the cases up to 6 months in situ, inflammatory cell infiltrates characteristic for early infection were seen. In 22% of the cases with longer implant duration, signs of late infection were found. In the tissues of the predominantly cemented prostheses, bone cement wear prevailed, which could 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 prostheses with ceramic ceramic couples. Due to the material abrasion, a foreign body reaction rich in macrophages developed with minimal lymphocytic infiltration. The degree of these tissue alterations and the amount of wear particles showed a statistically significant increase with increasing implant duration. In contrast, fibrin exudates, hemorrhages, and metaplastic ossifications were not dependent on the length of time in situ. Differences in respect to the amount of wear particles were found between prostheses with ceramic and metallic heads. Prostheses with metal-polyethylene combinations generated approximately twice as many polyethylene wear particles as prostheses with ceramic heads. Among the metal-polyethylene couples, the bipolar prostheses showed a markedly increased polyethylene wear, some of them with extensive osteolyses. Deposits of calcium pyrophosphate were twice as common in pseudocapsules as in capsules from joints with degenerative arthrosis. Because of the increasing frequency of revision surgery, knowledge of the histologic changes around joint prostheses seems to be important as these changes may indicate complications and give information in respect to the biocompatibility of implant materials.