IN-VIVO AND IN-VITRO ANALYSIS OF MEMBRANES FROM HIP PROSTHESES INSERTED WITHOUT CEMENT

Biochemical, histological, and immunohistochemical studies of interfac e membranes surrounding failed hip prostheses that had been inserted w ithout cement were done to examine specific factors involved in the de velopment of aseptic loosening. Membranes from sixty-four femoral comp onents were obtained from sixty-three patients during revision arthrop lasty. Fifty-seven membranes were from implants that articulated with polyethylene (thirty-two were made of cobalt-chromium alloy and twenty -five, titanium alloy), and seven were from unipolar endoprostheses ma de of cobalt-chromium alloy that did not articulate with polyethylene. The membranes from implants with a polyethylene articulation produced significantly higher levels of collagenase and interleukin-1 (p < 0.0 5). However, there was no significant difference in the levels of pros taglandin E(2) between the three groups. Furthermore, membranes from i mplants with roentgenographic evidence of focal osteolysis (endosteal erosion) released significantly higher levels of interleukin-1 (p < 0. 05) than did membranes from implants without focal osteolysis. Althoug h the membranes from the titanium-alloy implants tended to contain mor e metal debris than those from the cobalt-chromium-alloy implants, the biochemical findings were not significantly different between these t wo groups. Many macrophages that were filled with polyethylene and met al debris were present in the membranes from both groups with a polyet hylene articulation. Few T lymphocytes or B lymphocytes were identifie d in the three groups. CLINICAL RELEVANCE: This study demonstrates tha t macrophages activated by metal and polyethylene debris in interface membranes surrounding loosened femoral components that have been inser ted without cement are a source of biochemical mediators of bone resor ption. Such debris in these membranes may play an important role in th e initiation of femoral osteolysis and the biochemical process of asep tic loosening of femoral implants inserted without cement. Additional studies are needed to characterize the size, shape, and origin of the debris found in these interface membranes.