Synovium-like tissue from loose joint replacement prosthesis: comparison of human material with a canine model

The formation of synovium-like tissue is a biological response to a loose joint replacement prosthesis. Histological examination of this tissue has shown a synovial lining with a predominance of fibroblasts and macrophages, some multinucleated giant cells, and dispersed particles from the implant. Previous studies have reported elevated interleukin 1 (IL-1), prostaglandin E2 (PGE2), and collagenase in this tissue. We developed a canine model for the loose cemented femoral stem. Tissue harvested from the canine model was compared with human tissue retrieved at revision arthroplasty. Histology showed synovium, similar to that observed around loose human prostheses, adjacent to the canine cement sheath. Cells were isolated from this tissue and incubated in culture medium with or without naproxen for 3 days. Aliquots of the conditioned media were tested in the thymocyte proliferation assay to determine IL-1-like activity. IL-1 beta levels in human cell-conditioned media were analyzed by enzyme-linked immunosorbent assay, and PGE2 levels were measured by radioimmunoassay (RIA) using a PGE2 RIA kit (New England Nuclear). Human tissue contained levels of IL-1 beta in the range of 150 to 7,040 pg/mL and PGE2 levels of 82 to 952 ng/mL. The canine specimens contained IL-1-like activity and significant amounts of PGE2 (76 to 1,720 ng/mL). Naproxen decreased PGE2 levels in vitro. This animal model provides the means to investigate the in vivo and in vitro activity of the synovial cells around loose total joint prostheses.