Analysis of capsular tissue from patients undergoing primary and revision total hip arthroplasty

Late aseptic loosening of revision total hip replacements is a common cause of failure. At revision surgery, a foreign pseudo capsule membrane surrounding the implant develops. These tissues are thought to reflect a response due in part to an increase in particulate debris, generated by normal wear of the bearing surfaces. The foreign body membrane consists of macrophages and giant cells lying in between the bone and the implant. The cell types identified at the interface included lymphocytes, histiocytes, macrophages, and giant cells, and their contribution to implant loosening due to bone resorption is the focus of this investigation. Capsular tissues surrounding failed joint arthroplasties were characteristically different by gross morphological observations. The capsular tissue contained a region of tissue approximately 4-6 cell layers in depth lining the capsule, which resembled synovial like cells. This region of the capsular tissue consisted of loosely organized fibrous tissue containing numerous histiocytes and foreign body giant cells demonstrated by hematoxylin and eosin. Immunological staining of the capsular tissue for IL-1 activity showed the reactivity to be localized directly adjacent to the implant in well vascularized areas. Tissue farthest from the implant were less reactive and resembled tissue extracted from primary patients. Quantitative ELISA data for IL-1 activity from these areas reflect the observations observed by immunostaining.