The microscopic anatomy of the bone-cement interface in failed total hip arthroplasties.

Thirty specimens were removed from the bone-cement interface in 25 hips revised for aseptic loosening of total hip arthroplasty. Histologic examination of the membranous tissues revealed that histiocytosis, fibrosis, and necrosis were present in every specimen. Other prominent features included particles of acrylic cement, polyethylene debris, and fragments of necrotic bone. Mechanical failure was characterized by cement fractures, and microfracture of bone. The presence of cement debris and bone detritus in the membranes, and smooth appearance of the removed cement mantles substantiated the presence of mechanical failure. The process of loosening was characterized by the recruitment of histiocytes into the interface and the subsequent resorption of bone around the prosthesis. This may be a manifestation of the rate of cement wear and tear, particle size, and the immunologic predispositions of the host. These observations on interfaces of loosened prostheses are reexamined and reinterpreted in the light of radiologic observations on interface radiolucent zones and well-functioning prostheses.