HISTOMORPHOLOGICAL STUDIES OF THE LONG-TERM SKELETAL RESPONSES TO WELL FIXED CEMENTED FEMORAL COMPONENTS

Thirteen femora that were obtained at autopsy from patients in whom a cemented total hip replacement had been implanted from forty months to 17.5 years earlier were evaluated radiographically and morphologically. All of the patients had been functioning well, and only one of the prostheses showed radiographic evidence of loosening. Serial sections of the proximal portion of the femur that enclosed the femoral component of the prosthesis showed that the host bone was intimately and directly apposed to the cement, and fibrous tissue intervened only rarely. The bone-remodeling proceses had created a dense shell of substantial new bone around the cement-mantle that resembled a new cortex, attached to the outer cortex by new trabecular struts. Evidence of ingrowth of bone from this dense shell of bone into the undulating surface of the cement was found in many areas. In the adjacent femoral cortex, there was substantial osteoporosis and cortical thinning. The cement-bone interface was intact and excellent throughout, despite the presence of fractures within the cement-mantle and de-bonding at the cement-prosthesis interface in some specimens. The cemented femoral components were well tolerated by the skeleton over a long period of use, and fibrous tissue had rarely formed at the femoral cement-bone interface of these well fixed and clinically successful prostheses. The cement-mantle was well supported by extensive medullary bone-remodeling and formation of a dense shell of new bone. The internal bone-remodeling helped to maintain the cemented femoral components over time and did not cause loosening of the prosthesis.