[Reaction of the bone to a cement-free SL femur revision prosthesis. Histologic findings in an autopsy specimen 5 1/2 months after surgery].
A 65-year-old man underwent revision arthroplasty because of loosening of the femoral component. At revision, an SL revision femoral stem (Wagner) was inserted. The patient died unexpectedly five and a half months after this operation and it was possible to study the bony incorporation of the prosthesis microscopically in undecalcified sections with the implant in situ. The stem of the prosthesis was solidly anchored in the distal diaphysis of the femur. The press fit obtained at surgery allowed bridging of the small gaps between the endosteal surface and the eight wings of the stem by direct (primary) bone formation. The newly formed bone was found in direct contact with the titanium surface. Direct bone apposition and good bony anchorage were also found further proximally, especially on the medial aspect of the stem. The proximal shaft of the femur was severely altered by the loosening of the former femoral component. Congruency between the marrow cavity and the shaft of the prosthesis was only possible when the space was filled with a cancellous allograft. There were signs of revascularization and revitalization, but for the most part the graft was still avascular and functioning only as a spacer. The documentation of this specimen provides important information concerning the first and decisive phase of bony incorporation of cementless prostheses, i.e., on the period when the primary stability due to press fit is converted to secondary, possibly definitive, fixation by means of direct bone formation.