Comparative Histological and Morphometric Autopsy Study of Femora and Acetabula with Stable Cemented Hip Prostheses

To gain insight into the tissue reactions leading to non-infectious prosthesis loosening autopsy specimens of 9 stable cemented femoral and acetabular components 1 to 16 years in situ were analysed histomorphologically and morphometrically. In femora and acetabula, bone and cement were separated by an interface membrane composed of connective tissue and granulation tissue after short implant duration. After longer implant duration, infiltrates of macrophages containing wear particles of the bone cement and – though less abundant – polyethylene predominated. The interface membranes of the acetabula appeared three times as broad as in proximal parts of the femora. They showed no topographical variations. In the femora, however, the membranes were proximally considerably thicker than in distal parts. In both femora and acetabula, the adjacent spongiosa were infiltrated by macrophages as well. The cancellous bone showed remodelling with formation of a neocortical layer at the border between the spongiosa and the interface membrane. Focal metaplastic formation of cartilage was also present. The results indicate that in femora and acetabula, basically analogous mechanisms lead to non-infectious late loosening, which is connected with the accumulation of wear particles and macrophages in the interface membrane. A positive correlation of the width of the interface membrane with the implant duration was found only in the acetabulum. This could explain the comparatively frequent socket loosening.