Pathology of the bone-cement interface in loosening of total hip replacement

The histopathology of the bone-cement interface in nine retrieved hip prostheses is reported. Three cases presented features similar to those observed by Charnley in highly successful implants, and they were classified as stable prostheses, although signs of periprosthetic bone resorption were already present. In this group a macrophagic reaction was evident even in the presence of a stable bone-cement interface, supporting the view that the release of particles by the cement or by the prosthetic components can precede the mechanical instability and be the primary cause of loosening. In six prostheses the connective tissue layer between the cement and the bone was thick and no bone trabecula reached the cement surface. The polymorphous features of this connective membrane probably resulted from instability and movement at the bone-cement and stem-cement interfaces. On the basis of the pathological changes observed in the study, the process of loosening must be far advanced before it is detected on radiographs; it is suggested that scintigraphy is the best noninvasive technique to demonstrate macrophage activation and increased bone remodeling around the cement in the early phases of loosening.