Mechanical influences on tissue differentiation at bone-cement interfaces.

Retrieval studies have shown that tissue at the bone-cement or bone-implant interface can develop into fibrous tissue, fibrocartilage, and bone, and that tissue differentiation appears to be mechanically influenced. A prior histologic analysis of retrieved interface tissues supporting cemented Marmor unicondylar knee components found that beneath the central portion of these implants, a thick, mature layer of fibrocartilage consistently developed, whereas fibrous tissue formed beneath the prosthesis periphery and adjacent to the bone beneath the tibial spine. Finite-element analysis was used to model the interface tissue supporting a cemented Marmor tibial component and interpreted patterns of stress and strain generated in the interface according to a mechanically based tissue differentiation theory. Distortional strain and hydrostatic stress, mechanical stimuli that are hypothesized to be associated with fibrous matrix and cartilaginous matrix production, respectively, were found to correlate well with the previous histologic findings. Given the biologic environments in which the retrieved interface tissues developed, frequently applied hydrostatic stress of approximately 0.7 MPa may be sufficient to stimulate cartilaginous extracellular matrix production in the interface tissue, and frequently applied distortional strain of 10% may be sufficient to stimulate fibrous extracellular matrix production.