The cement-bone interface: Is it susceptible to damage adaptive remodeling?

The cement-bone interface is frequently used to identify early loosening in cemented hip arthroplasty (via the appearance of a radiolucent zone on radiographs). This is often assumed to be a biological reaction to wear debris but it is possible that it could also be influenced by bone adaptation due to excessive loading of the region. This study investigated if damage stimulated resorption can play a role in the degradation of this interface. A combined strain and damage stimulated bone adaptation algorithm was used. Constant rate resorption or formation occurs if local strain falls outside a quiescent reference strain range. Furthermore, damage accumulates as a function of tensile stress. Resorption and simultaneous repair is activated above a critical damage level. Model parameters are related to specific surface area expressed as a function of apparent tissue density. Elastic modulus was also a function of accumulated damage. This algorithm was applied in conjunction with an aseptic loosening algorithm for a retrospective dataset of hip replacement patients. Damage accumulation in the bone was predicted primarily at the cement-bone interface. Interfacial bone remodeling demonstrated oscillation in damage at the interface due to cycles of resorption of damaged regions and subsequent strain induced formation. This led to maintenance of bone near the interface in most cases. As the bone near the cement interface was not treated any differently than other regions of bone it was intriguing to find that damage accumulated almost exclusively in this region. Although more detailed investigation of the parameters in the model is needed, predictions did not indicate that damage adaptive remodeling was a risk for soft-tissue interface formation in the 17 cemented hip patients considered.