Long-term implant fixation and stress-shielding in total hip replacement

Implant fixation implies a strong and durable mechanical bond between the prosthetic component and host skeleton. Assuming the short-term impediments to implant fixation are successfully addressed and that longer-term issues such as late infection and mechanical failure of the components are avoided, the biological response of the host tissue to the presence of the implant is critical to long-term success. In particular, maintenance of adequate peri-prosthetic bone stock is a key factor. Two major causes of bone loss in the supporting bone are adverse bone remodeling in response to debris shed from the implant and stress-shielding. Here, I review some of the major lessons learned from studying stress-shielding-induced bone loss. It is well known that stress-shielding can be manipulated by altering implant design, but less well appreciated that the development of bone anabolic agents may make it possible to reduce the severity of stress-shielding and the associated bone loss by augmenting the host skeleton through the use of locally or systemically delivered agents. In most cases, mechanical, material and biological factors do not act in isolation, emphasizing that it is often not possible to optimize all boundary conditions.