(ii) Biomechanics of implant fixation

In joint replacement, stability of the implant is provided by a combination of the techniques adopted to fix the implant to the surrounding bone and the geometric features of the implant. Fixation techniques can either use cement or be cementless. Cemented fixation uses PMMA bone cement to grout the implant and bone together, while cementless fixation involves either a press-fit between the implant and bone, or specific design features that encourage bone growth into or onto the implant. Although both of these fixation techniques perform well in terms of longevity, each method functions better than the other in certain patient groups, and each has some positives and negatives. This article reports an overview of the fundamental aspects of the fixation techniques, their clinical advantages and disadvantages, associated clinical concerns and recent trends of fixation in clinical practice. This will be coupled with specific examples on how certain geometric features of an implant help in achieving initial and long-term stability and fixation.