Cementing constrained acetabular liners in revision hip replacement: clinical and laboratory observations

During revision hip arthroplasty, removal of a well-fixed, ingrown metal acetabular component may not be possible. Therefore, a new polyethylene liner can be cemented into the existing shell via the cement locking mechanism. This technique is well recognized, and the cement locking mechanism has proved to be sufficiently strong and durable for clinical use. A constrained polyethylene liner is designed to reduce the risk of hip dislocation by capturing the femoral head. However, there are increased shear forces created at the liner interface as the dislocation is resisted. If a constrained liner is cemented into an ingrown acetabular component, then there is the theoretical risk that these increased shear forces will damage the cement locking mechanism, thus leading to failure of the construct. There are a few clinical series in which a constrained liner has been used with the cement locking mechanism. Overall, the failure rate of the cement locking mechanism is no greater if a constrained liner instead of a standard liner is used. The cement locking mechanism can be strengthened by roughening the backside of a smooth polyethylene liner to improve the cement-polyethylene interface, or by using an all-polyethylene acetabular component that is designed to be used with cement. Whether a smooth metal shell needs to be roughened as well is a matter of debate.