Fixed versus mobile bearing knee arthroplasty: a review of kinematics and results

There are several total knee arthroplasty designs available with wide variation in features. The long-term results of total knee replacement with a fixed bearing design have shown a high degree of clinical success. However, implant loosening and polyethylene wear became recognized as long-term causes of late failure. Mobile bearing knee replacements were designed to create a durable surface articulation by using a polyethylene insert that articulates with a metallic femoral component and a metallic tibial tray. The purpose of this article is to review clinical and basic scientific studies comparing the clinical results, the biomechanical features, and the kinematic patterns of fixed versus mobile bearing knee designs. Beside the fact that in vitro kinematic studies have shown reduced polyethylene wear in mobile bearings due to increased implant conformity and reduced polyethylene contact stresses, which should hypothetically prolong polyethylene life, various independent studies for both mobile bearing and fixed bearing prostheses have documented results that are comparable in terms of survival and performance.