Comparisons between mobile-bearing and fixed-bearing total knee replacement

Abstract

Many articles have discussed the potential benefits of mobile-bearing total knee arthroplasty (TKA) when compared to fixed-bearing designs. Several manuscripts recently have been published that directly compare these two alternative designs. The goal of this review was to determine if the proposed theoretical advantages of mobile-bearing TKA result in any demonstrable improvement in clinical outcome. Mobile-bearing TKA was introduced in an effort to improve prosthetic longevity by minimizing polyethylene wear while reducing strain at the implant-bone interface. Knee simulator studies in vitro reveal superior wear characteristics for mobile-bearing prostheses when compared with fixed-bearing equivalent designs. The mobile-bearing design also has been shown to more closely match the kinematics of normal knees and patellofemoral joints. Suspicions regarding the disadvantages of mobile bearings, including bearing instability and the detrimental effects of backside wear, remain controversial but are not supported by recent literature. Longitudinal studies evaluating clinical outcomes, however, have been unable to reveal any significant advantage for either of these two different TKA designs. Both kinematic studies and in vitro investigations suggest certain theoretical benefits for mobile-bearing TKA when compared to fixed-bearing designs. Most importantly, however, clinicai outcome studies consistently fail to demonstrate the superiority of mobile-bearing TKA with regard to longevity or functional results.