LAUSR

Unicondlyar knee arthroplasty (UKA) implants are generally nonconstrained, allowing for more-normal rollback and rotation of the knee during knee flexion. Mobilebearing UKA implants provide a fully conforming bearing surface between the femoral component and tibial insert that allows AP movement and rotation between the tibial insert and tibial baseplate. By contrast, fixed-bearing UKA implants permit AP and rotational movement between the femoral component and relatively flat tibial bearing surface. The fully conforming nature ofmobile-bearingUKA implants results in greater ultra-high-molecularweight polyethylene (UHMWPE) contact area and lower contact stresses than fixed-bearing UKA, which has been associated with low UHMWPE wear in vivo [6, 12]. And although mobilebearing UKAs have demonstrated excellent long-term survivorship [10], they also have a risk of bearing dislocation, which can result in revision surgery [10, 17]. Prior to the mid-1990s, UHMWPE implants were sterilized by gamma irradiation in air, resulting in oxidative degradation and decreased wear resistance of the polymer [14], and during this time, studies reported excellent long-term survivorship and low wear for mobile-bearing UKA implants [4, 12]. But after gamma irradiation in air sterilization was abandoned as a solution to polyethylene oxidation [9], alternative sterilization methods emerged, including ethylene oxide, gas plasma, and gamma irradiation in an inert atmosphere. Crosslinking, which is currently used in most hip and many knee implants [15], can reduce UHMWPEwear. The benefit of mobilebearing UKA in reducing UHMWPE wear compared to fixed-bearing implants may be less important as improvements have been developed in UHMWPE sterilization and processing. Mobile-bearing TKAs are also associated with lower bone-implant interface stresses compared to relatively conforming fixed-bearing implants [2]. Cementless mobile-bearing UKA has been used successfully, which may be related to the reduced bone-implant interface stresses of these implants [16]. But sincemost of the currently available fixed-bearing UKA implants have relatively flat nonconforming surfaces, we may not find clinically relevant differences in interface stresses between the two implant types. Indeed, bothmobileand fixed-bearing UKA implants include gap balancing, computer navigation, and robotics, and currently available implant materials include more wear-resistant UHMWPE and abrasive-resistant counterface surfaces than what has been available in the past. In the current study, Ro and colleagues [13] demonstrated that the This CORR Insights is a commentary on the article “Bearing Dislocation and Progression of Osteoarthritis After Mobile-bearing Unicompartmental Knee Arthroplasty Vary Between Asian and Western Patients: A Meta-analysis” by Ro and colleagues available at: DOI: 10.1007/s11999. 0000000000000205. The author certifies that neither he, nor any members of his immediate family, have any commercial associations (such as consultancies, stock ownership, equity interest, patent/ licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article. All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request. The opinions expressed are those of the writers, and do not reflect the opinion or policy of CORR or The Association of Bone and Joint Surgeons. This CORR Insights comment refers to the article available at DOI: 10.1007/s11999. 0000000000000205. Michael D. Ries MD (✉), Reno Orthopaedic Clinic 555 N. Arlington Ave Reno, NV 89503 USA Email: [email protected] M. D. Ries, Reno Orthopaedic Clinic, Reno, NV, USA