CORR Insights®: Do Fixed or Mobile Bearing Implants Have Better Survivorship in Medial Unicompartmental Knee Arthroplasty? A Study From the Australian Orthopaedic Association National Joint Replacement Registry

This is the authors' abstract. We don't add key points for this paper.

Where Are We Now? Medial compartment knee arthrosis remains a leading cause of pain and disability [6]. Surgical treatment generally involves either unicompartmental knee arthroplasty (UKA) or TKA, with a recent resurgence in surgeon and patient interest in the UKA [5]. Historically, TKA procedures are more durable than their UKA counterparts [6], but there is continued debate regarding whether a successful UKA results in greater patient function compared to TKA. Patient selection and surgeon experience are major factors that contribute to a successful UKA [1, 2]. Further, UKA has been shown to reduce perioperative risks compared to TKA [6]. A number of factors are involved in the success of an arthroplasty procedure, including the type of implant, surgeon experience, patient, and hospital [4]. Joint registries can help identify factors that can lead to revision, they can help surgeons to compare different implant designs, and they usually involve the efforts of many, many surgeons of different levels of experience making real-world choices in their practices. Because of this, registry findings often generalize to community surgeons in ways that series from high-volume subspecialty referral centers may not. In the current study, Kannan et al. [3] use the Australian Orthopaedic Association National Joint Replacement Registry to determine whether fixed or mobile bearing implants have better survivorship in medial UKA. The authors found that a fixed modular UKA has the best survivorship among the modern implant designs examined in their study [3]. This finding is a critical component in advising our patients regarding the outcomes of UKA. Based on this discovery, surgeons should reevaluate their own choice of implant design to ensure that we are not using the worst performers and move toward the best performing implants. Where Do We Need To Go? Both patients and surgeons strive for the best combination of factors that allows for a rapid and full recovery with the longest lasting knee replacement. But even though the current study’s results point surgeons to a fixed-modular UKA [3], several key questions remain. For example, while surgical indications for UKA are increasing due to the improved knee function compared to TKA as well as the demands of an active and young patient population, what is the cost to not only the patient in terms of increased risk of revision but the healthcare system in terms of higher revision burden compared to TKA? Can technological advancements such as robotic assistance and personalized instrumentation reduce variability in surgical technique for UKA? Surgeon experience in both patient selection and technique have been shown to affect the outcome of UKA, yet access to these surgeons is not readily available for all potential UKA recipients due to geographic limitations. How Do We Get There? We need to not only compare the survivorship of various implants for UKA and TKA but also the perioperative risks and functional outcomes associated with the various implants. While large databases can tell us about the perioperative risks and revision rates for surgical procedures, we need to study both patient expectations and satisfaction with UKA in return to function and then compare those results to TKA. To answer questions on patient return to function after medial compartment arthrosis, researchers will need to develop studies comparing patient-reported outcomes of UKA with TKA Leveraging technology and remote access can improve participation in data gathering for future studies. Electronic activity trackers have become ubiquitous in our active lifestyles. Harnessing these data will help clinicians better understand our patients’ activity levels. Further, perioperative devices that measure ROM and function can be used to gather data on the speed of recovery between patients who underwent a UKA versus those who had TKA. These studies will provide meaningful outcomes to allow better consultation and shared decision-making with our patients. The goal is for the patient and surgeon to go beyond simply which implant will last longest, but which implant provides the best outcomes that the patient seeks. A risk calculator is one way to make that determination. Risk calculators can improve the accuracy of outcome predictions by taking into account patient factors (age, gender, BMI), implant factors (implant type and fixation type), surgeon factors (experience, intraoperative technique), and hospital factors (volume, regional variations). Although there is evidence that more surgeons are using UKA to treat medial compartment arthrosis [6], such evidence is limited at best. Ultimately, I think most surgeons see this for what it is—a trade-off: better function with lower perioperative risks (UKA) or better survivorship (TKA).