The optimal procedure for isolated end-stage medial compartment knee osteoarthritis (OA) remains uncertain, with debate persisting between unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA). The aim of this narrative review is to evaluate current outcome measures in knee arthroplasty (KA) and explore how evolving patient populations and technological advancements may necessitate the use of different patient-reported outcome measures (PROMs) for evaluating UKA. While UKA offers potential advantages over TKA in early pain relief and functional outcomes, most randomised control trials using traditional PROMs have failed to show definitive superiority. The recent introduction of robotic assistance may have further enhanced the benefits of UKA. However, it remains uncertain whether the advantages outweigh the higher revision rates associated with UKA. Although traditional PROMs, such as the Oxford Knee Score or Knee Injury and Osteoarthritis Outcome Score, were designed for the KA population of 30 years ago, they continue to be employed today. The current KA population, particularly those undergoing UKA, are typically younger, physically fitter, and have higher functional demands than those for whom traditional PROMs were originally designed. As a result, these PROMs are now limited by ceiling effects. High-performance PROMs, such as the Forgotten Joint Score-12 or the metabolic equivalent of task score, have recently been utilised for high-demand patients and do not have postoperative ceiling effects. Return to work and sport are also important outcomes that are often overlooked for younger, high-demand patients. Future studies should aim to define the differences between UKA and TKA populations, identify patient factors that predict UKA success, and validate high-performance PROMs for UKA. This will provide deeper insights into the functional benefits of UKA and TKA, enabling patients and surgeons to make more informed decisions regarding implant selection.
