Abstract
INTRODUCTION: In 2019, a new fixed-bearing implant for unicondylar knee arthroplasty (UKA) was introduced that incorporated a round-on-flat design featuring an Oxinium femoral component coupled with a highly crosslinked polyethylene bearing surface. Compared to prior implants, the design featured smaller size increments coupled with medial and lateral-specific tibial baseplates. The objective of this study is to describe our institution's early experience with this UKA implant system by evaluating survivorship, reasons for revision, and patient-reported outcome measures (PROMs). METHODS: The 944 UKAs that comprise the study population, including 814 medial and 130 lateral joint replacements, were performed by six surgeons from September 2019 through the end of December 2023. All UKA components were cemented, the mean age at surgery was 67.1±10.0 years, 57% (537/944) of the UKAs were performed among women, and the mean body mass index was 30.3±6.2 kg/m(2). Outcome measures included Kaplan-Meier survivorship using reoperation for any reason as an endpoint, reasons for reoperation, range of motion, and PROMs that were collected preoperatively and postoperatively at 4 weeks, 4 months, 1 year, and 2 years. RESULTS: Using reoperation for any reason as an endpoint, 1-year survivorship was 99.3% (95% CI, 98.7 to 99.9%) and 2-year survivorship was 98.2% (95% CI, 96.9 to 99.5%). There were nine reoperations among the 944 UKAs, including three for infection, two for tibial loosening, one for femoral loosening, one for progression of arthritis, one for patellar instability, and one for recurrent hemarthrosis. The mean time to reoperation was 0.82±0.68 years and all were performed among medial UKAs. Range of motion increased from 117±8 degrees preoperatively to 122±6 degrees at 1-year follow-up. PROMs, including the Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS JR) and the Patient-Reported Outcomes Measurement Information System (PROMIS) Global Health Physical score, demonstrated progressive increases from the preoperative assessment through 2-year follow-up. For UKAs with preoperative and 2-year KOOS JR scores, the mean change was 31±17. CONCLUSION: As new implants and technologies are introduced, documenting the early outcome from high volume centers can offer valuable insights to validate the effectiveness of implant systems before they are adopted by the broader orthopedic community. This study demonstrates encouraging early outcome data associated with a contemporary UKA system based on survivorship and PROMs. At this early stage, there are no implant-related concerns but obtaining additional follow-up will be important to quantify how revisions and PROMs evolve over time.