Early Experience with Mobile Bearing Unicompartmental Knee Arthroplasty

A mobile-bearing unicondylar device was approved in 2004. Availability and interest in UKA has led to a surge in use. Any new device requires review of early results to identify problems or highlight changes in indications and outcomes. This prospective study reviews the initial experience with a mobile-bearing UKA (MB-UKA). July 2004 to April 2006: 257 MB-UKA (219 patients) were implanted, making the study group available for minimum 2-year followup. Indications for medial MB-UKA included osteoarthritis, avascular necrosis, and posttraumatic disease with correctible full-thickness intraarticular varus deformity, intact lateral joint space on valgus stress radiograph, and an ACL. No other indications or contraindications were used, allowing investigation of demographics and location of preoperative pain as variables. Statistical analysis included student’s t-test and log-rank analysis of survivorship variables. Average followup was 18 months. Ten knees were revised for a survivorship of 96.11% at 45 months. BMI and age were not predictive of failure. Anterior knee pain or isolated medial pain was not predictive of survival. While the variables studied were not significant for failure; statistically higher KS scores (pain and total) were noted in patients with BMI <32 (p = 0.04), age older than 50 years (p = 0.003), isolated medial sided pain (p = 0.02), and absence of anterior knee pain (p = 0.004). The need for revision appears unaffected by demographics and pain location. Knee scores are lower in patients with BMI >32, younger than 50, and those with preoperative anterior knee pain or pain located other than on the medial side of the knee. Despite lower KS scores, MB-UKA may remain the best option in obese, younger, more active, or more demanding patients. Broader indications do not appear to affect the early survivorship of this device.