The purpose of this study was to identify patient factors and surgical characteristics predictive of Unicompatrmental Knee Arthroplasty (UKA) failure to determine additional perioperative factors associated with poor outcomes following UKA.
A prospectively maintained institutional joint registry was queried at a single academic center for all patients that underwent UKA between January 2010 – December 2016. Oxford outcome scores were collected both pre-operatively, at 6-months post-operatively, and annually from date of surgery. Patients were seen annually in clinic, and those without appointments were contacted via email for follow-up. The conversion to TKA was measured for all patients. Demographic, radiographic (joint space), comorbidities, and operative data was reviewed to determine factors related to conversion to TKA and survivorship of primary implant.
In total, 1,878 cases were performed, however, excluding multi-joint knees, there were a total of 1,186 knees in 1,014 patients with minimum 4-year follow-up. The mean age was 63.4±10.7 years and mean follow up was 76.4±17.4 months. Mean bmi was 32.3±6.5 kg/m2. (52.9% females, 47.1% males). There were 901 patients undergoing medial UKA, 122 patients undergoing lateral UKA, and 69 patients undergoing patellofemoral UKA. In total, 85 (7.2%) knees underwent conversion to TKA. Degree of preoperative valgus deformity (p=0.01), greater operative joint space (p=0.04), previous surgery (p=0.01), inlay implant (p=0.04), and pain syndrome (p=0.01) were associated with increased risk of revision surgery. Factors associated with decreased survivorship included patients with history of previous surgery (p<0.01), history of pain syndrome (p<0.01), and greater preoperative joint space (>2mm) (p<0.01). Lastly, there was no association of BMI to the predicted probability of conversion to TKA
Robotic-assisted UKA demonstrated favorable outcomes at 4-years with survivorship greater than 92%. The present series agree with emerging indications that do not exclude patients based on age, bmi, or degree of deformity, however, increased operative joint space, inlay design, history of surgery, and coexistence of pain syndrome are factors that increase risk of conversion to TKA.