Favourable mid-term outcomes following unicompartmental knee arthroplasty with wider patient selection: A single-centre experience.

Objective: The purpose of this study was to determine surgical outcomes of robotic-assisted UKAs utilizing a wider set of indications than traditionally utilized. Additionally, we seek to determine alternate predictive factors as potential surgical indications and contraindications.

Methods: A prospectively maintained institutional joint registry was queried at a single academic centre for all patients that underwent robotic-assisted UKA between January 2010-December 2016. Surgical indication included isolated medial or lateral compartment degenerative disease with a stable knee based on physical exam. In 2013, haemoglobin A1C levels over 7.5% were considered contraindications, which was lowered to 7.0% in 2015. Preoperative alignment, age, activity level and degree of pain were not contraindications for surgery. Preoperative demographics, Oxford scores, radiographic (joint space), comorbidities and operative data were collected and reviewed to determine factors related to conversion to TKA and survivorship of the primary implant.

Results: In total, 1878 cases were performed; however, excluding multi-joint knees, there were a total of 1186 knees in 1014 patients with a 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/m. (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. Preoperative factors such as the 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 implant survivorship included patients with history of previous surgery (p ​< ​0.01), history of pain syndrome (p ​< ​0.01) and greater preoperative joint space (>2 ​mm) (p ​< ​0.01). There was no association of BMI to conversion to TKA.

Conclusion: Robotic-assisted UKA with wider patient selection demonstrated favourable 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.

Level Of Evidence: Level III.