Robotic-Assisted Joint Line Preserving Unicompartmental Knee Arthroplasty Positioning Among Octogenarians

Introduction: Octogenarians undergoing unicompartmental knee arthroplasty (UKA) face increased risks of complications due to reduced bone support following osteoporosis. The aim of this study was to describe our preferred technique to balance robotic-assisted UKA in this specific patient population and to present its results. Methods: This retrospective analysis of prospectively collected data examined 121 consecutive octogenarian patients (median age 84 years, IQR 82-86) who underwent robotic-assisted medial UKA between September 2018 and December 2022 with ≥24 months follow-up. Patients aged ≤80 years, with ≤2 years of follow-up, or without informed consent were excluded. Data collection included radiographic measurements (HKA, LDFA, MPTA, joint line height), patient-reported outcome measures (Oxford Knee Score, Knee Society Score), and complications. Statistical analysis employed descriptive statistics, paired t-tests, Cohen's d for effect sizes, and the McNemar test for categorical variables. Results: The hip-knee-ankle angle improved significantly from 174.43° to 178.04° (mean difference 3.61°, 95% CI 3.13-4.09, p < 0.001). Patient-reported outcomes demonstrated substantial improvements: the Knee Society Score increased by 83.09 points (95% CI 79.76-86.42, p < 0.001, Cohen's d = 4.53), and the Oxford Knee Score increased by 17.09 points (95% CI 15.42-18.76, p < 0.001), with both exceeding minimal clinically important differences. Only 7.4% (9/121) of cases exhibited joint line lowering of >2 mm, with 1.7% (2/121) having both post-operative HKA <175° and joint line lowering of >2 mm. The implant survival rate was 100% with minimal complications, including two conservatively managed tibial plateau fractures and two cases of wound dehiscence with no further surgery needed. Conclusions: Robotic-assisted medial UKA can consistently preserve joint line height while achieving excellent alignment correction and clinical outcomes in octogenarians, potentially addressing failure risks in this specific population.