Abstract
Introduction
Robotic technology has been applied to unicompartmental knee arthroplasty (UKA) in order to improve surgical precision in prosthetic component placement, restore knee anatomic surfaces, and provide a more physiologic ligament tensioning throughout the knee range of motion. Recent literature has demonstrated high reliability of robotic-arm assisted UKA in component placement and executing a soft-tissue tensioning plan, with excellent short-term survivorship. Few studies have investigated survivorship and patients' satisfaction at longer follow-ups. Therefore, the purpose of the present study was to determine the survivorship, clinical results and patients' satisfaction of robotic-arm assisted UKAs at a mid-term follow-up, with a minimum of 5 years of follow-up.
Methods
The present retrospective study includes 252 patients (260 knees) who underwent robotic-arm assisted fixed bearing metal backed UKAs at a single centre between April 2011 and July 2013. The mean age at surgery was 66.2 years (SD 8.6). Post-operatively, patients were administered the Forgotten Joint Score-12 (FJS) and asked about their satisfaction level after knee surgery (grade from 1 to 5). Post-operative complications were recorded. Failure mechanisms, revisions and reoperations were also assessed. Kaplan-Meier survival curves were calculated, considering reoperation for all causes and revision as the events of interest.
Results
A total of 223 patients (231 robotic-arm assisted UKAs) were assessed at a mean follow-up of 5.8 years post-operatively (88.5% follow-up rate, min. 60 months, max. 87 months). In 219 cases, a medial robotic-arm assisted UKA was implanted, in 12 cases a lateral implant was performed. Five medial robotic-arm assisted UKAs were revised, resulting in a survivorship of 98% (C.I. 96.0%–99.1%). One case underwent revision for prosthetic joint infection, one for tibial aseptic loosening, one for post-traumatic tibial plateau fracture, and two for unexplained pain. No lateral robotic-arm assisted UKAs were revised, resulting in a survivorship of 100%. On average, the FJS and the satisfaction level resulted 75.6 (SD 26.1) and 4.2 (SD 1.0) in medial UKAs, and 81.7 (SD 15.3) and 4.4 (SD 0.8) in lateral UKAs, respectively. In medial UKAs 83% of the examined cohort reported good/excellent FJS outcomes, while 92% of the lateral UKA patients had good/excellent FJS results.
In medial UKAs, male patients resulted to have better FJS (p<0.01) and higher satisfaction level (p<0.03) compared to female patients, while no outcome differences were reported in patients with BMI>30 and among different age groups. Given the small number of lateral UKAs included in the present patients' cohort, no statistical analysis was performed on this group.
Conclusion
In the present study, survivorship and clinical outcomes of a large cohort of 223 patients undergoing medial and lateral robotic-arm assisted UKAs were assessed at a mean of 5.8 years of follow-up. The overall survivorship was found to be 98%, with unexplained knee pain as the most common reason for UKA revision. The present study shows that robotic-arm assisted UKA patients had lower revision rates for aseptic loosening and osteoarthritis progression compared to conventional UKA at mid-term follow-up, as reported in the literature. The good post-operative clinical scores highlight the efficacy of robotic-arm assisted UKA in restoring knee function and relieving pain.
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