Mid-term Survivorship and Patient Satisfaction of Robotic-Arm Assisted Medial Unicompartmental Knee Arthroplasty: A Multicenter Study by Kleeblad et al., Arthroplasty (2018), in press, accepted manuscript.

Abstract
Background
Studies have showed improved accuracy of lower leg alignment, precise component position, and soft-tissue balance with robotic-assisted unicompartmental knee arthroplasty (UKA). No studies, however, have assessed the effect on mid-term survivorship. Therefore, the purpose of this prospective multicenter study was to determine mid-tem survivorship, modes of failure, and satisfaction of robotic-assisted medial UKA.

Methods
473 consecutive patients (528 knees) underwent robotic-arm assisted medial UKA surgery at four separate institutions between March 2009 and December 2011. All patients received a fixed-bearing metal-backed onlay tibial component. Each patient was contacted at minimum five-year follow-up and asked a series of questions to determine survival and satisfaction. Kaplan-Meier method was used to determine survivorship.

Results
Data was collected for 384 patients (432 knees) with mean follow-up of 5.7 years (5.0 – 7.7). The follow-up rate was 81.2%. In total, 13 revisions were performed, of which 11 knees were converted to TKA and in two cases one UKA component was revised, resulting in 97% survivorship. The mean time to revision was 2.27 years. The most common failure mode was aseptic loosening (7/13). Fourteen reoperations were reported. Of all unrevised patients, 91% was either very satisfied or satisfied with their knee function.

Conclusion
Robotic-arm assisted medial UKA showed high survivorship and satisfaction at mid-term follow-up in this prospective multicenter study. However, in spite of the robotic technique, early fixation failure remains the primary cause for revision with cemented implants. Comparative studies are necessary to confirm these findings and compare to conventional implanted UKA and TKA.