Summary

Robotic-assisted UKA has a lower revision rate than the conventional technique at 5 years of follow-up minimum, mainly due to aseptic loosening and implants malpositioning.

Abstract

Purpose

The robotic-assisted systems for the unicompartmental knee arthroplasty (UKA) have demonstrated their short- and mid-term interests. But there are very little data in the long term. Therefore, this study aimed to compare functional and radiological outcomes, complications, and revision rates at a minimal follow-up of 5 years after UKA, performed with either an image-free robotic-assisted system or the conventional technique.

Methods

This retrospective case-control study included 143 UKA between 2013 and 2016, whose 66 robotic-assisted UKA and 77 mechanical UKA. The exclusion criteria were associated procedures (anterior cruciate ligament reconstruction, patellofemoral prosthesis) or UKA revisions. The implants were the same between both groups. Clinical data and radiographs were collected preoperatively, at 2 months, at 1 year, and the last follow-up. The preoperative demographic and radiological parameters were similar between both groups. The mean age was 66 years ±9. The mean BMI was 26.6 kg/m2 ±4 in both groups. After a minimum of 5 years, all patients have been reviewed and completed IKS and the Forgotten Joint Score (FJS). Complications, reoperation, and revision, and their etiology were recorded at the last follow-up.

Results

The mean follow-up was 6.69 years±0.9 for the robotic-assisted group and 6.66 years ±1.1 for the control group. The IKS function (87.3 ±14 in the robotic group versus 81.1±15 in the mechanical group, p=0.15) and IKS knee scores (88.9 ±15 versus 86.3 ±13, resp, p=0.52) and the FJS (95.9 ±8 versus 94 ±10, resp, p=0.3) were comparable between both groups. No difference was found for the radiological results. The rate of revisions was significantly higher in the mechanical group (18.2%, n=14) than the robotic group (4.5%, n=3) at the last follow-up (p=0.018). The revisions were performed after 1.2 years in the robotic group (vs 1.8 years in the mechanical group). The main causes of revision in the mechanical group were aseptic loosening, malalignment, and unexplained persistent pains.

Conclusion

The functional and radiological outcomes were comparable at 5 years minimum. Robotic-assisted UKA has a lower revision rate than the conventional technique at 5 years of follow-up minimum, mainly due to aseptic loosening and implants malpositioning. These results at longer-term confirmed the interest of the robotic system to perform UKA.