Medial unicompartmental knee arthroplasty (UKA) for isolated medial knee arthritis is a highly successful and efficacious procedure. However, UKA is technically more challenging than total knee arthroplasty (TKA). Research has shown that surgical technical errors may lead to high early failure rates. Haptic robotic systems have recently been developed with the goal of improving accuracy, reducing complications, and improving overall outcomes. There is little research comparing robotic-assisted UKA to standard UKA. The goal of this study was to compare clinical and radiographic data for matched cohorts who received robotic-arm assisted UKA or standard instrumentation UKA.

We performed a non-randomised, retrospective review of 30 robotic-arm assisted UKA and 32 manual UKA performed by single fellowship-trained joint arthroplasty surgeon (SKK) over 2.5 years. All procedures completed through a medial parapatellar approach. All components were cemented. All tibial components were a metal-backed onlay design. Average follow-up was 10.1 months (range 5–36). A full clinical/hospital chart review of demographic, intra- and post-operative measures was performed. Radiographic analysis of pre- and post-op images evaluating sagital and coronal alignment, and component positioning was performed by single observer (DCH), using OsiriX imaging system (Pixmeo; Geneva, Switzerland). Radiographs were available for analysis in 28 robotic-assisted and 30 manual patients. Statistical analysis was performed using SPSS v. 20. Comparison between group means was performed as well as calculation of variance in component placement within groups.

No demographic differences were seen between groups. Operative time was significantly longer in robotic-assisted UKA compared to the manual group. Minimal clinical post-op differences were seen between groups. The robotic group showed some early advantage in ambulation/ROM during inpatient stay. This ROM difference reversed at 2 weeks post-op. Continued medial-sided knee pain was reported more commonly in robotic group. Radiographic results showed no difference between groups in pre-op mechanical alignment. The robotic group was significantly more accurate at recreating femoral axis. Accuracy in recreation of tibial slope/ was similar between groups. Accuracy of the tibial component in the coronal plane was not significantly different between groups. The robotic group did have significantly larger variance in coronal alignment of the tibial component. Medial overhang of tibial component was significantly greater and more variable in the manual group. Non-significant decrease in resection depth found in robotic group.

There were minimal clinical and radiographic differences between techniques. Clinically, both cohorts did very well. Radiographically, both groups had quite accurate placement of components, with the most obvious difference being the increased tibial component overhang in the manual group. The increased variance in tibial component alignment in the robotic group is likely due to the ability to more specifically alter the resection to fit the patient's specific anatomy. Overall, our data suggests that the purported benefits of robotic UKA may be obviated in the hands of a surgeon with training and experience in manual UKA implantation.