Radiographic accuracy of implant positioning in unicompartmental knee arthroplasty, does an imageless robotic system make a difference?

BACKGROUND: Robotic-assisted technologies and evolving implant designs have been introduced in unicompartmental knee arthroplasty (UKA) to improve the accuracy and reproducibility of component positioning. However, the relative contribution of robotic assistance compared with conventional instrumentation to radiographic outcomes in experienced, high-volume centers remains unclear.

METHODS: This retrospective comparative study included 96 consecutive medial UKAs performed at a single high-volume institution. Patients were stratified into three groups: Journey I UKA implanted with NAVIO imageless robotic assistance (n = 38), Journey II Uni UKA implanted using conventional instrumentation (n = 27), and Journey II UK UKA implanted with CORI imageless robotic assistance (n = 31). Standardized standing long-leg weight-bearing radiographs were obtained preoperatively and postoperatively. Radiographic evaluation included hip-knee-ankle (HKA) angle, femoral component coronal angle (FCCA), tibial component coronal angle (TCCA), and sagittal alignment parameters. Tibial coronal alignment was interpreted according to the Cartier metaphyseal alignment philosophy. Intergroup comparisons were performed using appropriate statistical tests.

RESULTS: Baseline demographic characteristics and preoperative radiographic parameters were comparable among the three groups (all p > 0.05). Postoperative mean HKA was 177.1° ± 2.1° in the Journey I NAVIO group, 177.3° ± 2.5° in the Journey II Uni conventional group, and 177.7° ± 2.2° in the Journey II UK CORI group, with no statistically significant differences (p = 0.56). Femoral and tibial component coronal alignment, including TCCA, showed no significant intergroup differences. All cases across the three cohorts were within predefined safe zones for HKA, FCCA, and TCCA. Sagittal alignment parameters were also comparable between groups.

CONCLUSION: In a high-volume center adopting a consistent alignment philosophy, medial UKA achieves equivalent and highly accurate radiographic outcomes regardless of robotic assistance or conventional instrumentation.