Predictability of Polyethylene Insert Size Using an Imageless Robotic System in Total Knee Arthroplasty: A Single-Surgeon Experience

Background Imageless robotic-assisted total knee arthroplasty (TKA) relies on intraoperative landmark acquisition and gap balancing to guide implant positioning and polyethylene insert selection. While prior studies have demonstrated high accuracy in achieving planned alignment and resection targets, limited data exist evaluating the predictability of polyethylene insert thickness using standardized pre-resection planning strategies. This study evaluated the accuracy of a standardized 10-mm polyethylene planning strategy in imageless robotic-assisted TKA and assessed whether deviation from the planned insert thickness was associated with postoperative interventions. Methods A retrospective review of a prospectively maintained, single-surgeon series of 400 primary TKAs performed using the imageless ROSA robotic system between 2021 and 2023 was conducted. A kinematic alignment strategy targeting a balanced 22-mm flexion and extension gap corresponding to a planned 10-mm insert was used in all cases. Exact accuracy was defined as a final 10-mm insert; acceptable accuracy was defined as ±1 mm (10–11 mm). Associations between insert thickness, intraoperative re-resection, manipulation under anesthesia (MUA), revision, and learning curve effects were analyzed. Results A 10-mm insert was used in 73% of cases, and 88% achieved insert thickness within ±1 mm of the planned target. Intraoperative re-resection occurred in 8% of cases, with 94% consisting of 2-mm adjustments. The overall revision rate was 5.8%, and the MUA rate was 10.3%. No statistically significant association was identified between insert thickness, re-resection, and revision or MUA ( P > 0.05). Learning curve analysis of the first 30 cases demonstrated similar insert distribution and intervention rates. Conclusion Imageless robotic-assisted TKA using standardized 10-mm pre-resection planning demonstrated reproducible polyethylene insert selection. Deviation from planned thickness and minor intraoperative re-resections were not associated with increased postoperative intervention, supporting the reliability of imageless robotic workflows in primary TKA.