Robotic Total Knee Arthroplasty is Associated with Thinner and Less Constrained Polyethylene Inserts

Introduction: Accurate pre-resection assessment of gap measurements during total knee arthroplasty (TKA) may reduce the need for thicker polyethylene inserts or those with higher constraint by allowing the surgeon to address potential imbalance through guiding bony resections and implant position. This study aimed to determine whether robotic assistance with pre-planning allowed for the use of thinner and less-constrained polyethylene inserts compared to conventional methods. Materials and Methods: Records were retrospectively reviewed for 408 patients who underwent primary TKA. Patients were divided into cohorts based on the technique utilized—conventional, manual methods with a jig-based system (CM-TKA, 169 knees) versus robotic-assisted TKA (RA-TKA, 237 knees). Operative notes were reviewed for implant brand, thickness of the polyethylene insert, degree of constraint of the polyethylene insert, and whether robotic assistance was used to complete the operation. Statistical analysis was performed using Chi-square tests for categorical and t-tests for continuous variables. Results: There were no significant differences in demographic characteristics between the RA-TKA and CM-TKA groups. Statistically significant differences were observed between cohorts in mean polyethylene insert thickness (11.0mm ± 1.3mm vs. 11.7mm ± 1.7mm, p<0.0001), rate of use of the thinnest 10mm insert (43% vs. 34%, p=0.048), rate of “outlier” insert sizes ≥14mm (5% vs. 18%, p<0.0001), and rate of constrained insert use (4% vs. 18% of knees, p<0.0001). Conclusion: In a review of 408 consecutive TKA patients, use of robotic-assisted techniques allowed for the use of thinner polyethylene inserts, fewer “outlier” polyethylene sizes, and reduced need for constrained inserts compared to conventional, manual methods.