Robotic-Assisted Total Knee Arthroplasty Improves Accuracy and Reproducibility of the Polyethylene Insert Thickness Compared to Manual Instrumentation or Navigation: A Retrospective Cohort Study.

BACKGROUND

Increased accuracy and lower rates of component positioning outliers have been associated with better long-term survival and functional outcomes of total knee arthroplasty (TKA). This study investigates the accuracy of robotic-assisted TKA compared to navigation-assisted and manual instrumentation techniques, using polyethylene tibial insert thickness as a surrogate.

METHODS

Consecutive primary TKA by a single surgeon were retrospectively reviewed and divided in 3 groups: manual instrumentation, navigation-assisted, and robotic-assisted (RA-TKA). Polyethylene insert thickness, deviation from planned thickness, and rate of outliers were compared between the 3 groups using nonparametric analysis of variance, Kruskal-Wallis tests, and Bonferroni corrections. Logistic regression analysis was performed to identify predictors of polyethylene thickness ≥9 mm. The learning curve for RA-TKA was evaluated with a box plot graph of groups of 10 consecutive cases.

RESULTS

There were 474 patients in manual instrumentation TKA, 257 in navigation-assisted TKA and 225 in RA-TKA, with median polyethylene thicknesses of 6.0 (interquartile range 5.0-7.0), 6.0 (interquartile range 5.0-7.0), and 5.0 (interquartile range 5.0-6.0) millimeters, respectively (P˂0.001 RA-TKA compared to both other groups). Polyethylene inserts with a thickness ≥9 mm were used in 28 (5.9%) manual instrumentation TKA, 13 (5.1%) navigation-assisted TKA, and 1 (0.4%) RA-TKA ( = .004). Independent predictors for polyethylene thickness ≥9 mm included surgical technique, left side, and male sex. A learning curve of <30 cases was observed before consistent polyethylene thickness was achieved in RA-TKA.

CONCLUSIONS

Tibial polyethylene insert thickness, as a surrogate of surgical accuracy, is more reproducible in robotic-assisted than in navigation-assisted or manual-instrumentation TKA. The learning curve to reach high levels of reproducibility with this technique is relatively short.