Equivalent accuracy of image-based and imageless robotic platforms in achieving planned femoral rotation in primary total knee arthroplasty: A CT-based study

Robotic-assisted total knee arthroplasty (TKA) is increasingly adopted worldwide, yet comparative data on the rotational accuracy of image-based and imageless platforms remain limited. The aim of this study was to compare the accuracy of image-based and imageless robotic platforms in achieving planned femoral rotation in primary TKA. We hypothesized that the two platforms would be equivalent, with any difference within ±1°.

This single-surgeon retrospective cohort study included patients undergoing image-based and imageless robotic-assisted TKA for primary osteoarthritis. All patients underwent pre- and postoperative computed tomography (CT) scans. Native femoral rotation was defined using the transepicondylar axis (TEA)-posterior condylar axis (PCA) angle. Femoral rotation was planned intraoperatively relative to the PCA, and postoperative TEA-PCA was measured on CT. Accuracy was defined as the absolute difference between achieved and intended rotation. Measurements were independently performed by two blinded fellowship-trained knee surgeons. Statistical analysis included two one-sided tests (TOST) equivalence testing and analysis of covariance (ANCOVA). Significance was set at p < 0.05.

A total of 150 TKAs were included (imageless 79, image-based 71). Patients in the image-based group were younger (67.7 vs. 71.3 years, p = 0.007), with no other baseline differences. The mean rotational error was 1.3 ± 1.0° for imageless and 1.2 ± 1.2° for image-based TKA (p = 0.346; effect size -0.09). Equivalence testing confirmed statistical equivalence, with the 90% confidence interval (-0.23 to 0.31) lying within the predefined ±1° margin (p < 0.01). ANCOVA demonstrated a small adjusted difference of 0.51° (p = 0.045), with minimal explained variance (adjusted R² = 0.01). Intra-observer reliability was excellent (intraclass correlation coefficient [ICC] 0.91), while inter-observer reliability was good (ICC 0.82). No differences were observed in patient-reported outcomes, except lower pain scores in the image-based group at 12 months.

Image-based and imageless robotic platforms demonstrated equivalent accuracy in achieving planned femoral rotation in primary TKA. Any observed differences were not clinically meaningful.

Level III, retrospective comparative cohort study.