Objectives: Femoral component rotation affects knee function and component survival in total knee arthroplasty (TKA). However, the presence of posterior femoral condylar cartilage leads to discrepancies in the femoral posterior condylar axis (PCA) between robotic-assisted TKA and manual TKA. The purpose of this study was to investigate the relationship between the discrepancy in thickness of the medial and lateral posterior femoral condylar cartilage and the discrepancy between robotic-assisted and manual rotation of the femoral component.
Methods: In the computed tomography (CT) modeling simulation section, we retrospectively reviewed a total of 18 preoperative knee CT scans of patients who underwent robotic-assisted TKA with different femoral prosthesis sizes between January 2022 and January 2023 to measure the mean posterior femoral condylar distance between femurs of different sizes. In the prospective clinical study section, we prospectively measured the cartilage thickness of the medial and lateral posterior condyles in 60 patients who underwent Mako-assisted TKA between October 2023 and December 2024.
Results: According to our mathematical model of the difference between robotic and manual femoral component rotation in the presence of different femoral sizes and differences in medial and lateral posterior condyle cartilage thicknesses, the maximum value of angular discrepancy of PCA was 4.02° and the minimum value was 1.13°. The average cartilage thickness difference between the medial and lateral posterior femoral condyles was 0.29 ± 0.97 mm (−2.00 to 2.10 mm). The mean difference in femoral component rotation between robotic and manual TKA was 0.35° ± 1.21° (−2.61° to 2.82°).
Conclusion: For most patients with posterior femoral condylar cartilage, the PCA determined by robotic-assisted surgery was greater than that determined manually. Therefore, when surgeons perform TKA with robotic assistance, it is important to be aware of this discrepancy in femoral component rotation to avoid complications such as poor component survival due to inadequate rotation of the femoral component.
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2025 The Author(s). Orthopaedic Surgery published by Tianjin Hospital and John Wiley & Sons Australia, Ltd.
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