Optimizing femoral component rotation in TKA: The role of posterior condylar angle and condylar twist angle

Purpose

Femoral component rotation (FCR) is crucial in total knee arthroplasty (TKA). Currently, the optimal method to select FCR is unknown due to patient anatomy variation. Addressing the variability of femoral component rotation is critical to optimizing TKA outcomes and patient satisfaction. In this study, we aimed to identify outlier frequency and evaluate malrotation risk reduction by setting anatomic limits for FCR selection.

Methods

One hundred patients with end-stage knee osteoarthritis requiring TKA were included and categorized as normal rotation, internal rotation outlier, and external rotation outlier based on their expected FCR calculated intraoperatively using the modified gap balancing technique with a tensioning device. The computed FCR was then referenced to their Posterior Condylar Angle (PCA) and Condylar Twist Angle (CTA). The postoperative FCR and 1, 2-, and 5-years functional scores were also measured.

Results

Seventy-one knees (71%) were within the limits of PCA and CTA. The combined outlier frequency is 29%. The mean computed FCRs are 4.4° (±1.5), −1° (±2.6), and 8.0° (±3.4) for the normal, internal rotation, and external rotation groups, respectively. Whereas after setting the limits, the postoperative FCRs are 3.1° (±1.5), 3.9° (±1.7), and 2.5° (±1.4) for the three groups, respectively. The relative risk reduction against malrotation was 65%. At 1, 2, and 5 years post-TKA, all groups showed significant functional improvement, with no significant differences in functional outcomes between the normal and outlier groups.

Conclusion

The use of lower and upper limits for selecting the FCR based on CTA and PCA can be a valuable approach to reducing malrotation risk and achieving satisfactory functional outcomes in TKA. Addressing the individual patient's anatomic limits contributes to improved TKA outcomes and patient-specific component alignment, thus enhancing the overall success of the procedure.