Anatomical Assessment of the Distal Femur and Tibia for Optimal Femoral Rotational Alignment in Total Knee Arthroplasty

ABSTRACT

PURPOSE: This study aimed 1) to identify the rotational axis of the femur that provides a balanced 90degrees flexion space in TKA, 2) to assess the changes in the flexion space in deep flexion, and 3) to assess the changes in rotational alignment, with using the posterior condylar axis (PCA) as a guide, and as the changes are related to asymmetric cartilage erosion of the posterior condyle. MATERIALS AND METHODS: The axial MR images of the distal femur in knee extension and the coronal images of the distal femur and the entire tibia at 90 and 130degrees were examined in 40 healthy adults. RESULTS: The clinical transepicondylar axis (TEA) provides a balanced 90degrees flexion space on average. The balanced flexion space in 90degrees became an asymmetrical space with relative narrowing of the medial side in 130degrees. Every 1 mm of asymmetrical cartilage erosion between the posterior condyles changed the femoral rotation by approximately 1degrees when using the PCA as a guide. CONCLUSION: This study suggests that the clinical TEA is the rotational reference that provides a balanced flexion space. When using the PCA as a rotational reference, a surgeon should consider the potential change in the rotational angle that is caused by asymmetrical cartilage erosion.