Accepted landmarks for determining rotation include the posterior condyles, Whiteside’s line, arbitrary 3-4° of external rotation, and transepicondylar axis (TEA). All methods require anatomical identification, which may be variable.

The purpose of this study was to radiologically evaluate femoral component rotation (CT analysis) based on a method that references to the tibial axis and balanced flexion-tension.

Methods: CT scans of 38 randomly selected TKA were evaluated to determine femoral component positioning. Spiral CT scans of the femoral epicondylar region with eight 4mm cuts were performed to accurately identify medial and lateral epicondyles. Rotational alignment was measured in relation to the transepicondylar axis using CT-implemented software by two independent radiologists.

Results: Femoral component rotation ranged from 4° internal rotation to 5° external rotation with a mean of 0.0° = parallel to the TEA. All 38 cases had satisfactory clinical results, range of motion of over 90°, and showed perfect patello-femoral tracking and patellar congruency.

Conclusions: Femoral rotation position based on tibial axis and balanced flexion tension is patient specific, reproducible and results in predictable patella tracking. CT analysis in this study confirms that the tibial axis method produces a consistent femoral component positioning that relates accurately to the TEA. Tibial axis method avoids the need for arbitrary landmark identification, placing the femoral component predictably in an optimum position in relation to the tibia and patella.