Relationship between frontal knee alignment and reference axes in the distal femur

The two transepicondylar axes (the clinical and surgical epicondylar axes), the posterior condylar axis, and the anteroposterior axis were constructed using computed tomography scans in 111 (66 patients) knees with symptomatic arthritis. The relationships between angles made by these reference axes and two angles indicating frontal knee alignment (the tibiofemoral valgus angle and the femoral valgus angle) were investigated. In Y of the knees, the surgical epicondylar axis could not be constructed because the sulcus of the medial epicondyle was not recognizable. The condylar twist angle was almost constant and averaged 6 degrees when the femoral valgus angle was 9 degrees or less, but increased gradually when the angle was greater than 9 degrees. The difference between the condylar twist angle and the posterior condylar angle was constantly 3 degrees. The anteroposterior axis was almost at right angles to the clinical epicondylar axis, and the relationship between these axes was constant, independent of the femoral valgus angle. With 3 degrees to 6 degrees external rotation relative to the posterior condylar axis, the femoral component could be set parallel to the transepicondylar axis in common varus or neutral knees. In cases with a larger femoral valgus angle, the anteroposterior axis would be a more reliable reference axis. Preoperative computed tomography scans are recommended for patients with knees with severe valgus deformity or severe hypertrophic osteoarthritis.