Determine the valgus angle

Determine the valgus angle

The selection of distal femur cut valgus angle is mainly based on preoperative template measurement and some clinical factors. The goal of most knee arthroplasty is to restore the mechanical axis to neutral position. The most effective method is to draw the neutral axis of the distal femur and the neutral axis of the proximal tibia. When determining the valgus angle, a full length anteroposterior radiograph from hip joint to rotation neutral position of knee joint should be taken. Draw a line from the center of the hip to the center of the knee, and then draw a vertical line (perpendicular the line) on horizontal plane of the knee (Fig. 1A). Finally, measuring the angle between the anatomical axis of the femoral shaft and the line, the value is usually 5°to 7°(Fig. 1B).

Another advantage of preoperative template measurement is that it can indicate the relative cutting bone mass of the medial-lateral condyle. In addition of some cases of special osteotomy, fractures or dysplasia, the cutting bone mass is usually slightly higher on the medial side than on the lateral side. In the articular line, the vertical line determined by the neutral axis often passes through the ivory bone level in the medial femoral condyle, while the lateral side passes through the existing cartilage level, or the actual bone at the distal end of lateral condyle is about 2mm level (Fig. 2A). This result is very useful for distal osteotomy, and the operative procedure can be further compared with the results of preoperative X-ray template measurement. In some cases of severe knee valgus, the difference can be quite obvious (Fig. 2B)(Fig. 3).