Measurement of preoperative valgus stress angle (VSA) on a valgus stress radiograph of a knee obtained using a Telos device. Midpoints of the distal femoral shaft, which are 10 and 15 cm from the knee joint line, respectively, and the midpoints of the proximal tibial shaft, which are 7.5 and 12.5 cm from the knee joint line, were assigned and connected on each anteroposterior valgus stress radiograph. The angle between these two lines was defined as the VSA.