Fig. 3.

Conducting a standard valgus stress radiograph. a A cloth cushion was placed under the knee to form a 20° flexion. The surgeon kept the lower limb alignment neutrally and applied valgus stress manually. The X-ray beam was adjusted (yellow solid line) until it was parallel to the tibial plateau (yellow dotted line). b A 25 mm diameter round metal was placed in the center of the anteroposterior diameter of the distal femur to calibrate the magnification