Fig. 1

Irregularity Index System procedure

Firstly, DICOM data were input into the computer （Fig. 1a）. Secondly, captured images were converted into black and white images （Fig. 1b）. Thirdly, the contour of the femoral condyle was extracted, and the dimensions of both the upper and lower surfaces of the extracted contour were determined （Fig. 1c, d）.