Fig. 2

First, we marked a dot on the anterior tip of the distal tibia's articular surface on the sagittal CT view using freeware Image J. Second, we marked two more dots at 5 mm intervals from the first dot on the articular surface. Third, we calculated the coordinate of the center of a circle passing through these three dots, which correspond to the morphology of the anterior part of the tibial articular surface. Lastly, we marked a dot on the osteophyte tip and calculated the distance between the circle’s center and the dot on the osteophyte tips from their coordinates. If the distance is shorter than the circle’s radius by > 1 mm, osteophyte protrusion is confirm to be present