Morphology of Parsons' knob
The length of Parsons' knob was measured as b′–b (mm) (Fig. 2). The height of Parsons' knob was also measured using sagittal sections of Parsons' knob (Fig. 3). With these sections, a base line at the bottom of the knob was drawn parallel to the joint surface to connect the anterior and posterior edges of the knob (Fig. 3B). A perpendicular line was drawn from the top of the knob to the base line, and the length from the top to the intersection of the two lines was measured. Then, the height of the most medial portion [Fig. 3C(a)], most lateral portion [Fig. 3C(c)], and intermediate portion between both edges was measured [Fig. 3C