Ulnar size, not shape, differs between men and women

Understanding normal ulnar geometry is important for surgeons planning corrective ulnar osteotomies. We developed a statistical shape model of the ulna to investigate sex differences in its three-dimensional geometry. The model was based on the right and left ulnae of 20 males and 20 females, isotropically scaled to a uniform length. The first 7 shape modes captured 81% of the total ulnar shape variation. The only significant differences between males and females were in the first and fourth modes. These modes primarily captured volumetric scaling of the ulna. The remaining modes, which captured changes in the curvature of the ulna and the geometry of its anatomical features, were not significantly different. Based on these results, the ulna appears to differ primarily in size, rather than in shape, between males and females.