The ulna is much smaller than normal. The other bone of the forearm (the radius) is bowed and the hand turns out more.

Which arm bone is smaller?

Compared to the ulna, the radius is slightly shorter, thinner, and located on the medial side of the forearm. The radius is narrowest at the elbow and widens as it extends towards the wrist.

What is the shorter thicker bone in the forearm?

The radius is the thicker and shorter of the two long bones in the forearm. It is located on the lateral side of the forearm parallel to the ulna (in anatomical position with arms hanging at the sides of the body, palms facing forward) between the thumb and the elbow.