Radial head and olecranon ossification

(A) Limits of the border of olecranon ossification at birth, 8 years, and 12 years.
(B) Lateral view of elbow at age 6 months. The radial head is not visible and the proximal margin of the olecranon is perpindicular to the long axis of the ulna.
(C) Lateral view of the elbow at age 6 years. A small oval nucleus marks the initial ossification of the radial head. The proximal margin of the olecranon is now oblique to the long axis of the ulna.
(D) At 10 years of age, the radial head is now widened and flat and a secondary ossification center for the olecranon is forming along with a sclerotic border at the proximal olecranon metaphysis.
(E) Bipartite secondary ossification center of the olecranon. The larger center is the traction center (black arrow). The smaller, more proximal center is the articular center (white arrow).
(F) Before complete fusion of the radial head and olecranon, a partial line remains (arrows), bordered by a sclerotic margin.