Illustration showing the secondary centres of ossification (blue) in the elbow. Ossification is the formation of new bone, here from cartilage. Secondary ossification occurs throughout childhood as the bones continue to grow and take form. The elbow joint has six secondary ossification centres that appear in a consistent order as the person ages. In order they are the; capitulum (centre left at left and centre at right), radial head (right at right) adn lower left at left, internal (medial) epicondyle (right at left), trochlea (centre right at left), olecranon (left at right) and external (lateral) epicondyle (upper left at left). The ages the centres first appear is variable, and is often earlier in girls, but on average, in order, they appear at the ages of 1, 3, 5, 7, 9 and 11 years. For a version of this image with labels see C051/3516.