Growth of the capitellar ossification center and its relationship within the lateral condyle of the distal humerus in skeletally immature elbows: a study using MR images.

To more accurately interpret the anterior humeral and radiocapitellar lines on simple radiographs of pediatric elbow, we investigated age-related changes of the capitellar ossific nucleus (CON) by using MRIs. Elbow MRIs from 79 children aged 1-16 years and free from demonstrable lesions in the distal humerus were retrospectively reviewed. On coronal images, the distal cartilaginous vertex of the capitellum, which articulates with the center of the radial head, was situated about 15%p laterally from the center of CON regardless of age. On sagittal images, the anterior humeral line passed the center of CON in older children (>6 years), but passed anteriorly in children with an age ≤6 years. Also on sagittal images, the anterior cartilaginous vertex of the capitellum was positioned within 10% of the level of the center of CON in all age groups. Recognition of the capitellar ossification pattern within the lateral condyle would aid in more accurate assessment of pediatric elbows on simple radiographs. Based on the results of the present MRI study, the following points were identified for the interpretation of simple radiographs: (1) The radiocapitellar line on anteroposterior views intersects the CON by about 15%p laterally regardless of age; (2) The anterior humeral line on lateral views intersects the center of the CON in older children, but passes anteriorly in younger (≤6 years) children; and (3) The radiocapitellar line on lateral radiographs invariably passes the center of CON regardless of the age.