A radiographic study of pediatric ulnar anatomy

Background: The adult ulna has a unique bony architecture that has been described in the literature, but, to the best of our knowledge, the ulnar anatomy in children has not been described. Methods: We examined 75 anteroposterior (AP) and 64 lateral radiographs (29 were bilateral) of 50, 0.5- to 11-year-old, healthy children's forearms. On AP radiographs, the total ulnar length, the ulnar proximal angle, the ulnar distal angle, and the distance between each angle from the tip of the triceps insertion; and, on lateral radiographs, the ulnar length and bow deviation were measured. The correlation between age and radiographic measurements, differences based on sex, differences compared with adults' measurements, and interobserver/intraobserver reliability were assessed. Results: Age had a very strong/strong positive correlation with length/distance measurements on both AP and lateral radiographs. Only AP ulnar distal angle was significantly different between sexes (females > males). Compared with the adult ulnar studies, the AP proximal angle in children is significantly smaller and the location of this angle is significantly more distal. Interobserver and intraobserver reliability were very good for length/distance measurements on AP and lateral radiographs. Conclusions: The knowledge of pediatric ulnar anatomy could be helpful in the treatment of forearm deformities due to multiple hereditary exostosis and osteogenesis imperfecta, and in the treatment of ulnar fractures, particularly in Monteggia variants, where restoration of the correct forearm anatomy is essential to obtain good clinical and functional results. Level of evidence: Study of diagnostic test, Level II.