Hypothesis: No study has evaluated radiocapitellar joint alignment or proximal radioulnar joint alignment postoperatively in congenital radioulnar synostosis patients. The aim of this study was to clarify the postoperative clinical results and radiocapitellar joint alignment. Methods: Eight forearms in 7 patients (6 males and 1 female with a mean age of 8.8 years) with congenital radioulnar synostosis, who underwent surgery with a minimum of a year and a mean of 2.1 years of follow-up, were evaluated. The surgery consisted of division of the synostosis and interposition with a pedicled vascularized adipofascial flap between the radius and the ulna. A corrective radial osteotomy was performed in 3 patients at the radial neck, which had a great angular deformity, and in 1 patient at the mid-diaphysis, which had a great bowing deformity. Radiocapitellar joint alignment was evaluated in a lateral view radiograph and classified into 3 types as anterior, intermediate, or posterior, defined by whether the radial neck and head axis were above, within, or below the capitellum. This alignment was evaluated preoperatively and at final follow-up. The active range of prono-supination was also evaluated as a clinical outcome. There was no patient who had recurrence of bony union at the divided synostosis. Results: Preoperatively, there were 5 forearms of the anterior type, 1 intermediate type, and 2 of the posterior type. At final follow-up, there were 2 forearms of the anterior type and 6 of the posterior type. Four forearms were changed into a posterior type. At the final follow-up, the active range was 37.5 ± 8° in pronation and 20 ± 10° in supination in the anterior type, and was 41 ± 23° in pronation and 26 ± l8° in supination in the posterior type. There was no significant difference in pronation or supination between types. It was more difficult to improve supination than pronation in each type. Summary points: In this case series, it was difficult to reconstruct the proper radiocapitellar alignment. To better improve the range, especially of supination, reconstruction of the radiocapitellar joint or the proximal radioulnar joint with a more accurate corrective radial osteotomy or sigmoid notch plasty should be considered.
