A special type hereditary multiple osteochondroma in patients with proximal ulna osteochondroma

Background: Hereditary Multiple Osteochondroma (HMO) is a rare condition that frequently impacts the forearm and results in radial head dislocation. Consequently, orthopedic surgeons prioritize prognostication of factors contributing to radial head dislocation and implementing preventive measures. The purpose of this study was to introduce a specific type of HMO prone to radial head dislocation and provide potential therapeutic strategies for clinical prevention. We retrospectively reviewed the patients with HMO treated in our center between 2010 and 2021. Radiographic measurements included the presence or absence of osteochondromas in the entire forearm, degree of ulnar bow, and ulnar length percent. Patients were separated into 3 groups based on the status of the radial head: located, subluxated, and dislocated. Radiographic measurements were compared using a Brown-Forsythe and welch test with Tamhane’s T2 post-hoc analysis. Results: A total of 12 patients with 14 forearms were included in the study. Six forearms had the radial head dislocation, while 3 with radial head subluxation and 5 with located radial head at the initial visit. At the final follow-up, all patients with proximal ulnar tumors who did not undergo resection developed subluxation or dislocation. Simultaneously, all patients with proximal tumors exclusively in the radius remained free from subluxation or dislocation of the radial head throughout the follow-up period. The average ulna length percent in Located group was 1.07±0.05, while 1.09±0.03 in Subluxation group and 0.98±0.09 in Dislocated group. The average ulna bow in Located group was 12°±7°, while 9°±6°in Subluxation group and 15°±8°in Dislocated group. There was no significant difference among them. Conclusions: Osteochondroma of the proximal ulna poses a significant risk factor for radial head dislocation. Consequently, surgical excision of the proximal ulna tumor emerges as a potential therapeutic intervention to mitigate the occurrence of radial head dislocation in affected individuals.