Teaching Case

An 11-year-old male presented to the orthopedic clinic with painless inability to supinate his left forearm. The patient’s mother reported she first noticed a difference in his left upper extremity mobility when he was 6 years old, but he was not reporting any discomfort or symptoms at the time. The patient’s father is also known to have a congenital upper extremity deformity.

Forearm radiographs taken in anteroposterior and lateral views demonstrated a short segment of osseous synostosis between the proximal radius and ulna, with mild bowing of the radius. Otherwise, the radial head was normally located. There was no evidence of fracture. Patient positioning limitations while the radiograph was being obtained further increased suspicion of radioulnar synostosis as a cause of the patient’s symptoms. According to the Cleary classification, these radiographs are consistent with type II proximal radioulnar synostosis.

Background and clinical perspective

Congenital proximal radioulnar synostosis is a rare malformation of bone development in which the proximal radius and ulna fuse [1]. It is bilateral in 60-80% of cases and often diagnosed in childhood after beginning sports when the child notices decreased rotational passive and active movements [2,3]. Symptoms of radioulnar synostosis involve restricted pronation and supination of the forearm which is typically non-painful. The exact etiology is unclear, but appears to be X-linked dominant with paternal inheritance [1]. Radioulnar synostosis may also develop following trauma and has been suggested to develop in relation to posterior radial head dislocation [1].

Imaging perspective

Anteroposterior and lateral radiographs of the forearm and elbow are recommended for evaluation of proximal radioulnar synostosis. A bony or fibrous synostosis may be visible, in addition to a wide and bowed radius, narrow and straight ulna, and possible dislocation or malformation of the radial head. Classification is determined by the Cleary Classification of Congenital Proximal Radioulnar Synostosis [2,3]. Type I includes fibrous synostosis with a normal anatomical location of the radial head. Type II involves osseous synostosis with a normal anatomical location of the radial head. Type III involves osseous synostosis with a hypoplastic and posteriorly dislocated radial head. Type IV involves short osseous synostosis with an anteriorly dislocated mushroom shaped radial head.

Outcome

Treatment options include observation or surgical intervention. Observation is the most common treatment especially in asymptomatic or unilateral cases. Operative treatment may be indicated in patients with severe or bilateral deformities limiting activity. Synostosis excision with soft tissue interposition may be performed to provide active forearm rotation. The increase in forearm rotation is typically only mild and recurrence is common. Alternatively, forearm derotational osteotomy may be performed to place the forearm in a more functional position. This procedure usually results in improved forearm position and patient function with a low rate of recurrence [4]. Surgical interventions carry a risk of refusion, compartment syndrome, or neurologic deficits [5].

Take home message

Congenital proximal radioulnar synostosis is a rare condition resulting in the proximal radius and ulna fusing, resulting in reduced range of rotational movements. Imaging will demonstrate a bony or fibrous synostosis and may involve dislocation of the radial head. Treatment can include observation, synostosis excision, or forearm derotational osteotomy.

Written informed patient consent for publication has been obtained.