Radioulnar Synostosis 

Updated: Aug 29, 2018
Author: Raymond Wurapa, MD; Chief Editor: Harris Gellman, MD 

Overview

Background

Synostosis, or osseous union, of any two adjacent bones can involve any part of the upper extremity. In 1793, Sandifort provided the initial description of congenital radioulnar (radial-ulnar) synostosis. This condition is caused by a failure of segmentation between the radius and the ulna.[1, 2] Synostosis between the radius and ulna can take two general forms: congenital and posttraumatic. Each form may be further classified into types (see Classification).

Posttraumatic radioulnar synostosis is a separate entity from the congenital form, having a different cause, treatment, and prognosis.[3] The traumatic form can occur anywhere between the radius and ulna along the length of the interosseous membrane. Gros first described posttraumatic radioulnar synostosis in 1864, reporting on a vicious union found in autopsy specimens. Groves later postulated that the success of treatment depended on where in the forearm synostosis had occurred.[4, 5]

Pathophysiology

The skeletal anomaly includes varying degrees of proximal radial and ulnar fusion, with or without involvement of the radial head. If the radial head is involved, it may be dislocated anteriorly or posteriorly.[6] A fibrous synostosis may allow limited motion. Regional soft-tissue hypoplasia is often present in severe cases, including those in which atrophy and fibrosis of the brachioradialis, pronator teres, pronator quadratus, and supinator muscles occur. The interosseous membrane also may be abnormal.

Embryologically, the upper limb bud arises from the unsegmented body wall at 25-28 days. The elbow becomes visible at 34 days, and the humerus, radius, and ulna become visible at 37 days. Initially, the three cartilaginous analogues of the humerus, radius, and ulna are connected before segmentation. Therefore, for a short time, the radius and ulna share a common perichondrium. Abnormal events at this time can lead to a failure of segmentation. The duration and severity of the insult can determine the degree of subsequent synostosis.

Endochondral ossification then proceeds, and the cartilaginous synostosis ossifies, either partially or completely, in the longitudinal or transverse plane. In the forearm, congenital radioulnar synostosis usually occurs between the proximal radius and the ulna. Although the condition is present at birth, it usually is not discovered until early adolescence, when the patient presents with a lack of pronation and supination.

Initially, the union may be more of a synchondrosis, but as the skeleton matures, the osseous bridge between the radius and ulna becomes more radiographically apparent. Usually, motion between the two adjacent bones, if existent, is minimal.[7, 8, 9, 10, 11, 12]

Etiology

The most common cause of posttraumatic radioulnar synostosis is an operatively treated forearm fracture. Patients with high-energy comminuted open fractures appear to be more likely to develop this complication. Monteggia and proximal forearm fractures also appear to have a higher incidence of synostosis.[13] The use of bone graft and of screws protruding through the opposite cortex also increase the incidence of synostosis.

Additionally, radioulnar synostosis is described as a consequence of soft-tissue injury, reconstructive procedures, any trauma causing hematoma formation between the radius and ulna, or injury to the interosseous membrane.[14] Patients with closed head injuries (skull/cranial trauma) appear to be more prone to this complication, presumably for the same reason that they develop heterotopic ossification.[15, 16]

Epidemiology

Congenital radioulnar synostosis occurs rarely, with approximately 350 cases reported in the literature. The rarity of this condition often leads to a delayed clinical diagnosis. Cleary and Omer reported an average patient age at diagnosis of 6 years, with a range of from 6 months to 22 years.[17] There is no sex predilection in congenital radioulnar synostosis, and no particular inheritance pattern is apparent. Sixty percent of cases are bilateral.

Because congenital radioulnar synostosis is caused by an in-utero insult, its association with other abnormalities is not surprising. About one third of cases are associated with general skeletal abnormalities, such as hip dislocation, knee anomalies, clubfoot, polydactyly, syndactyly, Madelung deformity, ligamentous laxity, thumb hypoplasia, carpal coalition, and problems of the cardiac, renal, neurologic, and GI systems.

Some associated abnormalities and syndromes are genetically determined, including acrocephalosyndactyly, Apert syndrome, Carpenter syndrome, arthrogryposis, mandibulofacial dysostosis, William syndrome, Klinefelter syndrome, Holt-Oram syndrome, microcephaly, multiple exostoses, and fetal alcohol syndrome.[18, 19] In 20% of their patients, Cleary and Omer found a genetic basis for an autosomal dominant form (with variable penetrance) of congenital radioulnar synostosis.[17]

Prognosis

Overall, results of surgical treatment for posttraumatic radioulnar synostosis are fair at best, with high failure rates and, commonly, loss of approximately one half of the intraoperative rotation. The use of postoperative indomethacin or low-dose limited field irradiation within the first 5 days after surgery has been shown to be effective in limiting the recurrence of synostosis.

 

Presentation

History and Physical Examination

Functional deficits associated with congenital radioulnar synostosis depend on the severity of the deformity and on whether or not it is bilateral. In cases involving severe, fixed forearm pronation deformity, the patient cannot compensate for the resulting functional limitations by using scapular and glenohumeral motion. The forearm usually lies in the pronated or hyperpronated position.

Hypermobility at the midcarpal and radiocarpal joints can disguise this lack of forearm rotation, particularly with neutral or mild pronation deformities. There is usually full or nearly full elbow range of motion, with flexion contractures rarely exceeding 30º. An abnormal carrying angle of the elbow or a shortening of the forearm may be observed.

Pain is usually not a presenting symptom until the teenage years, when progressive and symptomatic radial head subluxation may be noted. This accounts for the delayed clinical diagnosis in many cases, but it also indicates that function may be satisfactory. The disability is most significant in bilateral cases with severe pronation. Children may initially have a reduced radial head and in adolescence may develop symptomatic radial head subluxation. Therefore, radiographic follow-up is necessary.

Classification

Wilkie divided congenital synostosis into the following two types on the basis of the proximal radioulnar junction[20] :

  • Type 1 - Complete synostosis has occurred, with the radius and ulna fused proximally for a variable distance
  • Type 2 - Less involved, and may exist as a partial union; this type involves the region just distal to the proximal radial epiphysis and is associated with radial head dislocation

Cleary and Omer described four types of congenital synostosis, as follows[17] :

  • Fibrous synostosis
  • Bony synostosis
  • Associated posterior dislocation of the radius
  • Associated anterior dislocation of the radius

Simmons et al considered congenital synostosis to be a spectrum of anomalies in which the synostosis occurred in varying lengths, with or without involvement of the radial head.[21]

Posttraumatic radioulnar synostosis has been classified into the following three types on the basis of location:

  • Type 1 - Least common; occurs in the distal forearm
  • Type 2 - Occurs in the midforearm
  • Type 3 - Occurs in the proximal forearm
 

Workup

Imaging Studies

Plain radiographic imaging in orthogonal (eg, posteroanterior [PA] and lateral) planes is recommended for the workup of patients with congenital or posttraumatic radioulnar synostosis. (See the images below.)

Radioulnar synostosis occurs as either congenital Radioulnar synostosis occurs as either congenital or posttraumatic condition.
Degree of fusion in radioulnar synostosis varies a Degree of fusion in radioulnar synostosis varies and may or may not involve radial head.
 

Treatment

Approach Considerations

Indications for surgical treatment of congenital radioulnar synostosis remain somewhat controversial but are related to bilaterality and to the degree of deformity. Patients with neutral rotation, mild pronation, or rare supination positions can compensate somewhat with ipsilateral shoulder motion. Wrist hypermobility allows further functional compensation. Severe pronation deformities (specifically, >60º) cause significant functional difficulty, especially with activities requiring supination. Therefore, indications for surgery must be based more on individual functional limitations than on absolute forearm position.

It is recommended that surgery be performed in childhood before patients reach school age. In patients with symptomatic subluxation of the radial head, the radial head may be excised at maturity. Appropriate workup includes plain radiography performed in orthogonal planes (eg, posteroanterior [PA] and lateral views).

The indication for surgery in posttraumatic radioulnar synostosis is functional limitation of forearm rotation. This limitation must be assessed on an individual basis. An appropriate workup includes taking plain radiographs in orthogonal (eg, PA and lateral) planes.

Surgery should be performed after the synostosis has matured and distinct radiographic borders are observed, so as to decrease the likelihood that the synostosis will recur. Waiting more than 3 years, however, adversely affects final outcome, probably because of soft-tissue contracture. A 100º arc of motion is desired so that the patient can perform all activities of daily living (ADLs), and a 60º arc is required to perform most ADLs without assistance.

The only contraindication for surgical correction is the presence of milder deformity in an older patient, if the patient has only minimal functional deficit and has already made adjustments in his/her activities to accommodate the synostosis.

Surgical Therapy

Attempts to achieve and maintain motion at the synostosis site usually are not successful. Synostosis typically recurs despite excision, the use of various medications, or the interposition of silicone, fat, or muscle. However, success has been reported with excision of the bony bridge and the interposition of vascularized fat graft, with an average rotation range of 74º being maintained at 2 years after surgery.[22]

Some mobilization procedures are combined with tendon transfers to achieve supination. The flexor carpi ulnaris can be transferred dorsally around the ulna, and the extensor carpi radialis longus can be transferred to the volar aspect of the wrist. Overall, the preferred surgical procedure has been osteotomy and derotation through the fusion mass, along with fixation with transcutaneous pins.[23, 24, 25]

The optimal position of correction varies according to the degree of involvement, the bilaterality of the synostosis, and the amount of compensatory shoulder or radiocarpal motion that the patient has. Severe deformities do not allow one-stage correction, because of the tension on vascular and fibrous structures. Gradual correction using a multiplanar external fixator decreases the risk of neurovascular compromise and allows the patient to select the most functional position.

Reports of the optimal correction position vary. In general, neutral rotation is used for unilateral deformities; for bilateral deformities, one side is placed in 20-30º of pronation and the other in 20-30º of supination.[26] Shortening of the forearm to decrease the risk of neurovascular compromise has also been recommended.

A long arm cast with 90º of elbow flexion is utilized postoperatively for 8 weeks. Transcutaneous pins are recommended for fixation after derotation. Unlike techniques that require open operative exposure, this pinning can easily be reversed if postoperative vascular compromise develops.[7, 27]

Simcock et al described the use of derotational osteotomy to treat 31 forearms in 26 children with congenital radioulnar synostosis and functional limitations.[28]  In all cases, union was successfully achieved by 8 weeks. No instances of compartment syndrome, vascular compromise, or loss of fixation occurred. The overall rate of complications was 12%, including two transient anterior interosseous nerve palsies (both in patients with rotational corrections >80º), one transient radial nerve palsy, and one symptomatic muscle herniation.

Hwang et al studied the use of one-stage rotational osteotomy of the proximal third of the ulna and distal third of the radius with segmental bone resection to treat congenital radioulnar synostosis in 25 patients (28 forearms).[29] In group 1, the ulnar osteotomy was stabilized with an intramedullary pin, whereas in group 2, no fixation was used. Surgical outcomes did not differ significantly between the two groups. The authors concluded that one-stage rotational osteotomy of the proximal third of the ulna and distal third of the radius with segmental bone resection is simple and safe in this setting and that internal fixation at the osteotomy site seems to be unnecessary.

Bishay prospectively studied 12 consecutive pediatric patients (14 forearms) with severe congenital proximal radioulnar synostosis (mean pronation deformity, 70.7°; range, 60-85°) that was corrected by menas of single-session double-level rotational osteotomy and percutaneous placement of intramedullary Kirschner wires (K-wires) in both radius and ulna.[30] After a mean interval of 30.4 months (range, 24-36 months), patients had a mean pronation deformity correction of 59.8°. All 12 patients showed improvement in functional activities; none had any loss of correction or nonunion, circulatory disturbances, neuropathies, or hypertrophic scars.

Satake et al studied the long-term (≥10 years) results of simple rotational osteotomy for congenital radioulnar synostosis in nine patients (12 forearms).[31] After the procedure, the forearm was fixed at an average of 4.2° of supination. At final follow-up, the average motion arc of the palm ranged from 26° of pronation to 62° of supination. No postoperative neurologic or circulatory complications were noted. Patients were much better able to perform ADLs, and all were satisfied with the results of surgery. The average score on the 11-item version of the Disability of the Arm, Shoulder, and Hand (DASH) scaore was 3.79 points at final follow-up.

In contrast to surgery for congenital radioulnar synostosis, surgery for the posttraumatic form of the condition restores motion through excision of the synostosis area.[4, 5, 32] Numerous interposition materials—including fat, muscle, fascia, silicone, and cellophane—have been proposed for use after resection to prevent a recurrence of synostosis, but these have met with varying degrees of success. Kelikian and Doumanian developed a metallic swivel prosthesis to restore motion, but no large series has been reported that supports its effectiveness.[33]

The goal of treatment, regardless of what interpositional material is used, involves resection of the entire bony synostosis. Careful dissection with minimal periosteal disruption prevents the further stimulation of bone, limiting recurrence. Identification and protection of neurovascular structures is essential, and the final range of motion should be assessed intraoperatively. Minimal postoperative immobilization is recommended.

Complications

Although the surgical procedure that is used to treat congenital radioulnar synostosis is not exceedingly difficult, it is associated with significant complications,[34] including neurovascular compromise and recurrence of ankylosis. The limiting factors for derotation are soft-tissue contracture and neurovascular compromise. Simmons et al recommended that derotations of more than 85º be performed in two stages.[21] A low threshold for fasciotomies should be maintained for suspected compartment syndromes.