eMedicine Specialties > Orthopedic Surgery > Hand & Upper Extremity
Radial-Ulnar Synostosis
Updated: Feb 9, 2009
Introduction
Synostosis, or osseous union, of any 2 adjacent bones can involve any part of the upper extremity. Synostosis between the radius and ulna can take 2 forms: congenital and posttraumatic.
Radioulnar synostosis occurs as either a congenital or a posttraumatic condition.
The degree of fusion in radioulnar synostosis varies and may or may not involve the radial head.
In 1793, Sandifort provided the initial description of congenital radial-ulnar (radioulnar) synostosis. This condition is caused by a failure of segmentation between the radius and ulna. 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 3 cartilaginous analogs 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 2 adjacent bones, if existent, is minimal.1,2,3,4,5,6
Posttraumatic radioulnar synostosis is a separate entity from the congenital form, having a different cause, treatment, and prognosis.7 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.8,9
Related eMedicine topics:
Radius, Distal Fractures
Forearm Fractures
Middle Third Forearm Fractures
Wrist and Forearm Amputations
Problem
Wilkie described 2 types of congenital synostosis, based on the proximal radioulnar junction.10 In type 1, complete synostosis has occurred, with the radius and ulna fused proximally for a variable distance. Type 2 is less involved, and may exist as a partial union. Type 2 involves the region just distal to the proximal radial epiphysis and is associated with radial head dislocation.
Cleary and Omer described 4 types of congenital synostosis, as follows11 :
- Fibrous synostosis
- Bony synostosis
- Associated posterior dislocation of the radius
- Associated anterior dislocation of the radius
Simmons and colleagues 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.12
Posttraumatic radioulnar synostosis has been classified into the following 3 types, based on location:
- Type 1 - Least common; occurs in the distal forearm
- Type 2 - Occurs in the midforearm
- Type 3 - Occurs in the proximal forearm
Frequency
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.11 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.13,14 In 20% of their patients, Cleary and Omer found a genetic basis for an autosomal dominant form (with variable penetrance) of congenital radioulnar synostosis.11
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.15 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.16 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.17,18
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.19 A fibrous synostosis may allow limited motion. Regional soft-tissue hypoplasia is often present in severe cases, including when atrophy and fibrosis of the brachioradialis, pronator teres, pronator quadratus, and supinator muscles occur. The interosseous membrane also may be abnormal.
Presentation
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.
Radioulnar synostosis occurs as either a congenital or a posttraumatic condition.
The degree of fusion in radioulnar synostosis varies and may or may not involve the radial head.
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 30 º. 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.
Indications
Indications for surgical treatment of congenital radioulnar synostosis still 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, those >60º) cause significant functional difficulty, especially with activities requiring supination. Therefore, indications for surgery must be determined based more on individual functional limitations than on absolute forearm position.
It is recommended that surgery be performed in childhood before patients are school-aged. 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, lateral) planes. Surgery should be performed following maturation of the synostosis and after distinct radiographic borders are observed, to decrease the likelihood that the synostosis will recur. Waiting more than 3 years, however, has been shown to adversely affect 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, and a 60º arc is required to perform most activities of daily living without assistance.
Contraindications
The only contraindication to 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.
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References
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Keywords
radial-ulnar synostosis, radioulnar synostosis, radial-ulnar osseous union, osseous union, congenital synostosis, posttraumatic synostosis
