 Radioulnar synostosis is a rare condition where there is an abnormal connection between the radius and ulna bones of the forearm.
This can be present at birth (congenital), when it is a result of a failure of the bones to form separately, or following an injury (post-traumatic)
It typically causes restricted movement of the forearm, in particular rotation (pronation and supination), though is not usually painful unless it causes subluxation of the radial head.[1]
- Definition
- bony bridge between the proximal radius and ulna
- Etiology
- forearm begins as a single cartilaginous anlage and divides from distal to proximal into the radius and ulna in the 7th week in utero
- failure of differentiation results in synostosis in proximal aspect of the forearm
- Epidemiology
- male > female (3:2)
- 60% bilateral
- 30% associated with other syndromes
- 20% with positive family history
- Genetics
 - familial cases with autosomal dominant inheritance
- associated with chromosomal abnormalities, particularly duplication of sex chromosomes
- Associated syndromes (30%)
- Apert syndrome (acrocephalosyndactyly)
- Carpenter's syndrome (acropolysyndactlyly)
- Arthrogryposis
- Mandibulofacial dysostosis
- Klinefelter's syndrome (XXY) and other sex chromosome abnormalities
| | Presentation | - Symptoms
- painless
- most commonly asymptomatic, noticed by parents and teachers
- difficulty with specific tasks
- keyboard, tabletop activities - deficient pronation
- eating, washing face, catching a ball - deficit supination
- Physical Exam
- average age of diagnosis is 6 years of age
- can go unnoticed until early adolescence, especially in unilateral cases
- elbow flexion usually preserved
- fixed forearm pronation
- average position is 30° of pronation
- compensatory motion
- shoulder abduction - compensates for loss of active pronation
- shoulder adduction - compensates for loss of active supination
- wrist hypermobility
| | Imaging | - Radiographs
- recommended views
- AP and lateral of forearm and elbow
- findings
- can see proximal synostosis
 - radius is wide and bowed
- ulna is narrow and straight
- radial head may be dislocated and/or malformed
| | Classification | - Cleary Classification
- based on appearance of the synostosis and radial head reduction
| | Treatment | - Nonoperative
- observation
- indications
- usually the preferred treatment, particularly when asymptomatic and unilateral
- Operative
- indications
- absolute
- deformity is limiting ability to participate in specific activities (sports, hygiene, eating)
- relative
- severe pronation deformity > 60°
- bilateral deformities
- general options
- mobilization of the synostosis - to restore active forearm rotation
- rotational osteotomy - to improve static forearm and hand position
- synostosis excision with soft tissue interposition
- goal
- restore active forearm rotation
- technique
- excise synostosis and interpose vascularized fascio-fat graft
- vascularized fat better than free fat graft
- interposed anconeus muscle did not prevent reossification
- excision alone without graft interposition results in nearly 100% recurrence of synostosis
- outcomes
- gain in active forearm motion is usually slight
- unsatisfactory results in most studies
- forearm derotational osteotomy
- goal
- place the forearm in more functional resting position
- technique
- perform between 3-6 years of age (average age ~5 years)
- osteotomy location
- radius and ulna proximal diaphysis at synostosis
- rotation takes place over narrow space - risks soft tissue tightness, loss of correction and neurovascular compromise
- radius and ulna diaphysis distal to synostosis, at different levels
- osteotomies at different levels distributes rotational correction - less soft tissue tightness and risk of neurovascular complications
- radius distal diaphysis alone
- timing of correction
- immediate correction at time of osteotomy
- delayed correction 10 days following osteotomy
- gradual correction with circular external fixator frame (Ilizarov)
- lowest rate of neurovascular complications (compartment syndrome, nerve palsies)
- positioning
- unilateral - fix the forearm in 0-30° pronation
- bilateral - fix dominant forearm in 0-15° pronation and nondominant forearm in neutral
- older studies state the nondominant forearm should be placed in 10-15° of supination; however, this was at a time when keyboards and mobile devices were not as ubiquitous and is no longer recommended
- stabilization
- casting alone (no fixation)
- circular external fixator frame (Ilizarov)
- outcomes
- most techniques result in improved forearm position and patient function with low rate of deformity recurrence
| | Complications | - Recurrence of synostosis
- nearly 100% recurrence of synostosis with excision alone or with interposition of anconeus muscle
- interposition of vascularized fascio-fat graft has 0% recurrence
- Recurrence of malrotation
- casting after derotational osteotomy associated with 15-20° loss of correction
- Compartment syndrome
- up to 36%
- associated with large rotational corrections > 60°
- close observation post-operatively
- some authors advocate for prophylactic forearm fasciotomies in acute and/or large deformity corrections
- Neurologic deficit
- PIN palsy - particularly with proximal (synostosis) osteotomy
- AIN palsy
- radial nerve palsy
- higher risk with acute/large deformity correction
- most resolve within 3 months
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Post-traumatic cases are most likely to develop following surgery for a forearm fracture, this is more common with high-energy injuries where the bones are broken into many pieces (comminuted).[1] It can also develop following soft tissue injury to the forearm where there is haematoma formation.
Treatment[edit]
It is sometimes possible to correct the problem with surgery, though this has high failure rates for treatment of post-traumatic radioulnar synostosis.[1]
References
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