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Updated: Jul 27 2021

Congenital Radial Ulnar Synostosis


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Images - lateral - colorado_moved.jpg synostosis.jpg
  • summary
    • Congenital Radial Ulnar Synostosis is a congenital condition caused by failure of differentiation that leads to the presence of a bony bridge between the proximal radius and ulna.
    • Diagnosis is made radiographically with the presence of a proximal radial ulnar bony connection. 
    • Treatment is usually observation in patients who are asymptomatic. Operative management is indicated in patients with deformity limiting ability to participate in specific activities or perform activities of daily living. 
  • Epidemiology
    • Demographics
      • male > female (3:2)
      • 60% bilateral
  • Etiology
    • Pathophysiology
      • 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
    • Genetics
      • familial cases with autosomal dominant inheritance
      • associated with chromosomal abnormalities, particularly duplication of sex chromosomes
      • 20% with positive family history
    • 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
      • Cleary Classification of Congenital Proximal Radioulnar Synostosis
      • Type 1
      • No osseous synostosis, radial head reduced
      • Type 2
      • Osseous synostosis, radial head reduced
      • Type 3
      • Long osseous synostosis, radial head hypoplastic and posteriorly dislocated
      • Type 4
      • Short osseous synostosis, radial head mushroom-shaped and anteriorly dislocated
  • 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)
            • percutaneous pins
        • 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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