Radius Ulna Synostosis / Congenital Radial Ulnar Synostosis


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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] 

It can be associated with dislocation of the radial head which leads to limited elbow extension.[2]


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Contents
1Types
1.1Congenital
1.2Acquired
2Treatment
3References
4External links

  • 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
    Cleary Classification of Congenital Proximal Radioulnar Synostosis
    Type 1No osseous synostosis, radial head reduced 
    Type 2Osseous synostosis, radial head reduced                      
    Type 3Long osseous synostosis, radial head hypoplastic and posteriorly dislocated   
    Type 4Short 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

    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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