Radius Ulna Synostosis / Congenital Radial Ulnar Synostosis

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]

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 1

Type 2

Type 3

Type 4

No osseous synostosis, radial head reduced

Osseous synostosis, radial head reduced

Long osseous synostosis, radial head hypoplastic and posteriorly dislocated

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

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

https://www.orthobullets.com/hand/6071/congenital-radial-ulnar-synostosis

https://en.wikipedia.org/wiki/Radioulnar_synostosis

Wurapa, Raymond (7 January 2017). "Radioulnar Synostosis: Background, Pathophysiology, Etiology". eMedicine. Retrieved 2 March 2017.

"Congenital radio-ulnar synostosis | Genetic and Rare Diseases Information Center (GARD) – an NCATS Program". rarediseases.info.nih.gov. Retrieved 2 March 2017.

"OMIM Entry - RADIOULNAR SYNOSTOSIS". omim.org. Retrieved 2 March 2017.

RADIOULNAR SYNOSTOSIS WITH AMEGAKARYOCYTIC THROMBOCYTOPENIA 1; RUSAT1". omim.org. Retrieved 2 March 2017.