Radioulnar synostosis


Radioulnar Synostosis

Description, Causes and Risk Factors:

Radioulnar synostosis is usually congenital (something your child was born with); but it may also occur after a forearm fracture or trauma. If your child has radioulnar synostosis, it means that he/she has an abnormal bony or soft tissue connection between the two bones of her forearm — the radius (forearm bone on the (thumb) side) and ulna (forearm bone on the (little finger) side).

The elbow joint is formed by the end of the humerus, radius and ulna. These three bones together allow for the arm to be flexed up to the mouth and extended fully, as well as contribute to the ability to place the hand in a palm up or palm down appearance. In the first six weeks of life, the embryo creates a projection which is called the limb bud. The limb bud will form these three bones, but certain hormonal or timing factors may not signal the radius and the ulna to form into two separate and discrete bones. If the bones do not form properly, the muscles that rotate the radius and ulna are often absent. This congenital abnormality is usually and isolated event.

Congenital radioulnar synostosis occurs rarely, with approximately 350 cases reported in the medical literature so far. 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. 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. In 20% of their patients, Cleary and Omer found a genetic basis for an autosomal dominant form (with variable penetrance) of congenital radioulnar synostosis.

While most cases of congenital radioulnar synostosis occur by chance (sporadically), about one in five cases is associated with a family history of the same condition.

Symptoms:

    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.

  • 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 degree. 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.

Diagnosis:

Your child's doctor will do a thorough medical history and careful physical examination. X-raysand/or CT scans may be used to confirm the diagnosis.

In milder cases, doctors may diagnose radioulnar synostosis late in the patient's childhood or adolescence, since the child rarely experiences pain, and some children do not experience too much limitation of movement. In fact, your child may notice only subtle differences in her ability to rotate her forearm.

In more serious cases, forearm rotation is much more limited and obvious, so the diagnosis can be made at an earlier age—typically around age 6.

Treatment:

In general, your child's doctor will determine treatment based on whether your child is having problems using her arm, rather than the absolute position of the forearm.

    Some children's forearms lie in functional positions, and never need surgery.

  • Children who have the problem in both arms, and/or in whom the forearm is fixed in a position that limits their ability to use their arm, may benefit from surgery, preferably before they reach school age.

  • Surgery can be performed either to remove the abnormal soft tissue or bony connection or to position the forearm in a more functionally acceptable position.

While it's rare that surgery can reconstruct a “normal” joint between the radius and ulna, some children see significant improvement in function from osteotomy (bone-cutting) procedures, in which the forearm bones are surgically repositioned.

NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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