Background

In 1930, Saint-Pierre reported congenital failure of clavicle formation. In 1963, Alldred reported nine cases of congenital pseudoarthrosis of the clavicle.^[8] Congenital failure of formation (ossification) of the central portion of the clavicle produces a painless prominence in the anterior superior chest in the absence of trauma.^{[9, 10]} The resultant synovial pseudoarthrosis usually develops on the right side. Functional impairment is uncommon in children. A case of pseudarthrosis of the clavicle causing thoracic outet syndrome is reported.^[11]

In patients with congenital pseudoarthrosis of the clavicle, a painless mass over the right clavicle is the most common finding that prompts parents to seek consultation with a physician. Treatment may consist of mere observation or resection of the pseudoarthrosis and osteosynthesis.^{[1, 2, 3, 4, 5, 6, 7]} Surgical intervention generally is recommended, to correct shoulder girdle hypermobility and an unsightly mass. Both problems can be treated by open reduction, resection of the pseudoarthrosis, and bone grafting.^[4] Resection alone produces pain.

Pathophysiology

The clavicle is the first bone to undergo membranous ossification. It connects the sternum to the acromion and provides support for shoulder function. Congenital pseudoarthrosis of the midportion of the clavicle occurs when an environmental insult or anatomic or mechanical event disrupts diaphyseal membranous ossification.

In congenital pseudoarthrosis of the clavicle, the two primary ossification centers fail to unite. The two portions of the clavicle produced are connected by a fibrous bridge that is contiguous with the periosteum, and a synovial membrane develops.^[2] The predominance of right-side involvement in the absence of situs inversus suggests that the vascular anlage of the subclavian artery that crosses the first rib just below the pseudoarthrosis site may be involved in the etiology.

Congenital pseudoarthrosis has never been associated with malignant degeneration.

Etiology

The etiology is unknown, and no relationship with neurofibromatosis has been demonstrated. Abnormalities in aortic arch angiogenesis have been postulated, which would explain, in part, the right-sided distribution. Failure of coalescence of the two primary ossification centers contributes to the pathology.^[15] Left-side involvement is seen in patients with dextrocardia and situs inversus. The incidence of associated cervical ribs is 15%. Spontaneous healing is extremely rare.

Epidemiology

Congenital pseudoarthrosis is rare. Fewer than 200 cases have been reported in the English literature. The exact incidence and prevalence are unknown. The abnormality occurs almost entirely on the right side. Involvement of the left side usually occurs with dextrocardia and situs inversus.^[12] Bilateral cases can occur but are rare and are typically associated with genetic syndromes.^{[13, 14]}

Prognosis

The outcome is usually excellent, with prompt healing, few complications, and normal function.