Multiple synostoses

Description

Synostosis is defined as the existence or persistence of osseous connection between bones that are normally separate in post-natal life. Developmental synostosis arises primarily from failure of complete segmentation of the cartilaginous template on which the osseous skeleton of the limb is patterned and from the failure of mesodermal structures or body clefts to intervene between cartilaginous plates developing in parallel (ray formation). The former results in synostoses involving bones normally separated by a joint space (e.g. humero-radial synostosis, carpal-carpal coalition) while the latter results in synostosis of bones of different rays in the middle or distal segments of the limbs or synostosis of bones of different limbs (e.g. syndactyly, symmelia). For the most part synostoses represent developmental anomalies associated with chromosomal abnormalities or single gene disorders (see Associated syndromes listing). Sporadic synostoses of unknown or environmental origin are also recognized and have a low recurrence risk. Fetal thalidomide exposure was an important cause of carpal and tarsal coalitions as well as tibio-fibular and radio-ulnar synostosis.

Diagnosis

The major clinical features of synostoses are joint stiffness, absent dermal creases and shortening of the involved segments. Movement between involved bones is limited or absent. Generally synostosis of long bones and phalanges occurs with the joints in extension or with a minor degree of flexion only. The exception is humero-radial synostosis where the elbow is fixed in 90 degrees or greater of flexion. When synostosis affects the bones of the limbs there are varying degrees of limb shortening. Radiographs are required to demonstrate osseous continuity between bones. Some changes, including humero-radial synostosis, may be present at birth.

Differential Diagnosis

Multiple congenital contractures (arthrogryposis multiplex congenita) and multiple pterygia may be hard to distinguish on antenatal ultrasound as reduced or absent movement across the affected joint may also be present. The presence of polyhdramnios may indicate an underlying neuromuscular disorder resulting in arthrogryposis.

Sonographic Features

Limitation of joint movement with fixed posture – usually extension.

Variable limb shortening

Associated Syndromes

  • Antley-Bixler
  • Apert (Acrocephalo-syndactyly)
  • Humero-radial synostosis
  • Nager acro-facial dysostosis
  • Pfeiffer
  • Sex chromosome aneuploidy
  • Thalidomide embryopathy

References

Schinzel A et al Antley-Bixler syndrome in sisters: A term newborn and a prenatally diagnosed fetus Am J Med Genet 14:139-147
Jacobson RL, Dignan PS, Miodovnik M, et al Antley-Bixler syndrome (Review) J Ultrasound Med 11:161-164
Robinson LK, Powers NG, Dunklee P, et al The Antlry-Bixler syndrome J Pediatr 101:201
da Silva EO, Filho SM de Albuquerque SC Multiple synostosis syndrome: study of a large Brazilian kindred Am J Med Genet 18:237