Causes / typical injury mechanism: Constriction ring syndrome (also known as amniotic band syndrome and Streeter dysplasia) is a congenital condition caused by loose, fibrous amnionic bands that rupture and entangle the normally developing structures of the fetus. This manifests as the presence of bands perpendicular to the longitudinal axis of the limb, with normal anatomy proximal to the band. In the hand, this can involve constrictive rings, hypoplasia, fusions, or even amputations.

Classic history and presentation: Patients present at birth with constrictive bands perpendicular to the longitudinal axis of the limb. Diagnosis can be made in utero during anatomic ultrasound scans.

Prevalence: 1:15 000 live births

• Age – Diagnosed at birth.
• Sex / gender – Males and females are equally predisposed.

Risk factors: There are no known risk factors, but associated conditions include clubfoot, syndactyly, cleft lip, cleft palate, craniofacial defects, cardiac defects, and encephalocele.

Pathophysiology: There is no well-established etiology; however, most experts agree that the disrupted amnion releases fibrous membranous strands. These strands wrap around the developing limb circumferentially, which restricts the remaining growth of that limb.

Grade / classification system: Patterson classification.

• Type 1: Simple constriction ring.
• Type 2: Deformity distal to ring (hypoplasia, lymphedema) with or without edema.
• Type 3: Fusions distally (such as syndactyly or acrosyndactyly).
• Type 4: Amputation.