Delta phalanx, also known as the delta bone, Δ bone, or longitudinal epiphyseal bracket (LEB), is a rare condition occurring in the hand or the foot. The affected bone may be the phalanges, metacarpal or metatarsal bones with both unilateral and bilateral distributions 1.
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Epidemiology
The delta phalanx can occur as an isolated finding or in association with polydactyly, clinodactyly, extra phalanges and a variety of congenital syndromes (e.g. Poland syndrome, mesomelic dysplasia, Rubinstein-Taybi syndrome, Carpenter syndrome) 1.
Clinical presentation
Patients present with shortening, angular deformity and clinodactyly of the hand and hallux varus deformity of the foot. Brachydactyly may also occur if multiple delta phalanges exist in the same digit 3.
Pathology
Delta phalanx occurs secondary to a defective epiphyseal ossification center which instead of being transverse in location, extends longitudinally along and brackets the diaphysis, causing restricted longitudinal growth and resultant shortening, angular deformities and clinodactyly of the hand and hallux varus deformity of the foot 2.
Radiographic features
Plain radiograph
Delta bone consists of a triangular bone with a C-shaped epiphysis extending along the shorter side of the phalanx in a proximal to distal direction.
MRI
Before the age of 2 years, the cartilaginous bracket is not ossified, hence this abnormality is not seen on plain films. In these cases, MRI is indicated to confirm the presence of an epiphyseal bracket before ossification occurs 1.
Treatment and prognosis
An early diagnosis allows early and rapid surgical intervention to minimize finger deformity 1.
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