Delta phalanx in a triphalangeal thumb

Clinical History

A 2-year-old otherwise healthy girl presented with fixed ulnar deviation of the interphalangeal joint of the left thumb. She was born to non-consanguineous parents, after an uneventful pregnancy, with no exposure to teratogenic agents or maternal history of any illness. There was no family history of limb malformations.

Imaging Findings

Radiograph of the left thumb disclosed a triangular proximal phalanx with a longitudinal cleft and an additional separate distal ossicle (supernumerary middle phalanx) (Fig. 1). There was ulnar angulatory deformity of the digit distal to the morphologically abnormal proximal phalanx. The distal phalanx was unremarkable.

Discussion

The delta phalanx (or longitudinally bracketed epiphysis), first described in 1964 by Blundell Jones, is a rare congenital abnormality that consists of a triangular/trapezoidal bone with a C-shaped epiphysis extending from its normal transverse position along the shorter side of the phalanx in a proximal to distal direction [1-5]. This abnormal configuration of the physeal plate may prevent the normal longitudinal growth of the digit, leading to progressive angulation and shortening of the affected finger, particularly if the bracket is complete [1-5].
This condition is thought to result from defective development of the primary ossification centre during the embryonic or early fetal period [3, 5, 6]. It most commonly involves the tubular bones with a proximal epiphyseal ossification centre, such as the phalanges, and also the first metacarpal and first metatarsal bones; therefore, the designation “delta phalanx” is considered a misnomer [2, 3, 5, 7-9].

Clinically, the abnormality most commonly manifests as clinodactyly (curvature of the digit more than 10 degrees off the longitudinal axis). It usually appears as an isolated finding, but can also occur as part of a wide variety of congenital malformation syndromes and dysplasias [2-9].
The most common example of a delta phalanx is found in the middle phalanx of both little fingers, producing clinodactyly toward the ring finger. A triphalangeal thumb that has a delta mid-phalanx and produces clinodactyly toward the index finger is uncommon [8]. The appearance in this case is that of a proximal delta phalanx with a supranumerary middle rudimentary phalanx, which, to our knowledge, has not previously been described in literature.

Radiographic appearances of the longitudinally bracketed epiphysis vary, depending on the degree of secondary ossification of the epiphysis [3, 5]. Although a cartilaginous bracket is present at birth; the involved bone is not ossified enough to demonstrate the bracket. Therefore, this abnormality is not seen on plain films until approximately 2 years of age [5-7].
An appropriate and prompt diagnosis allows early surgical intervention to reduce the deformity, improving the chance of adequate remodelling. Some authors have suggested MR imaging in early childhood deformities, in order to confirm the presence of an epiphyseal bracket before the ossification occurs. MRI can also provide a better assessment of the defect, degree and location of the bracket [6, 7].

When the deformity is minor, surgery or any other treatment may not be necessary. Reconstructive procedures for abnormalities with significant deforming potential include physiolysis, osteotomy, or both [2, 8].

Differential Diagnosis List

Final Diagnosis

Proximal delta phalanx in a triphalangeal left thumb

URL:	https://www.eurorad.org/case/10555
DOI:	10.1594/EURORAD/CASE.10555
ISSN:	1563-4086