CASE 7522 Published on 15.07.2009

Delta Phalanx of Thumb

Section

Musculoskeletal system

Case Type

Clinical Cases

Authors

Singh J, Altaf K, Ajis A

Patient

48 years, male

Clinical History
A male patient with a known case of phocomelia syndrome due to thalidomide presents with deformity and laxity of the thumb.
Imaging Findings
A 48-year-old male patient, known to suffer from phocomelia syndrome secondary to thalidomide, has lower limb agenesis and presented with deformity and laxity of his right thumb. He also exhibited symptoms of median nerve compression to his right hand. He is wheel chair bound as a result of his condition and relies on both hands for wheeling himself and going upstairs. He suffers from atopic eczema and anaemia. He is a smoker, (smokes 20/day) and had a previous history of substance abuse. He had previous surgical interventions on both hands for web space deformities, bowel operations and a lumbar spine fusion.

On examination he exhibited a lax right 1st metacarpophalangeal joint affecting pincer grip function as well as ulnar deviation of the right thumb terminal phalanx. Radiographs clearly showed an extra delta phalanx between the proximal and distal phalanges.
Discussion
Phocomelia is a congenital malformation where the upper appendage of an arm or leg is diminished or absent. The word phocomelia has Greek origins, combining ‘phoco’ (seal) and ‘melos’ (limb) to signify a ‘limb like a seal’s flipper’. Although various factors can be implicated the predominant causes of phocomelia are genetic and the use of thalidomide in pregnancy [1, 2]. Infants could be born with absent or shortened limbs, eye and ear abnormalities and congenital malformations of the gastrointestinal and/or genitourinary tract. Phalangeal malformations are also common, such as a delta phalanx in the thumb and the middle phalanx in clinodactyly/syndactyly [3-5].

Triphalangeal thumb (TPT) is characterized by presence of an extra phalanx between the two normal phalanges of the thumb. Three characteristic types of extra bone in the thumb can be found. One type consists of complete hyperphalangism with three normal appearing phalanges and joints. In the second type, the extra middle phalanx is small, triangular in shape, and is termed a delta phalanx. The proximal epiphysis is C shaped rather than straight and tends to lie on the shorter side of the abnormal bone. The peculiar arrangement of this epiphysis makes longitudinal growth of the digit impossible and causes an angular deformity so that the thumb appears bent inwards toward the index finger. A third type consists of a regular finger containing three phalanges that takes the place of the thumb [6].


Three hypotheses have been put forward to explain TPT [7]. It could be as a result of failure of fusion of the terminal and middle phalanges. Secondly, TPT may be considered a duplication of the index finger which replaces an absent thumb. The third hypothesis suggests that TPT could be the result of an attempt at formation of a bifid thumb, with the extra phalanx representing the base of the bifid thumb.
Triphalangeal thumb can occur either as an isolated defect or as a feature of several rare malformation syndromes. Delta phalanx of thumb is associated with wider anomalies like Klinefelter’s syndrome [8] polydactyly of the thumb or big toe, cleft feet, onychodystrophy, imperforate anus, defects of the tibia, cleft palate, congenital heart disease, and particularly Holt-Oram syndrome. It has also been observed in trisomy 13, in Juberg-Hayward syndrome, and as a result of maternal exposure to teratogens as in our case [7]. Apart from affecting the thumb, a delta phalanx can also appear in the little finger, metacarpals and metatarsals.

Treatment involves removing the extra phalanx in young children. In adults this is followed by arthrodesis of the distal phalanx to the remaining proximal phalanx [9].
Differential Diagnosis List
Triphalangeal thumb with delta phalanx
Final Diagnosis
Triphalangeal thumb with delta phalanx
Case information
URL: https://www.eurorad.org/case/7522
DOI: 10.1594/EURORAD/CASE.7522
ISSN: 1563-4086

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