Brachydactyly may be isolated or associated with a syndrome. Isolated forms of brachydactyly have been typed A1–5, B, C, D, E, IV, Sugarman brachydactyly, and Kirner deformity as an extension of the original Bell classification system. Isolated brachydactyly is rare except for types A3 (short middle phalanx of the little finger) and D (short distal phalanx of the thumb). Over 260 syndromes and genetic disorders have brachydactyly as a feature and several of them are listed below. Delta phalanx (longitudinally bracketed epiphysis) is a triangular phalanx with continuous epiphy-seal cartilage bridging the base and head (Fig. 5.100).
Fig. 5.100a, b Delta phalanx of the great toe (a) and thumb (b) in separate children.
Table 5.59 Classification of isolated brachydactyly
Type
Findings
Comments
A1
Short middle phalanges: first through fourth.
Acrodysostosis, diastrophic dysplasia, and Larsen, Saldino-Robinow, and brachydactyly-distal symphalangism syndromes.
A2
Short middle phalanx: second.
A3
Short middle phalanx: fifth.
Trisomy 21 and Aarskog, Noonan, Silver, and Shwachman syndromes.
A4
Short middle phalanges: second and fifth.
A5
Absent middle phalanges: second through fifth with nail dysplasia.
B
Absent or hypoplastic distal phalanges: second through fifth. Flattening, splitting, or duplication of the distal phalanx of the thumb. Feet are similarly affected.
Apical dystrophy. Must be distinguished from causes of acroosteolysis (see Table 5.61).
C
Brachymesophalangy of the second and third. The ring finger is usually the longest digit.
D
Short distal phalanx of the thumb.
Rubinstein-Taybi, hand-foot-genital, Carpenter, Pfeiffer, Apert, and Robinow syndromes.
E (brachymetatarsus)
Shortening of metacarpals ± metatarsals. Note: rare as an isolated finding. Usually associated with syndromes.
