Brachymesophalangia

Brachymesophalangia is the most common hereditary anomaly of the middle phalanges. It is more common in the small finger (brachymesophalangia-5 or brachymesophalangia-V) and is seen in up to 20% of the Japanese population and about 1% of the European population. About 2/3 of patients with Down syndrome have brachymesophalangia.

As seen in the image above, the short, often trapezoidal middle phalanx can result in angular deviation of the distal phalanx (clinodactyly).

In 1951, Bell classified brachydactyly into types A-E.

Type	Description
A1	Brachymesophalangia II-IV with brachybasophalangia I
A2	Brachymesophalangia II with absent epiphyses, delta phalanx, and radial clinodactyly
A3	Brachymesophalangia V with radial clinodactyly (case shown above)
A4	Brachymesophalangia II-V with bifid distal phalanx of thumb and dystelephalangia V
B	Brachymesophalangia with brachytelephalangia II-V (or absent distal phalanges)
C	Brachymesophalangia II, III, and V with hyperphalangia of index and middle finger proximal phalanges
D	Brachytelephalangia I with broadening
E	Brachymetacarpia III-V

Brachybasophalangia: Short proximal phalanges
Brachymetacarpia: Short metacarpals
Brachytelephalangia: Short distal phalanges
Dystelephalangia: Deformed terminal phalanx (Kirner deformity)

References

• Bell J. On brachydactyly and symphalangism. Treasury of human inheritance. Vol 5, part 1. London: Cambridge University Press, 1951.
• Freyschmidt J, Brossmann J, Wiens J, Sternberg A. Chapter 2 - Upper Extremity. In Freyschmidt's Köhler and Zimmer: Borderlands of normal and early pathologic findings in skeletal radiography. Fifth revised edition. Thieme (2003). Pp 85-86.