Arachnodactyly refers to the physical finding of elongated, thin "spider-like" fingers, which are a classic feature of Marfan disease, but by no means pathognomonic 1.
The metacarpal index was historically-used as a radiographic criterion for arachnodactyly. To obtain it, the length of the second, third, fourth and fifth metacarpals is divided by their width at the mid shaft. An index of greater than 8.4 is considered the upper limit of normal 2. It is no longer used due to its poor specificity and sensitivity.
History and etymology
From the Ancient Greek "arachno" refers to spiders and "dactyly" means fingers.
- other hereditary diseases of connective tissue
- 1. Rodney Grahame, Alan J. Hakim. Arachnodactyly—a key to diagnosing heritable disorders of connective tissue. (2013) Nature Reviews Rheumatology. 9 (6): 358. doi:10.1038/nrrheum.2013.24
- 2. Ha HI, Seo JB, Lee SH, Kang JW, Goo HW, Lim TH, Shin MJ. Imaging of Marfan syndrome: multisystemic manifestations. (2007) Radiographics : a review publication of the Radiological Society of North America, Inc. 27 (4): 989-1004. doi:10.1148/rg.274065171 - Pubmed