Arachnodactyly

• The thumb sign, or Steinberg sign, is protrusion of the thumb past the hypothenar border when the hand is clenched in a fist

• The wrist sign, or Walker–Murdoch sign, is overlap of the fifth finger and thumb when they encircle the wrist of the opposite hand

• The metacarpal index is a radiographic measure of arachnodactyly. It is the average of the length divided by the midpoint width for the second through fourth metacarpals (a value of 5.4 to 7.9 is normal, whereas >8.4 occurs in Marfan syndrome).

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Congenital Contractural Arachnodactyly - NIH

Metacarpal index - Radiopaedia