Arachnodactyly describe the appearance of long fingers and long limbs. The name implies
the resemblance to a spider. In the limbs there is a reduced upper to lower segment ratio.
Arachnodactyly is often seen in Marfan's syndrome.
There are ways of quantifying arachnodactyly if its presence is in question:
- the thumb sign is said to be positive if the thumb protrudes the palm when flexed across
- the wrist sign is said to be positive if the thumb and fifth fingers overlap when they
encircle the opposite wrist