Thumb Length and Thumb Placement Index

 

Parameters:

(1) location of thumb tip relative to index finger with the thumb adducted and held parallel to the fingers

(2) distance between the distal flexion crease at the wrist and the proximal crease at the base of the index finger with the thumb abducted to 90°

(3) distance between the distal insertion of the thumb (basal crease) and the proximal crease at the base of the index finger with the thumb abducted to 90°

Location of Thumb Tip When Adducted	Thumb Length
above the crease at the first interphalangeal joint of the index finger	long or digitalized
between the two creases	normal
below the proximal crease at the base of the index finger	hypoplastic or low set

 

thumb placement index =

= (distance in mm from distal insertion of thumb to proximal crease of index finger) / (distance in mm from distal flexion crease at wrist and the proximal crease of index finger)

 

Interpretation:

• The normal thumb placement index is about 0.50.