Reproducibility of measurements of thumb abduction.

The reproducibilities of various measurements of thumb abduction were compared. Two independent observers measured the thumb abduction in 30 volunteers by the following four methods: distance between the thumb tip and the flexion crease of the index finger proximal interphalangeal joint; distance between the flexion crease of the thumb interphalangeal joint and the proximal palmar crease; angle between the thumb and index metacarpals; and angle between the thumb and index proximal phalanx. Measurements were repeated in three weeks and their reproducibility was assessed by the intraclass correlation coefficient (ICC). Intra-observer reproducibilities by distances were high with ICCs between 0.74 and 0.89, compared with those by angles with ICCs between 0.28 and 0.71. Inter-observer reproducibilities by distances were also high (ICCs = 0.79 and 0.81) compared with those by angles (ICCs = 0.28 and 0.42). Assessment of thumb abduction based on distance in the first web is recommended in terms of reproducibility.