Digital clubbing: a numerical assessment of the deformity.

We describe a simple method that defines with numbers the drumstick deformity of the digits. We measured 2 circumferences on each of the 10 fingers at the nail bed (NB) and at the distal interphalangeal joint (DIP), the sum of the 10 ratios NB:DIP was termed Digital Index. Intraobserver variation of the Digital Index was small, with a Pearson's correlation coefficient of R = 0.979; interobserver variation was also not significant (R = 0.999). Making use of this Digital Index, we studied 22 patients with digital clubbing associated with cyanotic congenital heart disease and 66 healthy controls. Digital Index clearly separated patients from controls, 10.73 +/- 0.32 vs 9.33 +/- 0.27 (means +/- SD). The Index was independent of age or sex. Patients with hypertrophic osteoarthropathy had significantly higher indices than patients with clubbing alone.