Clubbed fingers: radiological evaluation of the nail bed thickness

It is established that there is an increase in soft tissue of the clubbed digits as demonstrated on previous histopathological examinations. In the present study, the nail bed thickness was assessed and measured on plain radiographs of index fingers in two groups of patients: one group with lung disease and fingers clubbing and one group of normal controls. A vertical x-ray beam was used with a focus-film distance of 1.0 m, with the index finger placed in lateral view directly over the film, without anti-diffusion grid. Three investigators, blinded to prevent bias measured the thickness of soft tissues between the nail root and the terminal phalanx on the radiographs. This method was used to evaluate a group of 85 clinically clubbed (hyponychial angle > 192.0 degrees) adult patients with lung disease and a control group of a 100 normal adult individuals with no clubbing (hyponychial angle < 188.0 degrees). The mean nail bed thickness in the patients with clubbing (n = 85) was 3.88 +/- 0.55 mm (3.00-5.50 mm). In comparison, in the normal subjects (n = 100), the mean was 2.38 +/- 0.27 mm (1.75-3.10 mm), revealing a significant difference (P < 0.001). Only two normal individuals presented nail bed thickness >or=3.0 mm. A good interobserver agreement on the measurements was found (P > 0.900). The radiographic evaluation of the nail bed thickness was easily performed, with good interobserver concordance. It is possible to distinguish between clubbed from nonclubbed fingers, in vivo, using plain radiograph.