Tactile sensibility on the fingernail.

Purpose: To measure tactile discrimination (static and moving 2-point discrimination) and threshold levels (Weinstein enhanced sensory test) over the nail plate in normal subjects and compare these values with those at the corresponding finger pulps.

Methods: Tactile discrimination and threshold values over the nail plates and finger pulps were measured on 300 digits in 30 healthy subjects with a mean age of 23 years. Subjects with cosmetic nail modifications, injuries, neurological deficits, dermatological conditions, or history of upper limb surgery were excluded. Equivalence testing was conducted to look for clinical equivalence between values obtained at both sites.

Results: The mean static 2-point discrimination, moving 2-point discrimination, and threshold value over the human nail were 6.7 mm, 2.4 mm, and 0.06 g, respectively. The corresponding values for the finger pulp were 2.4 mm, 2.2 mm, and 0.01 g, respectively. The static 2-point discrimination and threshold values were superior for the finger pulp, whereas moving 2-point discrimination values at both sites were clinically equivalent.

Conclusions: Our study suggests that tactile discrimination and threshold levels can be measured over the nail plate and that moving 2-point discrimination values are clinically equivalent to those obtained on the corresponding pulp. This highlights the importance of the nail plate in the sensory function of the fingertip. The normative data from this study may be useful in establishing the impact of nail injury and the contribution of the nail to the overall function of the hand.

Type Of Study/level Of Evidence: Diagnostic II.