SCIENTIFIC ARTICLE Tactile Sensibility on the Fingernail Benjamin Zhi Qiang Seah, Clement Chun Ho Wu, Sandeep Jacob Sebastin, MD, Amitabha Lahiri, MD 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. (J Hand Surg 2013;38A:2159e2163. Copyright Ó 2013 by the American Society for Surgery of the Hand. All rights reserved.) Type of study/level of evidence Diagnostic II. Key words Pulp sensation, nail sensation, normative values, tactile sensibility. T HE FINGER PULP has a high concentration of sensory receptors, and its sensibility has been likened to the eye as an organ of sensory exploration. The sensibility of the finger pulp has been well studied, and tests evaluating it are used in routine clinical practice. The fingernail has largely been considered as a passive support that enhances sensory perception of the pulp. Our observations suggest that the nail plate with its intimate relation- ship with the nailbed and nailfolds may act as an agent for the transmission of haptic sensation. Com- mon examples of such function are seen in daily life, such as running the edge of the nail plate on surfaces, which allows one to perceive the roughness and hardness of the object. In this study, we evaluated the sensibility of the nail plate for tactile discrimination (static and moving 2-point discrimination [s-2PD and m-2PD]), and threshold levels (Weinstein enhanced sensory test [WEST]) in young healthy volunteers and compared these against values obtained on the corresponding finger pulp. We hypothesized that the sensibility of the nail can be clinically quantified and that it will not be as discriminatory as the finger pulp. The normative s-2PD, From the Yong Loo Lin School of Medicine, National University of Singapore; and the Department of Hand and Reconstructive Microsurgery, National University Hospital, Singapore. Received for publication February 19, 2013; accepted in revised form August 19, 2013. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article. Corresponding author: Sandeep Jacob Sebastin, MD, Department of Hand and Reconstructive Microsurgery, Level 11, National University Health System, 1E Kent Ridge Rd., Singapore 119228; e-mail: sandeepsebastin@gmail.com. 0363-5023/13/38A11-0010$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2013.08.112 Ó 2013 ASSH r Published by Elsevier, Inc. All rights reserved. r 2159