Nail Anatomy and Physiology for the Clinician

Abstract

The nail plate is the final product of proliferation and differentiation of nail matrix keratinocytes. It emerges from underneath the proximal nail fold and grows distally at a median speed of 1–3 mm/month. The nail plate is firmly attached to the nail bed and detaches at the hyponychium, a small transverse band of epithelium that is in continuity with the pulp. Laterally, it is lined by the lateral nail folds. Each nail constituent has a role in production and growth of a healthy nail plate and if damaged produces typical nail symptoms: nail matrix damage will impair nail plate appearance and growth and nail bed and hyponychium damage with impair nail plate adhesion to the underlying tissues.

Examination of the nail should therefore include all parts of the nail apparatus: proximal and lateral folds, nail bed and hyponychium, and nail plate. The nail matrix is not visible directly, but only its distal part can be seen under the proximal nail plate and a distally convex crescent: the lunula.