The nail plate is the hard keratin cover of the dorsal portion of the distal phalanx. The nail plate is generated by the nail matrix at the proximal portion of the nail bed (Figure 1). As the nail grows, the distal part of the matrix produces the deeper layers of the nail plate, while the proximal portion makes the superficial layers. This production is important, because a disruption of function in the proximal matrix (as may occur in patients with psoriasis) results in more superficial nail problems (e.g., pitting). A disruption of the distal matrix may cause problems with the deeper layers, resulting in ridging or splitting. A transient problem causing growth disturbance may lead to the formation of transverse lines across the nail plate, as in Mees', Muehrcke's, and Beau's lines . Changes in the configuration of the capillaries in the proximal nail bed are responsible for some of the alterations that occur in patients with connective tissue disorders, while abnormalities in the periosteal vessels contribute to clubbing.

The nail is bound proximally by the eponychium (the skin just proximal to the cuticle), laterally by the nail folds, and distally by the distal nail fold (defined by the separation created by the anterior ligament between the distal nail bed and the nail plate; Figure