Nail matrix

The nail matrix is the specialized, proliferative epithelial tissue located beneath the proximal nail fold at the base of the nail unit. It is responsible for generating the majority of the nail plate through the differentiation and keratinization of matrix keratinocytes.

The matrix is divided into proximal and distal regions: the proximal matrix forms the superficial dorsal layers of the nail plate, while the distal matrix contributes to the ventral portion. The visible portion of the distal matrix is the lunula, which appears as a whitish, half-moon shape at the base of the nail plate.

The matrix epithelium overlies a distinct connective tissue compartment known as the onychodermis, which contains specialized onychofibroblasts and is analogous to the dermal papilla of hair follicles.

The matrix is bordered proximally by the proximal nail fold and laterally by the lateral nail folds, and it is separated from the underlying distal phalanx by a thin matrical dermis and, in some digits, by the extensor tendon.

The matrix lacks capillary loops but contains a rectangular plexus of capillaries aligned in the plane of the matrix.

Histologically, the nail matrix is characterized by a multilayered basal cell compartment and a keratogenous zone, with cells expressing both epithelial and hair-type keratins, reflecting its unique role in hard keratin production.

The integrity and function of the nail matrix are essential for normal nail growth and morphology.