Nail procedures require a detailed knowledge of the anatomy and physiology of the distal digit. A thorough understanding of nail unit structures and their functions will allow the surgeon to maximize diagnostic and therapeutic results while minimizing patient discomfort and postoperative deformity. A comprehensive anatomic review is beyond the scope of this text, but a brief primer will allow for better understanding of the procedures described subsequently.
The nail unit is composed of the nail matrix, nail bed, nail plate, and their bordering structures (Fig. 22-1). The nail matrix is the germinative epithelium that produces the keratinized nail plate on the dorsal aspect of the distal digit.1 A portion of the matrix is visible through the proximal nail plate as the pink–white, semicircular lunula. The lateral horns of the crescent-shaped matrix extend approximately 6 mm proximally from the visible edge of the nail plate. The proximal portion of the matrix forms the dorsal – or most superficial – portion of the nail plate, while the distal portion produces the ventral portion (Fig. 22-2). As the predominant germinative structure, the nail matrix is an irreplaceable component of the nail unit, and extreme care must be taken to minimize trauma. Procedures affecting the proximal matrix, responsible for up to 80% of the nail plate, are more likely to result in noticeable postoperative split-nail deformity.2
Anatomy of the nail. (Reproduced with permission from Dave Klemm. © 2007 Dave Klemm.)
Origin of nail layers. (Used with permission from P. Kechijian, MD.)
The matrix makes up the inferior and proximal portion of a cul-de-sac from which the nail plate emerges. The superior portion or “roof” of the cul-de-sac is formed by the proximal nail fold (PNF). Its ventral aspect, in contact with the nail plate, is often referred to as the eponychium. The most distal aspect of the PNF is the cuticle, a translucent rim of stratum corneum that seals the proximal fold to the nail plate, thereby preventing microorganisms and irritants from entering the cul-de-sac. The sides of the nail plate are bordered by the lateral nail folds (LNF), which are anatomically similar to the PNF but do not form a cuticle.
Abutting the matrix and comprising the majority of the base of the nail plate is the nail bed. Characterized by linear, parallel rete ridges, this highly vascular tissue lends a pink color to the nail. The nail bed is firmly adherent to the plate, to which it may contribute a small number of cells.2,3 The bed extends from the lunula to the hyponychium, which seals the potential subungual space and is the point at which the nail separates from the underlying epithelium. The distal ...