Learning Objectives

By the end of this article, you should be able to:

Describe the structure and function of the nail unit
Identify the key anatomical components of the nail unit
Explain the clinical significance of nail bed and matrix injuries

The nail unit is a specialised integumentary structure located on the dorsal surface of the distal phalanges of the fingers and toes. It is a complex anatomical system composed of the nail plate and surrounding soft tissues, working together to support digital function.

The nail unit serves two primary functions:

Protection – shields the distal digits from mechanical trauma
Sensation – enhances tactile discrimination by providing counter-pressure to the fingertip pulp

In this article, we will review the anatomy of the nail unit, including its component parts and important clinical correlations.l

Components of the Nail Unit

The nail unit consists of the nail plate and the surrounding specialised soft tissues.

Nail Plate

The nail plate is the visible, outer component of the nail unit. It is formed by dense layers of keratin, creating a structure that is hard yet flexible and translucent. The nail plate protects the distal phalanx and transmits pressure during fine motor tasks.

Nail Folds

The proximal and lateral nail folds are extensions of skin that surround and protect the margins of the nail plate. They act as a physical barrier against infection and trauma.

Nail Bed (Sterile Matrix)

The nail bed lies beneath the nail plate and attaches it firmly to the distal phalanx. It provides a smooth, vascular surface over which the nail plate slides during growth.
Importantly, the nail bed does not contribute to nail plate production.

Germinal Matrix

The germinal matrix is a region of specialised epithelium located proximal to the nail bed, beneath the proximal nail fold. Cells within this matrix actively divide and keratinise to form the nail plate. Continuous cell proliferation pushes the nail plate distally as it grows.

Hyponychium

The hyponychium is the thickened epidermal region located distal to the nail bed, beneath the free edge of the nail plate. It forms a protective seal that prevents pathogens from entering the nail bed.

Eponychium (Cuticle)

The eponychium, commonly known as the cuticle, is a layer of stratum corneum that extends from the skin onto the proximal nail plate. It provides an additional protective barrier over the germinal matrix.

Lunula

The lunula is the pale, crescent-shaped area visible through the proximal nail plate. It represents the visible portion of the germinal matrix.

Clinical Relevance

Nail Bed Injury

A nail bed injury refers to trauma involving the soft tissues beneath the nail plate, including the nail bed and germinal matrix.

Common Mechanisms

Crush injuries – e.g., finger caught in a door or struck by a hammer
Lacerations – e.g,. injuries from sharp tools such as circular saws

An X-ray of the affected digit is required to assess for associated fractures, as nail bed injuries are frequently accompanied by fractures of the distal phalanx.

Management

In cases of nail bed laceration, surgical repair may be indicated to optimise cosmetic and functional outcomes. The nail plate is removed, and the laceration is repaired using absorbable sutures.

Following repair: