Nailbed Injuries 

Nailbed injuries are common, with fingertip injuries being the most often seen type of hand injuries. The fingertip is frequently injured because it is the point of interaction between the body and one's surroundings in the majority of activities performed on a daily basis, and it is the most distal portion of the upper extremities.

In addition to long-term cosmetic consequences, injuries to the nail can affect daily living. The nail provides protection for the fingertip, offers the ability to pick up small objects, and plays a role in tactile sensation. It also serves as a counter force when the finger pad touches an object; two-point discrimination distance widens substantially with removal of a nail.

To fully appreciate the consequences and treatment of nailbed injuries, reviewing the anatomy of the nailbed and the surrounding tissues is useful.^{[1, 2, 3]}

• Nail - Hard structure composed of desiccated, keratinized squamous cells
• Perionychium - Composed of the nailbed and paronychia
• Nailbed - Soft tissue below the nail that is bound to the underlying periosteum of the distal phalanx and consists of the germinal and sterile matrix
• Paronychia - Lateral nail folds
• Hyponychium - Junction between the nailbed and fingertip skin that contains large numbers of polymorphonuclear leukocytes and lymphocytes, which protect the subungual tissue from infection
• Nail fold - Holds the proximal nail
• Eponychium - Commonly known as the cuticle, or the distal portion of the nail fold where it attaches to the dorsum of the nail
• Lunula - White opacity distal to the eponychium, caused by the presence of nail cell nuclei in the germinal matrix as they stream upward and distally to create nail

Nail formation is a collective production by 3 areas of the perionychium:

• The germinal (intermediate) matrix, covering the ventral floor of the proximal volar nail fold to the lunula, produces 90% of nail volume. It is immediately distal to the extensor tendon attachment to the distal phalanx. As the cells are produced, they force cells ahead to flatten and stream distally into the nail because of the confining boundaries of the nail fold. The nuclei of the cells disintegrate as they grow beyond the lunula, giving the nail its clear appearance.
• The sterile (ventral) matrix begins as the lunula ends and extends out to the hyponychium. It is closely adherent to the dorsal periosteum of the distal phalanx. It contributes a small amount to the nail but mostly provides adherence between the nail and the nailbed.
• The proximal half of the dorsal roof of the nail fold produces cells that give the nail its shine.

Longitudinal nail growth takes between 70 and 160 days to cover the entire length of the nail. After an injury, nail growth is stunted or absent for up to 21 days. The nail then grows rapidly for approximately the next 50 days and then slows again before a normal and sustained growth rate resumes. These relative accelerations and slowdowns in nail growth create the characteristic lump that is often observed on most nails that regrow after trauma.

As a result of scar tissue being unable to produce nail material, damage to specific components of the perionychium will lead to characteristic defects during regrowth of the posttraumatic nail. A scar of the dorsal roof of the nail fold creates a dull streak on the nail surface, while a scar of the germinal matrix may cause a split or absent nail, and a scar in the sterile matrix results in a split or nonadherent nail beyond the scar.

The nailbed is supplied by two volar arterial arches that are anastomoses between digital arteries of the finger or toe, just above the periosteum of the distal phalanx. Venous drainage coalesces in the proximal nailbed and proximal to the nail fold and drains over the dorsum of the finger. Abundant lymphatic vessels are present in the nailbed. The perionychium is innervated by the dorsal branches of the paired digital nerves, one to the nail fold, one to the fingertip, and one to the pulp.

Frequency

United States

The hand is involved in 11-14% of on-the-job injuries and 10% of all accident cases in US emergency departments. However, the exact prevalence of nailbed injuries is unknown since many patients with nailbed injuries do not bother to seek a physician's care for what they perceive as a minor trauma.

Mortality/Morbidity

Complications of nailbed injuries include nail loss, abnormal growth, nonadherence of new nail, splitting of the nail, soft tissue infection, and osteomyelitis of the underlying distal tuft.

Race

No racial predilection exists.

Sex

A 3:1 male-to-female predominance of injury exists.

Age

Nailbed injuries occur in all ages; however, the most common age group is between 4 and 30 years old. Fingertip injuries account for two thirds of hand injuries in children, and damage to the nailbed occurs in 15-24% of these injuries.^{[4, 5]}