The fingertip, the most sensitive area of the hand, is often our first contact with the environment. It has important functional roles in grasping and pinching, in addition to its sensory and cosmetic functions.1,2 The fingernail protects the fingertip and provides increased sensation to the volar pulp.3 However, it also conceals the true extent of fingertip injuries. Hand injuries, with the fingertips most frequently involved, are second only to back injuries as the most common occupational injuries resulting in loss of work days.4 Hence, it is important for the Emergency Physician to evaluate the full extent of the injury, to assess potential disabilities, and to recognize the need for prompt referral to a Hand Surgeon.
The fingernails are frequently injured due to their anatomic location and their functional role. Immediate primary repair is the ideal management when these injuries involve the nail bed and surrounding skin fold structures.3,5 Careful repair is necessary to avoid functional impairment and cosmetic derangement of the nail plate.6 The following discussion will refer primarily to the fingernail. The toenail has less importance, both cosmetically and functionally, as grasp and pinch are not needed. However, all the principles and recommendations made also apply to the toenail.7
Knowledge of the anatomy of the nail unit enables the Emergency Physician to recognize the types of injuries and provide anticipatory guidance of the consequences of these injuries to the patients. The “perionychium” or the nail unit consists of the nail fold, the nail plate, nail bed, and the hyponychium (Figure 104-1).1,2
Anatomy of the fingernail. A. Lateral view. B. Top view. The colored area represents the perionychium.
The nail plate enhances the sensibility of the fingertip by applying a counterforce to the pulp space nerve endings.3 The digital tip and the nail plate also function in unison to smoothly coordinate normal pinch and grasp, which are important for picking up fine objects such as coins and pins.3,8
The nail plate is comprised of compacted, flattened, and elongated anucleated cells that originate from cornified epithelial cells.9 There are three atomic sites where these cells exist.5,8 The nail bed contains two of the sites: the sterile matrix and the germinal matrix.8 The other location is the dorsal roof matrix (Figure 104-1A). Of these, the germinal matrix is the most important for normal nail growth.5 The germinal matrix is responsible for approximately 90% of the nail plate by volume.8 The sterile matrix is responsible for a small percent of the nail plate by volume and varies from individual to individual. This cell production accounts for the nail plate being thicker at its distal tip compared to its proximal origin.8 The nail cells ...