A 14-year-old boy presented to the office 1 week after slamming his finger in a car door. He was seen at an urgent care clinic after the acute event and told to follow-up in 1 week. A healing subungual hematoma was evident (Figure 166-1). He has full range-of-motion and no pain. Since there is no pain, there is no indication for nail perforation and drainage.

Subungual hematoma (blood under the fingernail or toenail) is a common injury. It is typically caused by a blow to the distal phalanx (e.g., smashing with a tool, crush in a door jamb, stubbing one’s toe). The blow causes bleeding of the nail matrix or bed with resultant subungual hematoma formation. Patients usually present because of throbbing pain associated with blue-black discoloration under the nail plate. Subungual hematomas may be simple (i.e., the nail and nail fold are intact) or accompanied by significant injuries to the nail fold and digit.¹ The patient may not be aware of the precipitating trauma, because it may have been minor and/or chronic (e.g., rubbing in a tight shoe).

Subungual hematoma is a common childhood injury.

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  The injury causes bleeding of the nail matrix and nail bed, which results in subungual hematoma formation. Pain is produced by the pressure in the contained space under the nail plate pressing against nerve receptors, although soft tissue or bony injury may also contribute to the pain when present (Figures 166-1 to 166-5).

  
  
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  In most cases the discoloration grows out with the nail plate, exhibiting a proximal border that reproduces the shape of the lunula. Occasionally, a hematoma does not migrate because of repeated daily trauma. An extended, nonmigrating “hematoma” should be considered suspicious. Nail plate punch biopsy can be performed if melanoma is a worry. If the dark area was only a hematoma the dark color lifts off with nail plate.

  
  
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  Potential complications of subungual hematoma include onycholysis, nail deformity (usually splitting as in Figure 166-6), and infection. Complications are more likely to occur when presentation is delayed or there is an underlying fracture.²