A subungual hematoma^[1] is a collection of blood (hematoma) underneath a toenail or fingernail which often results from a traumatic injury such as slamming a finger in a door. A laceration of the nail bed causes bleeding into the constricted area underneath the hard nail plate. Because the blood disrupts the connections between the nail bed and nail plate, throbbing pain is common. The nail develops a black discoloration overlying the laceration.

It may result from an acute injury or from repeated minor trauma such as running in undersized shoes.

The following image shows a subungual hematoma after trauma to the nail.

Subungual hematomas are treated by either releasing the pressure by drilling a hole through the nail into the hematoma (trephining) or by removing the entire nail. Trephining is generally accomplished by using a heated instrument to pass through the nail into the blood clot. It should be noted that a heated instrument is not used on acrylic nails because they are flammable. Removal of the nail is typically done when the nail itself is disrupted, a large laceration requiring suturing is suspected, or there is a fracture of the tip of the finger. Although anesthesia is generally not required, a digital nerve block may be performed if the nail is to be removed. Subungual hematomas typically heal without incident, though infection or disruption of the nail (onycholysis) may occur.

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