A subungual hematoma is a collection of blood trapped between the nail plate and the nail bed, often resulting from a crush injury like a smashed finger. This blood has nowhere to escape, creating significant pressure underneath the rigid nail structure. This rapid accumulation is the primary source of the immediate and often intense, throbbing pain. Severe pain suggests a buildup of pressure that may require intervention to alleviate symptoms and prevent potential complications.
Understanding the Injury: Subungual Hematoma
A subungual hematoma develops when crush trauma damages capillaries and small blood vessels within the nail bed tissue. Blood leaks and pools directly beneath the nail plate, which acts as a barrier, preventing drainage and pushing against the sensitive nail bed. The intense, throbbing pain is a direct consequence of this pressure buildup in a non-expandable space.
Clinically, the area appears as a dark discoloration, typically black, blue, or purple, beneath the nail. The severity of the pain is directly proportional to the amount of blood trapped under the nail.
Determining the Need for Drainage
The decision to drain a subungual hematoma centers on the severity of the patient’s pain and the size of the blood accumulation. If the pain is mild or the hematoma covers less than 25% of the visible nail area, the injury can often be managed with simple home care, such as rest, ice, and elevation. The body will naturally reabsorb the blood as the nail grows out.
Drainage, known as trephination, is generally considered when pain is severe and persistent, indicating high pressure. Intervention is often suggested if the hematoma covers more than 50% of the nail surface, though some practitioners may consider it for smaller, extremely painful accumulations. If blood is already spontaneously draining from under the nail, additional trephination is usually unnecessary.
Timing is also a significant factor. Trephination is most effective if performed within the first 48 hours following the injury. After this window, the blood often begins to clot, making successful drainage through a small hole difficult or impossible. Relieving the pressure by draining the hematoma is the fastest way to provide immediate relief from severe pain.
The Drainage Procedure: Trephination
Trephination is the procedure used to drain the trapped blood by creating a small opening in the nail plate to relieve internal pressure. This quick outpatient procedure leads to the immediate cessation of throbbing pain when successful. The opening must be made directly over the hematoma, avoiding the lunula—the white, crescent-shaped area at the base of the nail—to prevent damage to the underlying nail matrix.
Medical professionals use two main techniques: a sterile, large-gauge needle or a specialized electrocautery device. When using a needle, the practitioner employs a gentle twirling motion to bore through the nail until the blood is reached. The electrocautery method involves a heated tip that melts a clean, small hole through the nail plate.
The cautery method is often preferred because the heat seals the hole as it is made, and contact with the underlying blood quickly cools the tip, reducing the risk of damaging the nail bed. The procedure must be performed under strict sterile conditions by a healthcare provider to minimize infection risk. Attempting this procedure at home, especially with non-sterile items like a heated paperclip, significantly increases the risk of serious infection and further injury.
Urgent Medical Evaluation and Follow-Up Care
A comprehensive medical evaluation is necessary for any significant smash injury to the finger, as the trauma may have caused other injuries. An X-ray is routinely performed to check for an underlying fracture of the distal phalanx, the small bone at the fingertip. The presence of a fracture may influence management, but it does not necessarily prevent the hematoma from being drained.
The healthcare provider will also assess for signs of a nail bed laceration, especially if the nail is significantly damaged or detached. If the nail bed has a deep cut, the nail plate may need to be removed for surgical repair with fine sutures. Following trephination, the patient must keep the finger clean and dry, avoiding soaking the hand to prevent bacterial contamination.
The patient should monitor the finger for delayed signs of infection, such as increasing redness, swelling, warmth, or pus draining from the site. The damaged nail may eventually loosen and fall off, particularly if the hematoma covered a large area. A fingernail typically takes approximately four to six months to fully regrow from the nail matrix.