A subungual hematoma is a common injury where blood collects beneath the fingernail or toenail, typically following direct trauma such as crushing the finger in a door or hitting it with a hammer. The nail plate is tightly adhered to the nail bed, and when underlying blood vessels are damaged, the trapped blood has nowhere to go, leading to pressure buildup. This pooling of blood causes the characteristic dark discoloration—which can appear red, purple, brown, or black—and is often accompanied by intense, throbbing pain. Determining whether this pressure needs to be relieved through drainage is the primary decision point following a crush injury.
Identifying a Subungual Hematoma and Assessing Severity
The most immediate symptom of a subungual hematoma is the appearance of a dark, discolored area beneath the nail plate, resulting from the accumulation of blood. This discoloration is accompanied by significant, throbbing pain because the blood creates pressure on the nail bed tissue. The pain level is a direct indicator of the amount of pressure trapped underneath the nail.
Severity is gauged by visually estimating the percentage of the nail plate covered by the hematoma. A small hematoma, covering less than 25% of the nail, may cause only mild discomfort and resolves without intervention. However, a larger collection of blood, especially one covering 50% or more of the nail, signals a more extensive injury and a higher likelihood of significant pressure. Any trauma severe enough to cause a hematoma also carries the risk of damaging the underlying bone or soft tissue.
Criteria for Drainage and Pain Relief
Drainage, medically known as trephination, is primarily performed to relieve the pain caused by the pressure of the pooled blood. The procedure is generally indicated when a hematoma is painful and covers a significant portion of the nail, typically 25% to 50% or more of the visible nail plate. For patients with unmanageable pain, the benefits of immediate pressure relief usually outweigh the risks associated with the procedure. Drainage is most successful when performed within 48 hours of the injury, as the blood begins to clot and solidify after this time, making it difficult to evacuate through a small hole.
If a fracture of the distal phalanx (the fingertip bone) is suspected, or if the finger has other complex injuries like severe lacerations to the nail fold, drainage alone may be insufficient. In cases where a fracture is confirmed, drainage is still recommended if the hematoma covers 25% or more of the nail to prevent complications. If the nail plate is visibly split, torn, or lifted from the nail bed, immediate professional medical attention is required, as this suggests a more complicated injury that may require surgical repair of the nail bed, often preceded by X-ray imaging for fracture diagnosis. Simple, painless hematomas, regardless of size, do not require drainage and can be managed with conservative care.
The Drainage Procedure and Necessary Precautions
Trephination involves creating a small, controlled opening in the nail plate to allow the trapped blood to escape and relieve pressure. In a sterile medical environment, this is often achieved using an electrocautery device or a sterile, large-gauge needle, such as an 18-gauge needle, rotated manually like a drill. The heat from an electrocautery device or the pressure from the needle melts or bores a small hole through the nail material, which is painless because the nail plate itself has no nerves.
The primary precaution is maintaining sterility to prevent the introduction of bacteria into the now-open wound, which is why medical professionals use sterilized equipment and antiseptics. Attempting this procedure at home using non-sterile items like a heated paper clip carries a high risk of introducing infection or causing further injury to the nail bed beneath. The medical professional takes care to penetrate only the nail plate, avoiding deep contact with the nail bed, which could cause unnecessary pain or potential long-term nail deformity. Once the opening is created, the blood typically drains immediately, providing pressure relief.
Post-Procedure Care and When to Seek Professional Help
After trephination, the finger should be kept clean and dry, and a sterile dressing should be applied to the site, which may need to be changed regularly. It is normal for the site to continue draining blood or serous fluid for up to 36 hours following the procedure. Patients should avoid soaking the affected finger in water, as this can increase the risk of bacterial contamination and infection.
The injured nail will likely be shed over the following weeks or months as a new nail grows in from the base, a process that can take four to six months for a fingernail. Patients must seek professional help immediately if they observe any signs of infection, such as:
- Increasing redness
- Warmth
- Swelling around the nail
- The presence of pus
- The development of a fever
If the pain returns after successful drainage, it may indicate a re-accumulation of the hematoma or a blood clot forming in the drainage hole, requiring a follow-up appointment.