Nail trephination is creating a hole in the fingernail or toenail to release trapped blood from beneath the nail.
- Simple subungual hematoma (blood under nail bed with intact nail and fold) that is painful and typically covering > 50% of the nail bed
Subungual hematomas that are relatively painless, small, or have drained spontaneously (eg, under the distal edge of the nail) do not require trephination.
- Avulsion of the nail from the nail bed, splitting of the nail, or extension of a laceration from the nail bed to the skin: These injuries require nail removal.
- More than 1 to 2 days since injury: By this time, blood within a subungual hematoma will likely have clotted and trephination will not be effective.
- Infection (rarely)
- Minor nail bed injury resulting from the trephination device
Patients typically lose a nail that had a subungual hematoma, but this is because of the hematoma rather than the trephination. The nail subsequently regrows but may be deformed if the nail bed was damaged by the original injury. Inadvertent contact of the trephination device with the nail bed is painful but does not cause enough damage to produce nail deformity.
- Cleansing solution such as chlorhexidine
- Nonsterile gloves
- Syringes and needles to give local anesthesia
- Cautery device (eg, disposable pen) or 18-gauge needle
- Alternatives: A 29-gauge insulin needle with attached syringe or a mesoscission device (which determines depth of nail boring using skin electrodes)
- Sterile gauze
- Presence of a fracture does not contraindicate nail trephination; trephination does not increase the risk of infection.
- Fingertip or toe fractures, which can be diagnosed by x-ray, often occur if subungual hematomas comprise > 50% of nail matrix.
- The nail above a hematoma has no sensation, but the nail bed is exquisitely sensitive.
- The nail matrix under the base of the nail anchors the dermis to the periosteum of the distal phalanx and allows for nail growth. The distal matrix ends in the lunula (white crescent). Scarring of the nail eventually grows out, but scarring of the matrix can lead to nail deformity or permanent loss of the nail.
- Patient comfort with excellent exposure of nail
- Hand supported on a firm surface
Step-by-Step Description of Procedure
- Assess the finger or toe for neurovascular compromise and the extensor tendon for evidence of tendon disruption at the distal interphalangeal (DIP) joint (mallet finger or toe).
- Clean the nail and finger gently with a clean cloth or gauze and soap and water, or a mild antibacterial wound cleanser such as chlorhexidine.
- Reassure the patient that trephination takes only a few seconds and is almost painless—much less so than a digital block.
- If the patient cannot be reassured, anesthetize the distal finger with a digital block.
- Stabilize the operating hand on the same surface as the patient's hand.
- If using cautery, place the device over the center of the subungual hematoma, exert mild pressure with control until a “give” is felt and blood comes out; this takes < 1 second.
- If using a needle, use a rotating motion with moderate pressure to drill carefully through the nail.
- Alternative: Instead of the cautery device or large-bore needle, you can insert a 29-gauge insulin needle underneath the nail at the distal hyponychium and advance it proximally and parallel to the nail plate with gentle suction on the syringe until the hematoma begins to drain into the attached syringe.
- With successful drainage, there is an immediate, marked decrease in pain and visible diminution of the hematoma.
- If pain is not significantly relieved, consider whether another area of the hematoma requires drainage (usually one well-placed hole is sufficient).
- Dress with sterile gauze. Inform the patient that drainage through the hole may continue for 24 to 36 hours.
- Return of pain may indicate a trephination site clot. A warm soak can help remove the clot and relieve pain.
- Prophylactic antibiotics are not routinely needed even if a fracture is present.
Warnings and Common Errors
- Be sure to control the tip of the cautery or needle as it passes through the nail plate so the nail bed is contacted.
- Be sure not to go too shallow or slow with the cautery device, allowing the area to heat up.
- Avoid hot cautery with artificial nails, which can be flammable.