Hand Tendon & Nerve Lacerations

Any laceration over the palmar or dorsal hand or digit needs a specific tendon and nerve examination before it gets treated as “just a cut” — missing a partial tendon or digital nerve injury is what turns a five-minute wound into a permanent functional deficit.

For fingertip and nail bed trauma see Fingertip & Nail Bed Injuries; for bite wound antibiotics see Bites & Clenched-Fist Injuries.

Examine before you anaesthetise

Test sensation (static and moving two-point discrimination) and tendon function before any local anaesthetic — once the area is numb, you’ve lost the ability to test either properly. Loss of sensation in a digital nerve distribution after a sharp laceration means nerve transection until proven otherwise.

Test FDP and FDS separately. Flexor digitorum profundus (FDP) is the only tendon crossing the DIP joint — isolate it by holding the PIP joint extended and asking for active DIP flexion. Flexor digitorum superficialis (FDS) is examined by holding the other fingers fully extended (this locks out their shared muscle belly) and asking for isolated PIP flexion. Loss of the normal flexor cascade — fingers no longer resting in graduated flexion, and no passive flexor tone with wrist extension — points to a complete tendon transection.

The partial-laceration pitfall: a tendon that is more than half cut through can still move, just weakly and painfully. Painful digital flexion against resistance, not absent flexion, is the sign of a partial tendon injury — do not clear a tendon just because the finger still bends. For surgical planning, repair is generally reserved for a laceration through more than three-quarters of the tendon width, or half to two-thirds when triggering is present.

Check capillary refill of the pulp and nail bed; delayed refill suggests digital artery injury. X-ray for retained glass, metal or other radio-opaque foreign material and to exclude an associated fracture.

Zones, in brief

Flexor and extensor tendons are both described in numbered anatomical zones, and the zone drives management more than the length of the skin wound does:

• Flexor zone 2 (the segment where FDS and FDP run together inside the finger’s fibro-osseous sheath, historically called “no man’s land”) has the worst outcomes because of adhesion formation in a tight tunnel — but still needs formal repair, not lower expectations.
• Extensor zone 3 (over the PIP joint) disrupts the central slip and causes a boutonnière deformity if missed; test with the Elson test — flex the PIP to 90° over a table edge and ask for DIP extension against resistance. A lax DIP normally results; a rigid, extending DIP means central slip injury.
• Extensor zone 1 (at or distal to the DIP) is an open mallet finger.

You do not need to name the exact zone in the urgent-care room — you need to recognise that the wound is over a tendon and refer.

Fight bite — assume it until proven otherwise

Any wound over the dorsal MCP joint, especially from an altercation, should be treated as a human bite (clenched-fist injury) until proven otherwise, and a laceration over the MCP joint at the extensor tendon is managed the same way regardless of the stated mechanism. These need extended exploration, thorough irrigation, and are left open rather than closed primarily; antibiotics should be started after cultures are taken if infection is already present.

Management in the urgent-care room

• Irrigate and debride the wound, remove obvious foreign material, and assess tissue viability.
• Close skin loosely, don’t repair tendon primarily outside a hand theatre — splint to protect the injured tendon from retraction (flexion splint for a flexor injury, extension splint for an extensor injury) rather than attempting definitive repair in the urgent-care setting.
• Start antibiotics and check tetanus status, particularly for any bite mechanism or contaminated wound.
• Refer same-day for any confirmed or suspected tendon laceration, digital nerve injury, or bite over the MCP joint. Primary tendon repair works best within about a week — this is not something to defer to routine follow-up. Flexor repair is an injury treated promptly rather than urgently: the reported ideal window is within two weeks, and repairs carried out later than three weeks from injury have worse outcomes.