• Extensor tendon injury of the Hand is among the most common presented injuries to the ER.
  • The most common injured finger is the long (third) finger.

Anatomy

  • There are 9 extensor tendons to the hand:
    1. Abductor Pollicus Longus (EPL)
    2. Extensor Pollicus Brevis (APL)
    3. Extensor Carpi Radialis Brevis (ECRB)
    4. Extensor carpi Radialis longus (ECRL)
    5. Extensor Pollicis Longus (EPL)
    6. Extensor Digitorum Communis (EDC)
    7. Extensor Indicis Proprius (EIP)
    8. Extensor Digiti Minimi
    9. Extensor Carpi Ulnaris (ECU)
  • The extensor tendons pass from the forearm onto the dorsum of the hand through the six dorsal wrist compartments beneath the extensor retinaculum.

Zones of the extensor tendon system:

  • There are 8 zones that is divided into:
    1. Zone I: located at the level of distal interphalangeal joint (DIP).
    2. Zone II: located at the level of the middle phalanx.
    3. Zone III: located at the level of proximal interphalangeal joint (PIP).
    4. Zone IV: located at the level of the proximal phalanx.
    5. Zone V: located at the level of the metacarpophalangeal joint (MCP).
    6. Zone VI: located at the level of the metacarpal bones.
    7. Zone VII: located at the level of the wrist.
    8. Zone VIII: located at the level of the distal forearm.

Zones of the thumb:

  • There are 5 zones for the thumb:
    1. TI: located at the level of distal interphalangeal joint (DIP).
    2. TII: located at the level of the distal phalanx.
    3. TIII: located at the level of the metacarpophalangeal joint (MCP).
    4. TIV: located at the level of the first metacarpal bone.
    5. TV: located at the level of the wrist.

Extensor Tendon Injury based on the zones

Zone I injury

  • Extensor tendon injury in zone I is called Mallet finger.
  • Disruption of terminal extensor tendon at or distal to DIP joint
  • May be accompanied by bony avulsion injury from dorsal base of distal phalanx (bony mallet).
  • Clinically: Patient cannot actively extend at DIP joint, and finger remains in flexed posture.
  • Treatment:
    • If detected within 12 weeks of injury, closed management with full-time DIP joint extension splinting for at least 6 weeks, followed by part-time splinting for an additional 4 to 6 weeks.
      • Hyperextension should be avoided because skin necrosis can occur.
      • Surgical indication is a displaced bony mallet injury with significant volar subluxation of the distal phalanx:
        1. Closed reduction percutaneous pinning through DIP joint
        2. Extension block pinning.
        3. Open reduction internal fixation if large fragment bone (>50% articular surface)
    • Chronic mallet finger detected more than 12 weeks after injury:
      • Closed treatment only if joint supple, congruent, and without arthritic changes
      • Dynamic splinting, serial casting for contracted joint
      • Operative—tenodermodesis

Zone II injury

  • Mechanism of injury usually involves a dorsal laceration or crush component.
  • Partial disruptions (<50%) are treated nonoperatively with local wound care and early mobilization.
  • Direct repair may be attempted for greater than 50% lacerations.

Zone III injury

  • For closed extensor tendon injury in zone III , the Elson test is positive.
  • An acute boutonnière deformity results from central slip disruption and volar subluxation of the lateral bands, resulting in DIP hyperextension.
  • Closed injuries are treated with full-time PIP extension splinting for at least 6 weeks, followed by part-time splinting for an additional 4 to 6 weeks.

Zone IV injury

  • Treatment is similar to that for injuries in zone II.
  • A common complication in this zone is adhesion formation, with resulting loss of digital flexion.
  • Adhesion formation may be reduced with early protected ROM and dynamic splinting.
  • Failure of nonoperative management may require extensor tenolysis.

Zone V injury

  • Mostly a result of human bites.
    • It requires a surgical débridement of the MCP joint with loose or delayed wound closure.
  • A sagittal band rupture (“flea-flicker” injury) may result from forced extension of flexed digit.
    • Long finger most common injured.
    • Finger will be held in flexed position at MCP joint with no active extension.
    • Passive extension of the MCP joint is possible, and the patient can then usually maintain the finger in an extended position.
    • Acute injuries may be treated with 4 to 6 weeks of extension splinting of the MCP joint (one of the only exceptions to splinting the MCP joints in flexion).

Zone VI injury

  • It is usually associated with lacerations of superficial veins and nerves
  • Direct repair is indicated when the disruption constitutes more than 50% of the tendon.
  • Early protected motion advocated postoperatively.

Zone VII and VIII injuries

  • Lacerations at wrist level are usually associated with extensor retinaculum disruption, and postoperative adhesions are common.
  • The retinaculum should be repaired to prevent tendon bowstringing.
  • Static immobilization with the wrist held in extension and the MCP joints partially flexed is advised for the first 3 weeks, followed by protected motion.
  • The results of surgical repair in these zones are not as good as those in zones IV, V, and VI.

Partial or complete extension of the finger may be possible when a single extensor tendon injury occurs at the wrist because of the presence of accessory communicating tendons (juncturae tendinum).