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Zone II Flexor Tendon Injury

A Zone II flexor tendon injury involves damage to the flexor tendons within a specific anatomical area of the hand, leading to impaired ability to bend the finger. Understanding the anatomy, mechanism of injury, and appropriate management is essential to ensure optimal recovery.

Anatomy of Zone II

The flexor tendons in the hand allow the fingers to bend and grip objects. These include:

  • FDP tendon: Inserts into the base of the distal phalanx, allowing fingertip flexion.
  • FDS tendon: Splits and inserts into the middle phalanx, enabling flexion at the proximal interphalangeal (PIP) joint.
  • Tendon sheath and pulleys (A2 and A4): Keep tendons close to the bone, maintaining smooth gliding and finger movement.
  • Neurovascular bundles: Close proximity makes them vulnerable in injuries.

Damage in this area often disrupts the delicate balance between tendon gliding and pulley function, leading to complications like adhesions, stiffness, or loss of finger motion.

Tendon Problems

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Causes of Zone II Flexor Tendon Injuries

The most common causes include:

  • Sharp trauma: Such as knife cuts, glass injuries, or machinery accidents.
  • Crush or avulsion injuries: Tendon is pulled off from its attachment, sometimes with bone fragments.
  • Sports injuries: Sudden forceful extension against flexion can rupture the tendon.
  • Iatrogenic injuries: Rarely, tendon damage occurs during surgery on the hand or fingers.

Clinical Features

Patients with a Zone II flexor tendon injury may present with:

  • Inability to bend the finger joints (PIP or DIP).
  • Pain and swelling at the site of injury.
  • Tenderness along the flexor surface.
  • Open wound or laceration (in penetrating injuries).
  • Loss of normal finger cascade: When the hand is relaxed, fingers normally rest in a gentle curve; an injured finger remains straighter.
  • Loss of active grip strength.

Diagnosis

  • History and physical exam: Mechanism of injury, site of laceration, and functional deficits are carefully evaluated.
  • Tendon testing: Separate assessment of FDP and FDS.
  • X-rays: Used if fractures or foreign bodies are suspected.
  • Ultrasound or MRI: May be used to confirm tendon rupture or evaluate retraction.

Challenges of Zone II Injuries

  • Both FDS and FDP tendons are enclosed in a tight sheath.
  • Repairing both tendons can overcrowd the sheath.
  • Tendons are prone to adhesions and scarring, which limit gliding.
  • Injury may also damage pulleys, requiring reconstruction.

Treatment and Management

The primary goal of treatment is to restore tendon continuity, gliding motion, and hand function.

1. Initial Care:

  • Clean and dress the wound.
  • Administer antibiotics if contamination is present.
  • Immobilize the hand in a splint.

2. Surgical Repair:

  • Timing: Ideally performed within 24–72 hours for clean injuries. Delayed repair may be needed in contaminated wounds.
  • Multi-strand core suture techniques (e.g., 4- or 6-strand repairs) provide strength.
  • Epitendinous sutures add smoothness and reinforce repair.
  • Sometimes only FDP is repaired if FDS is too damaged or both cannot fit in the sheath.
  • Pulley preservation or reconstruction: Critical to prevent bowstringing of tendons.

3. Postoperative Rehabilitation:

  • Early controlled mobilization protocols (such as Kleinert or Duran methods) are used to prevent adhesions and promote tendon healing.
  • A dorsal blocking splint is applied, keeping the wrist flexed, MCP joints flexed, and IP joints extended.
  • Hand therapy involves gradual passive and active motion exercises under supervision.

Complications

Zone II injuries are prone to complications, especially if diagnosis or treatment is delayed. Common issues include:

  • Adhesion formation: Restricts smooth tendon movement.
  • Rupture of repair: If the tendon is overloaded during healing.
  • Joint stiffness or contractures.
  • Loss of flexion strength.
  • Pulley disruption leading to bowstringing.

Prognosis

  • Timing of repair (early treatment yields better results).
  • Surgical technique (strong, gliding repair methods).
  • Compliance with rehabilitation (dedicated therapy is crucial).

Conclusion

Zone II flexor tendon injuries, often referred to as injuries in “no man’s land,” represent some of the most technically demanding injuries in hand surgery. The close proximity of flexor tendons, pulleys, and tendon sheaths makes repair and rehabilitation complex. Early diagnosis, meticulous surgical repair, and strict adherence to structured rehabilitation protocols are critical to restoring optimal function. While challenges such as adhesions, stiffness, and re-rupture exist, modern techniques and improved therapy protocols have significantly improved outcomes, allowing many patients to regain useful hand function.

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