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  • Injury can be caused by laceration, trauma, or overuse
  • Epidemiology
    • most commonly injured digit is the long finger
    • zone VI is the most frequently injured zone
  • Mechanism
    • Zone I
      • forced flexion of extended DIP joint
    • Zone II
      • dorsal laceration or crush injury
    • Zone V
      • commonly from "fight bite"
      • sagittal band rupture ("flea flicker injury")
        • forced extension of flexed digit
        • most common in long finger
 Zones of Extensor Tendon Injuries
Zone I
 • Disruption of terminal extensor tendon distal to or at the DIP joint of the fingers and IP joint of the thumb (EPL)
 • Mallet Finger 

Zone II  • Disruption of tendon over middle phalanx or proximal phalanx of thumb (EPL)

Zone III  • Disruption over the PIP joint of digit (central slip) or MCP joint of thumb (EPL and EPB
 • Boutonniere deformity 
Zone IV  • Disruption over the proximal phalanx of digit or metacarpal of thumb (EPL and EPB)
Zone V  • Disruption over MCP joint of digit or CMC joint of thumb (EPL and EPB)
 •"Fight bite" common
 • Sagittal band rupture 
Zone VI  • Disruption over the metacarpal
 • Nerve and vessel injury likely
Zone VII  • Disruption at the wrist joint
 • Must repair retinaculum to prevent bowstringing
 • Tendon repair followed by immobilization with wrist in 40° extension and MCP joint in 20° flexion for 3-4 weeks 
Zone VIII  • Disruption at the distal forearm post
Zone VIII  • Extensor muscle belly 
 • Usually from penetrating trauma
 • Often have associated neurologic injury
 • Tendon repair followed by immobilization with elbow in flexion and wrist in extension

  • Zone I
    • Inability to extend at the DIP joint
  • Zone III
    • Elson test 
      • flex the patient's PIP joint over a table 90 degrees and ask them to extend against resistance
      • if central slip is intact, DIP will remain supple
      • if central slip disrupted, DIP will be rigid
  • Zone V
    • extensor lag and flexion loss common
    • junctura tendinae may allow partial/temporary extension by connecting with intact adjacent extensor tendons   
    • sagittal band rupture
      • rupture of stronger radial fibers of sagittal band may lead to extensor tendon subluxation
      • finger held in flexed position at MCP joint with no active extension
  • Radiographs
    • AP and lateral of digit to verify no bony avulsion (boney mallet)
  • Nonoperative
    • immobilization with early protected motion
      • indications
        • lacerations < 50% of tendon in all zones if patient can extend digit against resistance
    • DIP extension splinting
      • indications
        • acute (<12 weeks) Zone 1 injury (mallet finger)
        • nondisplaced bony mallet
        • chronic mallet finger (>12 weeks) if joint supple, congruent
      • techniques
        • full-time splinting for six weeks
        • part-time splinting for four to six weeks
        • avoid hyperextension, which may cause skin necrosis
        • maintain PIP motion
      • outcomes
        • noncompliance is a common problem
    • PIP extension splinting
      • indications
        • closed central slip injury (zone III)
      • techniques
        • full-time splinting for six weeks
        • part-time splinting for four to six weeks
        • maintain DIP flexion
    • MCP extension splinting
      • indications
        • closed zone V sagittal band rupture
      • techniques
        • full-time splinting for four to six weeks
  • Operative
    • immediate I&D
      • indications
        • fight bite to MCP joint
      • techniques
        • close loosely or in delayed fashion
        • treat with culture-specific antibiotics, although Eikenella corrodens is a common mouth organism
    • tendon repair
      • indications
        • laceration > 50% of tendon width in all zones
    • fixation of bony avulsion
      • indications
        • boney mallet finger with P3 volar subluxation
      • techniques
        • closed reduction and percutaneous pinning through DIP joint
        • extension block pinning
        • ORIF if it involves >50% of the articular surface
    • tendon reconstruction
      • indications
        • chronic tendon injury or when repair not possible
    • central slip reconstruction
      • techniques
        • tendon graft
        • extensor turndown
        • lateral band mobilization
        • transverse retinacular ligament
        • FDS slip
    • EIP to EPL tendon transfer
      • indications
        • chronic EPL rupture
Surgical Techniques
  • Tendon Repair
    • incision technique 
      • utilize laceration, when present,  and extend incision as needed to gain appropriate exposure
      • longitudinal incision may  be utilized across joints on the dorsum of digits, unlike the palmar side
    • suture technique
      • # of suture strands that cross the repair site is more important than the number of grasping loops
      • in general strength increases with increasing number of sutures crossing the repair site, thickness of the suture, and locking of the stitch
      • 4-6 strands provide adequate strength for early active motion 
    • circumferential epitendinous suture
      • Optional for reinforcement
    • repair failure
      • tendon repairs are weakest between postoperative day 6 and 12
      • repair usually fails at knots
  • Tendon Reconstruction
    • usually done as two stage procedure
      • first a silicon tendon implant is placed to create a favorable tendon bed
      • wait 3-4 months and then place biologic tendon graft
      • only perform single stage reconstruction if flexor sheath is pristine and digit has full ROM
    • available grafts include
      • palmaris longus (absent in 15% of population)
        • most common
      • plantaris (absent in 19%)
        • indicated if longer graft is needed
      • long toe extensor
    • pulley reconstruction
      • one pulley should be reconstructed proximal and distal to each joint
      • methods include belt loop method and FDS tail method
  • Tenolysis
    • indications
      • adhesion formation with loss of finger flexion
      • wait for soft tissue stabilization (> 3 months) and full passive motion of all joints
    • postoperative
    • follow with extensive therapy
  • Early active short-arc motion (SAM)
    • indications
      • after zone III central slip repair
    • advantages over static immobilization
      • increases total arc of motion
      • decrease duration of therapy
      • increase DIP motion 
      • creates 4mm of tendon excursion and prevents adhesions. 
  • Adhesion formation
    • leads to loss of finger flexion
    • common in zone IV and VII and older patients
    • prevented with early protected ROM and dynamic splinting (zone IV)
    • treatment
      • extensor tenolysis with early motion indicated after failure of nonoperative management, usually 3-6 months
      • tenolysis contraindicated if done in conjunction with other procedures that require joint immobilization
  • Tendon rupture
    • causes include poor suture material or surgical technique, aggressive therapy, and noncompliance
    • incidence
      • 5%
      • most frequently during first 7 to 10 days post-op
    • treatment
      • early recognition may allow revision repair
      • tendon reconstruction for late rupture or rupture with excessive scarring
  • Swan neck deformity
    • caused by prolonged DIP flexion with dorsal subluxation of lateral bands and PIP joint hyperextension
    • treatment
      • Fowler central slip tenotomy
      • spiral oblique ligament reconstruction
  • Boutonniere deformity (DIP hyperextension)
    • caused by central slip disruption and lateral band volar subluxation
    • treatment
      • dynamic splinting or serial casting for maximal passive motion
      • terminal extensor tenotomy, PIP volar plate release

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