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Flexor Pulley System-Fingers
  • Annular ligaments
    • A2 and A4 are critical to prevent bowstringing
      • most biomechanically important  
    • A1, A3, and A5 overlie the MP, PIP and DIP joints respectively 
      • originate from palmar plate  
    • A1 pulley most commonly involved in trigger finger
  • Cruciate pulleys
    • function to prevent sheath collapse and expansion during digital motion
    • facilitates approximation of annular pulleys during flexion
    • 3 total at the level of the joints
Flexor Pulley System-Thumb

  • Oblique pulley (3-5mm)
    • originates at proximal half of proximal phalanx
    • most important pulley in thumb 
    • functions like cruciate pulley in fingers
      • in fingers A1-A2-C1-A3
      • in thumb A1-Av-oblique-A2
    • facilitates full excursion of FPL
    • prevents bowstringing of FPL 
      • bowstringing will occur if both A1 and oblique pulleys are cut
  • Annular pulleys
    • A1 pulley (4-8mm)
      • at the level of the volar plate at the MCP joint
      • ~6mm in length
      • radial digital nerve is closest (2.7mm)
      • ulnar digital nerve is less close (5.4mm)
      • bowstringing will occur if both A1 and oblique pulleys are cut
    • Av pulley (annular variable pulley) (4-8mm)
      • between A1 and oblique pulleys
        • previously thought to be part of oblique pulley
      • function
        • helps prevent bowstringing
      • 3 types
        • Type I - transverse, parallel to A1, with gap between Av and A1  
        • Type II - no gap between Av and A1  
        • Type III - triangular/oblique Av pulley with fibers converging to radial side  
    • A2 pulley (5-10mm)
      • contributes least to arc of motion of thumb
      • if A2 is intact, cutting A1 or oblique pulley will not result in bowstringing
Pulley Reconstruction
  • Goals
    • preserve or reconstruct 3 or more pulleys
    • A2 is important
    • unclear if A4 reconstruction is absolutely necessary (can be sacrificed during acute flexor tendon surgery)
  • Graft material
    • extensor retinaculum 
      • synovialized pulley surface, provides least gliding resistance
    • excised tendon material
    • palmaris or plantaris
    • FDS
    • flexor tendon allograft
  • Techniques
    • first excise all scar dorsal to the flexor tendon
    • around-the-bone (encircling technique)
      • single-loop (Bunnell)  
      • triple loop (Okutsu)  
        • biomechanically strongest construct
      • complications
        • most worrisome is phalangeal fracture 
        • stiffness
        • persistent bowstringing
          • inadequate tensioning
          • failure to remove scar tissue dorsal to tendon (tendon is not pressed against bone)
    • nonencircling reconstruction
      • ever-present-rim (Kleinert)  
      • belt-loop (Karev)  
      • extensor retinaculum (Lister)
      • palmaris longus transplantation through volar plate (Doyle and Blythe)
  • Location Specific
    • proximal phalanx (for A2 pulley)
      • use 3 loops (around-the-bone) - strongest reconstruction
      • pass DEEP to extensor mechanism
    • middle phalanx (for A4 pulley)
      • use 2 loops (around-the-bone)
      • pass SUPERFICIAL to extensors
 

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