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Updated: Jun 20 2022

Flexor Pulley System

Images pulley thumb 2.jpg
  • 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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