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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Questions (1)

(OBQ08.274) Which of the following flexor tendon annular pulleys originate from palmar plates overlying joints? Review Topic

QID:660
1

A1, A3, A5

78%

(1576/2026)

2

A2, A4

16%

(316/2026)

3

A1, A2, A4

3%

(60/2026)

4

A1, A2, A3

1%

(20/2026)

5

A2, A4, A5

2%

(46/2026)

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PREFERRED RESPONSE 1

The pulley system governs the moment arm, excursion and joint rotation produced by the flexor tendons. The A2 and A4 pulleys are the most biomechanically important to these functions. A2 and A4 arise from the periosteum of the proximal half of the proximal phalanx, and the midportion of the middle phalanx, respectively. A1, A3 and A5 are joint pulleys arising from the palmar plates of the MP, PIP, and DIP joints respectively. C1, C2, and C3 are thin, condensable, cruciate sections of the flexor sheath which permit the annular pulleys to approximate each other during flexion.

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