Mateusz Gładysz FESSH prep

FESSH prep Anatomy Annular pulley positions and lengths, A2 and A4 as the essential pulleys, the palmar aponeurosis pulley, vincula and synovial diffusion as the nutrient pathway

Anatomy of the digital flexor sheath, pulleys and vincula

Last reviewed v1.0

FESSH-049Anatomy●○○ basic

Regarding the anatomy of the finger flexor tendon sheath, its pulleys and the vincula:

  1. 1.The A2 pulley overlies the proximal phalanx and the A4 pulley the middle phalanx, whereas A1, A3 and A5 lie over the volar plates of the metacarpophalangeal, proximal interphalangeal and distal interphalangeal joints.

  2. 2.The A4 pulley is the longest annular pulley of the finger, measuring about 17–20 mm.

  3. 3.The A2 and A4 pulleys are the two most important for preventing bowstringing, and the A1 pulley can be divided without significant loss of flexion.

  4. 4.The palmar aponeurosis pulley is formed by the longitudinal fibres of the palmar aponeurosis and lies distal to the A1 pulley.

  5. 5.Within the digital sheath, diffusion from the synovial fluid rather than vincular perfusion is the dominant route of flexor tendon nutrition.

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Question ID
FESSH-049
First published
Last reviewed
Version
v1.0
Answer key and explanations — open after answering

  1. 1. The A2 pulley overlies the proximal phalanx and the A4 pulley the middle phalanx, whereas A1, A3 and A5 lie over the volar plates of the metacarpophalangeal, proximal interphalangeal and distal interphalangeal joints.

    True

    Doyle's dissections describe a synovial sheath from the metacarpal neck to the distal interphalangeal joint, overlaid by the palmar aponeurosis pulley, five annular and three cruciate pulleys. Hauger's MR-anatomic correlation identifies A2 over the proximal phalanx and A4 over the middle phalanx (seen in 100 % of specimens), with A3 at the proximal and A5 at the distal interphalangeal joint; Lin classifies A2 and A4 as diaphyseal (fibro-osseous) pulleys and A1, A3 and A5 as volar-plate pulleys, which are mechanically weaker and more compliant.

    • Hauger O, Chung CB, Lektrakul N, Botte MJ, Trudell D, Boutin RD, et al.. Pulley system in the fingers: normal anatomy and simulated lesions in cadavers at MR imaging, CT, and US with and without contrast material distention of the tendon sheath. Radiology. 2000;217(1):201-12. PMID 11012445
    • Lin GT, Cooney WP, Amadio PC, An KN. Mechanical properties of human pulleys. J Hand Surg Br. 1990;15(4):429-34. PMID 2269832
    • Doyle JR. Anatomy of the finger flexor tendon sheath and pulley system. J Hand Surg Am. 1988;13(4):473-84. PMID 3418049

  2. 2. The A4 pulley is the longest annular pulley of the finger, measuring about 17–20 mm.

    False

    A2 is the longest and strongest annular pulley: Knott and Schmidt measured a mean length of 18.7 mm in the middle finger (6.7 mm in the thumb), and Altman's cadaver series a mean A2 length of 16.2 ± 3.5 mm, with about 23 mm between the distal edge of A2 and the proximal edge of A4. A4 lies over the middle phalanx and is only 6–7 mm long, restraining chiefly the profundus tendon.

    • Knott C, Schmidt HM. [Connective tissue reinforcing structures of the digital tendon sheaths of the human hand]. Gegenbaurs Morphol Jahrb. 1986;132(1):1-28. PMID 3710108
    • Altman PR, Fisher MWA, Goyal KS. Zone 2 Flexor Tendon Repair Location and Risk of Catching on the A2 Pulley. J Hand Surg Am. 2020;45(8):775.e1-775.e7. PMID 32408998

  3. 3. The A2 and A4 pulleys are the two most important for preventing bowstringing, and the A1 pulley can be divided without significant loss of flexion.

    True

    In Peterson's biomechanical study A2 was the single most important pulley for tendon function, followed by A4; both had to be present for near-normal function, and sacrificing A1 did not significantly reduce flexion. Rispler's cadaver model with the skin removed found no loss of efficiency after cutting a single minor pulley (A1 or A5), whereas loss of A4 produced the largest efficiency change and A2, A3 and A4 together were needed to preserve work and excursion efficiency; the two studies differ on whether A2 or A4 matters more, and their preservation requirements apply to those experimental models. They should not be generalized into an absolute clinical prohibition on pulley venting: selected clinical series report complete A4 or A2 release without clinically evident bowstringing when sufficient remaining pulley restraint is preserved.

    • Peterson WW, Manske PR, Bollinger BA, Lesker PA, McCarthy JA. Effect of pulley excision on flexor tendon biomechanics. J Orthop Res. 1986;4(1):96-101. PMID 3950813
    • Rispler D, Greenwald D, Shumway S, Allan C, Mass D. Efficiency of the flexor tendon pulley system in human cadaver hands. J Hand Surg Am. 1996;21(3):444-50. PMID 8724478
    • Moriya K, Yoshizu T, Tsubokawa N, Narisawa H, Hara K, Maki Y. Clinical results of releasing the entire A2 pulley after flexor tendon repair in zone 2C. J Hand Surg Eur Vol. 2016;41(8):822-8. PMID 27178574
    • Moriya K, Yoshizu T, Tsubokawa N, Narisawa H, Hara K, Maki Y. Outcomes of release of the entire A4 pulley after flexor tendon repairs in zone 2A followed by early active mobilization. The Journal of hand surgery, European volume. 2016;41(4):400-5. PMID 26676484

  4. 4. The palmar aponeurosis pulley is formed by the longitudinal fibres of the palmar aponeurosis and lies distal to the A1 pulley.

    False

    Manske and Lesker described the palmar aponeurosis pulley as a tunnel formed by the transverse fascicular fibres and paratendinous bands of the palmar aponeurosis at the proximal margin of the flexor sheath — proximal to A1, not distal — functioning together with the A1 and A2 pulleys. Doyle's 1988 restudy added it to the pulley system as the most proximal retinacular structure.

    • Manske PR, Lesker PA. Palmar aponeurosis pulley. J Hand Surg Am. 1983;8(3):259-63. PMID 6875224
    • Doyle JR. Anatomy of the finger flexor tendon sheath and pulley system. J Hand Surg Am. 1988;13(4):473-84. PMID 3418049

  5. 5. Within the digital sheath, diffusion from the synovial fluid rather than vincular perfusion is the dominant route of flexor tendon nutrition.

    True

    Manske's hydrogen-washout experiments in chickens showed that a tendon segment detached from every vessel took up nutrients like an intact tendon lying in its synovial bed, whereas a tendon separated from the synovium showed no uptake even with its vincular, muscular and periosteal attachments intact; Lundborg's tracer studies in dogs likewise found diffusion from synovial fluid the major transport route and the intrinsic vessels of minor importance. The vincula, supplied by four transverse branches of the digital arteries, carry the dorsal intrinsic vessels, leaving a volar avascular zone in the profundus tendon.

    • Manske PR, Whiteside LA, Lesker PA. Nutrient pathways to flexor tendons using hydrogen washout technique. J Hand Surg Am. 1978;3(1):32-6. PMID 621366
    • Lundborg G, Holm S, Myrhage R. The role of the synovial fluid and tendon sheath for flexor tendon nutrition. An experimental tracer study on diffusional pathways in dogs. Scand J Plast Reconstr Surg. 1980;14(1):99-107. PMID 7384761
    • Ochiai N, Matsui T, Miyaji N, Merklin RJ, Hunter JM. Vascular anatomy of flexor tendons. I. Vincular system and blood supply of the profundus tendon in the digital sheath. J Hand Surg Am. 1979;4(4):321-30. PMID 469207