First annular pulley - MRI finger of hand - Axial PD FS - e-Anatomy
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First annular pulley

Ligamentum anulare primum

Definition

The five annular pulleys (A1–A5), are transverse, well-defined areas of thickening of the tendon sheath. The main function of the annular pulleys is to fix the tendon sheaths to the bony skeleton, thus stabilizing the tendon during finger flexion and avoiding palmar “bowstringing:

  • The first annular pulley (A1) begins in the palmar plate of the MCP joint and extends to the base of the proximal phalanx.

  • The second annular pulley (A2) rises from the volar aspect of the proximal portion of the proximal phalanx and extends to the distal third of the proximal phalanx.

  • The third annular pulley (A3) is small and extends over the region of the PIP joint. 

  • The fourth annular pulley (A4) lies in the midportion of the middle phalanx

  • The fifth annular pulley (A5) is located in the region of the DIP joint. 

The A2 and A4 pulleys are the largest and thickest and also have the most constant morphology and prevalence.

References

Petchprapa CN, Vaswani D. MRI of the Fingers: An Update. AJR Am J Roentgenol. 2019 Sep;213(3):534-548. doi: 10.2214/AJR.19.21217. Epub 2019 Jul 3. PMID: 31268729.

Gupta P, Lenchik L, Wuertzer SD, Pacholke DA. High-resolution 3-T MRI of the fingers: review of anatomy and common tendon and ligament injuries. AJR Am J Roentgenol. 2015 Mar;204(3):W314-23. doi: 10.2214/AJR.14.12776. PMID: 25714317.

Clavero JA, Alomar X, Monill JM, Esplugas M, Golanó P, Mendoza M, Salvador A. MR imaging of ligament and tendon injuries of the fingers. Radiographics. 2002 Mar-Apr;22(2):237-56. doi: 10.1148/radiographics.22.2.g02mr11237. PMID: 11896215.

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