Fourth annular pulley
Ligamentum anulare quartum
Definition
The fourth annular pulley (A4) is a strong fibrous band located along the middle phalanx of each finger. It forms part of the fibrous flexor sheath that encloses the flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) tendons.
The A4 pulley is crucial for keeping the flexor tendons close to the bone as they cross the middle phalanx, preventing bowstringing and ensuring smooth, efficient finger flexion, especially at the proximal and distal interphalangeal joints.
Please click here for detailed description of the annular pulleys and the annular part of fibrous sheath of digit of hand.
References
Hauger, O., Chung, C.B., Lektrakul, N., Botte, M.J., Trudell, D., Boutin, R.D. and Resnick, D., 2000. 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, 217(1), pp.201-212.
Bianchi, S., Martinoli, C., De Gautard, R. and Gaignot, C., 2007. Ultrasound of the digital flexor system: normal and pathological findings. Journal of Ultrasound, 10(2), pp.85-92.
Makkouk, A.H., Oetgen, M.E., Swigart, C.R. and Dodds, S.D., 2008. Trigger finger: etiology, evaluation, and treatment. Current reviews in musculoskeletal medicine, 1(2), pp.92-96.
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.
