Annular part of fibrous sheath of digit of hand
Pars anularis vaginae fibrosae digiti manus
- Latin synonym: Pars anularis I-V
- Synonym: Anular part 1-5; A band 1-5
- Related terms: Anular part of fibrous sheath
Definition
The annular part of fibrous flexor sheath of digit of hand are that part of the sheath that consists of five transverse fibrous bands that encircle the long flexor tendons—the flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP)—along the palmar aspect of each finger.
These bands, known as the annular pulleys (A1, A2, A3, A4, and A5), thick, circular condensations of fibrous tissue that, together with the cruciate (C1 to C3) pulleys, form a strong osseofibrous tunnel along the palmar aspect of each finger. This tunnel guides and maintains the position of the flexor tendons within their synovial sheath.
Locations of Annular Pulleys
A1: Over the metacarpophalangeal (MCP) joint.
A2: Over the proximal phalanx.
A3: Over the proximal interphalangeal (PIP) joint.
A4: Over the middle phalanx.
A5: Over the distal interphalangeal (DIP) joint.
Function
The annular pulleys secure the flexor tendons close to the phalanges, preventing bowstringing during finger flexion. They also facilitate smooth gliding of the FDS and FDP tendons within their synovial sheath, ensuring efficient digital flexion and grip function.
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.
