Oblique annular pulley of thumb
Ligamentum anulare obliqum policis
Definition
The oblique annular pulley is a strong, constant fibrous band found along the palmar aspect of the proximal phalanx of the thumb. It runs obliquely, proximal to distal, from the ulnar to the radial side of the thumb, anchoring the flexor pollicis longus (FPL) tendon close to the bone.
The oblique annular pulley, along with the A1 and A2 pulleys, and also with the variable annular pulley (when present), functions to prevent bowstringing during thumb flexion and is essential for efficient pinch and grip function.
In relation to the other thumb pulleys:
The A1 pulley lies proximally over the metacarpophalangeal (MCP) joint of the thumb.
The A2 pulley lies distal to the oblique pulley, near the interphalangeal (IP) joint of the thumb.
The oblique annular pulley sits between A1 and A2, at the level of the diaphysis of the proximal phalanx (approx. in the centre). Whereas, the variable annular pulley (if present) lies proximal to the oblique pulley near the base of the proximal phalanx of thumb (between oblique pulley and the A1 pulley).
References
Hirschmann, A., Sutter, R., Schweizer, A. and Pfirrmann, C.W., 2014. MRI of the thumb: anatomy and spectrum of findings in asymptomatic volunteers. American Journal of Roentgenology, 202(4), pp.819-827.
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.
