Variable annular pulley of thumb
Ligamentum anulare variabile policis
Definition
The variable annular pulley of thumb, when present, is a thin and inconsistent fibrous band situated proximal to the oblique pulley, near the base of the proximal phalanx—between the oblique pulley and the A1 pulley. It follows a similar trajectory, proximal to distal, from the ulnar to the radial side of the thumb, running in parallel to the oblique pulley.
The variable annular pulley of thumb may provide additional stabilization of the flexor pollicis longus (FPL) tendon during motion but is not present in all individuals.
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.
