Annular part of fibrous sheath of digit of foot

The annular part of the fibrous sheath of the digit of the foot refers to the series of transverse, ligamentous bands—known as annular pulleys—that encircle the flexor tendons of the toes and anchor them to the phalanges and adjacent soft tissues. These structures are analogous to the annular pulleys in the fingers and serve to prevent bowstringing of the flexor tendons during toe flexion, maintaining efficient force transmission and tendon gliding.

In the lesser toes (II–V), there are typically four annular pulleys (A1–A4), while the hallux (great toe) has three. The annular pulleys are composed of dense, regular collagen fibers arranged transversely, forming a robust, fibrous tunnel. The pulleys are attached proximally to the phalangeal shafts and distally to the volar plates and periosteum. The A1 pulley is located at the metatarsophalangeal joint, A2 along the proximal phalanx, A3 at the proximal interphalangeal joint, and A4 at the distal phalanx. These pulleys are relatively thin but provide significant mechanical strength and stability.[1]

Histologically, the annular pulleys consist of a three-layered structure: an inner gliding layer rich in hyaluronic acid, a middle layer of dense collagen bundles with interspersed elastin fibers, and an outer layer of loose connective tissue containing vascular channels. This composition allows for both smooth tendon movement and resistance to mechanical stress.