Upper limb

Digital flexor pulley system of hand (Annular A1–A5 and Cruciform C1–C3 pulleys)

Ligamenta anularia et cruciformia digitorum manus (Pulleys A1–A5, C1–C3)

Origin

Palmar aspect of phalanges and volar plates of digits I–V

Insertion

Forms fibrous arches (annular pulleys A1–A5) and pliable cross-bands (cruciform C1–C3) over flexor digitorum tendons

Function

Prevents tendon bowstringing and optimizes mechanical excursion; A2 (proximal phalanx) and A4 (middle phalanx) are mechanically indispensable; A1 guides entry at MCP joint

Innervation

Digital nerves of median and ulnar nerves (C7–T1)

Movement & chain

Maintains flexor tendons in close proximity to phalanx during full fist formation

Palpation

A1 pulley palpable at distal palmar crease over metacarpal heads

Clinical

Trigger finger (stenosing tenosynovitis at A1 pulley causing painful locking); A2/A4 pulley rupture in rock climbers during crimp grip (bowstringing deformity).

Segmental innervation

C7–T1

In clinical practice

A1 pulley steroid injection or percutaneous release; H-taping and graduated loading in climber pulley injuries

Region in the model

Upper limb