Finger Flexor Pulley System

vaginae fibrosae tendinum digitorum (systema)

The annular pulley system is the fibro-osseous tunnel maintaining the flexor tendons against the phalanges. The A2 and A4 pulleys are biomechanically critical. Their loss produces bowstringing and loss of flexion efficiency. Trigger finger occurs when a nodular flexor tendon catches at the A1 pulley, producing painful locking of the finger. The annular pulleys are reconstructed using palmaris longus or extensor retinaculum strips when damaged during Zone II tendon repair.

Anatomical Data

Boundaries & Contents

Location	Palmar surface of each finger, from the metacarpal head to the distal phalanx
Boundaries	Attached to the margins of the proximal and middle phalanges and to the palmar plates of the MCP, PIP and DIP joints Thick annular pulleys A1 to A5 alternate with thin cruciate pulleys C1 to C3 Lined by a synovial sheath around the tendons
Contents	Flexor digitorum superficialis tendon Flexor digitorum profundus tendon Vincula carrying vessels to the tendons

Biomechanics

Function & Actions

Holds the long flexor tendons against the bones so that flexion is efficient and the tendons do not bowstring.

Clinical Relevance

Clinical Notes

A2 pulley rupture from rock climbing (crimping, forced finger flexion against resistance) produces the classic bowstring deformity with increased tendon-to-bone distance on ultrasound. Multiple pulley ruptures require reconstruction. A1 pulley release for trigger finger is the most common hand surgical procedure worldwide. It can be performed with a needle (percutaneous release) or open.

Pathology

Common Injuries & Conditions

A2 Pulley Rupture

Rock climbing crimp injury to the A2 pulley producing bowstringing managed with conservative treatment for single pulley and reconstruction for multiple pulley injuries.

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