Home Body Atlas Tendons Annular Pulleys (A2 and A4)
Tendon Hand & Wrist

Annular Pulleys (A2 and A4)

vaginae fibrosae digitorum (anuli A2 et A4)

The five annular (A1-A5) and three cruciate pulleys of each finger form the fibro-osseous flexor tendon sheath. The A2 pulley (at the proximal phalanx) and A4 pulley (at the middle phalanx) are biomechanically critical — their loss produces tendon bowstringing and significant flexion force reduction. Rock climbers stress the A2 pulley maximally during crimping, making it the most common pulley injury in climbing.

Region: Hand & Wrist
Biomechanics

Function & Actions

Maintain the flexor tendons close to the phalanges to maximise mechanical efficiency; prevent bowstringing

Clinical Relevance

Clinical Notes

A2 pulley rupture in rock climbers produces a palpable and audible pop during crimping, followed by bowstringing visible when the finger is flexed. MRI or ultrasound confirms the injury. Most partial tears heal conservatively with ring splinting; complete A2 tears may require pulley reconstruction with a tendon graft. The A2 pulley must be preserved during Zone II flexor tendon surgery.

Pathology

Common Injuries & Conditions

Climber's Pulley Injury

A2 pulley rupture during rock climbing producing bowstringing and audible pop managed with ring splinting for partial tears and pulley reconstruction for complete tears.

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