A1 pulley

The first of the fibrous bands (pulleys) that hold the flexor tendons against the finger bones, lying at the base of the finger over the metacarpophalangeal joint. It is the band that thickens in trigger finger and is divided in a trigger finger release; the A2 and A4 pulleys are the ones that must be preserved.

Related terms

• Condition

  Trigger finger

  A condition in which a finger or thumb catches, clicks or locks as it bends, because the flexor tendon no longer glides freely through the thickened first (A1) pulley at the base of the digit. Common in people in their fifties and sixties and in people with diabetes.

• Anatomical structure

  Bowstringing

  Anterior displacement of a flexor tendon away from the underlying phalanges during finger flexion, resulting from loss of the constraining annular pulleys (most consequentially A2 and A4). Visible as a cord across the palmar finger and clinically expressed as reduced flexion power, because the tendon's mechanical lever arm decreases as it travels along a chord rather than the curved path the pulleys would impose.

Articles mentioning this term

1. Patient information · 26 September 2026

   Trigger finger

   Why a finger catches or locks, who gets trigger finger, and how it is treated: splints, steroid injections and a small day-case operation.

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