Final answer:
The most commonly involved annular pulley in trigger finger is the A1 pulley.
Step-by-step explanation:
Trigger finger is a condition characterized by the inflammation and narrowing of the sheath that surrounds the flexor tendons in the finger or thumb. The most commonly involved annular pulley in trigger finger is the A1 pulley, located on the palm side of the hand. This pulley is responsible for guiding the flexor tendon, allowing smooth movement of the finger or thumb.