The A2 pulley is a small, ring-shaped band of tissue (an annular pulley) that wraps around the base of the finger. It holds the flexor tendons (FDP and FDS) close against the bone, so the tendon’s pull bends the finger instead of lifting away from it.
The A2 pulley carries the heaviest load during a closed crimp grip — the grip climbers use on small holds. That’s why researchers have found it’s the most commonly injured pulley in the sport.[1]
An A2 injury can range from a mild strain to a full tear, classified with the Schöffl grading system and usually confirmed with a dynamic ultrasound rather than an MRI.[2]
The anatomy and grading here are well established. What is not established is that any injectable peptide speeds up healing of this specific tissue — no human trial has tested one on a pulley injury of any grade.