We have pulleys on flexor side of hand which help in stabilizing the flexor tendons during flexion movement of fingers and thumb and prevent bowstring effect of tendons

https://climbingdoctor.wpengine.com/wp-content/uploads/2017/07/static1.squarespace-1.jpg

5 annular pulleys; 3 cruciate pulleys form a fibroosseous tunnel for the flexor tendons

A1-opposite metacarpal neck

A3-opposite PIP joint

A2 opposite proximal phalanx