https://drdongraham.com/hand/trigger-fingers/

In the fingers, there are tight bands called pulleys.  Tendons glide underneath these.  When there is inflammation, the tendons have a hard time fitting through that space, and can get stuck at the base of the finger.  This causes pain, as well as clicking and locking.  Sometimes you may even need to use other fingers to release it. This is called a trigger finger.