Anatomy of Trigger Finger:

The tendons that move the fingers are held in place on the bones by a series of ligaments called "pulleys".

These ligaments form an arch on top of the bone that creates a tunnel so that when the flexor muscles are contracted, the tendons can move along the bone in a straight path.

In order to make sure these tendons travel in a smooth manner and reduce friction of the tendon and its sheath, the body produces and coats the flexor tendons with a slippery coating called "tenosynovium" which allows the tendons to glide through the tunnel formed by the pulleys when the fingers/hands are used to grasp objects.