In trigger finger the level of tendon sheath constriction is found at the level of -

TRIGGER FINGER (DIGITAL TENOVAGINOSIS) A flexor tendon may become trapped by thickening at the entrance to its sheath; on forced extension it passes the constriction with a snap ('triggering'). Clinical features ,Any digit may be affected, but the thumb, ring and middle fingers most commonly; sometimes several fingers are affected. The patient notices a click as the finger is flexed; when the hand is unclenched, the affected finger initially remains bent at the PIP joint but with fuher effo it suddenly straightens with a snap. A tender nodule can be felt in front of the MCP joint and the click may be reproduced at this site by alternately flexing and extending the finger. Reference- Apley&;s system of ohopaedics 9th edn-pg no 423