Inability to extend the thumb is one of the symptoms of flexor tendon tenosynovitis, which mostly occurs in the thumb and middle finger. The dysfunction of the flexion and extension of the affected finger is particularly pronounced in the early morning and is relieved or disappears after activity. The pain sometimes radiates to the wrist. There may be pressure pain in the metacarpophalangeal joint flexion, and sometimes thickened tendon sheaths and pea-sized nodules may be palpable. When the affected finger is bent, it suddenly stays in the semi-bending position, the finger can neither be straightened nor flexed, as if it is suddenly stuck, and the pain is unbearable, after using the other hand to assist in triggering, the finger can move again, producing a trigger-like action and popping sound, so it is also called trigger finger or popping finger. Symptoms of thumb extension: 1. Pain in the palm of the hand, aggravated in the morning or during activity. Impaired extension and flexion of the affected finger. 2.A nodule can be felt on the palm surface of the affected finger at the metacarpal bone, and the nodule can be felt to slide when the finger is flexed and extended, and the pressure pain is obvious. 3.If there is stenosis, the finger flexion and extension have a boarder-like movement or popping sound. In severe cases, the fingers are interlocked in the flexed position and cannot be straightened or flexed in the straightened position.