The left thumb is as painful as the following three causes: 1. tendinitis of the thumb, common in middle-aged women who often use computers, knitting, playing sweaters or sewing machines, long-term finger activities lead to repeated friction of the long thumb tendon and short thumb tendon, resulting in some local inflammation, manifested as pain, popping and jamming when the patient flexes the thumb. 2. osteoarthritis of the thumb, seen in elderly patients The thumb is a joint that is arthritic and is characterized by interphalangeal hypertrophy and Herbent’s nodule on X-ray, which is associated with significant pain once the thumb is moved. 3. Rheumatism, rheumatoid arthritis, and metabolic diseases such as gout are relatively rare, but rheumatism, rheumatoid, and gout caused by hyperuricemia can also cause thumb joint of pain.