Left thumb pain may be caused by trauma such as squeezing, or it may be related to tendinitis, bursitis, synovitis, rheumatoid arthritis and other diseases. 1. Trauma: traumatic injuries such as crushing and collision can lead to soft tissue injury or even fracture of the fingers, which can cause pain in the left thumb, and may be accompanied by swelling, i.e., restricted movement. 2. Tenosynovitis: often caused by palmar puncture wounds or adjacent tissue infection, injury, overstrain, etc., manifested as pain and swelling of the affected finger and activity disorders. 3. Bursitis: often secondary to tenosynovitis of the thumb, manifested by pain and swelling of the thumb and interphalangeal area, the thumb can not be abducted and straightened, and straightening will cause severe pain. 4. Synovitis: aseptic inflammation caused by overstrain of the thumb joint, usually manifested as increased joint pain after activity, occasionally swelling, long time easy to lead to the normal activities of the joints are limited, and should be treated as soon as possible. 5. Rheumatoid arthritis: an autoimmune disease, the attack can lead to synovitis symptoms and joint destruction, manifested as persistent thumb joint pain, accompanied by tenderness and swelling of the joints, most of the morning stiffness, that is, getting up in the morning to appear stiff joints. When thumb pain occurs patients, if the pain persists unrelieved, should be timely hospital medical treatment, according to the specific circumstances of the symptomatic treatment, so as not to delay the condition.