The pain in the middle of thumb and index finger may be caused by tendonitis, tenosynovitis, gouty arthritis and so on. 1. Tendonitis: when the muscles in the middle of the thumb and index finger undergo flexion and extension activities for a long time as well as frequently, which causes degenerative changes in the joint tissues as well as abnormal bone hyperplasia, and irritates or presses the ligamentous joint tissues, the symptom of pain in the middle of the thumb and index finger may occur. 2. Tenosynovitis: when the tendon sheath tissue of the thumb has chronic aseptic inflammation due to long-term labor or activities, secreting excessive inflammatory factors, stimulating the local nerves and blood vessels, and if the symptoms are more serious, involving other soft tissues, the symptom of pain in the middle of the thumb and forefinger will appear. 3. Gouty arthritis: If due to genetic factors or unhealthy diet, the purine metabolism in the body is abnormal, resulting in more uric acid content in the body, deposited in the joints or synovial membrane and other soft tissues, causing inflammation of the local tissues, which may be manifested as the symptoms of pain in the middle of the thumb and forefinger. When uncomfortable symptoms, it is recommended that patients go to the hospital in time for examination and diagnosis, under the guidance of professional doctors to carry out targeted treatment, so as to avoid the impact on daily life.