Pain at the joint of thumb and index finger may be related to tenosynovitis, muscle strain, trauma and other causes. 1. Tenosynovitis: Aseptic inflammation of the tendon sheath of the flexor tendon of the thumb due to long-term and heavy activities of the thumb can cause hyperplasia and edema of the tendon sheath, resulting in pain at the joint between the thumb and the index finger. 2. Muscle strain: too much muscle activity, too high intensity of activity, or continue to maintain a certain static posture, making the muscles persistently tense, triggering local aseptic inflammation, which can lead to pain at the joint between the thumb and index finger. 3. Trauma: If trauma is not treated in time, it may lead to muscle infection and cause pain at the joint of thumb and index finger. It is recommended that people with pain at the joint of thumb and index finger go to the hospital in time to clarify the cause of the disease, and carry out standardized treatment under the guidance of the doctor.