Left thumb joint swelling and pain may be caused by trauma, tenosynovitis, rheumatoid arthritis, osteophytes and so on. 1. Trauma: left thumb joint pain may be caused by trauma, due to the external force will lead to the left thumb as well as the surrounding muscles, ligaments and other injuries, fracture, joint dislocation, soft tissue contusion and so on, which will lead to pain in the shoulder joint area. 2. Tendovaginitis: excessive friction caused by frequent activities increases the mechanical friction between tendons and tendon sheaths, which causes aseptic inflammatory reactions such as congestion, edema, and exudation of the tendon sheaths, resulting in swelling and pain in the joints of the left thumb, and as the condition develops, the pain will continue to worsen. 3. Rheumatoid arthritis: If the autoimmune response is impaired by heredity, infection, environment and other factors, the patient will experience swelling and pain in the joint of the left thumb, which is often accompanied by morning stiffness, fatigue, low-grade fever, muscle pain and other general symptoms. 4. Osteomalacia: If the patient is engaged in heavy physical labor, trauma, malnutrition and other factors, it will lead to the patient will appear in the left thumb joint swelling and pain, and some patients will have localized lumps, pain, activity limitation and other clinical symptoms. Causes of left thumb joint swelling and pain may also have cervical spondylosis and venous vascular embolism and other diseases, it is recommended that patients go to the regular hospital in a timely manner, under the diagnosis of the doctor, according to the patient’s specific condition, to take targeted treatment.