The tendinitis of the left thumb can be caused by poor blood supply to the tendon, trauma, local overuse, and bacterial infections such as staphylococcus, streptococcus, and gonococcus, etc. It is recommended to seek medical treatment promptly after discovering the relevant symptoms to avoid aggravation of the condition. 1. Poor blood supply to the tendon: Inadequate blood supply to the tendon of the left thumb affects the blood supply to the tendon sheath supporting ligaments, which in turn affects the distribution of synovial fluid within the tendon sheath. This can lead to tenosynovitis in the long run; 2, trauma: repeated minor trauma or severe trauma to the left thumb, trauma not effectively dealt with in a timely manner, the tendon sheath part of the sterile inflammation, gradually developed into tenosynovitis; 3, local overuse: long time typing, knitting sweater, etc., the thumb, wrist and other parts of the force is not correct, repeatedly excessive bending, back extension or drop, tendon sheath by mechanical The tendon sheath is mechanically stimulated and rubbed with sterile inflammation, resulting in pain and other discomfort; 4, bacterial infection: the left thumb is attacked by staphylococcus, streptococcus, gonococcus, etc., and the tendon sheath becomes inflamed and infected, usually with more obvious redness, swelling, pain and other symptoms; 5, other: in addition to the above factors can lead to left thumb tenosynovitis, previous rheumatoid arthritis, gout, Wright’s syndrome and other diseases can also trigger tenosynovitis. Tendonitis can be triggered.