Inability to extend the thumb is one of the symptoms of flexor tendon tenosynovitis, which mostly occurs in the thumb and middle finger. The dysfunction of the flexion and extension of the affected finger is particularly pronounced in the early morning and is relieved or disappears after activity. The pain sometimes radiates to the wrist. There may be pressure pain in the metacarpophalangeal joint flexion, and sometimes thickened tendon sheaths and pea-sized nodules may be palpable. When the affected finger is bent, it suddenly stays in the semi-bending position, and the finger can neither be straightened nor flexed, as if it is suddenly stuck, with unbearable pain. Inability to extend the thumb can be caused by injury, excessive strain (especially in the hands and fingers), osteoarthritis, some immune diseases, or even infection. Some occupations that require repetitive strain on the joints over a long period of time, such as typists, cargo handling, or those that require long hours of computer operation, can cause or exacerbate this condition. Commonly affected areas are wrists, fingers, shoulders and other locations. Women and diabetics are more likely to suffer from this disease. Patients may experience joint pain and morning stiffness, which is usually most pronounced upon waking up, and the symptoms do not ease significantly with more activity. The affected joints may swell and even pop, and joint movement may be impaired.