There are many reasons why the little finger cannot be straightened, the more common ones are rupture of the tendon of the little finger, stenosing tenosynovitis, adhesion of periarticular tissues, contracture of the palmar tendon membrane, and dislocation of the joint, etc., and it is necessary to improve the examination in order to clarify the cause of the disease. 1. Extensor tendon rupture: There is a clear history of trauma to the little finger. When the extensor tendon of the little finger is completely ruptured, the little finger loses the function of active finger extension. 2. Stenosing tenosynovitis: This is a sterile inflammatory disease related to trauma and strain injury to the tendon of the little finger, in which the tendon forms an enlarged nodule, which is jammed when passing through the stenosed tendon sheath and cannot pass through it, resulting in the inability of the little finger to extend straight. 3. Adhesion of periarticular tissues: it is mostly seen in fracture of hand, tendon rupture, after long time external fixation, the little finger is in flexion for a long time, which will lead to adhesion of periarticular tendons, affecting the movement of the little finger joints, and the case of inability to straighten will occur. 4. Palmar Tendonitis Contracture: It is a painless hard knot formed in the palm of the hand due to various reasons, and the fingers are contracted and cannot be straightened, especially the little thumb. 5. Joint dislocation: mostly caused by trauma, after the dislocation of the joint of the little thumb, the joint loses its normal anatomical position and function, so it cannot be straightened. It is recommended that the patient go to the hospital, complete the auxiliary examination, clarify the condition, and then give the relevant treatment by the professional physician for the cause.