Injuries to the little finger can not be straightened due to the following reasons: 1, after the injury of the little finger is not able to straighten the most common reason, is the little finger extensor tendon rupture. When the little finger is injured, the extensor tendon is particularly easy to rupture, especially in the little finger contusion and strong straightening state, may lead to the little finger thin extensor tendon rupture. 2, the little finger after the injury can not straighten, but also due to the fracture and dislocation of the little finger. After the fracture of the little finger, it will affect the function of finger flexion and extension, and if there is dislocation, it will further aggravate the dysfunction of little finger extension.