Patients who have this deformity can not straighten the middle joint of the finger. Flattening the finger is provided with a very complex mechanism. Extension of whole finger can be made by three tendons; the bigger in the middle extends two parts next to the palm, while the other two on both side of the middle one extend the finger part where the nail is located. Closed or open injuries which affect the middle extensor tendon may result in buttonhole(Boutonierre) deformity.