Klippel–Feil syndrome (KFS), also known as cervical vertebral fusion syndrome, is a rare congenital condition characterized by the abnormal fusion of any two of the seven bones in the neck (cervical vertebrae).: 578  It can result in a limited ability to move the neck and shortness of the neck, resulting in the appearance of a low hairline. Most people only have one or two of those symptoms so it may not be noticeable without medical imaging. The syndrome is difficult to diagnose, as it occurs in a group of patients affected with many different abnormalities who can only be unified by the presence of fused or segmental cervical vertebrae...