Klippel-Feil Syndrome (KFS) is a rare skeletal condition in which there is abnormal union or fusion (congenital synostosis) of two or more bones of the spinal column (vertebrae) within the neck (cervical vertebrae).
The spinal column or backbone is made up of 33 irregularly-shaped bones known as vertebrae. These bones are divided into different categories. The first seven vertebrae, beginning at the base of the skull, are known as the cervical vertebrae. KFS primarily affects the cervical vertebrae. Some affected individuals may have an abnormally short neck, restricted movement of the head and neck, and a low hairline at the back of the head (posterior hairline). The disorder is present at birth (congenital), but cases may go undiagnosed until later during life when symptoms worsen or first become apparent. In some individuals, KFS can be associated with a variety of additional symptoms and physical abnormalities. These may include abnormal curvature of the spine (scoliosis) and/or vertebral instability, spina bifida occulta, raised scapula (Sprengel’s deformity), absent rib(s) and other rib defects including cervical ribs, other skeletal abnormalities including skeletal malformations of the ear, nose, mouth and larynx including hearing impairment and cleft palate, malformations of the head and facial (craniofacial) area; anomalies of the urinary tract and/or kidney including absent or horse-shoe kidney; or structural abnormalities of the heart (congenital heart defects), mirror movements, webbing of the digits and digital hypoplasia. Neurological complications may result due to associated spinal cord injury. In some cases there may be progressive osteoarthritis.
Reproduced in part with permission from the National Organization for Rare Diseases.