Klippel-Feil syndrome (KFS) is a rare skeletal disorder primarily characterized by abnormal union or fusion of two or more bones of the spinal column (vertebrae) within the neck (cervical vertebrae). Some affected individuals may also 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 mild 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 & rib anomolies, 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. In addition, in some cases, neurological complications may result due to associated spinal cord injury. KFS can be associated with a wide variety of additional anomalies affecting many different organ systems of the body.
The progression and severity of KFS can vary greatly depending upon the specific associated complications and the Class of KFS. Some cases may be mild; others may cause serious, life-long complications.