Klippel-Feil syndrome (KFS) is a complex condition presenting due to an abnormal fusion of cervical vertebrae at C2 and C3, which is caused by a failure in the division or normal segmentation of the cervical spine vertebrae in the early fetal development. This leads to a characteristic appearance of a short neck, low hairline, facial asymmetry, and limited neck mobility. The anomalies can lead to chronic headaches, limited range of neck motion, and neck muscle pain. More importantly, it can also result in spinal stenosis, neurologic deficit, cervical spinal deformity, instability, and spinal stenosis. Patients can be polysyndromic in their presentation as well.
Etiology of KFS is not well known. Several studies have hypothesized that vascular disruption, global fetal insult, primary neural tube complications, or genetic related factors may be implicated in the development of KFS. It can co-present with fetal alcohol syndrome, Goldenhar syndrome, as well as Sprengel’s deformity.  In some families, mutations in the GDF6, GDF 3, and MEOX1 genes can cause Klippel-Feil syndrome and cane be inherited. GDF6 is involved in proper bone formation while GDF3 is involved in bone development. MEOX1 gene creates the homeobox protein MOX1 that regulates the separation of vertebrae. GDF6 and GDF3 abnormalities are inherited in an autosomal dominant pattern while MEOX1 mutations are autosomal recessive.
KFS was initially reported in 1912 by Maurice Klippel and Andre Feil. Klippel-Feil syndrome occurs in approximately 1 in 40,000 to 42,000 newborns worldwide with a slight preference to females. Nouri et al. illustrated 2.0% incidence of Klippel-Feil syndrome on MRI in a global cohort of 458 patients. Brown et al. reviewed 1400 skeletons and put the incidence at 0.71%. It is important to recognize that asymptomatic pediatric patients, who do not undergo cervical imaging and do not present with obvious physical deformity, are likely to graduate into adulthood unaware of their condition.
Faulty segmentation occurs during embryo development 3 to 8 week of gestation. This is a failure of normal segmentation or formation of the cervical somites.
A thorough and complete history and physical should be performed, including a detailed family genetic history. It is also important to recognize that patients with Klippel-Feil syndrome may be predisposed to congenital spinal stenosis. As such, a relatively low impact or low energy injury may induce a significant neurologic deficit.
Physical exam findings include a shortened neck stature and low-lying hairline. Neurologic symptoms may include radiculopathy and myelopathy. A thorough neurological examination including cranial nerves, sensory, motor, and reflexes and gait testing along with checking for signs of bowel or bladder incontinence is necessary.
The classic complete clinical triad of the low hairline, short neck, and restricted neck motion is only present 50% of patients with Klippel-Feil syndrome. This can be secondary to several reasons like time dependency of the congenitally-fused cervical patterns assessment and bias associated with the clinical assessment of the clinical triad.
The presentation may occur simultaneously with Sprengel’s deformity, Duane syndrome, renal agenesis, Wildervanck syndrome, and other vascular and cardiac abnormalities. Approximately 50% of patients with Klippel-Feil will present with concurrent scoliosis. Fifty percent may have atlantoaxial instability. Approximately 30% will present renal disease and 30% with deafness. All other systems need to be properly evaluated as well.
Laboratory tests should be done to rule out other conditions and assess for organ dysfunctions. The concern should be given to the possible presence of cardiac, gastrointestinal (GI), and urinary disorders and should include an echocardiogram, renal ultrasonogram, and intravenous pyelogram respectively.  An audiological evaluation for testing hearing would be useful as well. 
Radiographic evaluation of the cervical spine in patients with Klippel-Feil syndrome includes plain radiographs (X-rays), computed tomography (CT), and magnetic resonance imaging (MRI). A thorough evaluation of the cervical spine is important prior to procedures like intubation, laryngoscopy, head manipulation or intraoperative positioning due to risk of atlantoaxial subluxation and craniovertebral dislocation to avoid any risk of causing spinal cord injury.
Commonly performed to illustrate fusion of the vertebral bodies as well as facets and even spinous processes. The examination should include AP, lateral, and odontoid views in flexion and extension. These studies help to evaluate the stability of the atlantoaxial, atlantooccipital, and subaxial joints. The images of the thoracic and lumbar spine should be performed as well, since they may illustrate scoliosis, spinal bifida or hemivertebrae. A wasp-waist sign (anterior-posterior narrowing) may be present. In a clinically stable patient, flexion/extension x-ray may illustrate spinal stability and movement
These images would be useful in providing additional details about the spinal anatomy and the bony structures including the bony fusion. These studies are especially useful for the pre-operative planning, when recommended.
MRI is useful in assessing the integrity of the spinal cord, disc space, nerve rootlets, ligaments, and rest of the soft tissue structures. This study can also illustrate other spinal cord abnormalities such as Chiari malformations and diastematomyelia. MRIs are most useful in patients who presents with neurologic deficits.
Majority of the patients are managed non-operatively unless an acute neurological deficit, a cervical instability or a risk of chronic neurologic problems is present and an operative management is recommended. 
Non-Operative management: Overall, treatment is conservative and symptom driven. For patients with a 1 or 2 level fusions below C3, monitoring and conservative management is sufficient. They may play contact sports such as hockey and rugby with proper education.
Patients who are at high risk for spinal deformity should undergo activity modification. Those with a fusion above C3, especially to the occiput, should avoid contact sports and are more likely to be symptomatic and prone to risk of spinal injury. This also true for those patients with long fusions of the cervical spine.
Importance should also be placed on the poly-syndromic presentation of patients. For younger patients, pediatricians play a key role in coordinating care between a variety of specialists for cardiac, renal, or gastrointestinal congenital abnormalities. This interdisciplinary care becomes even more vital if patients are considered to be operative candidates.
Operative management: Patients with persistent neurological pain, myelopathy, new onset muscle group weakness, and documented spinal instability are considered to be operative candidates. Surgical decision making is driven by the spinal deformities and instability. Cervical fusion can occur from either anterior or posterior approaches secondary to evaluation. Anterior approach includes anterior cervical fusion or corpectomy with the placement of either synthetic or bone graft. Cervical total disc arthroplasty is being investigated as a surgical option. This modality has shown some positive benefit regarding the quality of life outcomes and prevention of adjacent level disease in the degenerative adult population. Posterior approaches can also be used including decompression and fusion through a variety of instrumentation procedure options. In certain cases of severe deformity, a combined anterior-posterior approach can also be used. Surgical or bracing intervention may be indicated for associated compensatory thoracic scoliosis.
Otolaryngological evaluation and treatment may be necessary for those with hearing impairment for placing cochlear implants and providing hearing devices where necessary.
KFS patients with fusion above C3 tend to be more symptomatic.
By definition, Klippel-Feil is a heterogeneous presentation. Prognosis can be related to the Samartzis classification system. 
Samartzis et al. noted that over an eight-year period approximately two-thirds of patients with Klippel-Feil syndrome had no symptoms. Those with a type-I deformity had more axial symptoms while those with type II and type III were the patients who developed myelopathy and radiculopathy. 
The degenerative changes throughout the cervical spine can lead to the following conditions, which would need to be monitored and managed in a timely manner. These include:
The diagnosis and management of patients with KF syndrome should include an interprofessional team consisting of a neurologist, orthopedic surgeon, pediatrician, nurse practitioner, physical therapist and a neurosurgeon among other medical staff personnel. The disorder can be managed non-surgically or surgically, depending on presence of symptoms. For patients with functional limitations orthotics and assistive devices may be necessary. However, these patients need to be educated about protection of the cervical spine. They should not participate in contact sports if there is absolute contraindication given the obvious risk of spinal injury. Those with moderate to severe spinal deformity should undergo lifestyle modification.
Several types of surgical procedures are available but the outcomes cannot be predicted. There is always a risk of serious complications, thus making it necessary to have an interprofessional team of surgical specialists including neurosurgeons, otolaryngologists, orthopedicians and oro-maxillofacial surgeons managing the patient. The outcomes of patients depend on the initial deformity. While some patients have no symptoms, a significant number have myelopathy and neuropathy, which significantly lowers the quality of life. (Level V)
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