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  • Summary
    • Klippel-Feil Syndrome (KFS) is a rare congenital condition caused by failure of normal segmentation or formation of cervical somites during embryological development that leads to abnormalities in multiple cervical segments.
    • Diagnosis is made from physical examination, medical history and imaging findings including congenital fusion of 2 or more cervical vertebrae.
    • Treatment is usually observation with restriction of contact sports if the anomaly extends proximal to C2. Surgical management is indicated in the presence of myelopathy, basilar invagination, or atlantoaxial instability.
  • Epidemiology 
    • Incidence
      • historically regarded as extremely rare
        • 1 in 40,000 live births (0.0025%)
      • recent literature suggests higher prevalence in asymptomatic individuals
        • 1 in 172 (0.58%) to 1 in 83 (1.20%)
    • Demographics
      • 60-70% of cases are female
  • Etiology
    • Pathophysiology
      • mechanism
        • due to failure of normal segmentation or formation of cervical somites at 3-8 weeks' gestation
      • affected levels
        • most common fusion levels are C2-C3 and C5-C6
    • Genetics
      • three major inheritance patterns
        • sporadic (most common)
          • often presents as isolated cervical fusion
        • autosomal dominant
          • GDF6 gene (chromosome 8)
          • GDF3 gene (chromosome 12)
        • autosomal recessive
          • MEOX1 gene (chromosome 17) most common
      • SGM1 gene (Chr 8)
      • Notch and Pax genes
    • Associated conditions
      • orthopedic conditions
        • congenital scoliosis
        • Sprengel's deformity (30%)
        • Wildervanck syndrome (cervico-ocular-acoustic dysplasia)
          • triad consists of:
            • Klippel-Feil syndrome
            • congenital ossicular anomalies; usually diffuse ossicular ankylosis and sensorineural deafness
            • Duane syndrome (ocular motility disturbance due to fibrosis of extraocular muscles
      • medical conditions & comorbidities
        • renal disease (aplasia in 33%)
        • auditory issues (deafness in 30%)
        • congenital heart disease/cardiovascular (15-30%)
          • most commonly ventricular septal defects (VSD)
        • brainstem abnormalities/basilar invagination
        • congenital cervical stenosis
          • MRI to rule out intraspinal cord abnormalities
        • atlantoaxial instability (~50%)
        • adjacent level disease (100%)
          • degeneration of adjacent segments of cervical spine that has not fused is common due to increased stress
  • Classification
    • KFS classification
      • KFS classification
      • Type I
      • Extensive fusion of most or all of the cervical spine
      • Sporadic mutation
      • Type II
      • Fusion or only 1 or 2 vertebrae in the cervical spine
      • Autosomal dominant
      • Type III
      • Fusion exists in part of the thoracic and/or lumbar spine, in addition to Type I or Type II KFS
      • Autosomal recessive
    • Despite this original classification, none is widely accepted
      • extent and locations of fusions is important
        • fusions above C3
          • more likely to be symptomatic and require abstaining from contact sports
        • fusions below C3
          • less likely to be symptomatic and most likely to have a normal life span
    • Samartzis classification
      • carries prognostic value
      • Samartzis classification (2006)
      • Type I
      • Single-level congenital fusion of cervical segment
      • symptoms tend to be more axial
      • Type II
      • Multiple, noncontiguous congenitally fused segments
      • tend to develop peripheral myelopathy or radiculopathy
      • Type III
      • Multiple, contiguous congenitally fused segments in the cervical region
      • tend to develop peripheral myelopathy or radiculopathy
    • Clarke classification
      • comprehensive classification system that addresses genotypic and phenotypic heterogeneity
      • Clarke Classification (1998)
      • Class
      • Vertebral Fusions
      • Inheritance
      • Possible Anomalies
      • Overlap with other classifications
      • KF1
      • Only class with C1 fusion
      • C1 fusion not dominant
      • Variable expression of other fusions
      • Fusions radiologically visible at birth
      • Autosomal Recessive
      • Very short neck, heart, urogenital, craniofacial, hearing, limb, digital, ocular defectsVariable expression
      • Variable expression
      • Types I, II, III (KFS Classification)
      • Recessive (Gunderson)
      • KF2
      • C2-3 fusion dominant
      • C2-3 fusion most rostral fusion
      • Cervical, thoracic and lumbar fusion show variable expression within a family
      • Fusions apparent postnatally
      • Autosomal Dominant
      • Includes SGM1 gene mutation
      • Craniofacial, hearing, otolaryngeal, skeletal and limb defects, etc
      • Variable expression
      • Types I, II, III (KFS Classification)
      • C2-3 dominant (Gunderson)
      • KF3
      • Isolated cervical fusions, includes single fusions at variable positions
      • Any cervical fusion except C1-2Includes single C5±6 fusion
      • Includes single C5-6 fusion
      • Autosomal Recessive or reduced penetrance
      • Craniofacial
      • Facial dysmorphology
      • Variable expression
      • Type II (K & F)
      • C5-6 recessive (Gunderson)
      • KF4
      • Fusion of cervical vertebrae
      • Limited data available
      • X-linked
      • Predominantly females
      • Hearing and ocular anomalies - abducens palsy with retractio bulbi
      • Heart defects possible
      • Commonly referred to as Wildervanck syndrome (includes Duane's syndrome)
  • Presentation
    • Symptoms
      • stiff neck
      • neck/back pain
        • mean age of onset 16 years
        • mean age of symptom worsening 28 years
    • Physical exam
      • inspection
        • classic triad (seen in fewer than 50%)
          • low posterior hairline
          • short webbed neck
          • limited cervical ROM
        • other findings
          • high scapula (Sprengel Deformity)
            • 6.4% to 16.7% of cases
          • jaw anomalies
          • partial loss of hearing
          • torticollis
          • congenital scoliosis
            • 53.5% of cases
          • myelopathy
            • KFS patient have higher rates of cervical myelopathy than the general population
  • Imaging
    • Radiographs
      • recommended views
        • AP, lateral, and open-mouth odontoid views
        • whole spine radiograph to look for multiple fused levels (KFS Type III)
      • findings
        • fusion
          • may be craniocervical (occiput to C2), subaxial, or both
        • basilar invagination
          • is seen on lateral view
          • defined as dens elevation above McRae's line
        • atlantoaxial instability
          • is present when the atlanto dens interval (ADI) is >5 mm
          • cervical spinal canal stenosis is seen when spinal cord canal <13 mm
        • degnerative changes
          • degnerative disease of the cervical spine is seen in 100%
        • calcifications
          • calcifications may be seen within the intervertebral space
            • resolution within 6 months is common
    • Ultrasound
      • abdominal ultrasound
        • renal aplasia/agenesis
      • echocardiogram
        • congenital heart conditions
          • most commonly ventricular septal defects
    • CT
      • cervical spine
        • preoperatively delineate bony anatomy and fusion patterns
    • MRI
      • concomitant CNS abnormalities occur in 19% of KFS patients
      • brain
        • brain stem abnormalities
        • basilar invagination
      • cervical spine
        • intraspinal cord abnormalities
        • smaller cross-sectional spinal cords with larger canal diameters at all levels
        • tethered cords
        • diastematomyelia
  • Differential
    • congenital scoliosis
    • postinfection/spine inflammatory disorders
    • Mayer-Rokitansky-Kaster syndrome
    • Sprengel's deformity
  • Treatment
    • Nonoperative
      • observation with ability to participate in contact/collision sports
        • indications
          • asymptomatic patients with fusions of 1-2 disc spaces below C3
          • Samartzis type II lesion at C3 and below with full range of cervical spine motion and lack of instability and spondylosis
      • observation and abstain from contact/collision sports
        • modalities
          • no standardized guidelines for sports participation
          • counseling important to avoid activities that place the neck at high risk of injury
            • contact sports, gymnastics, football, wrestling, trampoline, etc.
        • absolute contraindications to sports participation
          • asymptomatic patients with fusion involving C2
            • most common presentation
          • long fusions
          • multilevel fusions
          • any limitation in cervical motion
          • Samartzis type I and II lesions with limited range of motion, C2 involvement, instability or spondylosis, and occipitocervical anomalies
          • any patient undergoing surgical management of KFS
        • relative contraindications to sports participation
          • Samartzis type II lesion with known previous episode of transient quadriplegia
    • Operative
      • surgical decompression and fusion
        • indications
          • basilar invagination
          • chronic pain
          • myelopathy
          • associated atlantoaxial instability
          • adjacent level disease if symptomatic
          • progressive scoliosis deformity
            • 82% of KFS patients with congenital scoliosis will require surgical correction
        • phenotypes associated with higher rates of surgical intervention
          • subaxial cervical spine fusions and thoracic spine anomalies, associated with thoracolumbar and sacral surgical interventions
          • axial spine anomalies, which correlated with subluxations and cervical spinal fusion
          • Chiari malformations and associated neurosurgical procedures
          • thoracic spine anomalies, scoliosis, and sacral agenesis
  • Complications
    • Cervical spinal cord injury
      • usually associated with participation in high-impact contact sports
      • theory that smaller diameter spinal cords may create an increased risk for cervical spinal cord injury
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