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) login to view 1 more bullet autosomal dominant login to view 2 more bullets autosomal recessive login to view 1 more bullet SGM1 gene (Chr 8) Notch and Pax genes Associated conditions orthopedic conditions congenital scoliosis Sprengel's deformity (30%) Wildervanck syndrome (cervico-ocular-acoustic dysplasia) login to view 4 more bullets medical conditions & comorbidities renal disease (aplasia in 33%) auditory issues (deafness in 30%) congenital heart disease/cardiovascular (15-30%) login to view 1 more bullet brainstem abnormalities/basilar invagination congenital cervical stenosis login to view 1 more bullet atlantoaxial instability (~50%) adjacent level disease (100%) login to view 1 more bullet 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 login to view 1 more bullet fusions below C3 login to view 1 more bullet 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%) login to view 3 more bullets other findings login to view 9 more bullets 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 login to view 1 more bullet basilar invagination login to view 2 more bullets atlantoaxial instability login to view 2 more bullets degnerative changes login to view 1 more bullet calcifications login to view 2 more bullets Ultrasound abdominal ultrasound renal aplasia/agenesis echocardiogram congenital heart conditions login to view 1 more bullet 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 login to view 2 more bullets observation and abstain from contact/collision sports modalities login to view 3 more bullets absolute contraindications to sports participation login to view 7 more bullets relative contraindications to sports participation login to view 1 more bullet Operative surgical decompression and fusion indications login to view 7 more bullets phenotypes associated with higher rates of surgical intervention login to view 4 more bullets 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