Summary Klippel-Fiel Syndrome 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. Etiology Pathophysiology mechanism due to failure of normal segmentation or formation of cervical somites at 3-8 weeks' gestation Genetics SGM1 gene (Chr 8) Notch and Pax genes Associated conditions orthopedic conditions congenital scoliosis Sprengel's deformity (30%) medical conditions & comorbidities renal disease (aplasia in 33%) auditory issues (deafness in 30%) congenital heart disease/cardiovascular (15-30%) 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 Type II Fusion or only 1 or 2 vertebrae in the cervical spine Type III Fusion exists in part of the thoracic and/or lumbar spine, in addition to Type I or Type II KFS 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 Presentation Symptoms stiff neck 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) jaw anomalies partial loss of hearing torticollis scoliosis Imaging Radiographs recommended views AP, lateral, and odontoid views 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 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 observation and abstain from contact/collision sports indications asymptomatic patients with fusion involving C2 most common presentation long fusions modalities counseling important to avoid activities that place the neck at high risk of injury contact sports, gymnastics, football, wrestling, trampoline, etc Operative surgical decompression and fusion indications basilar invagination chronic pain myelopathy associated atlantoaxial instability adjacent level disease if symptomatic