Pathologies of the cervical spine in skeletal syndromes and dysplasias.

Skeletal syndromes and dysplasias include more than 150 entities, most often of genetic origin. Some of them cause abnormalities in the cervical spine, with or without instability, distortion or compression of the spinal cord. These abnormalities must be detected and treated if necessary because they can have serious consequences such as quadriplegia. Up to 30% of patients with Down syndrome are affected by occipitocervical or atlantoaxial instability. Dynamic cervical spine radiographs are the most common screening tool. Mucopolysaccharidoses (MPS) are a group of inherited lysosomal storage diseases that result in the accumulation of glycosaminoglycans sometimes responsible for craniocervical instability and cervical spinal canal stenosis. Their monitoring requires an MRI every two years. Neurofibromatosis type 1 and syndromes with connective tissue abnormalities (Marfan syndrome, Loeys-Dietz syndrome, Ehlers-Danlos syndrome) can cause severe and unstable cervical spine deformities that may remain asymptomatic for a long time. Cervical X-rays should therefore be performed if there is the slightest doubt. Some rare chondrodysplasias (punctate chondrodysplasia, Larsen syndrome, Metatropic dysplasia) or segmentation anomalies (Klippel Feil syndrome, Sprengel's disease) have cervical spine abnormalities that should be looked for. In case of progression of a deformity (usually kyphosis) or stenosis of the cervical spine, it is important to consider surgical treatment with correction and stabilization. Sometimes preceded by a period of Halo traction, the instrumentation must have "wide" limits and exceed the anatomical limits of the spinal deformity by at least 2-3 levels to prevent the development of an adjacent deformity. The increasing use of surgical navigation techniques allows for greater corrections and more efficient stabilizations, including severe cervical spinal deformities. Vigilance and the detection of these abnormalities remain the key to early and preventive treatment of the complications of these spinal anomalies on often difficult terrain. LEVEL OF EVIDENCE: >V (expert opinion).