Embryology Genetics homeobox, or Hox genes direct and regulate processes of embryonic differentiation and segmentation along craniocaudal axis see each segment for embryologic development Osteology The cervical spine contains 7 vertebral bodies C1 (atlas) C2 (axis) C1 to C7 have a transverse foramen vertebral artery travels through transverse foramen of C1 to C6 C2 to C6 have bifid spinous process C7 despite having a transverse foramen, the vertebral artery does NOT travel through it in the majority of individuals there is no C8 vertebral body although there is a C8 nerve root Alignment Normal sagittal lordosis (measured from C2 to C7) Spinal Canal Spinal canal normal diameter is 17mm <13mm indicates possible cord compression Atlas (C1) Has no vertebral body and no spinous process Embryology three ossification centers one for each lateral mass (posterior neural arches) lateral masses fuse to body at age 7 one for anterior arch anterior arch does not appear until 1 year of age Articulations occiput-C1 two superior concave facets that articulate with the occipital condyles makes up 50% of neck flexion and extension C1-C2 (see below) Axis (C2) Axis Osteology axis has odontoid process (dens) and body embryology develops from five ossification centers subdental (basilar) synchondrosis is an initial cartilagenous junction between the dens and vertebral body that does not fuse until ~6 years of age the secondary ossification center appears at ~ age 3 and fuses to the dens at ~ age 12 Axis Kinetmatics CI-C2 (atlantoaxial) articulation is a diarthrodal joint that provides 50 (of 100) degrees of cervical rotation 10 (of 110) degrees of flexion/extension 0 (of 68) degrees of lateral bend C2-3 joint participates is subaxial (C2-C7) cervical motion which provides 50 degrees of flexion/extension of cervical spine 50 degrees of rotation of cervical spine 60 degreesof lateral bend C2 Blood Supply a vascular watershed exists between the apex and the base of the odontoid apex is supplied by branches of internal carorid artery base is supplied from branches of vertebral artery the limited blood supply in this watershed area is thought to affect healing of type II odontoid fractures. Occipital-C1-C2 Ligamentous Complex Provided by the odontoid process and its supporting ligaments transverse ligament limits anterior translation of the atlas apical ligaments limit rotation of the upper cervical spine alar ligaments limit rotation of the upper cervical spine Subaxial Cervical Spine (C3 to C7) C1 to C7 have a transverse foramen vertebral artery travels through transverse foramen of C1 to C6 C2 to C6 have bifid spinous process C6 contains palpable carotid tubercle which is a valuble landmark for anterior approach to cervical spine C7 nonbifid spinous process despite having a transverse foramen, the vertebral artery does NOT travel through it in the majority of patients there is no C8 vertebral body although there is a C8 nerve root The superior articular facets of the subaxial cervical spine (C3-C7) are oriented in a posteromedial direction at C3 and posterolateral direction at C7, with a variable transition between these levels