Anatomy of Craniocervical Junction
The craniocervical junction (CCJ) is an osteoligamentous complex between the occiput, atlas and axis, which provides both structural stability and movement [1].
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Anatomy of Craniocervical Junction M. Alicandri-Ciufelli, M. Menichetti, M.P. Alberici, and L. Presutti
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Osseous Anatomy
The craniocervical junction (CCJ) is an osteoligamentous complex between the occiput, atlas and axis, which provides both structural stability and movement [1].
1.1.1 Occipital Bone The occipital bone extends from the clivus anteriorly to the lambdoid suture posteriorly, its embryologic origin being four primary cartilaginous centres laid down in the chondrocranium around the foramen magnum, and a fifth membranous element [2]. The superior nuchal line serves as a rough guide for the location of the transverse sinus, and the inion, found in the midline along this line, approximates the torcular herophili. The insertion of the semispinalis capitis may be the most accurate landmark for the confluence of the sinuses [3]. A fundamental anatomical part of the occipital bone is the foramen magnum, which has three parts:
1. The squamosal portion, located in the dorsal aspect of foramen magnum 2. The basal or clival portion located anterior to the foramen magnum 3. The condylar part that connects the squamosal and the clival parts [4] The most posterior margin of the foramen magnum is called the opisthion. The most anterior midline of the foramen magnum is termed the basion. The sagittal diameter of the foramen magnum should be 35 ± 4 mm. The transverse diameter at the equator of foramen magnum is slightly less. The condylar part includes the occipital condyles, which fall just at the level and anterior to the equator of the foramen magnum. The shape of these condyles positioned on either side of the foramen magnum allows the skull to articulate with the cervical spine, whilst the angles prevent excessive axial rotation at the craniocervical junction [5].
M. Alicandri-Ciufelli (*) • M. Menichetti • M.P. Alberici L. Presutti Head and Neck Surgery Department, University Hospital of Modena, Modena, Italy e-mail: [email protected]
© Springer International Publishing Switzerland 2017 S. Boriani et al. (eds.), Atlas of Craniocervical Junction and Cervical Spine Surgery, DOI 10.1007/978-3-319-42737-9_1
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1.1.2 Atlas (Fig. 1.1) The atlas, first cervical vertebra, has its origins in the fourth occipital and first cervical sclerotomes. It is unique among vertebrae in not having a body and is formed from three ossification sites: the anterior arch or centrum and two neural arches which fuse in later life to become a unified posterior arch, thereby completing the osseous ring which surrounds the spino-medullary junction [6]. An appreciation that this ring is incomplete in up to 5 % of patients is important if one is to avoid causing a durotomy or spinal cord injury when approaching the craniocervical junction posteriorly [7, 8]. The ring of the atlas consists approximately of one-fifth anterior arch, two-fifths posterior arch, with the remaining two-fifths being contributed by the lateral masses [9]. The longus colli muscles and the anterior longitudinal ligament, which contribute to a
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