4 Cervical Spine Anatomy • C3–C7 are defined as the subaxial spine. • Majority of flexion/extension of the neck and lateral bending occur here: – Maximal flexion occurs at C4/C5 and C5/C6. – Maximal lateral bending occurs at C2/C3, C3/C4, and C4/C5. • Lordotic curvature: 16 to 25 degrees. • Landmarks: – C2/C3: lower border of mandible. – C3: hyoid bone. – C4: thyroid cartilage. – C6: cricoid cartilage. • Vertebral body: – Concave superiorly. – Convex inferiorly. • Uncinate process: – Directly interacts with adjacent vertebral body above. – Contain articular surfaces. • Pedicle: – Angled medially and superiorly. – Pedicles smaller than those in thoracic and lumbar spine. • Transverse process: – Contains transverse foramen: ∘ All cervical vertebrae have transverse foramen. ∘ Anterior to nerve root groove. ∘ Allow for passage of vertebral artery. – C6 transverse process (Chassaignac’s tubercle) is palpable. • Lamina: – Bridge between lateral masses and spinous process. • Lateral mass: – Lateral to junction between pedicle and lamina. – Contains the superior and inferior articular processes: Fig. 4.1 Bony anatomy of cervical vertebrae. (Reproduced with permission from An HS, Singh K, eds. Synopsis of Spine Surgery. 3rd ed. New York, NY: Thieme; 2016.) ∘ Creates the facet joint with the adjacent vertebral articular processes. ∘ Superior articular facets exhibit posteromedial orientation, transitioning to posterolateral with caudal progression: ▪ Supports more flexion/extension. • Spinous process: – Bifid from C3 to C5. – C7 exhibits largest spinous process. • Anterior ligamentous complex: – Anterior longitudinal ligament (ALL): ∘ Traverses along anterior surface of vertebral bodies. ∘ Resists extension. – Annulus fibrosis of the intervertebral disk. • Middle ligamentous complex: – Posterior longitudinal ligament (PLL): ∘ Traverses along posterior surface of vertebral bodies. ∘ Resists flexion. • Posterior ligamentous complex: – Facet capsules: ∘ Support facet joint for adjacent vertebra articulation and resist distractive forces. – Interspinous and supraspinous ligament: ∘ Traverse between spinous processes: ▪ Midline avascular plane. ∘ Continuous with the ligamentous nuchae above C7. – Ligamentum flavum: ∘ Deepest structure posteriorly prior to reaching spinal canal. ∘ Connects the laminas of adjacent vertebrae. • Fascial layers (Fig. 4.2): – Platysma: ∘ Superficial muscle. – Superficial layer of deep cervical fascia: ∘ Contains anterior neck muscles (except longus colli) and trapezius posteriorly. – Prevertebral layer of deep cervical fascia: ∘ Contains all posterior neck muscles deep to trapezius. ∘ Covers ALL and longus colli. – Pretracheal fascia: ∘ Contains thyroid and trachea. – Carotid sheath: ∘ Contains carotid artery, internal jugular vein, and vagus nerve (cranial nerve X). • Muscular layers: – Anterior neck muscles (Fig. 4.3; Tables 4.1 and 4.2): ∘ Divided into two regions: anterior neck and anterior cervical triangle: ▪ Anterior cervical triangle primarily functions to move the hyoid bone. – Posterior neck muscles: ∘ Divided into three regions: posterior neck, occipital triangle, and suboccipital triangle: ▪ Posterior neck (Table 4.3, Figs. 4.4, 4.5). ▪ Occipital triangle (Table 4.4, Fig. 4.6): ❖ Borders: sternocleidomastoid (SCM; anterior), trapezius (posterior), and omohyoid (inferior). ▪ Suboccipital triangle: ❖ Borders: formed by the muscles it contains. ❖ See Chapter 3.
4.1 General Information
4.2 Bony Anatomy (Fig. 4.1)
4.3 Ligamentous Anatomy
4.4 Muscular Anatomy
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