2 General Spine Anatomy and Long Tract Pathways • Overview of the vertebral column (Table 2.1, Fig. 2.1). • Column classification: – Vertebral column divided into three anatomical classifications (Table 2.2, Fig. 2.2). – Moderate reliability for determining clinical degree of stability. • Surface landmarks (Table 2.3, Fig. 2.3). • Vertebral canal: – Spans from foramen magnum (cranial) to the sacral hiatus (caudal). – Formed by the vertebral foramina of each vertebra. – Contents (Table 2.4, Fig. 2.4). • Spinal cord regions and spinal nerves: – Five divisions and 31 spinal nerves (Fig. 2.5): ∘ Cervical: C1–C8 spinal nerves. ∘ Thoracic: T1–T12 spinal nerves. Fig. 2.1 Vertebral column. (Reproduced with permission from An HS, Singh K, eds. Synopsis of Spine Surgery. 3rd ed. New York, NY: Thieme; 2016.) Table 2.2 Column classification
2.1 Topographical Anatomy
2.1.1 General Vertebral Column Anatomy
2.1.2 General Spinal Cord Anatomy
Classification | Anterior boundary | Posterior boundary |
Anterior column | Anterior longitudinal ligament (ALL) | Anterior two-thirds of vertebral body and intervertebral disk |
Middle column | Posterior one-third of vertebral body and intervertebral disk | Posterior longitudinal ligament (PLL) |
Posterior column | Immediately posterior to PLL | Ligamentum nuchae (C1–C7) or supraspinous ligament (inferior to C7) |
∘ Lumbar: L1–L5 spinal nerves.
∘ Sacral: S1–S5 spinal nerves.
∘ Coccyx: coccygeal nerve.
– Spinal nerves exit vertebral canal through intervertebral foramina.
– Spinal nerve numbering:
∘ C1–C7 spinal nerves exit above their respective vertebrae.
∘ C8 spinal nerve exits below C7 vertebrae (C7/T1 intervertebral foramen).
∘ All remaining spinal nerves exit below their respective vertebrae.
Fig. 2.2 Column classification. (Reproduced with permission from Baaj AA, Mummaneni PV, Uribe JS, Vaccaro AR, Greenberg MS, eds. Handbook of Spine Surgery. 2nd ed. New York, NY: Thieme; 2016.)
• General features of the spinal cord:
– Adult spinal cord is two-thirds the length of the vertebral column:
∘ Origin: medulla (brainstem) at the foramen magnum.
∘ Termination: conus medullaris (L2).
– Thecal sac comprises a dura-surrounded sac that extends from the spinal cord and contains cerebrospinal fluid (CSF), nerve roots, and the cauda equina.
– Features (Table 2.5, Figs. 2.5, 2.6).
Table 2.4 Contents of the vertebral canal
Structure | Description |
Superficial | |
Extradural (epidural) space | Contains adipose tissue and internal vertebral venous plexus |
Internal vertebral venous plexus (anterior and posterior divisions) | Drains spinal cord and connects with external vertebral plexus. Lack of valves can lead to bidirectional blood flow |
Meningeal layers | |
• Dura mater (most superficial) | Composed of fibrous tissue. Continuous with the epineurium of spinal nerves |
Subdural space | Potential space between dura and arachnoid mater that can open secondary to trauma (i.e., subdural hematoma) |
• Arachnoid mater (middle) | Adherent to dura mater. Avascular and translucent |
Subarachnoid space | Between arachnoid and pia mater. Contains cerebrospinal fluid (CSF) |
• Pia mater (deepest) | Composed of thin fibrous tissue. Impermeable to CSF |
Denticulate ligaments | Reflections of pia mater that attach to the arachnoid and dura mater. 21 pairs, spanning craniovertebral junction to T12, provide stability to the spinal cord |
Spinal cord | |
Deep | |
Fig. 2.4 (a,b) Contents of the vertebral canal. (Reproduced with permission from Baaj AA, Mummaneni PV, Uribe JS, Vaccaro AR, Greenberg MS, eds. Handbook of Spine Surgery. 2nd ed. New York, NY: Thieme; 2016.)
• Spinal cord anatomy (Tables 2.6–2.7).
• Regional variation in spinal cord white and gray matter composition (Figs. 2.7, 2.8):
– Cervical region:
∘ Abundant gray matter for innervation of upper extremities.
∘ Region of most abundant white matter.
∘ Presence of both the fasciculus gracilis and cuneatus.
– Thoracic region:
∘ Reduced size of gray matter (no innervation to extremities).
∘ Less white matter than cervical region.
∘ Intermediolateral (IML) cell column:
▪ Small outpocketing of gray matter from lateral horn containing cell bodies of preganglionic sympathetic neurons.
∘ Fasciculus cuneatus only present superior to T6, while fasciculus gracilis is present over the entire length.
– Lumbar region:
∘ Abundant gray matter for innervation of lower extremities.
∘ Less white matter than superior regions.
∘ Presence of the fasciculus gracilis only.
∘ Presence of cauda equina.
– Sacral region:
∘ Comparatively little white or gray matter.
∘ Contains an IML cell column:
▪ Cell bodies of parasympathetic preganglionic neurons.
∘ Presence of cauda equina.
