Anatomy and Biomechanics of the Axial Spine

Question 1

Describe the general arrangement and shape of the spine

Answer 1

7 cervical, 12 thoracic, 5 lumbar, 5 sacral, ?? coccygeal.
Shape - Cervical lordosis 15 degrees, thoracic kyphosis 30 degrees, lumbar lordosis 45 degrees, sacral kyphosis 60 degrees. Means when spine is in balance, head is over hips and kyphosis/lordosis cancel each other out.

Question 2

Describe a typical Cervical vertebra

Answer 2

Small vertebral body, horizontal (transverse) articular processes, and bifid spinous process. Only needs to support head, but has a large spinal canal (same area as body).
Also has vertebral artery (transverse) foramina lateral to body.

Question 3

Describe C1 and C2

Answer 3

Atypical .vertebra
C1 (atlas) has no central body, just large facets.
C2 (Axis) has large facets and a vertical dentate process to allow rotation.

Question 4

Describe a typical Thoracic vertebra

Answer 4

Vertebral body larger than spinal canal. Has transverse processes for rib articulation, and pedicles joining body rest of vertebra. 3 costal facet joints on each side - 2 for its own rib one for the one below.
Articular processes are coronal (vertical).
Spinous process is elongated, downward sloping.

Question 5

Describe a typical Lumbar vertebra

Answer 5

Very large body (support weight), with small spinal canal. Largest vertebra in body. Large pedicles, with saggital (vertical) articular processes.
Spinous process is short and stubby.
Slender transverse processes for attachment of lumbar muscles.

Question 6

What is a typical body/canal ratio, spinous process, transverse process, and articular process of a cervical vertebra?

Answer 6

Body/canal - 1:1
Spinous - Bifid
Transverse - Foramen present
Articular - Horizontal plane

Question 7

What is a typical body/canal ratio, spinous process, transverse process, and articular process of a thoracic vertebra?

Answer 7

Body/canal - 3:1
Spinous - Sloping
Transverse - rib facet present
Articular - coronal plane

Question 8

What is a typical body/canal ratio, spinous process, transverse process, and articular process of a lumbar vertebra?

Answer 8

Body/canal - 5:1
Spinous - Square
Transverse - Elongated
Articular - Sagittal plane

Question 9

What is the arrangement of spinal muscles?

Answer 9

3 layers, deepest are shortest (only joining 2 levels), superficial are biggest (span long sections of spine)

Question 10

Outline spinal blood supply

Answer 10

Vertebral artery stems from aortic arch and travels through cervical vertebrae.
Venous drainage drains through segmental vessels to inf/sup vena cavae. Spinal veins don’t have valves, route for metastasis via retrograde spread.

Question 11

Outline the arrangement of the spinal curve and spinal nerves

Answer 11

Spinal cord starts at end of brainstem, terminates at L1. Cauda Equina continues to S5.
Cervical nerve roots emerge above their vertebrae, Others emerge below vertebrae.

Question 12

What is the relationship between intervertebral disc structure and function

Answer 12

2 vertebrae form a 3-way joint - disk and 2 facet joints. Can move in 3 axes (vertical, horizontal, AP), and can both rotate around and move along them (theoretically 6 degrees of movements). But you don’t get translational movement, so only 3 rotational planes of movement.

Question 13

Describe an Intervertebral disk.

Answer 13

Solid collagen with water - peripheral annulus gives strength with regular arrangement of fibres. Core is nucleus pulposis, with collagen arranged randomly instead of regularly, and lots of proteoglycans. Allows compression and then retaining shape.

Question 14

How does flexion and extension differ from rotation in the spine?

Answer 14

Lateral flexion - mostly in upper cervical (C2-6) and thoraco-lumbar area.
Rotation - most of it at C1-2, some through cervical and upper thoracic, and little bit in L5-S1.

Question 15

How does the spine protect against axial compression vs flexion/extension compresssion?

Answer 15

Axial compression takes 600N for even 1 mm
Flexion and extension takes only 2N per mm.
Easy to move the way it is meant to, very difficult to move in any other way.

Question 16

How can you protect a degenerating spine?

Answer 16

Muscle damping protects bones, acting as a spring on the spinal shock absorber. Single most important thing you can do to protect a degenerating spine is to build core muscle strength to protect the spine.