Posterior Spine - Thoracic/Lumbar

Question 1

Describe the mobility of the thoracic spine.

Answer 1

The T-spine is the second least mobile of the spinal regions (the first being the sacral and coccygeal regions)

The rib cage, along with the low ratio of IVD height to vertebral body height (1:5) account for low mobility

Question 2

Describe the thoracic osteology.

Answer 2

AP and transverse dimensions almost equal

Body height slightly higher posteriorly, leads to normal kyphosis of T-spine

Pedicles protrude directly posterior

Foramen is smaller than C-spine and L-spine d/t smaller spinal cord in thoracic region

Laminae are higher and wider, overlap like tiles on a roof (limits extension)

Transverse processes project laterally and slightly posteriorly, and become smaller moving down the spine

Spinous processes project posteriorly and inferiorly in the rule of threes.

Question 3

Describe the rule of threes.

Answer 3

Rule for determining how the spinous processes of the T-spine project.

T1-T3: spinous process at same level as body
T4-T6: spinous process at a half level below, on the bodies of T4/5, T5/6, and T6/7
T7-T9: spinous process on whole level below, on bodies of T8-T10
T10: whole level below, body of T11
T11: half a level below, body of T11/12
T12: same level, body of T12

Question 4

Describe the osteology of the lumbar spine.

Answer 4

Heavy vertebral bodies for weight bearing

Stout transverse processes that project posterolaterally

3/4 of superior and inferior body surfaces covered by hyaline cartilage end plate

Question 5

Describe the osteology of the sacrum.

Answer 5

5 fused sacral vertebrae

Base (top) - superior facets of S1 articulate with inferior facets of L5

4 sacral foramina translate nerves S1-S4 at the apex

Sacral hiatus: passageway that exposes lumbar cistern for caudal epidural

Question 6

Describe the components of an intervertebral disc.

Answer 6

Nucleus pulposus (NP) in the center, surrounded by annulus fibrosis rim.

NP:

- Gelatinous, hydrophilic (absorbs + attracts fluid)
- 90% fluid at birth and decreases to 70% as we age
- Conforms to pressure, maintains hydration by acting as a sponge
- No circulating blood 
- L-spine NP situated more posteriorly than C-spine

Annulus fibrosis:

- Laminated fibrocartilage that encapsulates the NP
- Made of 16-24 lamellae 
- 60 degree fiber angles
- Outer fibers have some nerve endings (pain-sensitive)
- No blood supply, nutrients come from adjacent vertebral bodies
- Compression + release (movement) circulates fluid through the disc
- Weakest posterolaterally, most susceptible to herniation here
- Anchors via the cartilage and plate, which connects IVD to VB 
* cartilage end-plate is first structure to fail in the onset of a disc lesion*