Spinal Mechanics Flashcards
Where does most flexion of the spine occur?
Lumbar spine
Where does most rotation of the spine occur?
Thoracic spine
Describe the nucleus of an intervertebral disc
Amorphous, collagen II, proteoglycan, elastin, 85% water
Describe the annulus of an intervertebral disc
Concentric lamellae, collagen I, proteoglycan, elastin, 70% water, fibres arranged in trabecular mesh-ike structure- angle of layers important for when tension applied
What is the difference between type I and type II collagen?
Collagen I is more spongy and involved in tension, collagen II is more turgid and strong and involved in compression
Why are intervertebral discs very stiff in compression?
. Contain lots of water, which is incompressible
. Collagen fibres stiff and aligned in way that is difficult to compress
Can intervertebral discs bend?
Yes, very easily because the elastin in the annulus can rearrange e.g. to allow you to bend over and touch your toes
How is elastin arrange in the nucleus of intervertebral discs?
In a kind of ‘starburst’ radiating pattern
Are there blood vessels in intervertebral discs? Why is this?
. No blood vessels because they would collapse under the negative pressure
. Intervertebral discs have a negative pressure to suck in nutrients and water by diffusion or advection
Where are nerves found in IV discs?
In the outer annulus, giving nerve supply to the end plate
Describe how load is distributed over the vertebral end plate
Load evenly distributed over end plate, with force always perpendicular to vertebral end plate (no matter which direction you’re bending/stretching)
Why aren’t IV discs good shock absorbers?
Because they are incompressible
How does the spine absorb shock?
Muscles around spine shorten and lengthen, the muscles themselves are very effective shock absorbers
What is the effect of a low strain rate on the spine?
Crush because bone marrow has time to disperse
What is the effect of a high strain rate on the spine?
Burst because bone marrow can’t move out the way
