1
Q
What are the structural parts of the disc?
A
- annulus fibrousus
- nucleus propulsus
- cartilagenous end plate
2
Q
What are the function of the proteoglycans in disc?
A
- provided weight bearing properties
- internal lubrication
- provide a matrix for concentration gradients for nutrient exchange
3
Q
What are proteglycans made of?
A
- GAG chains of long polysaccaride molecules that may or may not be sulfated
- GAG wrapped around protein core similar to a bottle scrubbing brush
4
Q
What GAGs are found in the disc?
A
- Keratin sulfate
- chondrotin 4-/6- sulfate
- hyaluronic acid
5
Q
What role does hyaluronic acid play in the disc?
A
- lubrication between collagen
2. fluid transportation for nutrition and waste
6
Q
How is the collagen content of the disc and annulus different?
A
nucleus -50-60% proteoglycans -80% collagen which is 80% type II and 0% type I annulus -20% proteglycans -50-60% collagen which is 80% type I
7
Q
How do the function of type I and Type II collagen differ?
A
type I- resists tensile forces
type II- resist compressive forces
8
Q
What are the lamellae of the disc?
A
- parallel collagen fibers arranged in 10-12 concentric layers
- thickest anterior and laterally
- thinnest posterior
- fibers run at about 30degrees from the vertical and alternate orientation in each successive layer
9
Q
What are the Sharpys fibers?
A
outer part of the annulus not covered by the vertebral end plate connected directly to the vertebral body
10
Q
What is the cellular structure of the cartilagenous end plate?
A
- Hylanine cartilage on the vertebral body side
2. fibrocartilage on the disc side
11
Q
How is the cartilagenous end plate attached to the surrounding structures?
A
- end plate is strongly bound to the disc by extensive collagen attachments
- loosely bound to the vertebral body
12
Q
What is the vascular supply of the disc and how does it change over time?
A
- at birth there is a rich vascular supply to the disc
- weight bearing makes pressure too great in the lumbar spine for vessels to survive
- cervical spine can have a direct flood supply until the third decade
- only the arteries from the metaphysial arteries penetrate the outer most fibers of the annulus
13
Q
How does diffusion into the disc occur?
A
- pH of GAG rich disc is usually 0.5 lower than surrounding tissues
- the osmolarity is higher than the surrounding fluids
- the fixed negative charge density facilitated by the ionic solutions creates a swelling pressure that imbibes fluid
14
Q
What processes does the disc use for metabolism?
A
glycolosis
15
Q
How are the nutrients moved in and out of the disc?
A
- occurs through cartilagenous end plates and blood supply of the vertebral body
- smaller nutrients such as oxygen and glucose are moved entirely by diffusion
- loading and unloading mover water, but not nutrients
- there is a steep concentration gradient from vertebral body to nucleus propulsis
16
Q
How does aging effect diffusion rates of the disc?
A
- end plate clarification
- proteoglycans become smaller and less effective
- calcification can lead to pores in the end plates large enough for proteglycans to pass through
- cytokinins or other damaging enzymes can pass into the disc from the enlarged pores
17
Q
What part of the disc in innervated?
A
- outer third and into the middle third
- pain and degenerative disc can have innervation as much as 2/3 of the the disc or NP, normally the NP has no innervation
18
Q
How does the disc impact movement of the spine?
A
- Greater disc height equates to greater segmental ROM
2. loading of the disc increases its stiffness and available ROM
19
Q
What are the weakest points of the disc when it is loaded?
A
- the end plates are the weakest point under axial loads
- with movement the posterior lateral AF absorb the greatest force because they are further from the axis of motion
- disc will not prolapse under compression alone and requires some bending in addition to the comprssion
20
Q
How does rotation impact the mechanical properties of the disc?
A
- increases stress on the AF
2. decrease the vertical and horizontal stress on the NP
21
Q
How is the disc volume effected by resting at night and a day of loading?
A
- rest increases disc height by as much as 10% and fluid volume can increases as much as 20-25%
- activity-decreases with in 8 hours or 4 hours carry 40% of body weight
22
Q
How does the disc distribute the vertical forces?
A
- it transmits vertical forces horizontally and circumferentially
- this stretches the AF
- as AF recoils energy restores disc form
- outer edges of disc bulge and the end plates deflect stress in an axial direction
23
Q
What structures resist distraction of the disc?
A
- sharp’s fibers
2. intervertebral ligaments
24
Q
What is the disc AF less capable of managing shear forces?
A
- since the annular rings collagen fibers run in alternating direction only have the fibers are availiable to manage the shear forces
- therefore only half the AF are stretched during shearing
25
What is a clinical sign for disc degeneration?
painful shearing of the disc
26
What structures protect the disc from excessive axial rotation?
1. facets
| 2. PLL
27
How much rotation is required to rupture a disc?
12-20 degrees and to accomplish this you would have to remove the posterior elements
28
What structure is most likely to fail with axial torsion of the spine?
facets since they are the primary limiter of rotation
29
Rotation in what position puts the disc at the greatest risk for injury?
1. flexion- facets allow greater rotation and you have increased shearing
2. loading increases shearing and rotational forces
30
How does rotation of the spine effect the disc height?
as the annular fibers are loaded they will pull in the circumferential displacement and separate the vertebral bodies
31
describe the movement of the nucleus within the disk?
1. nucleaus move like a gas under pressure
2. with flexion the tension in the posterior components so the NP is pushed forward
3. disruption of the fibers opens up a path for the NP to travel
32
what effect do the different postures have on disc pressure?
1. standing 0%
2. laying down -50%
3. flexed standing 25%
4. seated 50%
5. touching toes 400%
33
What is the goal for tissue based treatment of disc?
1. compression decompression with rotation
2. enhance transport of the solutes in and out of the disc
3. stimulate fibroblast via chondroblasts so that new collagen and proteglycans can be produced
34
what physiochemical changes that occur with a disc prolapse?
1. inflammitory response in epidural tissue
2. displaced hydrophilic GAG will double in size in a matter of hours
3. increased production of proinflammatory agents such as nitric oxide interlukin-6 and prostaglandin -E2
35
What two inflamatory chemicals have been inplicated in the supression of proteoglycan synthesis?
1. interlukin-6
| 2. prostiglandin E-2
36
How does the disc change with age?
1. decrease vasuclarization
2. end plate calcification and fibrosus of NP
3. Theses changes lead to decreased proteoglycans
4. AF is no longer attached to the end plate as well
5. fissure appear in the disc
6. Gross mechanical changes of the disc due to decreased capacity for managing forces
37
What are the four fundimental factors contributing to disc degeneration?
1. vascular-nutritional
2. pH
3. mechaincal
4. genetic
38
How do the histological characteristics of the disc change as we age?
1. cell density decreases
2. proteoglycan content decreases
3. callagenase and protease activity increases creating higher concentrations of collagen fibrils and non-aggregating proteoglycans
4. fibronectin and elastin appear in disc
39
What factors contribute to the ECM breakdown of mature discs
1. the disc is a large avascular tissue
2. adverse biomechanical loading
3. preprogrammed events
- notochondral cell loss
- mesenchymal cell reaching their life span
- loss of vascular and Ca ions from degeneration of the end plates
40
what structures supply the disc with its nutrients?
1. direct blood supply from the periphery
| 2. vertebral body vascularity through the end plates
41
Why is movement so importanct with the management of disc pathology?
1.its metabolic pathway is anerobic due to its low vscularization and movement is neccessary to remove the lactic acid and normalized disc pH in addition to nutritional exchange
42
What is the normal pH of the disc and what happens when the pH is too low?
1. normal 6.9-7.1 and is determined primarily by lactic acid concentrations
2. proteoglycan synthesis is impacted most by a decrease in pH
43
How does force transmission in the disc change with degneration?
1. transmision of force from end plate to end plate eventually travels through the annulus as the neucleus degenerates
2. the annules begins to break down as due to the compressive load
44
What are the three types of tears that typically occur with the disc?
1. radial- through mulitple laminar layers
2. circumfential- between laminal layers
3. rim- rupture of sharpy's fibers
45
What area is typically effected first with disc degeneration?
end plate in the posterior lateral quadrant
46
What makes up the herniated material of the disc?
GAG is always a part
1. end plates
2. NP younger people
3. AF with older
47
What and why is the OSR for disc?
1. modified tension in line of stress (rotation) with compression and decompression
2. AF collagen fibers are oriented for rotation
3. spiral nature of AF creates a distraction with rotaiton
3. chondrocytes of the NP requires compression to increase cellular metabolism
48
What are the motions of the spine in order of shearing potential greatest to least
1. flexion
2. SB
3. rotation- none
