Intervertebral discs Aging, pathology & rehabilitation

Question 1

properties

Answer 1

“The repair structure must have tensile properties similar to ligament, compressive properties similar to cartilage, and strong adhesion to adjacent tissues (particularly for the IVD), yet it must remain pliable and tough.”

• weight-bearing
• resist tensile forces
• flexible

Question 2

Gross structure lumbar intervertebral disc:

Answer 2

Vertebral endplates
Annulus fibrosus:
10 – 20 concentric layers
All fibres in 1 layer = same orientation & opposite to adjacent layers
650 angle to the vertical ( 1⁄2 to left: 1⁄2 to right)

Nucleus pulposus:
Up to 90% water (incompressible) Proteoglycans
Collagen

Question 3

4 zones of the intervertebral disc

Answer 3

3AF ZONES
IN YOUNG AND HEALTHY, GEL-LIKE NP, RICH IN PROTEOGLYCAN AND HYPOPHILLIC QUALITIES

# outer annulus fibrosus
collagen type 1 lamellae fibroblasts

• Inner annulus fibrosus
  collagen type II
  fibroblasts & chondrocytes proteoglycans

> transition zone
Acellular, thin fibrous layer

Nucleus pulposus
collagen type II chondrocytes proteoglycans

Question 4

IVD

Answer 4

AF
80% dry weight collagen type I
NP
20% dry weight collagen type II 50% dry weight proteoglycans

Question 5

Aging / Degeneration:

Answer 5

• Decline in proteoglycans in the NP
• decreases H2O binding capacity – decreases stiffness
• Change in relative proportions of GAG’s
• Apoptosis
• H2O content in AF decreases significantly with age (moreso than degeneration)
• Decrease in layers
• Spacing between collagen bundles in layer
• Damage to collagen
• Spindle shaped fibroblasts change to round chondrocyte like cells
• Vascular ingrowth into repairing areas

-With higher loads and greater water loss, load is transferred from the NP to the AF, and stress peaks are created throughout the AF.

Question 6

Aging / Degeneration: 2

Answer 6

NP 1st AF 2nd
Therefore change in load = change in structure
NP = loss amount of h2O, decreases ompressive stiffness > transfers stress to AF

Question 7

Degenerative biomechanics:

Answer 7

degeneration of a disk doesn’t change amount of strain the AF undergoes before failure

Question 8

Classification of tears:

Concentric tears

Answer 8

all age groups

75% of anterior AF 100% of posterior AF

Question 9

Classification of tears:

Radiating tears

Answer 9

10-30yrs: Anterior 47% Posterior 68% 51-80yrs: Anterior 75% Posterior 90%

Question 10

Classification of tears: Transdiscal tears

Answer 10

> 50 yrs

Question 11

Classification of tears:

Schmorl’s node

Answer 11

20% by 30yrs 30% in older Upper endplate

* some discs is extruding through vertebral endplate.

Question 12

Gross structure cervical intervertebral disc:

Answer 12

• Features reflect the increased mobility in this region
• Uncovertebral clefts
• Disc thickness contributes a higher proportion of vertebral column length in the cervical region than other regions.
• Absence of posterior / lateral AF
• by 10 yrs - uncovertebral joints forming
• 40 yrs - horizontal fissure which is adaptation for mobility - increases IVB = increase mobility of disk movement

Question 13

MRI asymptomatic populations:

Answer 13

10 yr follow-up 81% progressive degenerative changes