Joints, articular cartilage and synovial fluid L4: Intervertebral Discs- Aging, pathology & rehabilitation

Question 1

What are intervertebral discs?

Answer 1

• Between vertebral discs
• Weight bearing
• Undergoes tensile forces
• Nucleus pulposus VS annulus fibrosus

Question 2

What is the annulus fibrosus of an intervertebral disc?

Answer 2

• 10-20 concentric layers
• All fibres in 1 layer = same orientation & opposite
• to adjacent layers
• 65 degree angle to the vertical ( 1/2 to left: 1/2 to right)
• 80% dry weight collagen type I

Question 3

What is the nucleus pulposus of an intervertebral disc?

Answer 3

• Up to 90% water (incompressible)
• Proteoglycans
• Collagen
• 20% dry weight collagen type II
• 50% dry weight proteoglycan

Question 4

What are the 4 zones of the IVD?

Answer 4

1. Outer annulus fibrosus
2. Inner annulus fibrosus
3. > transition zone
4. Nucleus pulposus

Question 5

What is the outer annulus fibrosus zone of IVD made of?

Answer 5

• collagen type 1 lamellae
• fibroblasts

Question 6

What is the inner annulus fibrosus zone of IVD made of?

Answer 6

• collagen type II
• fibroblasts & chondrocytes
• proteoglycans

Question 7

What is the >transition zone of IVD?

Answer 7

• Acellular, thin fibrous layer
• Between AF and NP

Question 8

What is the nucleus pulposus zone of IVD made of?

Answer 8

• collagen type II
• chondrocytes
• proteoglycans

Question 9

What are the 4 roles of IDV in weight-bearing?

Answer 9

1. NP incompressible; Vertical compression of NP (decreases vertical height); Expands radially & exerts pressure on annular fibres
2. Annular fibres resist tension; Exert pressure back onto NP
3. NP &AF share the pressure; Pressure exerted onto vertebral endplates
4. Transmits load to inferior vertebra

Question 10

During ageing or degeneration, which part is affected first? NP or AF

Answer 10

NP 1st AF 2nd

Question 11

What occurs during ageing and degeneration?

Answer 11

• Decline in proteoglycans in the NP
  
  • decreases H2O binding capacity – decreases stiffness
• Change in relative proportions of GAG’s
• Apoptosis
  
  • Pre-programed cell death
• 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 o fibroblasts in CTP = resists tension
  
  • fibroblasts feel compression –> mechanotrasnduction –> change to chondrocytes
• 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 12

What are the 3 classifications of IDV tears?

Answer 12

1. Concentric tears
2. Radiating tears
3. Transdiscal tears

Question 13

What are concentric tears of IVD?

Answer 13

• all age groups
• 75% of anterior AF
• 100% of posterior AF

Question 14

What are radiating tears of IVD?

Answer 14

• 10-30yrs:
• Anterior 47%
• Posterior 68%
• 51-80yrs:
• Anterior 75%
• Posterior 90%
• Centre –> outwards

Question 15

What are transdiscal tears?

Answer 15

> 50 yrs

Question 16

What is Schmorl’s node?

Answer 16

• 20% by 30yrs
• 30% in older
• Upper endplate
• Disc extruding through vertebral end plates into the vertebral

Question 17

What are 3 distinct characteristics of the gross structure of cervical IVD?

Answer 17

1. Features reflect the increased mobility in this region Uncovertebral clefts
2. Disc thickness contributes a higher proportion of vertebral column length in the cervical region than other regions.
3. Absence of posterior / lateral AF