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Anatomy
  • Function
    • allows spinal motion and provides stability
    • links adjacent vertebral bodies together
    • responsible for 25% of spinal column height
  • Composition 
    • annulus fibrosus
      • outer structure that encases the nucleus pulposus
      • composed of type I collagen that is obliquely orientedwater, and proteoglycans
      • characterized by high tensile strength and its ability to prevent intervertebral distraction
      • remains flexible enough to allow for motion
      • high collagen / low proteoglycan ratio (low % dry weight of proteoglycans) 
      • fibroblast-like cells
        • responsible for producing type I collagen and proteoglycans
    • nucleus pulposus
      • central portion of the intervertebral disc that is surrounded by the annulus fibrosis
      • composed of type II collagen, water, and proteoglycans
        • approximately 88% water
      • hydrophilic matrix is responsible for height of the intervertebral disc
      • characterized by compressibility
        • a hydrated gel due to high polysaccharide content and high water content (88%)
          • proteoglycans interact with water and resist compression
            • Aggrecan is a proteoglycan primarily responsible for maintaining water content of the disc 
        • viscoelastic matrix distributes the forces smoothly to the annulus and the end plates
      • low collagen / high proteoglycan ratio (high % dry weight of proteoglycans)  
      • chondrocyte-like cells
        • responsible for producing type II collagen and proteoglycans
        • survive in hypoxic conditions
  • Blood Supply  
    • the disk is avascular with capillaries terminating at the end plates
    • nutrition reaches nucleus pulposus through diffusion through pores in the endplates 
      • annulus is not porous enough to allow diffusion 
  • Innervation
    • the dorsal root ganglion gives rise to the sinuvertebral nerve which innervates the superficial fibers of annulus
      • no nerve fibers extend beyond the superficial fibers
    • neuropeptides thought to participate in sensory transmission include
      • substance P
      • calcitonin
      • VIP
      • CPON
  • Fixation
    • attached to vertebral bodies by hyaline cartilage
Disc Biomechanics
  • Disc
    • viscoelastic characteristics
      • demonstrates creep which allows for deformity over time
      • demonstrates hysteresis which allows for energy absorption with repetitive axial compression
        • this property decreases with time
  • Stresses
    • annulus fibrosus
      • highest tensile stresses
    • nucleus pulposus
      • highest compressive stress
    • intradiscal pressure is position dependent
      • pressure is lowest when lying supine
      • pressure is intermediate when standing
      • pressure is highest when sitting and flexed forward with weights in the hands
      • when carrying weight, the closer the object is to the body the lower the pressure
  • Stability
    • following subtotal discectomy, extension is most stable loading mode
Pathoanatomy
  • Disc Herniation
    • herniated disks are associated with a spontaneous increase in the production of 
      • osteoprotegrin (OPG)
      • interleukin-1 beta
      • receptor activator of nuclear factor-kB ligand (RANKL)
      • parathyroid hormone (PTH)
  • Disc aging leads to an overall loss of water content and conversion to fibrocartilage. Specifically there is a 
    • decrease in 
      • nutritional transport 
      • water content
      • absolute number of viable cells
      • proteoglycans
      • pH
    • increase in
      • an increase keratin sulfate to chondroitin sulfate ratio 
      • lactate
      • degradative enzyme activity
      • density of fibroblast-like cells 
        • fibroblast-like cells reside in the annulus fibrosus only
    • no change in
      • absolute quantity of collagen
 

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(OBQ06.268) Recent studies have shown that cells of the intervertebral discs are biologically responsive and increase their production of matrix metalloproteinases, nitric oxide, interleukin-6, and prostaglandin E2 when stimulated by what molecule Review Topic

QID: 279
1

osteoprotegerin (OPG)

6%

(112/2024)

2

interleukin-1 beta

51%

(1039/2024)

3

transforming growth factor-beta

31%

(629/2024)

4

receptor activator of nuclear factor-kB ligand (RANKL)

9%

(174/2024)

5

parathyroid hormone (PTH)

3%

(58/2024)

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

(SBQ12SP.13) A 37-year-old male feels a "pop" in his low back while lifting a heavy object. Four weeks later he continues to have significant low back pain, with no complaints of symptoms in his leg. A T2-weighted MRI is shown in Figure A with a red arrow identifying abnormal signal intensity in an anatomic structure. What type of collagen is primarily responsible for the biological properties of this anatomic structure?
Review Topic

QID: 3711
FIGURES:
1

Type I

67%

(2645/3958)

2

Type II

28%

(1128/3958)

3

Type V

2%

(60/3958)

4

Type IX

2%

(95/3958)

5

Type XI

0%

(15/3958)

Select Answer to see Preferred Response

PREFERRED RESPONSE 1

(OBQ12.87) Which of the following are progressive changes seen with aging of the intervertebral disc? Review Topic

QID: 4447
1

Increase in water content

7%

(269/3878)

2

Increase in large aggregated proteoglycans

12%

(467/3878)

3

An increased keratan sulfate to chondroitin sulfate ratio

77%

(3000/3878)

4

A decrease in degradative enzyme activity

3%

(102/3878)

5

An increase in nutritional transport

1%

(21/3878)

Select Answer to see Preferred Response

PREFERRED RESPONSE 3

(OBQ12.45) Which of the following statements is true with regard to the aging process of the intervertebral disc along the endplate? Review Topic

QID: 4405
1

Water content increases with age

11%

(395/3737)

2

Proteoglycans increase with age

16%

(614/3737)

3

Degradative enzyme activity decreases with age

11%

(394/3737)

4

pH increase with age

18%

(661/3737)

5

There is a conversion to fibrocartilage

44%

(1657/3737)

Select Answer to see Preferred Response

PREFERRED RESPONSE 5

(OBQ06.271) Which of the following processes is involved in age-related intervertebral disc degeneration? Review Topic

QID: 282
1

increased cell number in the nucleus pulposus

3%

(36/1119)

2

increased matrix synthesis

2%

(26/1119)

3

increased disc height

1%

(15/1119)

4

increased degradative enzyme activity

85%

(955/1119)

5

increased chondrotin sulfate

8%

(85/1119)

Select Answer to see Preferred Response

PREFERRED RESPONSE 4
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Topic COMMENTS (3)
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