Disc Disease

Age Related Changes in the Intervertebral Disc

• Proteoglycan synthesis decreases with age thus the concentration of proteoglycans will diminish with age from 65% in early adult life to 30% by the age of 60 years
• The proteoglycans that persist are smaller in size and the concentration of chondroitin sulphate falls (keratan sulphate concentrations remain constant)
• This causes a drop in the water content from 88% at birth to 65% by age 75.
• However most of this dehydration occurs in childhood and early adolescence, with a decrease of only 6% from early adult life to old age.
• Collagen content increases in both the nucleus and the annulus but the concentration of elastin falls
• This loss of water and increase in collagen content causes the discs to become stiffer and less resistant to deformation and also less able to recover from creep deformation
• As the nucleus dries out and the becomes more fibrous it is less able to transmit forces to the annulus and the annulus then has to play a greater role in load transmission therefore subjecting it to greater stresses
• Contrary to popular belief the disc height does not decrease with age but stays constant, with any loss of disc height representing a degenerative process as opposed to an age related change

  Discogenic Pain

  • Normal discs have sensory nerve endings in the outer 1/3 of the annulus, so now are known to be a potential source of back pain
  • Disc stimulation studies (using either hypertonic saline or contrast media) have shown that when stimulated, normal discs do not cause pain
  • Disc stimulation is specific for painful discs and is in particular for radial annular tears
  • Reproduction of pain does not correlate with whether or not the disc is degenerated, only with the degree of fissuring of the disc
• Normal discs have sensory nerve endings in the outer 1/3 of the annulus, so now are known to be a potential source of back pain
• Disc stimulation studies (using either hypertonic saline or contrast media) have shown that when stimulated, normal discs do not cause pain
• Disc stimulation is specific for painful discs and is in particular for radial annular tears
• Reproduction of pain does not correlate with whether or not the disc is degenerated, only with the degree of fissuring of the disc