8 biomechanics of vertebral column effects of aging


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8 biomechanics of vertebral column effects of aging

  1. 1. 8.Biomechanics ofVertebral Column: Effects of AgingDr. D. N. BidSarvajanik College of Physiotherapy,Rampura, Surat – 395003.
  2. 2. Age-Related Changes• Over the life span, the vertebral column isexposed to recurrent loads that change themorphology of the column.• However, normal age-related changes also occurin the structures of the vertebral column.• The vertebral bone undergoes changes in theamount and form of the trabeculae.6/14/2013 dnbid71@gmail.com 2
  3. 3. • The numbers of both horizontal and verticaltrabeculae decrease with age, and thehorizontal trabeculae become significantlythinner.• This loss can decrease the loads that thevertebrae are able to withstand before failure.6/14/2013 dnbid71@gmail.com 3
  4. 4. • Each of the structures of the intervertebral disk undergochanges that include loss of the amount of proteoglycansand change in the specific type of proteoglycan, withresultant loss of water content.• In addition, there is an increase of collagen in thesestructures and loss of elastin.• This results in a loss of the ability for the disk to transferloads from one vertebra to another as the swelling abilityof the nucleus decreases.• The overall disk height will also decrease somewhat.6/14/2013 dnbid71@gmail.com 4
  5. 5. • The vascularization of the disk also changes. In utero, bloodvessels can be demonstrated within the fibers of the anulusfibrosus.• By the end of the second year of life, these havepredominantly degenerated.• Thus, the disk relies on the diffusion of nutrients throughthe vertebral end plate.• The vertebral end plate, with aging, gradually becomesmore collagenous, and the process of diffusion is hindered.6/14/2013 dnbid71@gmail.com 5
  6. 6. • The fibers of the anulus fibrosus in the cervical spine ofadults normally demonstrate lateral fissures that subdividethe disk into two halves at the uncovertebral joints.• These fissures can first be observed in children atapproximately 9 years of age.• After formation of these fissures, joint pseudocapsulesdevelop with vascularized synovial folds.• The formation of these fissures appears to be load-relatedand is located predominantly in the regions of C3 to C5.6/14/2013 dnbid71@gmail.com 6
  7. 7. • With large and/or repetitive loads, further changesoccur in the disks.• The disks demonstrate a dramatic decrease in theirelasticity and proteoglycans.• Eventually, the intervertebral disk will become so drythat it begins to crumble.• In the lumbar region, the inner layers of the anulusfibrosus begin to buckle outward, and the lamellaeseparate.6/14/2013 dnbid71@gmail.com 7
  8. 8. • Fissures and tears can occur within the anular fibers,which can decrease the ability of the disk to providestiffness during movement.• The vertebral end plates may become ossified.• The adjacent spongy bone of the vertebral body canbegin to sclerose.• On occasion, blood vessels grow into the disks andtrigger ossification.6/14/2013 dnbid71@gmail.com 8
  9. 9. • The disk can prolapse or protrude as a result of thepressure of the nucleus and the lack of ability of the anulusfibrosus to sustain it.• Schmorl’s nodes are formed when the nuclear materialprolapses through the vertebral end plate and into thecancellous bone of the vertebra.• This material may cause an autoimmune response when itcomes in contact with the blood supply in the cancellousbone.• This is typically labeled degenerative disk disease.6/14/2013 dnbid71@gmail.com 9
  10. 10. • In this case of degenerative disk disease, there is a moresubstantial loss of disk height, which causes all ligaments tobe placed on slack.• The ligamentous prestress normally provided by theligamentum flavum will decrease, which in turn will impairspinal stiffness.• This can also allow the ligament to buckle on itself withmovement, potentially compressing the spinal cord.• In addition, the ligamentum flavum begins to calcify withage, and this occasionally leads to ossification, which canalso potentially cause compression of the spinal nerve inthe vicinity of the zygapophyseal joints or the spinal cordwithin the canal.6/14/2013 dnbid71@gmail.com 10
  11. 11. • The zygapophyseal joints can also demonstrate age relatedchanges and eventual degeneration.• Some authors have argued that these changes in thezygapophyseal joints must be secondary to diskdegeneration, as a substantial amount of weight-bearingthrough these joints must occur to cause deterioration.• This increase in weight-bearing may be due to the loss ofdisk height. However, this is not always the case.• There have been descriptions of degenerativezygapophyseal joints without disk degeneration.6/14/2013 dnbid71@gmail.com 11
  12. 12. • The mechanism of this is not as well understood. If,however, the disks degenerate and a substantivedecrease in height occurs, what follows ishypermobility as a result of slackened capsules andlongitudinal ligaments.• The vertebra may also slip forward or backward on thevertebra below (listhesis or retrolisthesis).• There will be excessive shear forces generated, and thezygapophyseal joints will also become subject to moreload-bearing.6/14/2013 dnbid71@gmail.com 12
  13. 13. • The result of these changes becomes the same aswith what happens to the larger joints of theextremities: damage of the cartilage, includingfissures and cysts, and osteophyte formation.• These changes can lead to localized pain orpressure on spinal nerves or the central canal or,in the cervical region, compression of thevertebral artery in the transverse foramen.6/14/2013 dnbid71@gmail.com 13
  14. 14. • The joints of Luschka, or uncovertebral joints, arefrequent sites for age-related and degenerativechanges.• Osteophytes on the uncinate processes occurpredominantly in the lower segments C5/C6 orC6/C7.• The motion of lateral bending becomes extremelylimited when these osteophytes occur.6/14/2013 dnbid71@gmail.com 14
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  16. 16. Summary• In summary, it is extremely important to understand thenormal structure and function, including normal variability,of the vertebral column in order to understand thestructures at risk for injury and the best ways to treatpeople with dysfunction.• Injury or failure occurs when the applied load exceeds thestrength of a particular tissue.• Repetitive strain causes injury by either the repeatedapplication of a relatively low load or by application of asustained load for a long duration (prolonged sitting orstooped posture).6/14/2013 dnbid71@gmail.com 16
  17. 17. • The effects of an injury, aging, disease, ordevelopment deficit on the vertebral column maybe analyzed by taking the following points intoconsideration:– 1. the normal function that the affected structure isdesigned to serve– 2. the stresses that are present during normalsituations– 3. the anatomic relationship of the structure toadjacent structures– 4. the functional relationship of the structure to otherstructures6/14/2013 dnbid71@gmail.com 17
  18. 18. Thank you……..,,,End of Part - 86/14/2013 dnbid71@gmail.com 18