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Lumbar Discs Increase In Height and Volume with Aging

Increasing subject age was associated with increased lumbar disc height and increased lumbar disc volume at segment levels not effected by degenerative disc changes in a study by Pfirrmann et al. involving volunteers free of back pain.  Non-symptomatic degenerative lumbar discs exhibited a reduced disc height, reduced disc volume, and less disc convexity.  There was a stronger association between degeneration and decreased disc heights in older subjects as opposed to younger subjects. 


In an effort to define normal physiologic lumbar disc characteristics relative to the aging process (that may include painless disc degeneration), 70 asymptomatic individuals were recruited with 10 each from the 2nd to 8th decade of age.  Each subject underwent a lumbar spine MRI examination.  Disc height was measured following the Dabbs method and Farfan index.  Disc volume was determined through the point counting Cavalieri method.  Disc convexity was calculated as the ratio between central disc height and anterior/posterior mean disc height.


Midsagittal MR images were evaluated as to signal intensity and loss of annulus/nucleus distinction in order to classify the disc as normal or mildly, moderately, or severely degenerated.  Of the 350 discs assessed, 50.0% were normal while 26.6%, 19.1%, and 4.3% exhibited mild, moderate, and severe disc degeneration, respectively. 


The study also looked at the relationship between other independent variables and disc height, disc volume, and disc convexity.  Disc level showed a correlation with disc height (L5-S1 was generally higher than L1-2) and disc convexity (lower lumbar discs were less convex than upper lumbar disc) but no relationship to disc volume.  Subject weight and gender had no association with disc height or volume.  Subject height was positively related to disc volume but showed no impact on disc height.    


Osteoporosis may have been an unevaluated confounder in this study according to the authors.  If a vertebral end plate is weaken from decreased bone density and subject to pressure from an adjacent disc, the end plate may become concave causing a change in the disc shape.  A bone density measurement would allow for this variable to be assessed.



Article Title: Effect of Aging and Degeneration of Disc Volume and Shape: A Quantitative Study in Asymptomatic Volunteers


Publication: Journal of Orthopedic Research 24: 1086-1094, 2006


Authors: C W A Pfirrmann, A Metzdorf, A Elfering, J Hodler, and N Boos

This article originally appeared in The Ergonomics Report™ on 2006-08-16.