1995 Volvo Award in clinical sciences. Determinants of lumbar disc degeneration. A study relating lifetime exposures and magnetic resonance imaging findings in identical twins.
METHODS
Retrospective cohort.


OBJECTIVE
To investigate the effects of lifetime exposure to commonly suspected risk factors on disc degeneration using magnetic resonance imaging, and to estimate the effects of these suspected risk factors relative to age and familial aggregation, reflecting genetic and shared environmental influences.


BACKGROUND
Structural and biochemical changes associated with disc degeneration are suspected as the underlying conditions of many back-related symptoms. Little is known about the determinants of disc degeneration.


METHODS
Based on lifetime discordance in suspected environmental risk factors for disc degeneration, 115 male identical twin pairs were selected. An in-depth interview was conducted of occupational and leisure time physical loading, driving, and smoking. Disc degeneration was evaluated using observational and digital magnetic resonance imaging assessment methods.


RESULTS
Heavier lifetime occupational and leisure physical loading was associated with greater disc degeneration in the upper lumbar levels (P = 0.055 - 0.001), whereas sedentary work was associated with lesser degeneration (P = 0.006). These univariate associations did not reach statistical significance in the lower lumbar region. In multivariate analyses of the upper lumbar levels, the mean job code explained 7% of the variability in observational disc degeneration scores; the addition of age explained 16%, and familial aggregation improved the model such that 77% of the variability was explained. In the lower lumbar levels, leisure time physical loading entered the multivariate model, explaining 2% of the variability. Adding age explained 9%, and familial aggregation raised the variability in disc degeneration scores explained to 43%.


CONCLUSIONS
The present study findings suggest that disc degeneration may be explained primarily by genetic influences and by unidentified factors, which may include complex, unpredictable interactions. The particular environmental factors studied, which have been among those most widely suspected of accelerating disc degeneration, had very modest effects.
Battié
M C
MC
Department of Physical Therapy, University of Alberta, Edmonton, Canada.
Videman
T
T
Gibbons
L E
LE
Fisher
L D
LD
Manninen
H
H
Gill
K
K
D000328:Adult; D000368:Aged; D001363:Awards and Prizes; D015510:Clinical Medicine; D015331:Cohort Studies; D004200:Diseases in Twins / Q000175:diagnosis / Q000209:etiology*; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000473:pathology*; D008161:Lumbosacral Region / Q000473:pathology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D012189:Retrospective Studies; D012307:Risk Factors; D012586:Science; D012815:Signal Processing, Computer-Assisted; D013122:Spinal Diseases / Q000175:diagnosis / Q000209:etiology* / Q000473:pathology; D014430:Twins, Monozygotic