title: Progression and determinants of quantitative magnetic resonance imaging measures of lumbar disc degeneration: a five-year follow-up of adult male monozygotic twins.
abstract: METHODS
  A longitudinal study.
  
  
  OBJECTIVE
  Our goal was to explore the role of digital magnetic resonance imaging (MRI) data, by extending our earlier 5-year follow-up study of progression of lumbar spine degeneration with quantitative measures of disc degeneration.
  
  
  BACKGROUND
  A longitudinal study is optimal for investigating disc degeneration but only a few studies (with small sample sizes) or short follow-up studies include repeated MRI data.
  
  
  METHODS
  Subjects consisted of 134 male monozygotic twins (age 35-69 years). Quantitative MRI measures included changes in disc bulging and height. Inter-rater reliability coefficients were between 0.77 and 0.96. At baseline and follow-up, an extensive interview about exposures to suspected determinants was conducted.
  
  
  RESULTS
  Reduction in disc height and increases in bulges (worsening) were seen in 2/3 of subjects. The mean reduction in disc height was 2.2% to 3.6%. A mean increase in bulging of 7% to 10% was found in the L1-L4 discs and 4% in L4-S1 discs. Although the mean changes were small, few reverse changes were observed. Familial aggregation, a proxy for genetic influences, explained 17% of changes in disc height, and 11% and 0% of changes in the sizes of anterior and posterior bulges in the regression models. Higher maximal occupational lifting (AR2 = 4.9%) and smoking (AR2 = 3.5%) during follow-up predicted more disc height reduction. Greater increases in bulging (AR2 = 7.4%-10.2%) were predicted by smaller bulges at baseline.
  
  
  CONCLUSIONS
  The mean annual changes in disc heights (<1%) and bulges (<2%) were small, and included both decreases and increases, with only a few subjects showing more major changes in either direction. The role of genetics was largest except in posterior bulges, but lifting and smoking were also associated with disc height reduction but none of the other studied risk factors were associated with anterior or posterior disc bulging. Different degenerative findings have different determinants of progression.
authors.affiliation: Faculty of Rehabilitation Medicine, University of Alberta, Alberta, Canada. tapio.videman@ualberta.ca
authors.forename: Tapio
authors.initials: T
authors.lastname: Videman
authors.forename: Michele C
authors.initials: MC
authors.lastname: Battié
authors.forename: Eric
authors.initials: E
authors.lastname: Parent
authors.forename: Laura E
authors.initials: LE
authors.lastname: Gibbons
authors.forename: Pauli
authors.initials: P
authors.lastname: Vainio
authors.forename: Jaakko
authors.initials: J
authors.lastname: Kaprio
mesh_terms: D000328:Adult; D000368:Aged; D018450:Disease Progression; D005387:Finland; D005500:Follow-Up Studies; D020022:Genetic Predisposition to Disease; D006801:Humans; D007403:Intervertebral Disc / Q000473:pathology*; D017770:Lifting; D008159:Lumbar Vertebrae / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D012107:Research Design; D012307:Risk Factors; D012815:Signal Processing, Computer-Assisted; D012907:Smoking / Q000009:adverse effects; D013122:Spinal Diseases / Q000209:etiology* / Q000235:genetics / Q000473:pathology*; D013997:Time Factors; D014430:Twins, Monozygotic