Study design: 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.
Summary of background data: 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.
Conclusion: 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.