Correspondence between bone mineral density and intervertebral disc degeneration across age and sex

Summary

The distribution of bone tissue within the vertebra can modulate vertebral strength independently of average density and may change with age and disc degeneration. Our results show that the age-associated decrease in bone density is spatially non-uniform and associated with disc health, suggesting a mechanistic interplay between disc and vertebra.

Purpose

While the decline of bone mineral density (BMD) in the aging spine is well established, the extent to which age influences BMD distribution within the vertebra is less clear. Measures of regional BMD (rBMD) may improve predictions of vertebral strength and suggest how vertebrae might adapt with intervertebral disc degeneration. Thus, we aimed to assess how rBMD values were associated with age, sex, and disc height loss (DHL).

Methods

We measured rBMD in the L3 vertebra of 377 participants from the Framingham Heart Study (41–83 years, 181 M/196 F). Integral (Int.BMD) and trabecular BMD (Tb.BMD) were measured from QCT images. rBMD ratios (anterior/posterior, superior/mid-transverse, inferior/mid-transverse, and central/outer) were calculated from the centrum. A radiologist assigned a DHL severity score to adjacent intervertebral discs (L2–L3 and L3–L4).

Results

Int.BMD and Tb.BMD were both associated with age, though the decrease across age was greater in women (Int.BMD, ??2.6 mg/cm³ per year; Tb.BMD, ??2.6 mg/cm³ per year) than men (Int.BMD, ??0.5 mg/cm³ per year; Tb.BMD, ??1.2 mg/cm³ per year). The central/outer (??0.027/decade) and superior/mid-transverse (??0.018/decade) rBMD ratios were negatively associated with age, with similar trends in men and women. Higher Int.BMD or Tb.BMD was associated with increased odds of DHL after adjusting for age and sex. Low central/outer ratio and high anterior/poster and superior/mid-transverse ratios were also associated with increased odds of DHL.

Conclusions

Our results indicate that the distribution of bone within the L3 vertebra is different across age, but not between sexes, and is associated with disc degeneration.