Age- and Pathology-Specific Measures of Disc Degeneration

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Abstract

Study Design.

A measurement study.

Objective.

To develop more accurate and specific measures of disc degeneration, which could better capture and distinguish systemic effects of aging and isolated disc irregularities using routine magnetic resonance imaging (MRI) and to examine their construct validity.

Summary of Background Data.

Knowledge of the etiopathogenesis of disc degeneration and pathology is fundamental to advancements in common spinal disorders. The quality of measures of disc degeneration is currently limited progress in this area.

Methods.

Subjects were 519 twins, 35 to 70 years old, from a population-based cohort. Lumbar structures were traced and image software measured selected disc areas and T2 signal parameters of sagittal and axial images of lumbar spine with 1.5 Tesla MRI scanners. All signal measures were adjusted by adjacent cerebrospinal fluid signal. The mean adjusted disc signal, its standard deviation, and an irregularity measure were used to estimate the overall desiccation stage and signal variation across the disc. Associations with risk factors were examined to support or refute measurement validity.

Results.

The signal-based measures introduced were highly reproducible (inter-rater reliability ICC = 0.95–1.00). Age explained more of the signal-based disc measures (AR2 = 16%–32%) than did the qualitative measures of disc degeneration in common use (AR2 = 3%–8%) in L1–L4 discs, supporting the validity of the new measures. The signal-based measures were also more highly associated with physical loading and familial aggregation, further supporting their validity. Age and physical loading had higher associations with the sagittal than the axial measures and with upper rather than lower lumbar discs. Adjustment of signal-based measures by cerebrospinal fluid is critical and increased the associations between age and the measures by 2- to 10-fold.

Conclusion.

The new signal-based measures show promise in their potential to better capture and perhaps distinguish aspects of disc degeneration than current assessment methods using standard MRI. Their use may enhance research on potential determinants of disc degeneration.

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