Early pattern of degenerative changes in individual components of intervertebral discs in stressed and nonstressed segments of lumbar spine: An in vivo magnetic resonance imaging study

STUDY DESIGN.: A retrospective imaging review. OBJECTIVE.: To assess differences in burden and pattern of disc degeneration in segments of lumbar spine with and without signs of increased mechanical stresses. SUMMARY OF BACKGROUND DATA.: Young patients with magnetic resonance imaging signs of increased mechanical stress in pedicles or pars interarticularis provide an excellent in vivo model to study early effects of mechanical stresses on lumbar intervertebral discs without the confounding effects of genetics or environmental factors. Detailed in vivo evaluation for early degenerative changes in all individual disc components of stressed intervertebral discs has not been done. METHODS.: Using magnetic resonance imaging, 2 radiologists assessed intervertebral discs around 93 stressed lumbar spinal segments in 87 patients ( 55 males, 32 females; mean age, 15.3 ± 3.3 yr; range, 5-25 yr) as well as lumbar discs in nonstressed segments for signs of degeneration in annulus fibrosus, nucleus pulposus, and endplates. Differences between stressed, control, and loading-matched control discs were assessed using Wilcoxon signed rank sum test. RESULTS.: Burden of annular tears, radial tears, herniations, and nuclear degeneration was significantly higher in stressed discs ( 0.70 ± 0.34, 0.48 ± 0.39, 0.07 ± 0.19, and 0.17± 0.31, respectively) than control ( 0.29 ± 0.25, 0.09 ± 0.17, 0.01 ± 0.04, and 0.02 ± 0.08, respectively) or loading-matched control discs ( 0.44 ± 0.47, 0.16 ± 0.36, 0.01 ± 0.04, and 0.01 ± 0.11, respectively) ( P < 0.01 for all). Stressed segments did not show any significant increase in endplate degeneration. CONCLUSION.: Intervertebral discs in stressed spinal segments show an increased burden of disc degeneration involving annulus fibrosus and nucleus pulposus, but not the endplates.