MRI‐based measurement of in vivo disc mechanics in a young population due to flexion, extension, and diurnal loading

Abstract

Background Intervertebral disc degeneration is often implicated in low back pain; however, discs with structural degeneration often do not cause pain. It may be that disc mechanics can provide better diagnosis and identification of the pain source. In cadaveric testing, the degenerated disc has altered mechanics, but in vivo, disc mechanics remain unknown. To measure in vivo disc mechanics, noninvasive methods must be developed to apply and measure physiological deformations. Aim Thus, this study aimed to develop methods to measure disc mechanical function via noninvasive MRI during flexion and extension and after diurnal loading in a young population. This data will serve as baseline disc mechanics to later compare across ages and in patients. Materials & Methods To accomplish this, subjects were imaged in the morning in a reference supine position, in flexion, in extension, and at the end of the day in a supine position. Disc deformations and vertebral motions were used to quantify disc axial strain, changes in wedge angle, and anterior–posterior (A‐P) shear displacement. T 2 weighted MRI was also used to evaluate disc degeneration via Pfirrmann grading and T 2 time. All measures were then tested for effect of sex and disc level. Results We found that flexion and extension caused level‐dependent strains in the anterior and posterior of the disc, changes in wedge angle, and A‐P shear displacements. Flexion had higher magnitude changes overall. Diurnal loading did not cause level‐dependent strains but did cause small level‐dependent changes in wedge angle and A‐P shear displacements. Discussion Correlations between disc degeneration and mechanics were largest in flexion, likely due to the smaller contribution of the facet joints in this condition. Conclusion In summary, this study established methods to measure in vivo disc mechanical function via noninvasive MRI and established a baseline in a young population that may be compared to older subjects and clinical disorders in the future.

Reference Data for Diagnosis of Spondylolisthesis and Disc Space Narrowing Based on NHANES-II X-rays

“…The average disc height reference data were very similar when developed using side-lying versus standing X-rays. Although diurnal changes in disc heights have been documented [57,58], the NHANES-II X-rays were presumably collected without specific control over the daily loading history up to the time of imaging, so it is likely the NHANES-II data represent a wide range of diurnal variation, and thereby account for this variation in the standard deviations. In the analysis of the NHANES-II radiographs, there was an exponential relation between age and the standardized average disc height metric (p < 0.0001, R 2 = 0.12) such that by age 74, the standardized disc height would be expected to be −1.4.…”

The relationship between acceleration during running at optimal speed and changes in the T2 times of the lumbar intervertebral disc

“…Therefore, IVDs may have been more susceptible to anteroposterior loading, and L3/L4 and L4/L5 [22], with greater flexion range of motion positively correlated with the application of optimal intradiscal pressure. In contrast, L5/S1 had greater posterior shear forces due to flexion than the other levels [21]. Shear forces may induce IDD [23, 24], and a negative correlation may be observed between different ranges of trunk motion and applied internal pressure at different IVDs levels.…”

Can axial loading restore in vivo disc geometry, opening pressure, and T2 relaxation time?

“…MRI can provide non‐invasive, serial evaluation of disc structure and T2 relaxation time and disc OP can be evaluated to collectively assess the changes that arise from dissection, sample preparation and applied loading conditions. 22 , 33 , 36 , 37 , 38 , 39 The purpose of this work was to quantify the progressive disc geometry (structure), MRI T2 relaxation time (composition), and nucleus pressure changes (mechanical function) in the intervertebral disc from live to excised bone‐disc‐bone segments . To detect when changes occur, we conducted sequential isolation and reduction processes.…”