Statistical shape modeling of MRI-based morphological response of lumbar intervertebral discs to a unilateral side...

The acute response of lumbar intervertebral discs (IVD) to spinal rotation mobilization (SRM) is poorly understood. We evaluated sustained morphological changes in lumbar IVDs following a rotation mobilization commonly used to relieve discogenic pain.

In this cross-sectional study, five asymptomatic participants underwent MRI of the lumbar spine before and after 2 min of sustained passive unilateral SRM. Pre-SRM acquisition was completed twice, repositioning between acquisitions to assess test-retest reliability. Five lumbar IVDs per participant were segmented independently by two raters, and compared between timepoints using Dice similarity coefficients (DSC). We used statistical shape modeling (SSM) to assess magnitude and direction of shape changes as defined by principal component analysis (PCA). Primary analysis evaluated the PCA scores from the SSM models of all IVDs; secondary analysis assessed each IVD individually.

Significant changes were observed in IVD shape following SRM (p < 0.001), represented by significant differences in PCA scores following SRM for two modes (Mode 4 PCA score difference: -2.60 [95%CI: -4.79; -0.41]; Mode 7: -1.51 ([-2.65; -0.37]), demonstrating anterolateral IVD expansion ipsilateral to rotation direction. Similar results were observed in the secondary analyses for mode 3 of the L1-L2 IVD (-6.28 [-11.03; -1.51], p = 0.01) and mode 4 of the L2-L3 IVD (-4.08 [-8.13; -0.04], p = 0.02), with no significant changes in more caudal IVDs. Reliability within and between raters and timepoints was excellent (mean DSC >0.9).

SRM induces measurable, direction-specific changes in healthy IVDs. Future research should evaluate symptomatic IVDs, examining relationships between morphology, symptoms, and therapeutic parameters.