Associations between Patient Report of Pain and Intervertebral Foramina Changes Visible on Axial-Loaded Lumbar Magnetic Resonance Imaging

Abstract

The intervertebral foramen may influence spinal nerve roots and, therefore, be related to the corresponding dermatomal pain. In vivo evaluation of the intervertebral foramen-dermatome relationship is essential for understanding low back pain (LBP) pathophysiology. The study aimed to correlate the lumbar MRI unloaded-loaded foraminal area changes with dermatomal pain in the patient's pain drawings. Dynamic changes of the dermatomal pain distribution related to the intervertebral foramen area changes between quantitative conventional supine MRI (unloaded MRI) and axial-loading MRI (alMRI) were analyzed. The MRI axial-loading intervertebral foramen area changes were observed, and the most significant effect of reducing the foraminal area (-6.9%) was reported at levels of L2-L3. The incidence of pain in the dermatomes increases linearly with the spine level, from 15.6% at L1 to 63.3% at L5 on the right and from 18.9% at L1 to 76.7% at L5 on the left. No statistically significant effect of changes in the intervertebral foramen area on the odds of pain along the respective dermatomes was confirmed. Changes in the foraminal area were observed between the unloaded and loaded phases, but differences in area changes between foramen assigned to painful dermatomes and foramen assigned to non-painful dermatomes were not significant.

Keywords: axial loading; dermatome; foramen area; in vivo; low back pain; lumbar intervertebral foramen; lumbar spine; magnetic resonance imaging; stenosis.

Figure 1

A patient on the MRI scanner with the compression device (DynaWell). A harness is attached with straps to a footplate, applying an axially directed load.

Figure 2

Image analysis. The sagittal cross-section area of the vertebral foramen without axial loading (A) and after axial loading (B).

Figure 3

Cumulative pain distribution based on patient perception of pain within L1–L5 dermatomes in a final group of 90 patients.

Figure 4

Error bar plot of the loaded-unloaded changes in the intervertebral foramen area at each vertebral level on the right side (top) and the left side (bottom). Circles represent mean values of the percentage changes in the area of the intervertebral foramen, and the vertical line segments indicate a 95% confidence interval.

Figure 5

Sagittal magnetic resonance cross-section through the L2–L3 foramen. (A) Unloaded MRI shows normal relationships between the foramen and surrounding structures with no perineural fat obliteration nor root morphological changes; (B) axial-loaded MRI shows perineural fat obliteration surrounding the nerve root in the transverse direction (arrow); changes in the area of the intervertebral foramen at L2–L3 seen without (C) and with (D) axial loading.

Figure 6

Sagittal magnetic resonance cross-section through the L5–S1 foramen. (A) Unloaded MRI shows perineural fat obliteration surrounding the nerve root in the transverse direction and root morphologic change (arrow). (B) Axial-loaded MRI shows normal relationships between foramen and surrounding structures with no perineural fat obliteration nor root morphologic changes. (C) The image shows the intervertebral foramen area at L5–S1 without axial loading. (D) The image presents the L5–S1 intervertebral foramen area with axial loading.

Figure 6

Sagittal magnetic resonance cross-section through the L5–S1 foramen. (A) Unloaded MRI shows perineural fat obliteration surrounding the nerve root in the transverse direction and root morphologic change (arrow). (B) Axial-loaded MRI shows normal relationships between foramen and surrounding structures with no perineural fat obliteration nor root morphologic changes. (C) The image shows the intervertebral foramen area at L5–S1 without axial loading. (D) The image presents the L5–S1 intervertebral foramen area with axial loading.