The purpose of this single group, prospective, repeated-measures design with responder analysis was to determine differences in the changes in diffusion of water within the lumbar intervertebral discs between those subjects with low back pain (LBP) who did, and did not, report a within-session reduction in pain intensity following a single treatment of spinal manipulative therapy (SMT). There is a scarcity of research that describes the physiologic events related to analgesia following intervention for people with low back pain. Post-intervention increases in the diffusion of water within various soft tissues of the spine may be 1 of many potential mechanisms linked to pain reduction. Nineteen adults between the ages of 19 and 45 participated in this study. All participants reported LBP of at least 2 on an 11-point (0-10) verbally administered numeric rating scale at the time of enrollment. Participants underwent T2- and diffusion-weighted lumbar magnetic resonance imaging scans immediately before, and after, receiving a single treatment of SMT. Participants who reported a decrease in current pain intensity of more than 2 following treatment were classified as “within-session responders,” while the remainder were classified as “not-within-session responders.” The apparent diffusion coefficient (ADC), representing the diffusion of water in the nucleus pulposis, was calculated from “ADC maps” derived from the mid-sagittal diffusion-weighted images. Two-way repeated measures ANOVAs indicated significant group-by-time interactions. Participants in the within-session responder group (n=12) had a post-intervention increase in ADC at L1-2 (P=.001), L2-3 (P=.002), and L5-S1 (P=.01) when compared to those participants in the not-within-session responder group (n=9). Large effect sizes in ADC between responder groups were observed at L1-2 (d=1.74), L2-3 (d=1.83), and at L5-S1 (d=1.49). No significant group-by-time interactions were observed at the L3-4 and L4-5 levels.
The study found that changes in the diffusion of water within the lumbar intervertebral discs at the L1-2, L2-3, and L5-1 levels seem to be associated with differences in within-session pain reports after a single treatment of spinal manipulative therapy.