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The within-session change in low back pain intensity following spinal manipulative therapy is related to differences in diffusion of water in the intervertebral discs of the upper lumbar spine and L5-S1.

STUDY DESIGN
Single-group, prospective, repeated-measures design with responder analysis.


OBJECTIVE
To determine differences in the changes in diffusion of water within the lumbar intervertebral discs between participants with low back pain who reported a within-session reduction in pain intensity following a single treatment of spinal manipulative therapy and those who did not.


BACKGROUND
There is a paucity of research that describes the physiologic events associated with analgesia following intervention for low back pain. Postintervention increases in the diffusion of water within various soft tissues of the spine may be one of many potential mechanisms linked to pain reduction.


METHODS
Nineteen adults between 20 and 45 years of age participated in this study. All participants reported low back pain of at least 2 on an 11-point (0-10) verbally administered numeric pain 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 spinal manipulative therapy. Individuals who reported a decrease in current pain intensity of more than 2 following treatment were classified as "within-session responders," and the remainder were classified as "not-within-session responders." The apparent diffusion coefficient (ADC), representing the diffusion of water in the nucleus pulposus, was calculated from ADC maps derived from the midsagittal diffusion-weighted images.


RESULTS
Two-way, repeated-measures analyses of variance indicated significant group-by-time interactions. Participants in the within-session-responder group (n = 12) had a postintervention increase in ADC at L1-2 (P = .001), L2-3 (P = .002), and L5-S1 (P = .01) compared to those in the not-within-session-responder group (n = 7). Large effect sizes in ADC between responder groups were observed at L1-2 (d = 1.74), L2-3 (d = 1.83), and L5-S1 (d = 1.49). No significant group-by-time interactions were observed at the L3-4 and L4-5 levels.


CONCLUSION
Changes in the diffusion of water within the lumbar intervertebral discs at the L1-2, L2-3, and L5-S1 levels appear to be related to differences in within-session pain reports following a single treatment of spinal manipulative therapy.