There have been no full-scale trials of the optimal number of visits for the care of any condition with spinal manipulation.
To identify the dose-response relationship between visits to a chiropractor for spinal manipulation and chronic low back pain (cLBP) outcomes; to determine the efficacy of manipulation by comparison to a light-massage control.
Practice-based randomized controlled trial.
Four hundred participants with cLBP.
The primary cLBP outcomes were the100-point Modified Von Korff pain intensity and functional disability scales evaluated at the 12 and 24-week primary endpoints. Secondary outcomes included days with pain and functional disability, pain unpleasantness, global perceived improvement, medication use, and general health status.
One hundred participants with cLBP were randomized to each of four dose levels of care: 0, 6, 12, or 18 sessions of spinal manipulation from a chiropractor. Participants were treated three times per week for six weeks. At sessions when manipulation was not assigned, they received a focused light massage control. Covariate-adjusted linear dose effects and comparisons to the no-manipulation control group were evaluated at 6, 12, 18, 24, 39, and 52 weeks.
For the primary outcomes, mean pain and disability improvement in the manipulation groups was 20 points by 12 weeks and sustainable to 52 weeks. Linear dose-response effects were small, reaching about two points per six manipulation sessions at 12 and 52 weeks for both variables (P < .025). At 12 weeks, the greatest differences from the no-manipulation control were found for 12 sessions (8.6 pain and 7.6 disability points, P < .025); at 24 weeks, differences were negligible. At 52 weeks, the greatest group differences were seen for 18 visits (5.9 pain and 8.8 disability points, P < .025).
The number of spinal manipulation visits had modest effects on cLBP outcomes above those of 18 hands-on visits to a chiropractor. Overall, 12 visits yielded the most favorable results, but was not well distinguished from other dose levels.