Objectives: To determine the short-term effects of a modified Flexion-Distraction (FD) technique in comparison with a high-velocity low-back spinal manipulation (HVLA-SM) protocol on patients suffering from chronic low-back pain (CLBP).

Design and methods: A randomized controlled trial. The sample was composed of 150 patients suffering from CLBP, who were randomly assigned to either a FD (n = 75) or a HVLA-SM (n = 75) group. The variables used to study pain were the scores of the Visual Analogue Scale (VAS) and the Pressure Pain Threshold (PPT) on trigger points (TrPs) of the quadratus lumborum. In addition, the Oswestry Disability Index (ODI) was used to measure disability, and Schober's test and the Finger Floor Distance test (FFDT) to measure changes in low-back spine motion. An Analysis of Covariance (ANCOVA) was used to measure group effect, and Number Needed to Treat (NNT) for effect size.

Results: Greater improvements occurred in the FD group, with a statistically significant group effect (p < 0.001) for all outcome variables. The ETA2 value was larger than 0.100 in the Schober's and FDD tests, larger than 0.200 in the case of ODI and PPT, and larger than 0.300 for VAS. OR = 0.07 [IC 95% = 0.03 to 0.18] and NNT = 2.08 [IC 95% = 1.64-2.84) yielded improved values for the FD group.

Conclusion: For patients suffering from CLBP, greater improvements in pain and function were observed in the group receiving the modified FD treatment than in the HVLA-SM group.