The effectiveness of Sustained Natural Apophyseal Glide on Flexion Rotation Test, pain intensity, and functionality in subjects with Cervicogenic Headache: A Systematic Review of Randomized Trials.

No trial blinded the therapist giving the treatment, only two blinded the assessor and six of the eight did not blind the patients, so how much of the improvement came from expecting to get better is unknown. The authors call this performance bias the biggest risk in their evidence. The review had no registered protocol, so its methods cannot be checked against what was planned in advance. Only published studies in five languages were included and no grey literature was searched, so relevant trials may have been missed. The eight trials were too different to combine, so every conclusion rests on a handful of small studies, the smallest with 23 participants. Three trials did not report how participants were allocated to groups, and four did not report an intention-to-treat analysis. How the technique was performed varied between trials (sitting, standing or lying) and therapist training was often not reported, so it is unclear which version of SNAG was actually tested. One trial is counted as favouring SNAG on the flexion rotation test even though the review's own summary table records its three groups as similar.

The article text supplied contains no funding statement and no conflict-of-interest declaration, so there is nothing to report on who paid for the review or what the authors declared.

Do not read this as SNAG being clearly better than the other hands-on options for cervicogenic headache. Two of the eight trials found the comparison treatment did better, and in three trials SNAG was given together with another treatment, so its own contribution cannot be separated. No trial blinded the therapist delivering it.