To carry out a systematic review of the literature examining the effectiveness of spinal manipulation for the treatment of headache disorders, computerized literature searches were carried out in Medline, Embase, Amed and CISCOM. Studies were included only if they were randomized trials of (any type of) spinal manipulation for (any type of) headache in human patients in which spinal manipulation was compared either to no treatment, usual medical care, a ‘sham’ intervention, or to some other active treatment. Two investigators independently extracted data on study design, sample size and characteristics, type of intervention, type of control/comparison, direction and nature of the outcome(s). Methodological quality of the trials was also assessed using the Jadad scale. Eight trials were identified that met our inclusion criteria. Three examined tension-type headaches, three migraine, one ‘cervicogenic’ headache, and one ‘spondylogenic’ chronic headache. In two studies, patients receiving spinal manipulation showed comparable improvements in migraine and tension headaches compared to drug treatment. In the 4 studies employing some ‘sham’ interventions (e.g. laser light therapy), results were less conclusive with 2 studies showing a benefit for manipulation and 2 studies failing to find such an effect. Considerable methodological limitations were observed in most trials, the principal one being inadequate control for nonspecific (placebo) effects. Despite claims that spinal manipulation is an effective treatment for headache, the data available to date do not support such definitive conclusions. It is unclear to what extent the observed treatment effects can be explained by manipulation or by nonspecific factors (e.g. of personal attention, patient expectation). Whether manipulation produces any long-term changes in these conditions is also uncertain. Future studies should address these two crucial questions and overcome the methodological limitations of previous trials.
