From searching five electronic databases up to January 10, 2017, we found 118 eligible reviews for our synthesis. The most frequently described adverse events (AEs) were stroke, headache, and vertebral artery dissection. When appraising the opinions communicated by the reviews, 54 reviews (46%) expressed that SMT is safe, 15 (13%) expressed that SMT is harmful, and 49 reviews (42%) were neutral or unclear. Incidence estimates for SAEs were reported in 13 reviews, and they roughly ranged from 1 in 20,000 to 1 in 250,000,000 manipulations. Overall, the reviews had low methodological quality, with a median of 4 of 11 AMSTAR (A MeaSurement Tool to Assess systematic Reviews) items met (interquartile range, 3 to 6). Reviews meeting the requirements for each of the AMSTAR items (i.e. good internal validity) had a higher chance of expressing that SMT is safe.
Our work showed that it is currently not possible to provide an overall conclusion about the safety of SMT; however, the types of SAEs reported can indeed be significant, sustaining that some risk is present. High quality research and consistent reporting of AEs and SAEs are needed.
For more information on the study, please contact PARKER.Frederiksberg@regionh.dk