Study design: Blinded parallel-group randomized controlled trial.
Objective: Establish the frequency and severity of adverse effects from short-term usual chiropractic treatment of the spine when compared with a sham treatment group.
Summary of background data: Previous studies have demonstrated that adverse events occur during chiropractic treatment. However, as a result of design limitations in previous studies, particularly the lack of sham-controlled randomized trials, understanding of these adverse events and their relation with chiropractic treatment is suboptimal.
Methods: We conducted a trial to examine the occurrence of adverse events resulting from chiropractic treatment. It was conducted across 12 chiropractic clinics in Perth, Western Australia. The participants comprised 183 adults, aged 20 to 85 years, with spinal pain. Ninety-two participants received individualized care consistent with the chiropractors' usual treatment approach; 91 participants received a sham intervention. Each participant received 2 treatments.
Results: Completed adverse questionnaires were returned by 94.5% of the participants after appointment 1 and 91.3% after appointment 2. Thirty-three percent of the sham group and 42% of the usual care group reported at least 1 adverse event. Common adverse events were increased pain (sham 29%; usual care 36%), muscle stiffness (sham 29%; usual care 37%), and headache (sham 17%; usual care 9%). The relative risk (RR) was not significant for adverse event occurrence (RR = 1.24; 95% CI: 0.85-1.81), occurrence of severe adverse events (RR = 1.9; 95% CI: 0.98-3.99), adverse event onset (RR = 0.16; 95% CI: 0.02-1.34), or adverse event duration (RR = 1.13; 95% CI: 0.59-2.18). No serious adverse events were reported.
Conclusion: A substantial proportion of adverse events after chiropractic treatment may result from natural history variation and nonspecific effects.
Level of evidence: 2.