The incidence of severe adverse events after chiropractic spinal manipulative therapy

This study examined the incidence and severity of adverse events (AEs) of patients receiving chiropractic spinal manipulative therapy (SMT), with the hypothesis that < 1 per 100,000 SMT sessions results in a grade ≥ 3 (severe) AE. A secondary objective was to examine independent predictors of grade ≥ 3 AEs.

The researchers retrospectively identified patients with SMT-related AEs from January 2017 through August 2022 across 30 chiropractic clinics in Hong Kong. AE data were extracted from a complaint log, including solicited patient surveys, complaints, and clinician reports, and corroborated by medical records. AEs were independently graded 1–5 based on severity (1-mild, 2-moderate, 3-severe, 4-life-threatening, 5-death).

Among 960,140 SMT sessions for 54,846 patients, 39 AEs were identified, two were grade 3, both of which were rib fractures occurring in women age > 60 with osteoporosis, while none were grade ≥ 4, yielding an incidence of grade ≥ 3 AEs of 0.21 per 100,000 SMT sessions (95% CI 0.00, 0.56 per 100,000). There were no AEs related to stroke or cauda equina syndrome. The sample size was insufficient to identify predictors of grade ≥ 3 AEs using multiple logistic regression.

The authors concluded that, in this study, severe SMT-related AEs were reassuringly very rare.

This is good news for all patients who consult chiropractors. However, there seem to be several problems with this study:

• Data originated from 30 affiliated chiropractic clinics with 38 chiropractors (New York Chiropractic & Physiotherapy Center, EC Healthcare, Hong Kong). These clinics are integrated into a larger healthcare organization, including several medical specialties and imaging and laboratory testing centers that utilize a shared medical records system. The 38 chiropractors represent only a little more than 10% of all chiropractors working in Hanh Kong and are thus not representative of all chiropractors in that region. Is it possible that the participating chiropractors were better trained, more gentle, or more careful than the rest?
• Data regarding AEs was obtained from a detailed complaint log that was routinely aggregated from several sources by a customer service department. One source of AEs in this log was a custom survey administered to patients after their 1st, 2nd, and 16th visits. Additional AEs derived from follow-up phone calls by a personal health manager. This means that not all AE might have been noted. Some patients might not have complained, others might have been too ill to do so. And, of course, dead patients cannot complain. The authors state that “the response to the SMS questionnaire was low. It is possible that severe AEs occurred but were not reported or recorded through these or other methods of ascertainment”.
• The 39 AEs potentially related to chiropractic SMT included increased symptoms related to the patient’s chief complaint (n = 28), chest pain without a fracture on imaging (n = 4), jaw pain (n = 3), rib fracture confirmed by imaging (n = 2), headache and dizziness without evidence of stroke (n = 1), and new radicular symptoms (n = 1). Of the 39 AEs, grade 2 were most common (n = 32, 82%), followed by grade 1 (n = 5, 13%), and grade 3 (n = 2, 5%). There were no cases of stroke, transient ischemic attack (TIA), vertebral or carotid artery dissection, cauda equina syndrome, or spinal fracture. Yet, headache and dizziness could be signs of a TIA.
• Calculating the rate of AEs per SMT session might be misleading and of questionable value. Are incidence rates of AEs not usually expressed as AE/patient? In this case, the % rate would be almost 20 times higher.

Altogether, this is a laudable effort to generate evidence for the risks of SMT. The findings seem reassuring but sadly they are not fully convincing.