A majority of the current evidence on the characterization of adverse events after manual therapies is focused on chiropractic high-velocity thrust techniques.
10 Case series reports indicated that 36 major adverse events from cervical spine manipulation occurred between 1995 and 2001, most commonly arterial dissection leading to stroke.
12 Other events included disk herniation, retinal artery occlusion, epidural hematoma, phrenic nerve paralysis, and death in 2 cases.
12 A systematic review of adverse events from spinal manipulation in the pediatric population reported 9 serious adverse events, consisting of significant neurologic and orthopedic complications and 2 deaths, as well as 2 moderate and 3 mild adverse events.
13 Although larger studies did not identify serious adverse events following manual therapy, the incidence of mild to moderate adverse events is noteworthy. After manual therapy, 60.9% of 465 patients reported at least 1 posttreatment reaction, most commonly headache (19.8%), stiffness (19.5%), local discomfort (15.2%), radiating discomfort (12.1%), and fatigue (12.1%).
14 Most of these reactions began within 4 hours of treatment and generally resolved within 1 day.
14 In another study evaluating patient response of 1058 new patients after 4712 treatments by chiropractors in Norway, 55% of the patients reported at least 1 adverse event after a treatment.
15 Adverse events included local discomfort (53%), headache (12%), tiredness (11%), and radiating discomfort (10%). A majority of the adverse events were reported within 4 hours of the treatment, and almost 75% had resolved within 24 hours.
15 The most recently published randomized controlled trial (RCT) looking at adverse events in manual therapy evaluated chiropractic spinal manipulative therapy for migraineurs.
16 For the 703 interventions applied to 70 participants, the most common adverse events were local tenderness, tiredness, and neck pain. The incidence of adverse events was 21% in the spinal manipulative therapy group and 8% in the placebo group; no serious adverse events were reported.
16 The incidence rate of mild to moderate adverse events was approximately 41% in cohort studies and 22% in RCTs.
10 The lower incidence rate in RCTs was attributed to underreporting because adverse events were not the primary outcome and were often poorly described.