A Review of the Largest Studies Published on the Topic Including the Years 2022 and 2023
Everyone will eventually die. Nearly everyone will have an ongoing relationship with a healthcare provider. Many will be actively under the care of a healthcare provider for their illness at the moment of their passing.
As a rule, healthcare providers are not judged solely by the clinical outcome of their patients. This is because, despite the healthcare provider’s best efforts, a patient’s clinical status may worsen.
Consequently, healthcare providers are often judged by an elusive concept called standard of care.
Standard of Care
The standard of care is unique and specific to each healthcare discipline. As an example, the standard of care is different for a medical doctor vs. a chiropractor vs. an acupuncturist vs. a physical therapist, etc. Also, the standard of care is often different for various specialties within a profession. As an example, an emergency room physician vs. a dermatologist vs. a rheumatologist. Yet, they are all medical doctors.
Licensing boards and other jurisdictions evaluate licensed healthcare professionals based upon that profession’s or discipline’s standard of care. Sometimes these standards are written, reducing ambiguity. Other times these standards are less clear.
Often, in a broad sense, the standard of care will be legally defined by the state. Therefore, the precise language will vary somewhat state to state. As a general concept, healthcare providers are expected to perform in a manner consistent with the behavior of other members of their discipline who are of ordinary learning, judgement, and skill, with respects as to what would or would not be done under the same or similar circumstances.
Often, the standard of care will include a concept called informed consent. Informed consent is the informing of perspective patients about potential problems associated with proposed treatments and receiving the patient’s consent before delivering those treatments. In some jurisdictions, informed consent is oral, and the patient is told (informed) about risks of proposed procedures. In some jurisdictions, informed consent is written. Sometimes it is both oral and written.
What Should Be Included in Informed Consent for Chiropractors?
There is no universal consensus as to what should be included in a chiropractic informed consent. In very general terms, most agree that informed consent should include issues that are statistically common and/or uncommon but are potentially serious. A typical list of topics in a chiropractic informed consent might include:
- Vascular injury and stroke.
- Intervertebral disc injury, and/or disc herniations.
- Nerve injury, including irritations, inflammation, compression.
- Spinal cord injury, including irritations, inflammation, compression.
- Cauda Equina Syndrome.
- Soft tissues injuries, primarily sprains and strains.
- Rib and/or other fractures.
How Safe Is Chiropractic Care and Spinal Manipulation?
Recent epidemiological studies have looked at large numbers of chiropractic patients in an effort to identify and quantify potential harms from chiropractic care and spinal manipulation. Several of these studies are reviewed below, including two very large epidemiological studies that were published this year, 2023.
In 2001, a study was published in the Canadian Medical Association Journal and titled (1):
Arterial Dissections Following Cervical Manipulation: The Chiropractic Experience
The lead author, Scott Haldeman, is a historic and contemporary giant in the chiropractic profession. His list of accomplishments includes a chiropractic degree (DC), a medical degree (MD), a PhD, and a DSc. Dr. Haldeman is a clinical professor of neurology at the University of California, Irvine.
The authors of this study reviewed all malpractice data from the Canadian Chiropractic Protective Association to evaluate all claims of stroke following chiropractic care over a 10-year period of time. This data was compared with the number of cervical manipulations performed each year by chiropractors covered by the Canadian Chiropractic Protective Association.
The authors note that there were more than 4,500 licensed chiropractors in Canada during the study period. These chiropractors performed approximately 134.5 million cervical manipulations during the 10-year assessment period, or approximately 13.45 million cervical manipulations per year.
The findings were:
There were 23 cases of stroke or vertebral artery dissection following cervical manipulation reported during this 10-year period, or 2.3 cases per year. An analysis of these numbers revealed:
- 1 event per 8.06 million chiropractic office visits
- 1 event per 5.85 million chiropractic cervical manipulations
- 1 event per 1,430 chiropractic practice years
- 1 event per 48 chiropractic practice careers
The authors concluded:
“[These numbers are] significantly less than the estimates of 1 per 500,000–1 million cervical manipulations calculated from surveys of neurologists.”
In 2017, a study was published in the Journal of Stroke and Cerebrovascular Diseases, and titled (2):
Risk of Carotid Stroke after Chiropractic Care: A Population-Based Case-Crossover Study
The lead author, J. David Cassidy, is also a historic and contemporary giant in the chiropractic profession. His list of accomplishments includes a chiropractic degree (DC), a PhD, and a DrMedSc degree. Dr. Cassidy is currently working at the University of Toronto.
The objective for this study was to investigate the risk of carotid artery stroke after chiropractic care. All incident cases of carotid artery stroke admitted to hospitals in Ontario, Canada, over a 9-year period were identified. The study base includes the entire population of Ontario, CAN, over a 9-year period, representing 109,020,875 person-years of observation. This study is the first population-based, controlled study to address the risk of carotid artery strokes after chiropractic care.
The authors note that internal carotid artery dissection is a relatively rare event with an annual incidence estimated at 1.72 per 100,000 population. The authors concluded:
“Overall, there were few cases exposed to chiropractic care prior to their strokes.”
“We found no excess risk of carotid artery stroke after chiropractic care.”
“To date, there are no reported cases of stroke as an adverse event in the published trials of cervical spine manipulation.”
The authors include a discussion on protopathic bias, noting that protopathic bias “occurs when an exposure (e.g., health care) is delivered in the early prodrome of a disease (e.g., for dissection-related neck pain or headache) before it is diagnosed (e.g., before the dissection causes a symptomatic ischemic event).” The authors conclude:
“In case–control studies, protopathic bias can lead to the illusion that the exposure caused the outcome, even though it is not on the causal pathway.”
“Our results suggest that the association between chiropractic care and carotid artery stroke is explained by protopathic bias.”
In 2018, a study was published in the European Spine Journal, and titled (3):
Chiropractic Care and Risk for Acute Lumbar Disc Herniation: A Population-based Self-controlled Case Series Study
The lead author, Cesar A. Hincapié, is quite accomplished. In addition to his chiropractic degree (DC), he has a PhD in injury epidemiology. Dr. Hincapié is currently the head of musculoskeletal epidemiology research at the University Spine Centre Zurich at Balgrist University Hospital in Switzerland.
The authors note that there is “no valid epidemiologic assessment of the risk for acute disc herniation following chiropractic treatment that is available in the scientific literature.” Consequently, the objective of this study was to investigate the association between chiropractic care and acute lumbar disc herniation. This robust study also assessed a population of more than 100 million person-years. The authors’ conclusion is:
“We found no evidence of excess risk for acute lumbar disc herniation with early surgery associated with chiropractic compared with primary medical care.”
Similar to the carotid artery article above (2), the authors have a discussion pertaining to protopathic bias. They note that many patients present, in the early (prodromal) phase of lumbar disc herniation, with low back pain, which “then progresses to radicular leg pain with or without neurologic signs.” Individuals in the early prodromal phase of a symptomatic lumbar disc herniation often complain of back pain. As the condition progresses, most develop sciatica. The authors state:
“If chiropractic treatment occurs before a lumbar disc herniation progresses to radiculopathy or neurologic deficit and is thus diagnosed, then the treatment itself can be erroneously blamed for causing the lumbar disc herniation.”
“This systematic error—known as protopathic bias—is a type of reverse-causality bias due to processes that occur before a diagnosed or measured outcome event.”
“Given that deteriorating outcome can initially present as low back pain, it is possible that these patients seek chiropractic care in the prodromal phase of deteriorating outcome, implying that an observed association between chiropractic care and acute deteriorating outcome may not be causal.
In 2023, a study was published in the journal Scientific Reports, and titled (4):
A Retrospective Analysis of the Incidence of Severe Adverse Events Among Recipients of Chiropractic Spinal Manipulative Therapy
This study examined the incidence and severity of adverse events (AEs) in 54,846 patients who received 960,140 chiropractic spinal manipulations. Data originated from 30 chiropractic clinics using 38 different chiropractors. All patients received spinal manipulative therapy (SMT) administered via manual thrust (i.e., a hands-on impulse applied to the spinal joints).
As the numbers indicate, this study is massive. It represents one of the largest to examine potential spinal manipulative therapy-related adverse events.
The authors of this study defined an adverse event as any new complaint which was not present at baseline or a worsening of a presenting complaint. Pain severity was measured with the numeric pain rating scale, from 0 to 10, with 10 being the most severe pain.
Adverse events were graded 1–5 based on severity:
Mild symptoms and therapeutic interventions not indicated
Local or noninvasive therapeutic intervention indicated
Medically significant but not life-threatening
Urgent intervention indicated
This study “focused on adverse events related to spinal manipulative therapy (SMT) involving a thrust or impulse, a treatment commonly used by chiropractors to treat spinal conditions.”
In slightly fewer than a million spinal manipulation sessions, 39 adverse events were identified. There were no deaths (grade 5) or life-threatening (grade 4) events.
There were 2 severe (grade 3) adverse events. Both were rib fractures occurring in women who were older than age 60 with known osteoporosis. Therefore, the incidence of adverse events graded severe or greater was 0.21 per 100,000 spinal manipulation sessions, or 0.0000021%.
The details of the 39 adverse events include:
- 28 Increased symptoms related to chief complaint
- 4 Chest pain without fracture
Two of these patients had a history of osteoporosis.
- 3 Jaw Pain
Two of these patients had a history of dental procedures that were potentially relevant.
- 2 Rib Fracture
Both cases of rib fracture occurred in females over 60 with a history of osteoporosis.
- 1 Headache & Dizziness
- 1 New Radicular Symptoms
The authors concluded:
“In this study, severe spinal manipulative therapy-related adverse events were reassuringly very rare.”
“There were no adverse events related to stroke or cauda equina syndrome.”
“There were no cases of stroke, transient ischemic attack, vertebral or carotid artery dissection, cauda equina syndrome, or spinal fracture.”
“No adverse events were identified that were life-threatening or resulted in death.”
“No adverse events were reported to be permanent.”
In this study, the chiropractors informed patients that mild adverse events were common and transient prior to administering spinal manipulation. Most of these patients signed an informed consent document which described that they may experience increase of pain following spinal manipulation. When patients reported mild soreness after spinal manipulation, they were reassured that these symptoms were typical.
Between the chiropractors’ verbal and written informed consent and reassurance that soreness symptoms were typical and to be expected, patients were much less inclined to formally report a mild adverse event.
It is noteworthy that this study was published in the journal Scientific Reports. Scientific Reports is a top tier Q1 (top quartile) journal that is owned by Nature Publishing. At the time of publishing, Scientific Reports was the 5th most referenced journal in the world.
Also, in 2023, a study was published in the journal Healthcare, and titled (5):
Safety of Chuna Manipulation Therapy in 289,953 Patients with Musculoskeletal Disorders: A Retrospective Study
Chuna manipulation therapy (CMT) is a form of manual therapy employed by Korean medical doctors. It involves traditional joint manipulation, similar to that in chiropractic. In fact, it was adapted from chiropractic therapy and encompasses manipulation techniques that employ “high-velocity, low-amplitude and thrust.” As in chiropractic, it is used to treat structural or functional pathologies. It emphasizes the balance between function and structure.
This type of manual therapy has been incorporated into the Korean health care system and has been administered in 16.4% of inpatients and 83.6% of outpatients with musculoskeletal disorders in Korean medicine hospitals specializing in spine and joint diseases.
The authors make these observations:
“Manual therapy is performed in various forms by chiropractors, osteopaths, and physical therapists across the world, including the United States, Europe, and Australia.”
“The use of spinal manipulation has increased in recent decades in Western countries, as has the popularity of chiropractic therapy among American adults.”
“The UK National Institute for Health and Clinical Excellence guidelines now recommend manual therapy for treating persistent or subacute lower back pain.”
This study was also massive. In total, the authors assessed 2,682,258 manipulation procedures that were performed on 289,953 patients from 14 different facilities. The authors state:
“In this study, 289,953 patients and more than 2.5 million cases of CMT were reviewed, making it a rare, very wide-ranging, and reliable investigation of severe adverse events.”
The authors consider their analysis to be exceptionally accurate because Korean medical doctors check for adverse events at every patient visit, and nurses communicated with patients before and after each treatment to follow up on their post-treatment status.
Adverse events were graded as follows:
asymptomatic or mild symptoms
minimal, local, or non-invasive intervention indicated
severe or medically significant but not immediately life-threatening; hospitalization or prolongation of hospitalization indicated
urgent intervention indicated
In total, this study identified 50 adverse events, as follows:
- 29 cases of increased musculoskeletal pain
“Most cases of worsening pain involved radiation of pain in the lumbar region and lower limbs (n = 23), with additional reports of cervical pain (n = 2), knee-related symptoms (n = 2), worsening hip pain (n = 1), and the onset of temporomandibular joint pain (n = 1).”
“None of the patients with increased pain after CMT had a dural tear or spinal cord injury.”
- 11 cases of rib fracture
All fractures occurred in female patients. The minimum age of onset was 54 years; 9 cases were over 60 years of age, with a median age of 70 years.
“Female sex hormones play a crucial role in maintaining bone mineral density; therefore, although menopause is not necessarily a contraindication, postmenopausal women require careful monitoring during joint manipulation.”
- 6 cases of falls while getting onto/off the adjusting table
“All six cases of falls resulted in mild contusions that did not require additional treatment.” The median age of the patients who experienced falls was 63.5 years.
- 2 cases of chest pain
Both patients were in their 70s and had no abnormal radiographic or ultrasound findings, and the pain had improved 1 month later.
- 1 case of vertigo
“One patient had headache and vertigo that persisted for 5 days….this may be interpreted as a normal response to mobilization or stimulation of periarticular soft tissue.”
The 38-year-old patient had no abnormal brain MRI or MR angiography findings.
- 1 case of mild non-musculoskeletal discomfort
“One patient in our study complained of an unpleasant sensation during CMT, which was because of receiving CMT while wearing a skirt.”
One might argue that of the 50 adverse events identified in this study, many should not have been counted. This includes in-office falls, feeling uncomfortable as a consequence of attire, and post-adjustment soreness.
The authors state:
“Our analysis of 289,953 patients and 2,682,258 cases of CMT indicates that both mild–moderate and severe AEs are rare after CMT.”
“The incidence of mild to moderate AEs was 1.83 per 100,000 treatment sessions, and that of severe AEs was 0.04 per 100,000 treatment sessions.”
“Adverse events of any level of severity were very rare after CMT.”
“There were no instances of carotid artery dissection or spinal cord injury.”
“There were two cases of worsened neck pain; however, no life-threatening or severe adverse events were observed that would support previous [artery injury/stroke] concerns.”
The authors discuss that the only severe adverse event identified occurred in a patient who developed hip pain after CMT and was found to have avascular necrosis of the femoral head that required surgery. However, since the pre-CMT radiograph indicated a preexisting avascular necrosis of the femoral head, “it is difficult to conclude that CMT was the cause; however, as the patient experienced increased pain, the possibility that CMT aggravated the avascular necrosis cannot be excluded.”
These studies continue to document the incredible safety of chiropractic care. Severe adverse reactions are nearly unheard of. Minor reactions such as soreness are also incredibly rare and are self-limiting. The only noteworthy precaution is the potential to fracture ribs in the elderly, primarily women, usually with known osteoporosis. Yet, rib fractures are also incredibly rare and are self-limiting. Each chiropractic provider, depending upon the nature of their techniques and patients, should construct the appropriate informed consent for their practice.
- Haldeman S, Carey P, Townsend M, Papadopoulos C; Arterial Dissections Following Cervical Manipulation: The Chiropractic Experience; Canadian Medical Association Journal; October 2, 2001; Vol. 165; No. 7; pp. 905-906.
- Cassidy JD, Boyle E, Côté P, Hogg-Johnson S, Bondy SJ, Scott Haldeman S; Risk of Carotid Stroke after Chiropractic Care: A Population-Based Case-Crossover Study; Journal of Stroke and Cerebrovascular Diseases; April 2017; Vol. 26; No. 4; pp. 842–850.
- Hincapié CA, Tomlinson GA, Côté P, Rampersaud YR, Jadad AR, Cassidy JD; Chiropractic Care and Risk for Acute Lumbar Disc Herniation: A Population-based Self-controlled Case Series Study; European Spine Journal; July 2018; Vol. 27; No. 7; pp. 1526–1537.
- Chu E, Trager RJ, Lee L, Niazi IK; A Retrospective Analysis of the Incidence of Severe Adverse Events Among Recipients of Chiropractic Spinal Manipulative Therapy; Scientific Reports; January 23, 2023; Vol. 13; No. 1; Article 1254.
- Kim S, Kim G, Kim H, Park J, Lee J, and nine more; Safety of Chuna Manipulation Therapy in 289,953 Patients with Musculoskeletal Disorders: A Retrospective Study; Healthcare; February 2, 2023; Vol. 10; No. 2; Article 294.
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