Many complementary techniques are practiced by healthcare professionals with formal training, in accordance with the standards of national organizations. However, this is not universally the case, and adverse effects are possible. Due to limited research, in some cases only limited safety information is available.
Because there is not a systematic surveillance system or a reliable large prospective study, the true prevalence of side effects due to spinal manipulation is not known (306). Estimates of the frequency of adverse effects range from 0.2-0.5% (307-310), with serious complications such as stroke occurring in 1-5 out of every 100,000 patients undergoing neck manipulation (311-318), or some estimates at fewer than 1 in a million (319-324). However, other authors believe that these events are much more common. Recent research suggests that the odds of experiencing a stroke/dissection after cervical spine manipulation may be more that six times greater than in people who do not undergo manipulation (325-327).
Lower back manipulation is generally regarded as being safer than neck (cervical spine) manipulation (328). Some authors suggest that chiropractic manipulation is safer than treatment with non-steroidal anti-inflammatory drugs (329), spine surgery (330), or hospitalization (331), although these areas are not well studied.
There are several possible causes of inaccuracies in estimates of prevalence. If people seek spinal manipulation for relief of symptoms related to underlying conditions that are the true causes of complications such as stroke, over-reporting of stroke due to manipulation would occur (324;332-340). In contrast, much higher rates of adverse effects have been proposed as being due to under-reporting (341-347). Collections of adverse event reports by professional organizations in the Unites States, Europe, and Australia have brought further attention to the serious risks associated with spinal manipulation (318;346;348-351).
It is unclear if there is an increased risk of adverse events in patients with preexisting abnormalities of blood vessels in the neck or brainstem, which potentially could be identified with pre-treatment questioning or imaging tests (352-354). Pre-treatment screening with cervical spine extension-rotation to assess for symptoms does not appear to be effective (355-358). Other attempts at pre-treatment testing to identify at-risk individuals have not been clearly successful (359-362).
Reported adverse effects
Stroke & vertebrobasilar/carotid artery dissection: There are many cases of stroke and arterial dissection following cervical manipulation reported in the medical and legal literature, often occurring in young individuals (20 to 60 years old) (315;333;363-393). Ischemic stroke may occur immediately during or after the procedure, with possible conversion to hemorrhagic stroke. Symptoms may not appear until several days or weeks later, based on reported cases. Various parts of the brain have been affected, including brainstem, cerebellum, occipital, parietal, and frontal lobes. Residual neurologic deficits may remain long-term (307;315;394-449).
Reported symptoms include headache, vertigo, vomiting, neck pain, nausea, Horner’s syndrome, double vision, blurred vision, vision loss, slurred speech (dysarthria), facial droop, hearing impairment, arm or leg weakness, ataxia, nystagmus, numbness, loss of consciousness, as well as reports of paralysis (315;384;385;450;451), coma, and death (300;333;383;387;433;452-459).
These events are most often associated with vertebral artery dissection, a process that involves an expanding hematoma (blood collection or clot) within the wall of the blood vessel or blockage of the blood vessel by a small flap of vessel wall that develops due to trauma during neck manipulation movements. Carotid artery dissection and thrombosis have also been reported with neck manipulation (365;460-463). Involvement of the basilar and cerebral arteries is also reported (464-467).
Spinal bleeding/blood clots: Bleeding and blood clots in the cervical (upper), thoracic (mid), and lumbar (lower) spine following manipulation have also been reported, including cervical spine epidural hematoma (468;469), thoracic spinal hemorrhage in a patient using the anticoagulant drug warfarin (Coumadin®) (470), thoracic or lumbar spine epidural hematoma (471) or aneurysm (472), and intraspinal bleeding (473).
Spinal cord/nerve root compression & disc herniation: Spinal cord injury, cord compression/cauda equina syndrome, and nerve root compression have been reported with neck and back manipulation (474-477), due in some cases to vertebral body fracture (478-480), development of hematoma (481), or to disc herniation/rupture in the cervical, thoracic, or lumbar spine (482-492). Brachial plexus damage has been reported with cervical manipulation (493;494). Nerve root damage from lumbar disc herniation has been associated with cauda equina syndrome, including low back pain, sciatica, saddle sensory disturbances, bladder and bowel dysfunction, and lower extremity motor/sensory loss (490;495-497). Impaired diaphragmatic function can occur (498-500).
Bone/vertebral fracture: Individuals with osteomyelitis (bone infection) (501), cancer involving bone (502), vertebral fractures, severe degenerative joint disease (osteoarthritis), osteoporosis, and ankylosing spondylitis may be at increased risk of fracture or spinal damage leading to nerve disorders or spinal cord damage (503-505). Fracture of the temporal bone complicated by subdural hematoma has been reported with chiropractic manipulation (506).
Anticoagulant (blood-thinning) therapy: Thoracic spinal hemorrhage after manipulation has been reported with the use of the anticoagulant (“blood thinning”) drug warfarin (Coumadin®) (507). Patients with blood clotting disorders or taking anticoagulant therapies may be at increased risk of adverse effects such as spinal bleeding following manipulative therapy.
Musculoskeletal: There are reports of muscle strains, sprains, and spasm following chiropractic manipulation, although it is not clear if these problems were actually related to the therapy, or were preexisting conditions (508;509). Osteomyelitis (bone infection) in the spine has been reported, although chiropractic was likely not the cause, but rather was sought as a therapy due to pain related to infection (510).
Blood pressure effects: The effects of spinal manipulative techniques on blood pressure remain controversial. It has been hypothesized that nervous system effects of spinal manipulation can lower both systolic and diastolic pressure. Numerous trials, reviews, and commentaries have been published in this area (209;217;218;511-521). Although some studies are suggestive, overall the existing evidence remains indeterminate due to methodologic weaknesses and variability between studies. Better research is necessary before a firm conclusion can be drawn.
Radiation exposure: Some authors suggest that exposure to radiation during x-rays ordered by chiropractors may pose a health risk, since approximately 96% of new U.S. patients and 80% of follow-up patients undergo x-rays (72% in Europe) (522). Although the amount of radiation from plain x-rays is generally considered to be small, regular use of x-rays may increase the risk of some types of cancer.
Tracheal damage: Prior surgery of the trachea (“windpipe”) or tracheostomy may increase the risk of tracheal rupture during neck manipulation (523).
Cardiovascular complications: There is a report of a heart attack which occurred in a 38-year-old man during cervical spine manipulation (524). It is not clear if manipulation played a causative role in this event.
Underlying conditions that may increase risk
Patients with existing blood vessel aneurysms (such as abnormalities in brain blood vessels or aortic aneurysms), atherosclerotic disease (“hardening” of the arteries, including carotid artery disease), collagen disorders, vasculitis, other underlying blood vessel abnormalities, or collagen vascular diseases (such as systemic lupus erythematosus) may be at increased risk of stroke or blood vessel dissection (525;526). Individuals with osteomyelitis (bone infection) (527), cancer involving bone (502), vertebral fractures, severe degenerative joint disease (osteoarthritis), osteoporosis, and ankylosing spondylitis may be at increased risk of fracture or spinal damage leading to nerve disorders or spinal cord damage (528-530). Prior surgery of the trachea or tracheostomy may increase the risk of tracheal rupture (531). Underlying tumors of the brain or near the spinal cord may result in adverse outcomes such as tumor rupture or delayed diagnosis (532-537). Patients with blood clotting disorders or taking anticoagulant (“blood thinning”) therapies such as warfarin (Coumadin®) may be at increased risk of adverse effects such as spinal bleeding following manipulative therapy (538). Caution should be used in patients with low blood pressure or taking medications that may lower blood pressure further due to inconclusive reports of lowered blood pressure with the use of manipulative techniques (209;217;218;539-549). Neck pain following cervical manipulation may be a warning sign for stroke (550;551).
Delayed diagnosis/additional care
Use of spinal manipulation for symptoms/conditions should not delay the time to diagnosis or treatment with more proven methods. Individuals who experience persistent symptoms or develop neck pain after manipulation should seek further medical attention without delay, as this may be a warning sign for stroke (532;552-557). Patients are advised to discuss spinal manipulation/chiropractic with a primary healthcare provider before starting treatment.