Chiropractors now make up the third largest group of health-care providers in the United States, after physicians and dentists (Pelletier, 2000). There are more than 50,000 chiropractors in the United States who treat about 50 million patients annually. 

How can these facts be explained? This is a reasonable question, considering how far chiropractic has come in a little more than a century. 

From its beginnings in the late 1800s, chiropractic has had a stormy relationship with orthodox medicine. 

In the 1960s, the American Medical Association (AMA) declared that its members could not ethically consult with any members of the "cult of chiropractic" (Pelletier, 2000). However, after legal actions against the AMA and other medical organizations in the 1970s and 1980s, the profession began to gain increasing acceptance among conventional physicians. 

Chiropractic is now widely accepted as a legitimate therapy for musculoskeletal pain in selected patients, particularly back pain. 

An increasing number of studies support the benefits of chiropractic over alternative treatments for back and neck pain in selected patient groups. 

A 1996 RAND report (Hurwitz, et al.; Pelletier, 2000) concluded that, based on the results of a systematic literature review and me4ta-analysis of 67 studies, spinal manipulation was more effective than alternative treatments for patients with acute or sub-acute low-back pain that was uncomplicated by sciatica. 

When cervical manipulation was analyzed, it was concluded that manipulation was effective for neck pain and for muscle-tension-related headache (Pelletier, 2000). 

In a 1995 study reported in the British Medical Journal (Meade, et al.), 741 patients with low-back pain received either chiropractic manipulation or outpatient hospital management. At three years follow-up, according to Oswestry back pain scores, the chiropractic-treated patients' scores were about 29% better than those receiving hospital treatment (Table 1). 

In a 1995 retrospective study (Dabbs and Lauretti), it was concluded that cervical manipulation for neck pain is much safer than the use of non-steroidal anti-inflammatory drugs (NSAIDs), by as much as a factor of several hundred times.  

Manipulation of the cervical spine has been questioned more frequently than any other chiropractic procedure, and reports of complications appear intermittently in the medical literature.  

Stroke is the most serious complication resulting from cervical manipulation. 

A 1999 article in the Journal of Neurology (Hufnagel, et al.) described 10 patients who suffered ischemic stroke secondary to vertebral artery dissection or internal carotid artery dissection, all following chiropractic manipulation of the cervical spine. All of the patients had no or mild risk factors and no predisposing factors. Nine cases were documented by magnetic resonance imaging (MRI) or computerized tomography (CT), with an onset of symptoms immediately or within two days of the manipulation. All of these patients had residual effects ranging from mild neurological deficits to a persistent vegetative state, according to the study. 

The researchers concluded that patients at risk for stroke after chiropractic manipulation couldn't be identified before treatment. Moreover, neurological deficits may be permanent, severely disabling and life-threatening.  

One main blood supply to the brain comes from the vertebral artery, which follows a tortuous course through the cervical vertebrae into the brain. According to William Lauretti, D.C., a doctor of chiropractic in Maryland, it is possible that by vigorously rotating the neck, the vertebral artery can become traumatized. A tear can occur, or the injured area can become the site of a blood clot and subsequently a stroke (although the risk of this event is rare).  

To help put this risk into perspective, Lauretti noted that similar events can result from the administration of anesthesia during surgery or during neck extension for radiography. 

The risk for death following cervical spinal manipulation is about equivalent to the risk for death during a 20-mile round-trip drive to a chiropractic office, according to Lauretti. For cervical manipulation, the estimated risk for serious complications is 6.39 per 10 million manipulations (see also Hurwitz, et al., 1996). 

For lumbar manipulation, the estimate is one serious complication per 100 million manipulations.  

These data compare the risk of serious complications per manipulation with one surgical procedure or one course of treatment with an NSAID. Repeated manipulations increase the risk. 

Recognizing high-risk patients (such as those with predisposing factors for vertebral or carotid artery dissection) before treatment can further reduce adverse events, although one study cited above noted the difficulty in identifying that patient subgroup prior to therapy.  

John Russo Jr., PharmD, is senior vice president of medical communications at Vicus.com. He is a pharmacist and medical writer with more than 20 years of experience in medical education.  

This story was updated on 7 Sept. 2000.