This chapter summarizes what has been learned from clinical trials about the benefits of spinal manipulation for specific problems and from case reports about the risks of spinal manipulation. In addition, findings of studies examining the ability of spinal manipulation to increase patient satisfaction, decrease cost, or increase cost-effectiveness of care are summarized.

A. Evidence for Benefits of Spinal Manipulation from Clinical Trials

For any health care intervention, it is hoped that the expected benefits exceed the expected risks. The most rigorous method for establishing efficacy of a treatment is the randomized controlled trial (RCT). There have been many RCTs of spinal manipulation for a variety of different patient presentations, as well as many reviews of these RCTs (Assendelft, 1995). This section summarizes both primary data and reviews of studies of the impact of spinal manipulation on patient outcomes, particularly symptoms and function.

1. Musculoskeletal Conditions
    Low Back Pain

There have been at least 36 randomized clinical trials of spinal manipulation for patients with low back pain (Koes, 1996). These studies have been of variable quality, as assessed both explicitly and implicitly by several independent investigators. The two highest quality reviews of spinal manipulation for low back pain reached somewhat different conclusions (Koes, 1991, 1996; Shekelle, 1992). The first review, conducted in 1991 and updated in 1996, noted the heterogeneity in study quality and treatments, and did not attempt statistical combinations of individual studies (Koes, 1991,1996). These reviews concluded that it is not conclusively proven that spinal manipulation is beneficial for any low back pain clinical syndrome.

A 1992 meta-analysis concluded that in some patient presentations spinal manipulation is more efficacious than both sham manipulation and the medical therapies to which it has been compared (Shekelle, 1992). This meta-analysis included nine studies of manipulation for patients with acute or subacute (less than a few weeks' duration) low-back pain uncomplicated by sciatica. The two best quality studies found a clinically and statistically significant benefit of manipulation in terms of functional status in patients whose pain had persisted between 2 and 4 weeks prior to treatment (Hadler, 1987; MacDonald, 1990). These studies used sophisticated composite measures of functional status, and the authors of the meta-analysis did not feel it valid to combine these two studies with the other studies, which used different outcome measures. The results of the remaining seven studies, along with the meta-analytic statistical combination of their results, are shown in Figure 5. The combined results of these studies indicated that spinal manipulation is more efficacious than the comparison treatments (Shekelle, 1992). Specifically, the probability of recovery 3 weeks after initiation of treatment was an average of 0.17 higher in the groups receiving manipulation, representing a 34 percent improvement in recovery.

The Shekelle study (1992) also reported that there are insufficient data to reach a conclusion for patients with chronic low back pain or sciatica. The three trials of manipulation for sciatica were all of mediocre quality and their statistical combination favored manipulation but did not quite reach conventional levels of statistical significance. The controlled trials of spinal manipulation for chronic low back pain included in the 1992 review reached conflicting conclusions and their heterogeneity precluded statistical combination.

Since the Shekelle and Koes reviews were completed, at least eight additional clinical trials have been published that compare treatments including spinal manipulation with various other treatments for patients with low back pain (Herzog, 1991; Koes, 1992; Wreje, 1992; Blomberg, 1994; Erhard, 1994; Pope, 1994; Triano, 1995; Meade, 1995). The results of these trials are mixed. Of the four studies including patients with acute low back pain, one study of patients felt to have sacroiliac joint dysfunction did not show a benefit for spinal manipulation in relief of pain (Herzog, 1991), another study demonstrated that the addition of spinal manipulation to exercise therapy improved functional and pain outcomes measured at one month (Erhard, 1994), and two "pragmatic" studies found manipulation combined with other treatments to be superior to conventional nonmanipulative therapy (Koes, 1992; Blomberg, 1994). Another study of patients with subacute low back pain showed a nonsignificant trend toward improvement in pain in the group receiving manipulation (Pope, 1994).

For patients with chronic back pain, the one new study that specifically compared spinal manipulation to an artfully conducted sham showed, as other studies have, a benefit in terms of pain relief (but not improved function) after 2 weeks of manipulation (Triano, 1995). Two other studies recently reported long-term followup of patients treated with manipulation by either physiotherapists or chiropractors compared to other forms of care. Both studies reported somewhat better outcomes after one or more years for the patients who received manipulation (Koes, 1992; Meade, 1995). The addition of these new trials would not seem to alter the conclusions of the prior review and meta-analysis. Based on the available evidence, convincing conclusions cannot be made regarding net benefits of spinal manipulation for patients with chronic low back pain or sciatica. Depending upon whether one accepts or rejects the validity of statistical combinations of studies, there either is or is not conclusive evidence that spinal manipulation is of benefit to patients with uncomplicated acute low back pain. These evidence-based conclusions are in general accordance with those of a multidisciplinary expert panel convened to rate the appropriateness of spinal manipulation for low back pain syndromes (Shekelle, 1991).

A recent systematic review of the literature assessed the evidence for the effectiveness of chiropractic treatment for patients with low back pain (Assendelft, 1996a).

An exhaustive search of the literature identified eight randomized clinical trials. Four of these studies were restricted to patients with chronic pain while the remainder included both acute and chronic pain. All of the studies had serious design flaws and because they used a wide variety of outcome measures and followup intervals the results were not statistically combined. The findings of the eight studies were mixed. The authors concluded that their review failed to find convincing evidence for the effectiveness of chiropractic for acute or chronic low back pain and that higher quality studies would be needed before firm conclusions for or against the effectiveness of chiropractic could be reached (Assendelft, 1996a).

It should be noted that, in the back pain literature, seriously flawed studies that reach inconsistent conclusions are not unique to studies of spinal manipulation. In fact, a recent evidence-based review of conservative and surgical interventions for acute back pain failed to identify any interventions supported by multiple high-quality scientific studies (Bigos, 1994). Thus, despite the poor quality of many of the studies evaluating its effectiveness, there is as much or more evidence for the effectiveness of spinal manipulation as for other non-surgical treatments for back pain.

Neck Pain

After low back pain, neck pain is the most common symptom for which patients seek chiropractic care. Only five randomized clinical trials have examined the efficacy of spinal manipulation for neck pain (Koes, 1992; Cassidy, 1992; Howe, 1983; Sloop, 1982; Vernon, 1990). Like those for low back pain, the clinical trials of manipulation for neck pain varied widely in terms of quality. Most study results favored the group treated with manipulation, although conventional levels of statistical significance were reached for only some of the outcomes. The best quality study compared physical therapist-provided manipulation to nonmanipulative physical therapy (Koes, 1992), detuned diathermy, and usual general practitioner care for patients with nonspecific low back pain and neck pain syndromes. Overall, this study concluded that both of the physical therapist-treated groups had better outcomes than the other two groups, and that the group receiving manipulation did slightly but statistically significantly better at one year than the group receiving nonmanipulative physical therapy. Results of analysis restricted to the 64 persons with neck pain alone favored the manipulated group but did not reach statistical significance, possibly due to the small sample size (less than 20 persons per group).

A recent meta-analysis reviewed studies of patients with several neck pain clinical syndromes who had received a variety of "manual therapies" including manipulation and mobilization (Aker, 1996). This analysis found a benefit for the manual therapy-treated group. However, because of the heterogeneity among patient types and treatments, one cannot directly attribute this benefit to manipulation or to any particular patient presentation.

Headache

For patients with muscle tension type headache, the best quality clinical trial showed statistically significant improvements for the manipulated group, compared to a group treated with amitriptyline, in terms of headache intensity assessed 4 weeks after concluding 6 weeks of therapy (Boline, 1995). Two studies of lesser quality also reported short-term benefits for the group treated with manipulation (Hoyt, 1979; Jentsen, 1987). The only clinical trial of manipulation for patients with migraine headache compared it to mobilization and reported decreases in pain intensity in the patients treated with manipulation but no differences with respect to mean frequency or duration of attacks, or mean disability (Parker, 1978).

Other Musculoskeletal Conditions

The potential benefits of manipulative therapy for other musculoskeletal conditions are largely unknown and limited to case series reports. There is a clear need for research in this area.

2. Nonmusculoskeletal Conditions

Based on personal experience, some chiropractors believe that manipulation can beneficially influence the body's overall healing capacity. However, there is little evidence to support this and it is possible that some of the more dramatic reports of recovery from nonmusculoskeletal conditions resulted from original misdiagnoses, the effect of concurrent treatments, or from remissions that would have occurred regardless of treatment.

Many of the nonmusculoskeletal conditions believed by some to respond to manipulative therapy may be conditions of a functional nature that lack a well-defined medical treatment regimen (e.g., somatization). These conditions are often caused or exacerbated by psychological stress and therefore may be responsive to attention from a caring healer who conveys to the patient a sense that he or she can help. While it is also possible that manual (hands-on) therapy causes a neurological response that leads to reductions in stress-related symptoms and improvements in the functional disorder, this remains speculative. The interrelationship among functional disorders, stress, and the status of the neuromusculoskeletal system is in need of additional research.

There is now a small body of published studies examining the effect of chiropractic manipulative care on nonmusculoskeletal health conditions. The conditions studied include, but are not limited to hypertension (Vernon, 1986; McNight, 1988; Christian, 1988; Nansel, 1991; Yates, 1988); asthma (Hviid, 1978; Nilsson, 1988; Jamison, 1986; Nielson, 1995); dysmenorrhea (Kokjohn, 1992; Liebl, 1990; Arnold-Frochot, 1981; Thomason, 1979), infantile colic (Klougart, 1989); otitis media (Hobbs, 1991); childhood enuresis (Reed, 1994); dizziness/vertigo (Jirout, 1985; Droz, 1985; Gorman, 1993); and chronic pelvic pain (Browning, 1989; Hawk, 1997).

A recent systematic review of the literature concerning the efficacy of spinal manipulative therapy (SMT) for nonmusculoskeletal conditions concluded that "SMT seems to be nonefficacious in the treatment of hypertension and chronic moderately severe asthma in adults" but that the evidence was not strong enough to proscribe the use of SMT for these conditions (Bronfort, 1996). The review further concluded that, because of the small number and poor quality of the available studies, "there is insufficient evidence to advise for or against the use of SMT in the treatment of vertigo, nocturnal childhood enuresis, dysmenorrhea, chronic obstructive pulmonary disease, duodenal ulcer, and infantile colic."

Chiropractic researchers are currently planning or undertaking (as of 1997) randomized trials or cohort studies of the effectiveness of manual treatment procedures for childhood asthma, chronic pelvic pain, otitis media, vascular lability in migraine headache patients, dysmenorrhea, mild hypertension, and migraine headache.

B. Risks of Spinal Manipulation

Until recently, there have been no systematic reports of the complications or risks of spinal manipulation, and all that was known came from case reports and clinical trials (Assendelft, 1996b). Recently, however, data from a prospective study of side effects of spinal manipulation performed by 102 Norwegian chiropractors on 1,058 new patients have become available (Senstad, 1997). After an average of about 4.5 visits, 55 percent of the patients reported at least one reaction to the manipulation. The most commonly reported reactions were: local discomfort (53 percent), headache (12 percent), tiredness, (11 percent) and radiating discomfort (10 percent). Only 15 percent of reactions were considered "severe" and no serious complications were reported. Most reactions appeared within 4 hours of treatment and had disappeared within 24 hours. Reactions were more likely to be reported by women, following the first treatment, when multiple spinal regions were treated and when only the thoracic spine was treated (Senstad, 1996). A cause-and-effect relationship between the manipulation and the reactions has not been established and it is likely that some of the reactions attributed to manipulation were, in fact, coincidental.

No systematic reports of the rate of serious complications of spinal manipulation have been conducted in the United States. Case reports may underestimate the true number of adverse events, including serious ones, or be so poorly documented that a true cause-and-effect relationship is not established. Furthermore, the total number of persons who have received spinal manipulation, and their clinical presentation, is unknown. Nevertheless, using data from case reports on the number of complications and epidemiologic estimates of the number of lumbar spinal manipulations received during the time period covered by the case reports, it was possible to roughly estimate the rate of occurrence of the most serious complication of lumbar manipulation, the cauda equina syndrome, as about 1 case per 100 million manipulations (Shekelle, 1992).

It is probably higher in patients with a herniated nucleus pulposus, and lower in patients without this anatomic abnormality. As there are no systematic data about the rate of serious complications due to spinal manipulation, it is not known if the rate varies by provider type. In the best documented study published to date, Haldeman (1992) describes the outcomes of 10 patients with cauda equina syndrome believed to have been caused by spinal manipulation (without anesthesia). Most of these patients subsequently underwent surgical decompression and were left with residual neurologic deficits that ranged from paresis to mild constipation.

Serious complications of cervical spine manipulation are also rare (none having been reported in any of the clinical trials), but appear to be more common and severe than complications of lumbar manipulation. The most serious complication of cervical spine manipulation is related to compromise of the vertebrobasilar artery, leading to stroke or death. As with lumbar manipulations, limited data preclude an exact estimate of the frequency of this complication, or identification of risk factors for its occurrence. Anecdotal evidence suggests that the risk is higher for manipulation involving rotation plus extension of the cervical spine than for other types of manipulation, and that persons who have suffered manipulation-related vertebrobasilar artery compromise do not have the same clinical characteristics as patients who suffer vertebrobasilar artery compromise due to atherosclerotic disease. The best estimate of the incidence of vertebrobasilar artery compromise related to cervical spine manipulation is that it occurs once in 1 million manipulations (Hurwitz, 1996; McGregor, 1995).

It should be kept in mind that, while spinal manipulation has its risks and benefits, so do other treatments for back and neck pain. For example, medications commonly used for back pain can cause significant complications (Anker, 1994; Bjarnason, 1993) as can lumbar surgery (Hoffman, 1993; McGregor, 1995). However, most randomized clinical trials directly comparing spinal manipulation with other types of nonoperative treatment have reported no complications in either group, suggesting that the risks of these nonoperative treatments are low. The risks and benefits of spinal manipulation have not been compared to those for surgery. Optimal care of back pain patients will require balancing the risks and benefits of alternative treatments. At present, however, comparative data for these largely low-risk therapies are not available.

C. Patient Satisfaction with Chiropractic Care

Observational studies have consistently found that low back pain patients receiving chiropractic care, which typically includes (but is not restricted to) spinal manipulation, are more satisfied than those receiving medical care (Cherkin, 1989; Carey, 1995; Kane, 1974). How much of this enhanced satisfaction is a specific result of the spinal manipulation per se is not known. There are other reasons why one might expect chiropractic care to be more satisfying than medical care. For example, chiropractors have more frequent and closer contact with their patients, they are more comfortable and confident dealing with back pain, they provide patients with a clearer explanation of the cause of their problem (often documented on an x-ray), and they do not need to refer the patient for physical treatment (Cherkin, 1988; Coulehan, 1985). In addition, persons who choose to see chiropractors may differ in some way from those who see medical doctors.

D. Cost and Cost-Effectiveness of Chiropractic Care

The annual cost of chiropractic care in the United States is not known with certainty, but has been estimated at $3.5 billion in 1987 (Nichols, 1996). In the United States. In 1990, an estimated $13.7 billion was spent on all types of unconventional medicine and chiropractors were by far the unconventional practitioner most often seen (Eisenberg, 1993).

The relative cost-effectiveness of chiropractic care and medical care has not been convincingly established (Assendelft, 1993; Manga, 1994). Most studies have failed to compare equivalent patients, measure clinically useful outcomes, and include both direct and indirect costs in the comparison.

To date, no randomized clinical trials including explicit measures of direct and indirect costs have been published. What is available are many case-control studies of costs (but not patient outcomes) using Worker's Compensation data (Assendelft, 1993), a few studies of only cost based on claims data analyses (Blue Cross/Blue Shield, 1986; Stano, 1993; Mushinski, 1995; Stano, 1996), a randomized controlled trial of effectiveness that imputed (but did not explicitly measure) total costs (Meade, 1995), and a recent prospective observational study of patients with acute low back pain which reported outcomes as well as calculated direct costs (Carey, 1995).

Although the majority of these studies have found that chiropractic care was less expensive than medical care (Assendelft, 1993), some have found the opposite to be true (Nyiendo, 1991; Greenwood, 1985). The main limitation of all these studies is their inability to adequately control for differences in the types of patients served by chiropractors and medical doctors. It is possible that persons choosing treatment from a chiropractor differ substantially from those seeking medical care in ways that cannot be adequately controlled for using the limited data that are usually available from databases designed for billing purposes. In the one observational study that prospectively measured both clinically relevant outcomes and calculated direct medical costs, clinical outcomes were no different between medically (primary care or orthopedist) and chiropractically treated patients, but chiropractic care and orthopedic care cost more (Carey, 1995). Chiropractic patients, however, were more satisfied with their care. This study involved only a single State (North Carolina) that had had virtually no managed care experience with chiropractic services. Ultimately, randomized clinical trials that include cost measures will be needed to satisfactorily answer this question.

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