SPINAL MANIPULATION

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0733-8619/99 $8.00

LOWER BACK PAIN

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SPINAL MANIPULATION Current State of Research and Its Indications Gert Bronfort, DC, PhD

Spinal manipulation includes maneuvers in which the hands are used to stretch, mobilize, or manipulate the spine and paravertebral tissues for the purpose of relieving spinal-related pain and dysfunction. The first credible documentation of spinal manipulation dates back to the fifth century BC, although it is likely that this form of therapy was used earlier.61 The first physician to describe spinal manipulation was Hippocrates (460 to 359 BC).81There is evidence that spinal manipulation has been practiced since antiquity in Asia, the Middle East, and Europe by both physicians and lay manipulators not only for spinal related pain and scoliosis but also to some extent for internal disorders.81Very few physicians used or advocated spinal manipulation during modern medicine’s emergence in Europe in the eighteenth and the nineteenth century, and the practice of spinal manipulation was carried out mainly by folk practitioners known as bonesetters at that time. In the late nineteenth century, osteopathy and chiropractic appeared as separate disciplines of spinal manipulation, and just before the turn of the century, the first osteopathic and chiropractic teaching institutions were established in the United States? Osteopathy was later largely absorbed by mainstream medicine, whereas chiropractic remained an independent health care profession. Manual medicine has emerged during this century as a medical discipline in several parts of the world. In Europe, spinal manipulation is commonly practiced by physical therapists. In the United States, chiropractors are by far the main providers of spinal manipulation.82 From the Department of Research, Wolfe-Harris Center for Clinical Studies, Northwestern College of Chiropractic, Bloomington, Minnesota

NEUROLOGIC CLINICS OF NORTH AMERICA

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VOLUME 17 NUMBER 1 * FEBRUARY 1999

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THEORIES ON THE MECHANISM OF SPINAL MANIPULATION

There are several, although not mutually exclusive, theories on what constitutes the underlying mechanism of spinal manipulation. The primary premise is that spinal manipulation results in improved spinal mobilit~.~’ Impaired motion of synovial joints can have detrimental effects on the integrity of the joint cartilage and lead to premature degenerative change^.^,'^ Decreased spinal motion has been shown to have an adverse effect4O and increased spinal motion an enhancing effect on the metabolism of the intervertebral disk.70There is also suggestive evidence that spinal manipulation can reduce muscle spasm, alleviate spinal nerve root compression, normalize neurogenic reflex activity,72,106 and increase paraspinal cutaneous pain tolerance levels.96Spinal manipulative therapy (SMT) is defined as the application of high-velocity, low-amplitude manual thrusts to the spinal joints slightly beyond the passive range of joint motion.49 This type of manual thrust is usually accompanied by an audible joint sound, caused by a temporary vacuum phenomenon in the posterior spinal joints. When performed by skilled providers, SMT can be administered with minimal risk of inducing trauma to the adjacent vascular, nerve, muscular, joint capsular, and ligamentous structure^.^^ Spinal mobilization (MOB) is defined as the application of manual force to the spinal joints within the passive range of joint motion that does not involve a thrust. For the purpose of this overview, the term spinal manipulation will cover both SMT and MOB unless otherwise specified. REVIEW OF THE LITERATURE

The following review of the literature is based in part on a systematic review of randomized clinical trials (RCTs), reported in detail elsewhere and conducted by Bronfort et a121on SMT or MOB for neck and back pain. This review used a methodology from the ”best evidence” synthesis method first described by S l a ~ i nIn . ~this ~ approach it is considered that the best evidence in any field comes from studies with the highest internal and external validity that use well specified a priori inclusion and exclusion criteria. Best evidence synthesis emphasizes numeric findings (effect sizes), but the conclusions do not depend on a single estimate as in metaanalysis. Another important function of best evidence synthesis is that it can be used to explore and to explain inconsistencies in results between similar studies. Studies with design and analysis flaws (low methodological quality) most likely yield biased results that were omitted from evidence determination. Availability of RCTs of high methodological quality was needed to establish strong or moderate evidence of efficacy or inefficacy. Minimal clinically important differences in patient-oriented outcomes were identified when spinal manipulation was compared with other therapies to determine relative efficacy. It was required for entry

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into evidence that combination-therapy studies isolate the unique contribution of SMT or MOB to the overall treatment effect. Finally, as many outcomes as possible were transformed to a common scale of percentage points and effect sizes, allowing a standard comparison across different studies. Acute low back pain (LBP), chronic LBP, and a mix of the two as well as sciatica are summarized separately. A total of 39 RCTs were reviewed.

Acute Low Back Pain

The summary of the RCTs on acute LBP is provided in Tables 1 and 2. The trial by Hadler et a148included an a priori stratification of patients into two strata: 2-week and a 2- to 4-week duration. The study showed that one session of SMT was superior to one session of MOB used as control, in the stratum of a 2- to 4-week duration. After 3 days there was a clinically important difference [statistically significant-(SS)] in low back disability. A 50% reduction in disability was reached more rapidly in the SMT group (SS).In contrast, the trial by Glover et a145found a shortterm advantage of one session of SMT in comparison with detuned diathermy only in the subgroup of patients who had less than a l-week duration. Mathews et aP5found that the subgroup of patients who had LBP accompanied by sciatica recovered faster with SMT compared with heat found that at 2 weeks (SS). Like the Hadler trial, MacDonald and SMT was better than low back education, but only in the subgroup of patients who had a 2- to 4-week duration. In the study by Farrell and Tw0mey,3~patients receiving SMT recovered much faster than patients receiving a combination of diathermy, exercise, and ergonomic instruction (SS), although the lack of difference in patient-rated pain at 1 and 3 weeks, did not corroborate with this finding. These five RCTs were too dissimilar in terms of patient characteristics and number of treatments to allow for any statistical pooling. However, a subgroup of patients in the trials by Hadler et a14sand MacDonald and were sufficiently similar in terms outcome measures, severity, and duration of symptoms (2 to 4 weeks) to conduct statistical pooling of results. A meta-analysis resulted in an overall moderate to large effect size difference in favor of SMT. In the trials by Bergquist and Larsson,” Blomberg et al,13-15Waterworth and Hunter,Io4Delitto et al,29and Erhard et a1,36the effect of SMT could not be evaluated in isolation from the other treatments with which it was combined. Gemmel and Jacobson4’examined the immediate posttreatment effect of one session of SMT, and the RCTs by Rasmussen,78 Godfrey et a1,46and Helliwell and C ~ n n l i f f ewere ~ ~ of low methodological quality and were therefore not considered in the determination of the strength of evidence of efficacy. Based on the aggregate results of the eligible RCTs in Table 1, there is moderate evidence of short-term efficacy for spinal manipulation in the treatment of acute LBP.

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Table 1. RCTs ON ACUTELOW BACK PAIN IN WHICH IT WAS POSSlBLETO ISOLATE THE UNIQUE CONTRIBUTION OF SPINAL MANIPULATION/MOBILIZATlONTO THE OVERALL TREATMENT EFFECT Author (Reference)

Study Groups (n)

Methodological Quality

Results

Glover et a145 G1: 1 SMT-MD + 4 1974 daily sessions of detuned diathermy, (43) G2: 5 daily sessions of detuned diathermy (placebo), (41) R a s m ~ s s e n ~ ~G1: SMT-MD/PT, (12) 1979 G2: Short-wave diathermy, (12) Farrell and G1: Passive MOB/ T w ~ m e y ~ ~ SMT-PT, (24) 1982 G2: Diathermy abdom. exercise ergonomic instruction, (24)

Moderate

G1 had more pain reduction after the first Tx. No important difference after 3 and 7 days.

Low

G1 had many more symptomfree patients as rated by MD at 2 weeks SS A much higher percentage of patients in G1 reached symptom-free status in <15 days

Godfrey et a P GI: SMT-MD/DC + low e-stimulation, (48) G2: Min. massage + low e-stimulation (42) Helliwell and GI: SMT-MD (6) C ~ n n l i f f e ~ G2: ~ Sham SMT (8) 1987

Low

+

Moderate

+

ss.

Low

Hadler et aP8 1987

G1: SMT-MD, (26) G2: MOB-MD, (28)

High

Mathews et aP5 1987

G1: SMT-PT, (165) G2: Heat, (126)

Moderate

MacDonald and Be1P2 1990

G1: SMT-DO + LBP education and advice (49) G2: LBP education and advice (46)

Moderate

Gemmel and Jacobson I 1995

G1: SMT-DC (16) G2: Activator instrument (14)

High

No important group difference in pain reduction at 1 and 3 weeks. G1 had more patients rating significant improvement in pain at 2 weeks. No group difference in improvement activities of daily living at 2 weeks G1 had more improvement in symptoms at 1 week-but not at 2 days and 1 month. No group difference in sickleave days after 1 month. 50% reduction in low back disability score (Roland-Morris) reached more rapidly in G1 than G2 SS but only in subgroup with duration of 2-4 weeks No important group difference in subgroup of patients who have simple LBP and who recovered at 2 weeks. No difference in relapse rate between groups during the followup year. G1 had higher reduction in low back disability scores (Roland-Morris) at 1 and 2 but not at 3 weeks, and only in subgroup of patients who had a duration of 2-4 weeks. Test of immediate effect after 1 treatment: No important group difference in pain reduction.

Abbreviations: Tx, treatment; MD, medical doctor; DO, osteopathic doctor; DC, chiropractor; PT, physiotherapist; LBP, low back pain; G1, group 1; SMT, spinal manipulative therapy; MOB, spinal mobilization; and SS, statistically significant ( p 5 0.05).

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Table 2. RCTs ON ACUTE LOW BACK PAIN IN WHICH IT WAS NOT POSSlBLETO ISOLATE THE UNIQUE CONTRIBUTION OF SPINAL MANIPULATION/MOBILIZATlON TO THE OVERALL TREATMENT EFFECT Author (Reference)

Study Groups (n)

G1: SMT-PT + exerBergquistcise (68) Ullman and Larsson" G2: Back school 3 h, 1977 (70) G3: Low-intensity heat, (placebo) (79)

Methodological Quality

Moderate

G1: SMT-PT and/or McKenzie exercise, (38) G2: Heat + exercise, (34) G3: Anti-inflammatory drug, (36) G1: SMT-MD + steroid inj. + autotract (15%) + home exercise, (48) G2: Exercise + back school + electrical modalities, (53)

Moderate

Delitto et a129 G1: SMT/McKenzie extension exercise, 1993

Moderate

Waterworth and Hunter'OI 1985

Blomberg et 1992, 1994

Moderate

(14)

G2: Flexion exercise, (10) Erhard et a136 G1: SMT-MOB/extension + flexion ex1994 ercise, (12) G2: McKenzie extension exercise, (12)

Moderate

Results

G1 had faster recovery than G3 SS, but was equal to G2. G1 had fewer days with inability to work than G3 but more than G2. Equal numbers of relapses during followup year in all three groups No important group difference in pain reduction at 4 and 12 days. No important group difference in improvement 12 days.

G1 had higher pain reduction at 1,2, and 3 weeks SS and at 3 months SS. G1 had higher reduction in low back disability at 1, 2, and 3 weeks SS, but not at 3 months. G1 had the lowest number of days of work-loss during the 8 month follow-up SS G1 had higher reduction in low back disability scores after 3 and 5 days SS. G1 had higher reduction in low back disability scores after 3 and 5 days SS.

Abbreviations: MD, medical doctor; PT, physiotherapist; G1, group 1; SMT, spinal manipulative therapy; MOB, spinal mobilization;and SS, statistically significant ( p 5 0.05).

Chronic Low Back Pain

The summary of the RCTs on chronic LBP is provided in Tables 3 and 4. The Koes et a159,60 trial compared SMT and MOB with standard physical therapy, care by medical general practitioners (GP), and placebo treatment. SMT and MOB was shown to have a clinically important advantage over GI' treatment and placebo in severity of main complaint and perceived global improvement at 6 weeks (SS).Pope et a175found a clinically

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Table 3. RCTs ON CHRONlC LOW BACK PAIN IN WHICH IT WAS POSSBLETO ISOLATE THE UNIQUE CONTRIBUTION OF SPINAL MANlPULATlONlMOBlLlZATlON TO THE OVERALL TREATMENT EFFECT Author (Reference)

Study Groups (n)

Evans et aP7 1978

G1: SMT-MD, (17) G 2 Analgesics, (15)

Coxhead et al'" 1981

Factorial study with 16 different combinations

Methodological Quality Low Moderate

Of

1: SMT-PT 2: Traction 3: Exercise 4: Corset 5: No Tx (all the combination groups also received backschool and diathermy.) G1: SMT-DO, (41) Gibson et alJ2 G2: Diathermy active, (34) G3: Detuned diathermy, (34) Arkuzewski5 G1: Drugs, physiotherapy, 1986 + SMT- MD, (50) G 2 Drugs, physiotherapy, (50) Waagen et a P 2 G1: SMT-DC, (11) 1986 G2: Sham SMT-DC, (18) G1: SMT-DC (19) Herzog et alS4 ex1991 G2: Back education ercise, (18) G1: SMT-PT + MOB, (36) Koes et alsq,M 1992 G2: Massage + ex + heat + pt- modalities, (36) G3: GP Tx analgesic/antiinflam + advice on rest, ex, posture, (32) G4: Detuned modalities, (40) Pope et a1751994 G1: SMT-DC, (70) G2: Massage, (36) G3: TENS, (28) G 4 Corset, (30) TimmgR1994 G1: MOB-PT, (50) G2: Hot packs, TENS, usound, (50) G3: Low-tech exercise, (50) G4: High-tech exercise, (50) G5: No treatment control, (50) Triano et al'" G1: SMT-DC, (70) G2: Sham SMT-DC, (70) 1995 G3: Back education, (69)

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Bronfort et al"' 1996

G1: SMT-DC + strength exercise (71) G2: NSAID + strength exercise, (52) G3: SMT-DC + stretch exercise, (51)

Results G1 had higher percentage of patients rating tx as effective/highly effective at 3 weeks at crossover. Main effect of SMT (G1) resulted in more pain reduction than the other treatments at 4 weeks SS. 87% of patients improved with combinations of 3-4 Txs vs 70% with 1 or no Tx SS.

Moderate

G3 had highest reduction in daytime pain at 2 and 12 weeks.

Moderate

G1 higher reduction in pain at 1 and 6 month post-tx followup

Moderate

G1 higher reduction in pain at 2 weeks. No important group differences in pain and low back disability reduction at 4 weeks. G1 higher reduction in severity of main complaint than the 3 other groups at 6 weeks but not at 12 weeks and than G2 at 12-month followup ss.

Low High

Moderate

G1 had higher pain reduction than G3 at 3 weeks SS but not importantly different from G2 and G4.

Moderate

G3 and G4 had higher reduction in low back disability scores than G1, G2, and G4 at 8 weeks SS. Outcomes in GI and G5 were similar.

Moderate

G1 had a small clinical advantage at the end of treatment and 2 weeks later for pain and disability com.? pared with G No important group differences in pain and low back disability reduction at 3, 6, and 12 months.

High

Abbreviations: Tx, treatment; MD, medical doctor; DO, osteopathic doctor; DC, chiropractor; PT, physiotherapist; GP, general practitioner; GI, group 1; SMT, spinal manipulative therapy; MOB, spinal mobilization; and SS, statistically significant ( p 5 0.05).

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Table 4. RCTs ON CHRONlC LOW BACK PAIN IN WHICH IT WAS NOTPOSSlSLETO ISOLATE THE UNIQUE CONTRIBUTION OF SPINAL MANlPULATlON/MOBlLlZATION TO THE OVERALL TREATMENT EFFECT. Author (Reference)

Study Groups (n)

Ongley et a173 G1: Forceful SMT-MD 1987 + 6 proliferant injections, (40) G2: Sham SMT-MD + 6 placebo injections, (41) Sims-Williams G1: SMT-PT + MOB et alS71978 + traction, (43) G2: Placebo PT, (44) (general practice patients) Sims-Williams G1: SMT-PT + MOB et alS81979 + traction, (48) G2: Placebo PT, (44) (hospital patients)

Methodological Quality

High

Results

G1 had higher reduction in pain and low back disability scores at 1, 3, and 6 months

ss.

Moderate

Moderate

G1 had lower percentage of patients who had work loss at 1 month SS. No important group difference in pain reduction at 1 and 3 months. No important group difference in pain reduction and work loss 1 and 3 months.

Abbreviations: MD, medical doctor; PT, physiotherapist; G1, group 1; SMT, spinal manipulative therapy; MOB, spinal mobilization, and SS, statistically significant ( p 5 0.05).

important advantage of SMT over transcutaneous electrical nerve stimulation (TENS) in pain improvement (SS). The differences between SMT and light massage and corset use were of questionable clinical importance. The trial by Triano et a199compared two weeks of SMT with sham SMT and back education. There was a small clinical advantage at the end of treatment and 2 weeks later for pain and disability in favor of SMT. Coxhead et aIz8utilizing a factorial design, showed that the effect in the SMT groups was superior to the non-SMT groups (traction, exercise, corset, and no treatment) (SS). The trial by Waagen et allo2did not include analysis of between-group differences and did not provide data to allow us to calculate effect sizes and p-values. A clinically important advantage of SMT over placebo in pain reduction was reported, however, after 2 weeks of treatment. Timm et a198found exercise to be superior to physical modalities and MOB at 8 weeks (SS). MOB was no better than the no treatment control. Bronfort et alZoshowed equal short- and long-term improvements in pain and disability whether exercise was combined with SMT or nonsteroidal anti-inflammatory drug (NSAID) therapy. The trial by Gibson et a142lacked group comparability at baseline, and the trial by Arkuzewski5had no patient-rated outcomes. These two trials were therefore not included in the determination of the strength of evidence. The trial by Ongley et al?3 and the two trials by Sims-Williams et a187,88 combined SMT with other treatment modalities, preventing us from assessing the effect of SMT or MOB alone. The RCTs by Evans et a137and Herzog et al?4 were of low methodological quality and therefore were not considered in the determination of the strength of evidence of efficacy.

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The aggregate results of the eligible trials in Table 3 on chronic LBP provides moderate evidence that SMT, including MOB, is efficacious when compared with placebo and commonly used therapies such as general medical practitioner management. Mix of Acute and Chronic Low Back Pain The summary of the RCTs on a mix of acute and chronic LBP is proshowed a 2- to 4-percentage-point advided in Table 5. Meade et a166,67 vantage of chiropractic SMT over hospital outpatient management (84% received SMT or MOB) in terms of patient-rated low back disability at followups of 6 weeks and 6 months and of 1, 2, and 3 years. The differences at 6 months and at 2 and 3 years were SS but not considered clinically important as suggested by Meade et al.66,67 the authors. The trial by Bronfort18suggested that, at 3 and 6 months, SMT was superior to medical GP management for improvement and for reduced work-loss, but the trial was aborted prematurely and conclusions could not be reached. In the Zylbergold and Piper'07 study, it was concluded that after 1 month, SMT and heat were better than flexion exercise and heat when pain and disability were used as outcomes, but the study did not have adequate statistical power. In the Doran and NewelP2study (also underpowered), SMT resulted in greater improvement after 3 weeks when compared with either physiotherapy, corset, or analgesics. No important group differenceswere apparent after 6 weeks and 3 months. Hoehler et aP5 found important pain reduction in subjects receiving SMT compared with subjects receiving light (placebo)massage at discharge and 3 weeks later. Although pain reduction did not show a SS difference between groups, a higher proportion of subjects in the SMT group did report that the treatment was effective 3 weeks after discharge 6s).The RCTs by Rupert and Ezzeldin,so Postacchini et al,76Kinalski et a1,56and Wreje et alla5were of low methodological quality and were therefore not considered in the determination of the strength of evidence of efficacy. The observed variability in the results of the RCTs on a mix of acute and chronic LBP renders the evidence inconclusive regarding the shortterm efficacy of SMT for the treatment of a mix of acute and chronic LBP patients but.is not inconsistent with the results of the trials on acute or chronic LBP. Sciatica The summary of the RCTs on sciatica is provided in Table 6. In the large, hospital-based trial by M a t h e ~ s , significantly 6~ more patients in the SMT group were recovered at 2 weeks when compared with the group that received heat alone. Coxhead et al,28.evaluating 16 combinations of conservative therapies, found that at 4 weeks there was a SS advantage in pain reduction for the groups receiving SMT compared with the non-

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Table 5. RCTs ON A MIX OF ACUTE AND CHRONIC LOW BACK PAIN IN WHICH IT WAS POSSlBLETO ISOLATE THE UNIQUE CONTRIBUTION OF SPINAL MANlPULATlONlMOBlLlZATlONTO THE OVERALL TREATMENT EFFECT Author (Reference)

Study Groups (n)

Methodological Quality

G1: SMT-MD, (116) G2: Physiotherapy, (114) G3: Corset, (109) G4: Analgesics, (113)

Moderate

Zylbergold and G1: Heat + SMT-PT, (8) flexion ex., 'Pipe;"', 1981 G2: Heat (10) G3: Ergonomic instruction, (10) Hoehler et a155 GI: SMT-MD, (56) G2: Soft-tissue massage, 1981 (39)

Moderate

Doran and Newe113*1975

+

Rupert and Ezzeldinso 1985 Postacchini et a1761988

G1: SMT-DC, (?) G2: Placebo touch, (?) G3: Drugs bedrest, (?) G1: SMT-DC?, (87) G2: Drugs, (81) G3: Massage + diathermy, (78) G4: Bedrest, (29) G5: Back school, (50) G6: Placebo ointment, (72)

Moderate

Low

+

Kinalski et a156 G1: SMT-MD, (61) G2: Heat traction 1989 ex.?, (50)

+

+

Low

Low

BronfortI81989 GI: SMT-DC, (11) G2: GP-MD (Drugs injections phys. ther. + advice), (10)

Moderate

G1: SMT-MD, (23) G2: Friction massage, (23) Meade et a W 7 G1: SMT-DC, (384) G2: PT + SMT-PT, (357) 1990,1995

Low

+

Wreje et al"ls 1992

+

High

Results G1 had a higher percentage of patients than the 3 other groups rating moderate to complete relief at 3 weeks. No important group differences at 6 weeks and 3 months. G1 had the highest reduction in pain and low back disability scores at 1 month.

G1 had higher reduction in pain after 1 tx SS and at discharge and 3 weeks post- discharge No important group difference in percentage of patients reporting Tx being effective at discharge; but, 3 weeks later, G1 was superior SS. G1 had higher reduction in pain at 8 weeks. For acute patients, G1 had highest increase in global improvement index score at 3 weeks but no important group difference at 2 and 6 months. For chronic patients, G1-3 had higher increase in global improvement index score than G6 at 3 weeks and at 6 months. No important group difference in MD-rated improvement, but G1 had lower treatment time in days. No group difference in patientrated improvement at 1 month, but G1 superior to G2 at 3 and 6 months. G1 had lowest number of workloss days during the 6-month followup. G2 had higher reduction in pain and fewer days on sick leave after 3 weeks. No clinically important group difference in pain and low back disability (Oswestry) scores at 6 weeks and at 6,12,24, and 36 months scores.

Abbreviations: MD, medical doctor; DC, chiropractor;PT, physiotherapist; G1, group 1; SMT, spinal manipulative therapy; and SS, statisticallysignificant ( p 5 0.05).

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Table 6. CLINICAL TRIALS FOR SCIATICA IN WHICH IT WAS POSSBLETO ISOLATE THE UNIQUE CONTRIBUTION OF SPINAL MANIPULATION TO THE OVERALL TREATMENT EFFECT Author (Reference)

Study Groups (n)

Methodological Quality

Results

Coxhead et a P Factorial study of 322 1981 patients who have 16 different combinations of I: SMT 2: Traction 3: Exercise 4: Corset 5: No treatment (In addition, all the combination groups received back school and diathermy education) Mathews et G1: SMT-PT, (165) aP51987 G2: Infrared heat, (126)

Moderate

Main effect of SMT in subgroup of patients who have sciatica higher at 4 weeks than those who did not receive SMT SS.

Moderate

Nwuga’I 1982 G1: Oscillatory, SMTMD, (26) G2: Heat + low-intensity exercise, (25) Siehl et aP6 G1: Conservative care 1971 + SMT-DO, (21) G2: Conservative care, (7) G3: Disc surgery, (19)

Not rated

In subgroup of patients who have sciatica, G1 had higher recovery rate at 2 weeks SS. No difference in relapse rate between groups at 1 year. G1 had higher increase in range of motion and straight leg raise at 6 weeks.

Not rated

G3 had more electromyographic and clinical improvement than the 2 other groups.

Abbreviations: MD, medical doctor, DO, osteopathic doctor, PT, physiotherapist, G1, group 1, SMT, spinal manipulative therapy, SS, statistically significant (p c 0.05)

SMT groups. In the study by N w ~ g asignificant ,~~ improvement in spinal flexion and straight leg raise occurred in the group receiving SMT versus the group receiving short-wave diathermy and low-intensity exercise. In contradistinction, the study by Siehl et als6found that patients receiving SMT showed less clinical improvement than patients receiving disc surgery. In the one study addressing chiropractic SMT, Postacchini et a176 assessed a mixed population of acute and chronic low back sufferers with or without radiculopathy. He found that in a subgroup of acute LBP patients, SMT was superior to NSAIDs, physiotherapy, and .placebo treatment in the short term. Although these studies suggest that SMT is a promising therapeutic approach of lumbar radiculopathy, note that they are of questionable methodologicalq ~ a l i t y . Future ~ ~ , ~well-designed ~,~~~ studies are needed before definitive conclusions regarding the evidence of efficacy of SMT in the management for lumbar radiculopathy can be drawn.

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DISCUSSION Side Effects and Complications

In two recent systematic reviews of all of the published RCTs on the efficacy of spinal manipulation for a variety of conditions involving approximately 2600 patient^,'^,^^ transient side effects have been reported, but no serious complications. In evaluating any therapy weighing the potential risks against the potential benefits is a crucial issue. The adverse reactions associated with spinal manipulation can be divided into three categories. The first category consists of relatively common benign transient side effects, such as muscle and joint soreness, which rarely lead to even short-term impairment in functional status.33The second category consists of reversible serious complications, which are relatively uncommon, such as vertigo or dizziness of a few minutes duration, sternocostal cartilage separation, rib fracture, transient ischemic attacks caused by vertebral artery irritation, and progression of neurologic deficits because of cervical and lumbar disk h e r n i a t i ~ nAdditionally, .~~ misdiagnosis leading to delay in optimal treatment, e.g., cancer presenting as a spinal pain syndrome falls into this category. The third category consists of irreversible complications, which are extremely rare. Cauda equina syndrome, which can sometimes be reversed with prompt surgical intervention5"and vascular injuries, mainly involving the vertebrobasilar arteries following cervicle manipulation and leading to partial or complete paralysis or even death are included in this category.97 The literature to date on the second and the third categories of complications consists mainly of single cases or series of case reports totaling approximately 300 cases.8Individual estimates and the results of retrospective surveys consistently suggest a risk of serious cerebrovascular complication to be approximately 1 per 1 million cervical manipulation^.^^ This, however, does not apply to lumbar manipulation; the risk of irreversible cauda equina syndrome is estimated to be as low as 1 in 100 million lumbar spine manipulation^.^^,^^ Overall, serious or severe complications from spinal manipulation seem to be very rare. Although underreporting in the literature is a likely phenomenon, some reports may have wrongly attributed side effects to spinal manipulation when such causal association has not been clearly e ~ t a b l i s h e dThus . ~ ~ the existing estimates are associated with substantial uncertainty and will only improve when data become available from well-designed prospective studies.8 Cost Effectiveness

Cost effectiveness is defined as the cost associated with a specified clinical intervention per unit of a selected health outcome, such as pain reduction, improvement in disability, and functional status.25Several studies based on workers' compensation data in North America have attempted to compare chiropractic treatment (mainly SMT) and medical

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treatment for musculoskeletal complaints.6All studies were retrospective in nature and most of the early studies were of questionable methodological quality, primarily in terms of comparability of diagnostic codes and condition severity. The more recent studies, which include some, but insufficient, adjustment for confounding factors, have shown mixed results regarding the cost effectiveness of SMT in comparison with other forms of treatment. For cost effectiveness to be determined, the patient conditions under comparison must be sufficiently described in terms of age, gender, severity, duration, and location before treatment is initiated. Comparability of patients in terms of demographics, condition severity, and diagnostic codes must be documented, and all direct and indirect costs must be taken into account. The choice of diagnostic codes are often influenced by health insurance reimbursement rules and are generally used inconsistently within and between health care professional^.^^ Health care costs of patients receiving chiropractic therapy for a variety of musculoskeletal disorders have been compared with those treated by medical and osteopathic doctors based on retrospective analysis of health insurance data of a representative sample of more than 400,000 patient^.^^,^^,^^ Eliminating data from plans that restricted benefits for chiropractic care and after controlling for various confounding demographic and insurance plan types, it was concluded that chiropractic care was associated with substantially lower costs than medical care. If costs associated with hospitalizations were excluded, however, the costs of chiropractic services were higher than medical services when four of the most common musculoskeletal diagnostic codes are considered. It was unclear to what extent patients receiving chiropractic care also required hospitalization. The authors of these studies acknowledge the claims data used did not permit accurate definition of severity and duration or complaint~,9~ and except for satisfaction with care, there was no available data on patient-rated outcomes necessary for valid cost-effectiveness analysis. One major criticism of the earlier studies on cost comparison between different provider services for back pain was that the calculation of cost was often based on the visits and services specifically associated with undefined episodes of back pain. Using predefined episodes of care for back pain as a basis for cost determinations, secondary analysis of the RAND Health Insurance Experiment data in the United States showed that orthopedists had the highest total cost per episode, caused mainly by associated hospitalization Chiropractors had the highest cost per outpatient episode and general practitioners the lowest. This study showed that none of the patients managed by chiropractors, with SMT as the predominant therapy, later required hospitalization for the same complaint, but the study does not provide a basis for concluding this was because of SMT. This could have been a chance phenomenon, given the small number of hospitalizations in relation to the total number of episodes, or it could have been that patients needing hospitalization may have preferentially consulted medical providers. Additionally, it has been shown that a large proportion of hospitalizations for back pain may be unnecessary.31The best evidence to date comes from a prospective obser-

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vational study of more than 200 randomly selected health care providers of acute low back care in North Carolina, including chiropractors, orthopedists, and medical GPs. More than 90% of eligible patients were enrolled, and the outcome status of 95% of more than 1600 patients were available at 6-month followup. After controlling for relatively small differences in demographic and baseline clinical characteristics, the results show that the time to functional recovery was very similar for patients regardless of provider type. The total outpatient charges were highest for patients managed by orthopedists and chiropractors and lowest for medical GPs. In one trial on efficacy of spinal manipulation, the authors argue the potential cost savings over a 3-year period was higher for patients who had LBP managed by chiropractors than for patients managed by hospital outpatient department^.^^,^^ The outcome difference in low back disability between the two therapeutic managements was relatively small (2 to 3 percentage points) and has been regarded as being of questionable clinical importance by several clinical scientist^.^ One Canadian health economist considers the available evidence of cost effectiveness of chiropractic SMT overwhelming compared with medical and other forms of t h e ~ a p y . He ~”~~ has recommended to health policy makers that chiropractic care be included in public health care plans, which would result in substantial cost savings in LBP care. However, the limitations of the existing studies addressing the cost effectiveness discussed above must be carefully considered. If one accepts the premise that clinical efficacy and its relationship to cost is best addressed in prospective randomized studies, the weight of evidence is clearly insufficient to make any conclusions regarding the cost effectiveness or cost benefit of SMT in comparison with other health care choices for LBP or any other condition. Efficacy and Provider Type

No study so far has shown whether SMT is more efficacious if performed by chiropractors (who likely have the most extensive training in spinal manipulation) compared with osteopaths, medical physicians, and physical therapists (P.T.s) (with various degrees of training). The magnitude of treatment effects of trials considered as evidence for this review allows for some interesting comparisons. For acute LBP, no chiropractic trials qualified. SMT was provided by osteopaths, MDs and P.T.s, resulting in similar effect sizes (medium to large) in the shortterm when compared with commonly used therapies such as MOB, heat, exercise, and back education. For chronic LBP, the effect sizes were also of similar magnitude in the short term, regardless of whether SMT was performed by P.T.s or chiropractors. In the trial by Meade et a166,67 involving a mix of acute and chronic low back patients, the effect size difference between chiropractic treatment (99% of patients received SMT) and hospital-based physical therapy (84% of patients received SMT or MOB) was not of clinical importance (effect size range of 0.1 to 0.2). Given the avail-

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able data from RCTs, there is now no clear basis to suggest that SMT is more efficacious if performed by a particular provider type. Systematic Reviews

Qualitative reviews have been criticized as being overly biased, whereas systematic reviews are credited for applying more rigid scientific principles to reduce random and systematic errors. In the mid-1970s G ~ ~ sdefined s ~ ~ meta-analysis , ~ ~ as ”the statistical analysis of a large collection of results from individual studies for the purpose of integrating their findings.” In the 1970s and the early 1980s, meta-analytical techniques were used predominantly by social scientists, but have since become popular in the fields of medicine and public health. Many meta-analytical methods have been used to combine results of clinical trials. These methods are discussed in several standard references or textbook^.^^,^^,^^,^^ Data methods for combining experimental results most commonly use fixed-effects models. This assumes that every study estimates differences with exactly the same outcomes, risk ratios, or odds ratios. In reality however, this scenario is rarely the case. Several tests are used for determining whether studies can be statistically pooled, but the usual chi-square test has low power to detect study heterogeneity.To perform this test, to find it to be negative, and then to proceed as if homogeneity has been established is not always an appropriate action. Random effects model meta-analysis is an attempt to control for study heterogeneity, but is at best only a partial solution that normally provides a more conservative estimate of the overall effect size or odds ratio. International groups which met to address the problems of published meta-analyses have recently concluded that a large proportion of the published metaanalyses suffer from many shortcomings. One of the most important limitations identified was inadequate control for clinical heterogeneity among synthesized studies. There is currently little consensus on decision rules regarding statistical pooling of study result^.^^,^^ An alternative to meta-analysis has been proposed by Slavins9called ”best evidence synthesis.” This method was the main basis for a systematic review by Bronfort et aL2I Methodological quality or validity scores have been increasingly utilized in systematic reviews; however, weighting the credibility of trial results with these quality scores is still controversial. Detsky et a130 suggested several ways of incorporating quality scores in the determination of the evidence. Most research methodologists are in agreement that quality but unclear as to how much quality really matters. There is some evidence that suggests that nonrandomized and unblinded trials, cases series, and trials with historical controls tend to overestimate the magnitude of a difference or an e f f e ~ t . *However, ~ , ~ ~ there is little evidence that quality scores assigned to RCTs are good predictors of the magnitude and the direction of outcomes of therapy.3s

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Several systematic reviews of studies evaluating spinal manipulation for back pain have been published since 1985. The first attempt at statistical pooling was performed by Ottenbacher and DiFabi0,7~who calculated effect sizes for pain and flexibility in 92 subcomparisons within nine trials on SMT for LBP, two of which were nonrandomized. From a median overall effect size of 0.37, he concluded that there was only limited empirical support for the efficacy of SMT. Anderson et a14 used the same technique of effect size pooling for 23 trials, of which 5 were nonrandomized, and concluded that the resultant mean pooled effect size of 0.38 showed that SMT was consistently more effective than several comparison therapies. This group also performed a sensitivity analysis, including only the studies with relatively high methods scores. This slightly lowered the pooled estimate. In 1991, Koes et a158published a systematic review of back and neck pain and concluded that, even though some results were promising, the efficacy of spinal manipulation had not been convincingly demonstrated. They chose not to perform statistical pooling but to look primarily at trial results as reported by authors and relate the methodological quality to negative and positive outcomes. The review included systematic qualitative assessments of 34 RCTs on LBP. They also concluded that the quality of the trials was disappointingly low and much more attention needed to be paid to methodology in future trials. A recent update of the Koes et a157review involving three additional trials did not change their conclusions. In 1992 Shekelle et als3evaluated acute LBP and isolated seven clinical trials of which one was nonrandomized. They concluded that SMT is of short-term benefit in some patients, particularly those with uncomplicated LBP. This was based on a higher probability of faster recovery at 3 weeks compared with other therapies. Shekelle et alx3decided that there was no basis for meta-analyzing the available chronic low back trials and found there were insufficient data to reach conclusions regarding the efficacy of SMT for chronic LBP. This group also methodologically scored the trials, but did not weight them according to methodological quality in their analysis. The criteria for pooling the studies was mainly based on the ability to look at different probabilities of recovery, although most of the trials have used quantitative outcome measures such as pain and disability. As a result, a substantial number of trials were excluded from their analysis. Two reviews by Assendelft et aPIO (1992 and 1996)have focused entirely on trials addressing the efficacy of SMT for patients who have LBP in which the SMT was delivered by chiropractors. The result of the second review (which was an update of the first review) involving a total of eight RCTs was that no convincing evidence of efficacy of chiropractic SMT for either chronic or acute LBP could be demonstrated. These aut h o r ~considered ~ performing statistical pooling, but decided that it was not possible because of the heterogeneity of the trials. The most recent systematic reviews for LBP were performed by van Tulder et al.looThey followed a protocol similar to that used by Koes et aIs8for quality scoring and abstracting but with the addition of specific

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rules to determine the presence and strength of evidence of efficacy. They concluded that for acute LBP there was limited evidence to suggest that spinal manipulation is better than placebo treatment, physical therapy, exercise, and short-wave diathermy. For chronic LBP they found strong evidence that spinal manipulation was better than placebo treatment and moderate evidence that it was better than general practitioner, massage, bed rest, and analgesics. The systematic review by Bronfort et alZ1differs in methodology from other published systematic reviews on spinal manipulation by isolating its unique effect-not relying on author's conclusions-and by applying more stringent criteria for determining strength of evidence for efficacy. Despite this, the reviews by van Tulder et alloo and Bronfort et alZ1arrive at similar conclusions.

Clinical Guidelines

Since 1987, several published clinical guidelines have included an assessment of the role of spinal manipulation for LBP.1,12,16,24,27,38,84,91,101,10 Official LBP guidelines have been sponsored by national health care agencies, advisory groups, or family medicine groups in North America, Europe, Israel, New Zealand, and Australia. Different criteria have been used for prioritizing and incorporating scientific evidence in the development of these documents, and therefore it is not surprising that the recommendations vary substantially.The United StatesI2and the most recent British guidelineslo3followed explicit rules for the determination and the weighting of the scientific evidence and are of the highest methodological quality and validity. Neither of these two sets of guidelines have assessed the efficacy on chronic LBP but both conclude that there is efficacy for and recommend the use of spinal manipulation in the treatment of acute LBP.

Future Research The efficacy of spinal manipulation for lumbar disk syndromes and sciatica is undetermined. The identification of specific characteristics of patients who have a high probability of benefiting from spinal manipulation and the optimal dose response of this type of therapy are important but, as of yet unanswered, research questions. The potential long-term effect of spinal manipulation and its possible role as primary or secondary prevention of new episodes of LBP, needs further exploring. Also, the relative cost effectiveness compared with other commonly used therapies has not been established. Furthermore, the relative efficacy of spinal manipulation in the hands of different providers is unknown. More RCTs of high methodological quality need to be conducted to answer these questions and to arrive at better estimates of the strength of the existing evidence of efficacy for spinal manipulation.

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SUMMARY AND INDICATIONS

From the most recent and comprehensive systematic reviews, there is moderate evidence of short-term efficacy for SMT in the treatment of acute LBP and for SMT combined with MOB for chronic LBP. This moderate evidence of efficacy rests on a very small percentage of the conducted RCTs. Although available RCTs and prospective studies show promising results, there is insufficient data available to draw conclusions regarding the short-term efficacy of SMT for the treatment of lumbar radiculopathy. The evidence is also inconclusive for the long-term efficacy of SMT and MOB for the treatment of any type of LBP.

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