Kathryn T. Hoiriis, DC, Bruce Pfleger, PhD, Frederic C. McDuffie, MD,
George Cotsonis, MA, Omar Elsangak, MBBCh, DC, Roger Hinson, DC,
Gregoria T. Verzosa, DC
College of Chiropractic,
Chiropractic Sciences Division,
Marietta, Ga 30060, USA.
OBJECTIVE: To compare the relative efficacy of chiropractic adjustments with muscle relaxants and placebo/sham for subacute low back pain.BACKGROUND: The adult lifetime incidence for low back pain is 75% to 85% in the United States. Investigating appropriate care has proven difficult, since, in general, acute pain subsides spontaneously and chronic pain is resistant to intervention. Subacute back pain has been rarely studied.
DESIGN: A randomized, double-blind clinical trial.
METHODS: Subjects (N = 192) experiencing low back pain of 2 to 6 weeks’ duration were randomly allocated to 3 groups with interventions applied over 2 weeks. Interventions were either chiropractic adjustments with placebo medicine, muscle relaxants with sham adjustments, or placebo medicine with sham adjustments. Visual Analog Scale for Pain, Oswestry Disability Questionnaire, and Modified Zung Depression Scale were assessed at baseline, 2 weeks, and 4 weeks. Schober’s flexibility test, acetaminophen usage, and Global Impression of Severity Scale (GIS), a physician’s clinical impression used as a secondary outcome, were assessed at baseline and 2 weeks.
RESULTS: Baseline values, except GIS, were similar for all groups. When all subjects completing the protocol were combined (N = 146), the data revealed pain, disability, depression, and GIS decreased significantly (P <.0001); lumbar flexibility did not change. Statistical differences across groups were seen for pain, a primary outcome, (chiropractic group improved more than control group) and GIS (chiropractic group improved more than other groups). No significant differences were seen for disability, depression, flexibility, or acetaminophen usage across groups.
CONCLUSION: Chiropractic was more beneficial than placebo in reducing pain and more beneficial than either placebo or muscle relaxants in reducing Global Impression of Severity Scale (GIS).
From the FULL TEXT Article:
In all groups, for each outcome measure, there was improvement after 2 weeks of care and further improvement at the 4-week follow-up, so these subacute subjects appear to improve in a manner similar to acute pain sufferers. [4, 5] The improvements in the placebo group likely represent natural history.
After the 2-week intervention phase, chiropractic adjustments were shown to be statistically more beneficial than placebo in reducing pain and more beneficial than placebo or muscle relaxants in reducing GIS; however, there were no differences across groups for disability. For the disability measure, post hoc analysis revealed the power of the present study to be 59%. Further, assuming means and variances seen in the present study and a power level of 80%, increasing the sample population to 72 subjects per group could have yielded significant advantages for chiropractic adjustments. No group differences were seen with the Modified Zung, as would be expected since depression is mild during the acute/subacute phase, nor were differences observed for flexibility or analgesic usage.
Previous comparisons of SMT to medical care for LBP have shown mixed results. A study of subjects with 3 to 26 weeks of LBP showed no additional benefit for osteopathic manipulation over standard medical care, which included medicines and physical modality.  Similarly, a study of acute LBP showed manipulative physiotherapy was no more beneficial than nonsteroidal anti-inflammatory drugs (NSAIDs).  In chronic LBP, no group differences were seen for trunk-strengthening exercises supplemented by either chiropractic manipulation or NSAIDs.  Conversely, other chronic spinal pain studies have shown spinal manipulative procedures more beneficial than NSAIDs  and spinal manipulation more beneficial than continued care using analgesics and NSAIDs.  In light of the differing methodologies across studies, it is difficult to draw any strong conclusions.
In this study, care was restricted to 2 weeks, although in practice, chiropractors typically see patients for longer periods. Other trials comparing chiropractic adjustments to medical care for LBP allowed for 9 visits over 1 month,  10 treatments over 1 year,16 or, in a childhood asthma study, 20 to 36 visits over 4 months.  Though improvement was marked and rapid in the present trial, providing the chiropractors with more latitude in their care plan might have provided additional benefit. As follow-up extended only to 4 weeks, long-term benefits of the interventions are unknown.
Outcomes in randomized drug therapy trials often include assessment of global improvement and 5 specific domains of back pain: local pain, muscle spasm, range of motion, tenderness to palpation, and activities of daily living.  The GIS used in this study has not been tested for reliability and validity and is subjective by its very nature. It is, therefore, limited in its usefulness and significance. The measure did provide a broadly based assessment, was normally distributed, demonstrated a useful range, and was responsive to 2 weeks of intervention/time. In a clinical perspective, the severity of a patient presenting for care is often subjectively rated. In this study, the GIS represented a blinded evaluation of severity by the medical doctor using his own scoring method. There was overlap in outcome assessments, since GIS was formed from 5 measures, 2 of which were analyzed individually. However, analysis of GIS data without the VAS or Schober’s components did not change the results. The GIS showed that subjects given chiropractic adjustments and placebo medicine improved more than subjects who received placebo medicine or muscle relaxants did (in combination with sham adjustments). However, it should be noted that the chiropractic group mean was worse at baseline, giving a slightly more favorable advantage toward improvement based solely on natural history.
In this study population, only modest changes in flexibility were seen and no difference among groups emerged using Schober’s test. The reliability and validity of Schober’s test for testing lumbar flexibility have been debated. Researchers have found Schober’s test works as well as the computerized CA-6000 Spinal Motion Analyzer (Orthopedic Systems Inc, Union City, Calif) in assessing lumbar flexion and that a modified Schober test is superior to double inclinometer methods for flexion, while another study suggests use of a modified Schober could introduce systematic errors and its use is questionable. [59-61]
Although lifetime usage figures are not available, approximately 7% to 10% of the overall population uses chiropractic in a given year. [62, 63] The study population was not naïve to chiropractic interventions. Since 40% also reported previous LBP (exclusion criteria: occurrence >18 months prior), it is not surprising to find a 41% lifetime history of chiropractic care (exclusion: occurrence >18 months prior). Even so, the post hoc analysis found no significant association of previous chiropractic care with blinding, dropout rate, or changes in VAS for pain.
Although blinding procedures directed toward the providers and assessors were successful, whether subjects remained blinded is debatable. A high percentage of subjects in the chiropractic and medical groups responded correctly to questions regarding the intervention received. This is not unusual in clinical trials, since many interventions deliver a powerful and readily apparent effect. However, it is difficult to interpret why statistically more control subjects than chiropractic subjects in this study thought they were receiving true medications. It would seem that the blinding procedures used here were no less successful than those used in other rigorous randomized clinical trials. [56, 57, 64]
Blinded, randomized clinical trials are considered the gold standard of experimental design. [9, 15, 21, 65] Yet, blinding remains elusive in studies where the intervention may be invasive (eg, surgery, acupuncture) or involve physical contact between the subject and the care provider (eg, chiropractic, osteopathy, massage). An appropriate chiropractic sham procedure requires a maneuver that makes subjects think they are getting a spinal adjustment without actually causing osseous rearrangement. Joint cavitation commonly occurs during activities that approach endpoint range of motion, and this may cause changes in the spine. Joint cavitation was noted twice in the present study during lumbar sham procedures. Even well-designed sham procedures could cause inadvertent correction. Further, there is the possibility that palpation of spastic paraspinal muscles and other contiguous tissues may cause spinal changes. Thus, previous rigorous sham-controlled studies in chiropractic that demonstrated global benefits to all intervention groups while failing to show differential benefits  may have been inadvertently providing benefit to the control group.
In a factorial design, a fourth group could have been randomized to receive both active interventions. Furthermore, this study did not provide for a 1-year follow-up. Possibly, long-term follow-up could help to identify different recovery patterns in these groups. Stratification on the study population for the wide ranges in pain and disability scores (large SD) in a separate analysis may provide characteristics of responders versus nonresponders for both types of interventions.
Health care providers often rate the severity of presenting complaints of patients using subjective means. The GIS used for a blinded assessment by the medical physician needs to be tested for reliability and validity; therefore, the significance of the results for GIS should be interpreted cautiously.
Increasing the sample size according to power analysis, lengthening the care phase to 6 weeks to provide care more in line with practice standards, and providing a 1-year follow-up would improve future studies.
This study identified a sample population of subacute low back pain sufferers for which chiropractic care provided an equally effective management to the conservative medical care of muscle relaxants. However, as subjects responded well to time (and placebo), these design changes may not provide the strong clinical evidence needed to recommend a particular intervention for management of subacute back pain.
Statistically, the chiropractic group responded significantly better than the control group with respect to a decrease in pain scores.