Research Review By Dr. Brynne Stainsby©

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Background Information:

Pertinent Results:

• The cohort included 2162 participants; 874 (40.4%) females; the average age was 43.3 (SD: 13.4); and 522 (24.1%) were referred for imaging at the first visit (i.e. exposure group).
• In the exposure group, 505 (96.7%) were referred for x-ray alone; 8 (1.5%) for x-ray and MRI; 7 (1.3%) for MRI alone; and 2 (0.4%) for x-ray, CT and MRI.
• Participants referred for imaging were more likely to be female, older, have more than 3 months of pain duration, expect an imaging referral, have a high risk of poor prognosis, report at least one comorbidity, and have a clinical suspicion of underlying pathology.
• Low back disability was higher in those that received an imaging referral at all time points. Global perceived effect of “much better” was lower in those that received an imaging referral to 2-weeks follow-up. All other outcomes were similar.

Clinical Application & Conclusions:

Study Methods:

• A matched cohort study design was performed using the Danish Chiropractic low back pain cohort (ChiCo) study (19). A prospective, longitudinal, observational study with one year follow-up was performed between November 2016 and December 2019.
• The total ChiCo cohort included 2818 patients who presented to Danish chiropractors with new or recurrent LBP, with or without leg pain, for which they were not already undergoing a current course of treatment. Those with a confirmed diagnosis of fracture, infection, cancer or other pathology were excluded from the ChiCo study. To be included, subjects had to be 18 years of age or older and have the ability to complete electronic questionnaires in Danish (19).
• Treatment was provided as needed and was not impacted by participation in the study. No limitation was placed on health care access.
• For the cohort study discussed in the current review, participants identified by the chiropractor at baseline to have previous imaging relevant to their current clinical presentation were excluded (n = 656).
• Baseline questionnaires were completed by participants and chiropractors, and participants also underwent a baseline clinical assessment. Follow-up questionnaires were completed by participants at two weeks, three months and one year.
• Participants who were referred for diagnostic imaging by the chiropractor at the first visit (x-ray, CT or MRI) were defined as the exposure group; participants not referred for imaging at the first visit were defined as the non-exposure group.
• Matching was performed using baseline variables considered by the research team to potentially affect the decision to refer for imaging, as well as those associated with outcome measures on regression analysis. These included: age, sex, LBP intensity, duration of LBP, leg pain intensity, LBP disability, risk of poor prognosis, previous imaging, previous surgery, previous LBP treatment, chiropractor suspicion of serious pathology, chiropractor intention to treat with spinal manipulation, participant expectation of imaging, and presence of co-morbidities.
• The primary outcomes of the study were participant-reported LBP intensity and disability at three months. The secondary outcomes were participant-reported LBP intensity and disability at two weeks and one year, as well as global perceived effect on LBP and satisfaction with care at two weeks.
• Missing data were imputed, depending on the type and reason for the missing data. Participants with missing outcome data were removed from the analyses.
• Exposure and non-exposure groups were matched on baseline variables using coarsened exact matching (CEM) (20, 21), which assigns individuals to strata of baseline characteristics, and discards any strata that do not include at least one exposed and one non-exposed participant.

Study Strengths / Weaknesses:

• This cohort study used prospective, longitudinal observation data from a large sample of patients seeking care for LBP in a real-world practice setting.
• The statistical methods used in this study to investigate causal methods by matching exposed and unexposed participants approximates the effect of randomization.
• The baseline variables used for matching were predetermined as variables likely to impact clinical decision making regarding referral for imaging.
• The authors compared the results to published medical literature.

• Given this is an observational study, although the statistical methods approximate randomization, it cannot account for unknown variables.
• It should be noted that participants with missing outcome variables were excluded from the analysis.
• Although referral for all types of diagnostic imaging was assessed, chiropractors only referred for CT or MRI in 3.3% of cases, meaning that the results of this study predominantly reflect the use of x-ray. While this limits the conclusions drawn, it is likely reflective of typical referral patterns in a chiropractic practice environment.

Additional References:

1. Qaseem A, Wilt TJ, McLean RM et al. Noninvasive treatments for acute, subacute, and chronic low back pain: a clinical practice guideline from the American College of Physicians. Ann Intern Med 2017; 166: 514-530.
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3. Chou R, Qaseem A, Owens D et al. Diagnostic imaging for low back pain: advice for high-value health care from the American College of Physicians Ann Intern Med 2011; 154: 181-189.
4. Karel YH, Verkerk K, Endenburg S, et al. Effect of routine diagnostic imaging for patients with musculoskeletal disorders: a meta-analysis Eur J Intern Med 2015; 26: 585-595.
5. Chou R, Deyo RA, Jarvik JG. Appropriate use of lumbar imaging for evaluation of low back pain Radiol Clin North Am 2012; 50: 569-585.
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12. Graves JM, Fulton-Kehoe D, Jarvik JG, et al. Health care utilization and costs associated with adherence to clinical practice guidelines for early magnetic resonance imaging among workers with acute occupational low back pain. Health Serv Res 2014; 49: 645-665.
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14. Jenkins HJ, Downie AS, Moore CS et al. Current evidence for spinal X-ray use in the chiropractic profession: a narrative review Chiropr Man Ther 2018; 26: 48.
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18. Slade SC, Kent P, Patel S et al. Barriers to primary care clinician adherence to clinical guidelines for the management of low back pain: a systematic review and meta-synthesis of qualitative studies. Clin J Pain 2016; 32: 800-816.
19. Kongsted A, Nielsen OL, Christensen HW et al. The Danish chiropractic low back pain cohort (Chico): description and summary of an available data source for research collaborations. Clin Epidemiol 2020; 12: 1015.
20. Blackwell M, Iacus S, King G et al. Coarsened exact matching in Stata Stand. Genomic Sci 2009; 9: 524-546.
21. Iacus SM, King G, Porro G. Causal inference without balance checking: Coarsened exact matching. Polit Anal 2012; 20: 1-24.