Spine (Phila Pa 1976) 2019 (May 1); 44 (9): 647–651 ~ FULL TEXT
Ron D. Hays, Ph.D., Karen L. Spritzer, B.S., Cathy D. Sherbourne, Ph.D.,
Gery W. Ryan, Ph.D., Ian D. Coulter, Ph.D.
Division of General Internal Medicine & Health Services Research
UCLA Department of Medicine
911 Broxton Avenue
Los Angeles, CA
STUDY DESIGN: Prospective observational study.
OBJECTIVE: To evaluate group-level and individual-level change in health-related quality of life among persons with chronic low back pain or neck pain receiving chiropractic care in the United States.
SUMMARY OF BACKGROUND DATA: Chiropractors treat chronic low back and neck pain, but there is limited evidence of the effectiveness of their treatment
METHODS: A 3–month longitudinal study of 2,024 patients with chronic low back pain or neck pain receiving care from 125 chiropractic clinics at 6 locations throughout the United States was conducted. Ninety-one percent of the sample completed the baseline and 3–month follow-up survey (n = 1,835). Average age was 49, 74% females, and most of the sample had a college degree, were non-Hispanic White, worked full-time, and had an annual income of $60,000 or more. Group-level (within group t-tests) and individual-level (coefficient of repeatability) changes on the Patient-Reported Outcomes Measurement Information System (PROMIS) v2.0 profile measure was evaluated: 6 multi-item scales (physical functioning, pain, fatigue, sleep disturbance, social health, emotional distress) and physical and mental health summary scores.
RESULTS: Within group t-tests indicated significant group-level change (p < 0.05) for all scores except for emotional distress, and these changes represented small improvements in health (absolute value of effect sizes ranged from 0.08 for physical functioning to 0.20 for pain). From 13% (physical functioning) to 30% (PROMIS-29 Mental Health Summary Score) got better from baseline to 3 months later according to the coefficient of repeatability.
CONCLUSIONS: Chiropractic care was associated with significant group-level improvement in health-related quality of life over time, especially in pain. But only a minority of the individuals in the sample got significantly better ("responders"). This study suggests some benefits of chiropractic on functioning and well-being of patients with low back pain or neck pain.
Key Words: low back pain, neck pain, chiropractic, PROMIS®, health-related quality of life,
within group change, responders, observational
From the FULL TEXT Article:
Musculoskeletal disorders are among the most prevalent health problems and the second
leading cause of disability worldwide.  Low back pain prevalence for adults in the United States (U.S.) is about 20% and estimated to cost $34 billion in 2010.  The authors of one cross-sectional study concluded that prevalent neck pain was weakly associated with the SF-36 physical health summary score and not significantly related to the SF-36 mental health summary score after controlling for comorbidities.  Similarly, another study reported no significant association between neck pain and the SF-36 mental health summary score but found a dose response association with the SF-36 physical health summary score, even after adjusting for age, education, arthritis, low back pain, and depressive symptoms.  These authors reported similar ssociations in a different study for those with low back pain. 
More than 50% of U.S. adults have sought care from a chiropractor and about 30% of those with spinal pain in the U.S. have used chiropractic care.  Chiropractors treat chronic low back and neck pain, but there is limited evidence of the effectiveness of their treatment.  The UK back pain, exercise and manipulation study documented significant improvements over 3 months attributable to manipulation of 2.5 and 2.9 points on the SF-36 physical and mental health summary scores, respectively. 
We conducted a longitudinal observational study of a sample of chronic low back pain (CLBP) and chronic neck pain (CNP) patients receiving chiropractic care to evaluate change in health-related quality of life (HRQOL) using the Patient-Reported Outcomes Measurement Information System (PROMIS®) measure recommended by the National Institutes of Health Task Force on Research Standards for Chronic Low Back Pain  and administered along with the Neck Disability Index in a recent study.  This study is unique because it provides information on a representative sample of chiropractic patients in care for chronic pain. It provides important information on the effect of chiropractic care for those with long-lasting pain.
Chiropractic care was associated with significant improvements on all PROMIS-29 v2.0 measures except emotional distress in this sample of patients with chronic low back pain or neck pain. The absence of associations of back and neck pain with emotional distress is consistent with previous research. [3–5] The largest mean improvements were observed for pain, sleep disturbance, the PROMIS-29 v2.0 mental health summary score (weighted combination of fatigue, emotional distress, ability to participant in social roles and activities and sleep disturbance), social health, and fatigue. These improvements over 3 months are consistent with prior estimates of minimally important group-level differences of about 2–3 points for PROMIS measures. [19, 20] In addition, the magnitude of change is similar to what was reported for the SF-36 physical and mental health summary scores in the UK back pain, exercise and manipulation study using the SF-36 health survey.  Note that the corresponding PROMIS-29 v2.0 and SF-36 summary scores correlated 0.82 with one another. 
While some have suggested that group-level minimally important differences can be used to identify “responders” to treatment (e.g., Coons & Cook ), using hese thresholds to identify responders is inappropriate because of the larger standard errors associated with individual change estimates (23). Responders need to be identified based on the significance of individual change. We used the coefficient of repeatability in this study to show that for the scales that showed statistically significant mean improvement, from 13% (physical functioning) to 30% (PROMIS-29 Mental Health Summary Score) could be classified as responders. These estimates are in the ballpark of what was observed over a decade ago in an observational study of patients receiving care at the UCLA Center for East-West Medicine  and more recently in a sample of patients treated for chronic myofascial pain. 
This study illustrates the importance of reporting the proportion of responders in addition to the significance of group-level change. Observational studies and clinical trials should routinely report responders based on the significance of individual change. Using group-level estimates to identify individuals who have changed needs to be avoided. “A minimum criterion for a responder is that the individual improved significantly (i.e., individual change is greater than the measurement error associated with the PRO measure. There are a variety of related ways to estimate the significance of individual change and one or more of these should be used to determine if individual change is significant or not” (McLeod et al., p. 5 ).
The results of this study contribute to the literature by providing evidence that chiropractic care is associated with improvements in functioning and well-being among individuals with chronic low back or neck pain. The study findings provide empirical verification of why some chronic pain patients utilize chiropractic care on a regular basis. It supports the use of chiropractic care as one option for improving functioning and well-being of patients with chronic low back pain or neck pain. While we are unable to infer the underlying mechanism for the observed improvements in patients, spinal manipulation is designed to relieve pain and improve physical functioning. Studies of the biomechanics indicate that spinal manipulation produces reflex responses and movements of vertebral bodies in the paraphysiologic zone. 
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