Kosloff et al. Chiropractic & Manual Therapies (2015) 23:19
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Table 6 Estimated odds ratios and 95% confidence interval (Commercial) Exposures All Age < 45 yr
Age > =45 yr
Odds ratio
95% CI
Odds ratio
95% CI
Odds ratio
95% CI
Any DC Visit 0-1 day
1.09 1.14 1.03 0.82 1.23
0.30-3.91 0.46-2.83 0.48-2.25 0.40-1.68 0.73-2.06 6.30-21.21 5.29-11.35 3.95-6.93 3.36-5.35 2.66-3.89
* * * *
* * * *
1.09 1.20 1.07 0.88 1.24
0.30-3.91 0.48-2.30 0.49-2.33 0.43-1.81 0.72-2.14 5.96-21.11 4.93-10.86 3.73-6.68 3.37-5.46 2.58-3.83
0-3 days 0-7 days 0-14 days 0-30 days
1.14
0.24-5.50
Any PCP Visit 1-1 day
11.56
16.00 16.00 10.00
1.79-143.2 3.40-75.35 3.14-31.88 1.62-8.53 2.17-7.68
11.22
1-3 days 1-7 days 1-14 days 1-30 days
7.75 5.23 4.24 3.22
7.31 5.00 4.29 3.14
3.72 4.08
*Insufficient data to compute an estimate.
between recent PCP visits and VBA stroke is more likely attributable to the background risk related to the natural history of the condition [32]. A secondary goal of our study was to assess the utility of employing chiropractic visits as a surrogate for SMT. Our findings indicate there is a high risk of bias associ- ated with using this approach, which likely overesti- mated the strength of association. Less than 70% of stroke cases (commercial and MA) associated with chiropractic care included SMT. A somewhat higher proportion of chiropractic visits included SMT for the control groups (commercial = 76%; MA = 88%). There are plausible reasons that support these find- ings. Internal analyses of claims data (not shown) con- sistently demonstrate that one visit is the most common number associated with a chiropractic episode of care. The single visit may consist of an evaluation without treat- ment such as SMT. Further; SMT may have been viewed as contraindicated due to signs and symptoms of vertebral artery dissection (VAD) and/or stroke. This might explain the greater proportion of SMT provided to control groups in both the commercial and MA populations. Overall, our results increase confidence in the findings of a previous study [32], which concluded there was no excess risk of VBA stroke associated chiropractic care compared to primary care. Further, our results indicate there is no significant risk of VBA stroke associated with chiropractic care. Additionally, our findings highlight the potential flaws in using a surrogate variable (chiropractic visits) to estimate the risk of VBA stroke in association with a specific intervention (manipulation). Our study had a number of strengths and limitations. Both case and control data were extracted from the same source population, which encompassed national health plan data for approximately 36 million
include SMT as an intervention. Differences between studies in the proportion of cases reporting SMT may have affected the calculation of risk estimates. Also, there were an insufficient number of cases hav- ing cervical and/or headache diagnoses in our study. Therefore, our sample population may have included proportionally less cases where cervical manipulation was performed. Our results were consistent with previous findings [32,33] in showing a significant association between PCP visits and VBA stroke. The odds ratios for any PCP visit increase dramatically from 1 – 30 days to 1 – 1 day (Tables 6 and 7). This finding is consistent with the hypothesis that patients are more likely to see a PCP for symptoms related to vertebral artery dissection closer to the index date of their actual stroke. Since it is unlikely that the services provided by PCPs cause VBA strokes, the association Table 7 Estimated odds ratios and 95% CI (Medicare) Exposures Odds ratio 95% CI Any DC Visit 0-1 day * * 0-3 days * * 0-7 days * * 0-14 days 0.26 0.03-2.00 0-30 days 0.32 0.08-1.39 Any PCP Visit 1-1 day 3.66 1.85-7.26 1-3 days 3.38 2.07-5.51 1-7 days 2.37 1.68-3.34 1-14 days 2.09 1.60-2.73 1-30 days 1.81 1.46-2.25 *Insufficient data to compute an estimate.
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