The study flowchart is presented in . Adherence to attendance of study visits was sufficiently uniform across groups. The figure shows that at least 75% of the patients in each group attended 3/4 of the visits. On average, participants complied with 86% of the required visits and 70% of the participants attended all study visits. Compliance with follow-up questionnaires was also uniform; 80% to 85% of patients returned the mailed 12-week questionnaire and 85% to 95% returned the 24-week questionnaire. The 7 dropouts were participants who refused to continue care past 2 weeks or provide follow-up data. Ten persons sought care from a provider outside the study during the treatment phase: broken down as 6 LM and 4 SMT patients, and as 6 low-dose and 4 high-dose patients. Only 4 patients received SMT outside the study. Outside care visits were balanced across groups, and uncorrelated with pain improvement between 4 and 24 weeks (P > .05).
Patient flow diagram. All patients were assigned 16 visits where they received spinal manipulative therapy (SMT), light massage (LM), or attention control physical exam (att). Adherence to study visits and compliance with follow-up are identified.
shows the baseline characteristics for the 4 study groups. Participants tended to be young (mean = 36), white, non-Hispanic (85%) women (80%). The overall mean CGH pain and functional disability scale values were 54.3 and 45.0 respectively. The sample averaged approximately 4 CGHs per week and less than one “other” headache per week. About 1/4 of subjects reported suffering from migraine, 1/2 had low back pain, and 2/3 identified another comorbid condition. Participants took some form of oral medication about 5 times per week on average: mostly over-the-counter analgesics with little prescription drug use.
Baseline participant characteristics
Participants were asked if they could discern their CGH from other headaches they experienced at baseline and each follow-up time point. Between 89% and 94% of the patients reported that they could distinguish CGH from other types “most of the time” or “always.” Also, chi-square analysis showed no significant difference between groups in discernment at any time point (P > .05).
CGH pain and disability
Group means with standard deviations, as well as adjusted mean differences with 95% confidence intervals for the main and interaction effects are presented in for follow-up at 12 weeks, 24 weeks, and the full profile over all time points. Adjusted pair-wise comparisons are included in . The adjusted mean differences between groups were consistently smaller than unadjusted comparisons due to baseline differences in the covariates.
Observed Mean outcomes (±SD) and adjusted mean differences (95% CI) between groups*
Adjusted mean differences (95% CI) for pair-wise group comparisons*
For the MVK pain scale, the primary outcome, shows that there were no clinically important main effects of dose (|AMD| < 2). further shows pair-wise comparisons were small in magnitude (|AMD| ≤ 5.6). There were, in contrast, clinically important and statistically significant main effects of intervention favoring SMT over LM. The AMD was -8.1 for the entire profile, -10.3 at 12 weeks, and -9.8 at 24 weeks (). The largest pair-wise effects of SMT were found for 16 treatment sessions, AMD = -11.9 to -14.4, as opposed to 8 sessions, AMD = -4.2 to -6.4 (). The effects were smaller for the profile than for the individual time points because the profile included data from 4 weeks, which was only half way through study care.
shows the adjusted follow-up means for the CGH pain scale for all time points. The baseline value in the figure is the overall sample mean (54.3). It is included here because adjusted pain outcomes are determined relative to this common value for all groups. Inspection of shows that most improvement in the MVK pain scale was achieved by the end of care at 8 weeks and was durable to 24 weeks. SMT performed better than LM at all time points However, the graphs show further room for patient improvement.
Adjusted mean cervicogenic headache pain. Predicted follow-up means were computed using simultaneous regression analysis adjusted for the baseline covariates. The analysis assumes all groups start at the grand baseline mean pain (shown at week 0).
Dose and intervention effects for CGH disability demonstrated similar trends to that of CGH pain. Most AMDs were slightly smaller in magnitude, and less likely to be statistically significant because of greater variability in the data.
There were statistically significant intervention main effects favoring SMT for the profile (AMD = -2.6) and at 12 weeks (AMD = -3.6) for the number of CGH in the prior 4 weeks (). Significant intervention effects were also found for 16 sessions in . Dose effects were smaller, particularly for SMT. shows that the adjusted mean number of CGH was decreased by more than half in participants receiving SMT and that the improvement was sustained to 24 weeks.
Fig3 Adjusted mean number of cervicogenic headaches. Predicted follow-up means were computed using simultaneous regression analysis adjusted for the baseline covariates. The analysis assumes all groups start at the grand baseline mean pain (shown at week 0). (more ...)
“Other” headaches were rare compared to CGH. The mean number at baseline was 3.4 compared to 15.7 in the prior 4 weeks. Findings for “other” headache numbers paralleled those for CGH. The intervention effects were smaller in magnitude (), but larger in proportion to baseline number of headaches. Of note was the benefit of SMT over LM at 24 months (AMD = -2.1). At this time point, only SMT patients demonstrated improvement from baseline.
Neck pain and disability
The main effects were similar to those of CGH pain and disability but generally of lesser magnitude. Dose effects were mostly small, with the exception in of a clinically important advantage of higher dose SMT over lower dose SMT. showed some statistically significant intervention effects for disability. However, the advantage for SMT in pain and disability consistently reached clinical importance only for the higher dose, 16 treatment sessions (). The study did not have power to reach statistical significance here.
Dose effects were unremarkable for oral medication. shows that improvement in over-the-counter usage achieved at 12 weeks was only sustained for SMT patients at 24 weeks. The SMT patients were using a third less medication compared to baseline at 24 weeks and there was a statistically significant advantage for SMT over LM at this time point (AMD = -6.0).
Secondary analysis: 50% symptoms reduction
shows the percentage of participants that achieved a 50% reduction in outcomes at 12 and 24 weeks, and for the profile over all follow-up time points. Dose effects were small. On the other hand, SMT was considerably more likely to achieve a 50% reduction in symptoms (adjusted odds ratio > 1.8). In fact, the adjusted odds ratios for CGH pain were greater than 3.0.
Patients achieving a 50% reduction in symptoms and adjusted odds ratios (95% CI)*
The sensitivity analysis using original data without imputation for CGH pain scale (primary outcome) showed the same general trends presented above in . However, there were some notable differences from the data in . A clinically important dose effect was observed favoring 16 SMT sessions over 8 SMT sessions: the profile AMD = -9.4 (95% CI = -17.4 to -1.5), 12-week AMD = -13.1 (-27.0 to 0.8), and 24-week AMD = -11.4 (-26.6 to 3.9). In addition, the advantage of SMT over LM was somewhat larger for patients receiving the higher dose of care: 12-weeks AMD = -20.4 (-33.4 to -7.3) and 24-week AMD = -14.4 (-28.7 to -0.2). Adjusted odds ratios for symptom reduction were also consistent with the findings in .