RecruitingClinical trialDifferences in Characteristics of Headache Patients With a Positive or Negative FRT: a Cross-sectional Comparison.An observational study will be conducted to evaluate the differences in headache characteristics between a subgroup of cervicogenic headache patients with a positive and negative flexion-rotation test at the C1-C2 level. Differences may guide future treatment allocation and the use of more individualized treatment options.