INTRODUCTION: Neck pain and headaches are common, with a reported lifetime prevalence of up to 66%. Upper cervical segmental dysfunction has been implicated as meaningful in neck pain and multiple headache types. Several tests have been described to assess upper cervical joint dysfunction, including the flexion-rotation test (FRT), the side bend-rotation test (SBRT), and joint play assessment (PA). The purpose of this study was to determine the diagnostic validity of the SBRT to detect C1-2 dysfunction in a sample of people with medically diagnosed sinus headaches and controls. METHODS: Design: prospective diagnostic accuracy study, occurring during an observational case-control study in a sample of individuals with medically diagnosed sinus headaches. All participants were assessed using the SBRT, FRT, and C1-2 joint play assessments. The diagnostic accuracy of the SBRT was assessed using a reference standard of concurrent positive FRT (a loss of at least 10° from expected ROM (≤34°)) and restriction of C1-2 joint play. Cut-off scores for the SBRT were determined using ROC curve analysis, and tests of diagnostic accuracy were calculated using 2 × 2contingency tables. RESULTS: A total of 80 individuals (40 headache, 64 female, mean age 32.9 ± 13.8 yrs.) were included in the study. Mean ROM for the tests was: SBRT 31.4 ± 9.4°, FRT 44.9 ± 9.5°, and C1-2 mobility 22 hypomobile/58 normal. An SBRT cutoff score of <
25° was confirmed using ROC curves. Using this cutoff score, the SBRT demonstrated 100% sensitivity and 62% specificity to detect C1-2 hypomobility. DISCUSSION/CONCLUSION: The SBRT, using a cutoff score of ≤25°, appears to be a sensitive test to detect C1-2 dysfunction. Based on the strong sensitivity and negative predictive values, scores greater than 25° may effectively rule-out C1-2 dysfunction. The SBRT should be considered as part of a sequential clinical decision-making process when screening for C1-2 dysfunction, although further research is required to improve generalizability of these findings.