Concurrent validity of a novel digital dynamometer for assessing performance on the Cranio-Cervical Flexion Test

Introduction: The Cranio-Cervical Flexion Test (CCFT) is a validated clinical test used to evaluate deep cervical flexor muscle function. A pressure biofeedback unit (PBU) has traditionally been the reference device. Recently, a new portable digital device known as the Neuromuscular Cranio-cervical Device (NOD) has been developed as a potential alternative. Methods: In this cross-sectional concurrent validation study, 88 participants were recruited from four outpatient physiotherapy practices, including individuals with current neck pain and individuals with a previous history of neck pain. All participants performed the CCFT using both devices. The PBU was inflated to a baseline pressure of 20 mmHg, with the participant then performing C-CF to increase the pressure in increments of 2 mmHg over five progressive stages, while the NOD was calibrated to corresponding force targets. Agreement and concurrent validity between the devices were assessed, and C-CF range of motion (ROM) was analyzed using linear mixed-effects models. Results: Agreement between CCFT performance scores obtained with the NOD and the PBU was 94.3%, with a very strong positive correlation (Spearman's ρ = 0.930, p < 0.001). The NOD measured slightly greater C-CF ROM than the PBU (mean difference 0.68°), with significant differences at lower CCFT stages that converged at higher stages of the test. Conclusion: These findings demonstrate strong concurrent validity between the NOD and the PBU, supporting the NOD as a valid digital alternative for assessment of the CCFT.