Introducing the Modified Cobb Angle for Measuring Cervical Spine Curvature During Swallowing

The C2-C7 Cobb angle is used to measure cervical spine curvature, an anatomical parameter that may be associated with swallowing difficulties in some patients. Challenges in visualizing lower cervical vertebrae on videofluoroscopic swallow study images led to the proposal of the C2-C4 modified Cobb angle (MCA) for use in swallowing research. Despite its initial promise, less than optimal reliability and validity suggested a need for improvement and further research. In this study, we aimed to explore the measurement properties of the MCA and a C2-C4 revised-MCA across key timepoints in healthy swallowing of thin liquid boluses.

This exploratory analysis examined inter- and intra-rater reliability, as well as criterion validity of the C2-C4 MCA and C2-C4 revised-MCA in comparison to other measures of cervical spine curvature and head extension (C0-C2, C2-C6, and C2-C7 Cobb angles). Videofluoroscopic images from 35 healthy participants were analyzed using frames from still positioning, bolus passing the mandible, maximum pharyngeal constriction, and swallow rest. Data were analyzed using intraclass correlation coefficients (ICCs), Pearson correlations, and mixed model analysis.

The C2-C4 revised-MCA showed superior intra- and inter-rater reliability and moderate positive correlation with the C2-C6 Cobb angle, demonstrating criterion validity. No differences in C2-C4 revised-MCA were found across swallowing frames, or as a function of participant age, sex, or head extension.

The findings suggest that the C2-C4 revised-MCA has stronger psychometric properties than the MCA, confirming its utility as a cervical spine curvature measurement during swallowing.

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