Dynamic motion analysis of the cervical spine during normal swallowing

This study aims to clarify the dynamic changes in the cervical lordotic angle (CLA) during normal swallowing using an automated motion analysis method. Physiological cervical lordosis is crucial for spinal alignment and musculoskeletal function. While previous studies have noted the relevance of cervical curvature in clinical contexts, its dynamic modulation during swallowing has not been well studied. Videofluoroscopic swallowing examinations were conducted in 39 healthy individuals without cervical spine disease. A 2-dimensional template matching technique was applied to automatically track the cervical spinous processes and vertebral bodies over 61 frames spanning 1 second before and after the pharyngeal phase. The CLA was calculated using the angle between the cervical baseline (fitted to vertebral centroids) and reference lines (drawn between vertebral body and spinous process). Subjects were categorized by baseline lordotic angle into 4 groups: <0°, 0° to 10°, 10° to 20°, and ≥20°. Across all participants, the CLA decreased during the pharyngeal phase, peaking at the time of maximum hyoid elevation. Group-wise analysis revealed minimal change in the < 0° group. The 0° to 10° group showed early reduction before the pharyngeal phase. The 10° to 20° group demonstrated the most synchronized and prominent angular transition centered around the pharyngeal phase. In the ≥ 20° group, lordosis decreased but showed limited restoration post-swallowing. Cervical spine motion during swallowing varies with baseline lordotic angle. Moderate lordosis (10-20°) is associated with the most efficient and coordinated motion. This suggests that optimal cervical alignment may facilitate safe and effective deglutition. Quantifying such dynamic motion could support future diagnostic tools and rehabilitation strategies for dysphagia or cervical dysfunction.