Internal and external sagittal craniovertebral alignment: A comparison between radiological and photogrammetric approaches in asymptomatic participants

Background: Photogrammetric measures are a commonly applied, highly reliable tool for appraising craniovertebral postures during clinical assessments, rehabilitation, and research interventions. Objective: This study aimed to compare and contrast three external measures of postural alignment (EMPA) using photogrammetric and radiological approaches, and to discuss whether the craniovertebral angle (CVA) reflects the shape of the underlying cervical spine. Design: Cross Sectional Correlation Study. Method: Young adults attended three assessment sessions (S1, S2 and S3). S1 involved a standardised photogrammetric protocol. S2 involved radiographic image acquisition. S3 followed the same protocol in S1 but excluded the self-balancing procedure. Each sessions EMPA were compared through either paired or independent samples t-tests. The different radiographic cervical subtypes and their corresponding CVAs were assessed. Results: There were no significant differences in any EMPA between the two photogrammetric sessions. The CVA was the only EMPA to show a significant difference between photogrammetric (S3) and radiographic approaches. Cervical subtype variability is present throughout the full CVA range. Conclusions: Despite the statistically significant difference in the CVA between approaches, the mean difference was small and unlikely to be clinically meaningful. Accordingly, the quantification of EMPA can be undertaken with high levels of precision and reliability using standardised photogrammetric procedures. The CVA, however, does not provide an indication of the shape of the underlying cervical spine. The distinct radiological differences in the inter-segmental orientation of each vertebral motion segment in conjunction with the differences in the overall global cervical alignment, both within and between participants, negate this possibility.