Two-dimensional versus three-dimensional measurement of infant cervical active motion

Introduction Upright infant active cervical motion (ACM) is difficult to measure accurately by a single examiner. Clinically, physical therapists use visual estimation, which has limited reliability and concurrent validity with gold standards. Consistent, reliable, and valid active motion measurements are needed to document infant status and response to intervention. Purpose Two-dimensional (2D) photo digitization measurements were compared to three-dimensional (3D) motion analysis measures of infant active neck rotation and lateral flexion. Methods Typically-developing infants participated (five boys, nine girls; 3-7.5 months). An experienced pediatric physical therapist and six novice raters marked photographs and used two different 2D methods to measure cervical rotation and three different 2D methods to measure cervical lateral flexion in photographs. To determine the intra- and interrater reliability of the 2D measurement methods and their concurrent validity with the 3D measures, a subset of lateral flexion photos was marked and measured by 14 experienced pediatric physical therapists. Results Novice and experienced examiner measurements of 2D ACM exhibited moderate to excellent intra- and inter-rater reliability. The results of the 2D lateral flexion ACM measurements completed by novice and experienced raters consistently differed from those obtained using the 3D measurement methods. Conclusion The 2D rotation ACM measurement methods were reliable and demonstrated concurrent validity with the gold standard 3D measure. Infants' lateral flexion ACM examined using 2D measures did not correlate with the results of 3D measurements. This indicated that 2D measurements of active infant cervical lateral flexion could not be used as a valid indicators of 3D motion.