Photo-Based Range-of-Motion Measurement: Reliability and Concurrent Validity in Children With Cerebral Palsy.

Purpose: To investigate intrarater and interrater reliability, agreement, and concurrent validity of a smartphone photography-based application compared with a universal goniometer in children with cerebral palsy.

Methods: Range of motion of hip abduction, popliteal angle, and ankle dorsiflexion was measured with a universal goniometer and a photography-based application in children with cerebral palsy, Gross Motor Function Classification System levels I to V.A 2-way random-effects intraclass correlation coefficients and Bland-Altman plots, standard error of measurement, and smallest detectable change were used for analyses.

Results: The application had good to excellent reliability and concurrent validity compared with a universal goniometer, while the large measurement error of both methods suggests that changes of 10° to 23° are needed to be certain that changes over time are not results of measurement error.

Conclusions: A photography-based goniometer can be a reliable and valid tool when measuring range of motion in children with cerebral palsy.