Validity and reliability of a smartphone goniometer application for measuring hip range of motions

BACKGROUND: Mobile applications which are designed to assess the range of motion (ROM) are widely used. OBJECTIVE: The aim of this cross-sectional observational study was to determine the inter-observer and intra-observer reliability of a smartphone application "PT Goniometer" (PTG) and determine the correlation between PTG and universal goniometer (UG) regarding active ROMs of the hip in healthy participants. METHODS: Thirty-four healthy young participants were included in the study. Two physiotherapists performed active hip flexion, abduction, internal rotation and external rotation ROM measurements of dominant legs of the participants by using PTG and UG. Intraclass correlation coefficients (ICC) were calculated to determine the intra-observer and inter-observer reliability. Level of correlations between PTG and UG were used to establish concurrent validity of PTG. RESULTS: The PTG demonstrated excellent inter-observer and intra-observer reliability (ICC > 0.90) for all measured hip movements. The minimum detectable change (MDC 95 ) was ranged from 3.29 degrees to 5.1 degrees for the intra-observer reliability, and from 2.55 degrees to 3.21 degrees for the inter-observer reliability. Additionally, the concurrent validity was found excellent (r= 0.91-0.93). CONCLUSION: The results of the present study suggest that PTG is a valid and reliable mobile technology for measuring hip ROMs.