Reliability and Criterion Validity of the Smartphone Inclinometer Application to Quantify Cervical Spine Mobility

STUDY DESIGN: In this observational study, we compare fluid inclinometer and smartphone measures to analyze active cervical range of motion (ACROM) in healthy individuals. OBJECTIVE: The purpose of this study was to investigate the reliability and the criterion validity of a smartphone application to analyze head movements. SUMMARY OF BACKGROUND DATA: Recent studies on the reliability and the validity of customized smartphone applications to measure ACROM show good results for frontal and lateral planes' movement analysis, but poor results for the transverse plane. This can be due to the surrounding magnetic fields that affect the compass application used during head rotation valuation. METHODS: Twenty-three individuals were asked to perform neck maximal (end-range) movements (frontal flex-extension and left-right side flexion in the sitting position, left-right rotation in the prone position). Two separate examiners took all ACROM measures and were assigned to each device (iPhone 5c and the inclinometer) contemporary for each individual. RESULTS: All measurements were taken twice to assess the intraobserver reliability. Interobserver and intraobserver reliabilities were evaluated using the intraclass correlation coefficient (ICC). The criterion validity between the 2 instruments was also assessed in terms of the ICC. The procedures used in this investigation for measuring ACROM yielded good validity (Pearson r≥0.99 and ICC≥0.99) between the 2 instruments for all movements. The Bland and Altman's 95% LoA ranged from -1.8 to 1.15 degrees. Percentage error values ranged from 1% to 3%. The intrarater and the interrater reliabilities were good (ICC≥0.9) for both instruments in all movements including the rotation movements (ICC>0.95). The minimal detectable change (MDC95) ranged from 4 to 8 degrees. CONCLUSIONS: This study confirms that the tested smartphone is valid and reliable to measure ACROM on the frontal and the sagittal planes; furthermore, it also demonstrates its usefulness for rotation movement analysis, using the inclinometric application.