Context: Assessment of upper cervical range of motion (UCROM) and mobility is commonly performed in the clinical setting for patients suffering from headache, neck pain and vestibular dysfunction. Reliable and reproducible measurement of this motion is often difficult or too expensive to perform in the clinical setting. Smartphone applications, utilizing the device's internal gyroscope, offer an easy and inexpensive means of measuring UCROM, but their reliability has not been reported in the literature.

Objective: Assess the reliability of an inclinometer application, installed on two different devices (iPhone6 (IP), Andriod (AN)), to measure UCROM in a healthy population.

Design: Two examiners assessed passive UCROM. Each examiner was assigned to a specific smartphone and a repeated measures design consisting of three trials for each examiner-phone was performed. The order of testing was randomized and the examiners were blinded to UCROM measures.

Setting: Laboratory Participants: 38 subjects (19F, 19M; 23.8±1.2 yrs) without pain or injury to the neck and spine for at least 3 months.

Intervention: Each examiner passively flexed the head fully and then rotated the head fully in one direction then in another. Peak rotation measures were recorded from each smartphone. Three trials were performed for each phone with a 2-minute break between examiners/phones.

Main Outcome Measures: Intraclass Correlation Coefficient (ICC) using a two way mixed, absolute agreement model were obtained (1) between each examiner-phone and (2) within each examiner-phone for the measurements in each rotation direction.

Results: Inter-phone/examiner reliability comparing average peak and total UCROM for each device were excellent (0.87, 0.81). Intra-phone/examiner reliability, determined across three trials, was also excellent (AN Right Rot. = 0.91, AN Left Rot. 0.96, IP Right Rot. = 0.98, IP Left = 0.95 Rot.).

Conclusion: UCROM can be reliably measured using a smartphone inclinometer application.