Reliability and validity of an iPhone® application for the measurement of lumbar spine flexion and extension range of motion

Background Measurement of lumbar spine range of motion (ROM) is often considered to be an essential component of lumbar spine physiotherapy and orthopedic assessment. The measurement can be carried out through various instruments such as inclinometers, goniometers, and etc. Recent smartphones have been equipped with accelerometers and magnetometers, which, through specific software applications (apps) can be used for inclinometric functions. Purpose The main purpose was to investigate the reliability and validity of an iPhone® app (TiltMeter© -advanced level and inclinometer) for measuring standing lumbar spine flexion–extension ROM in asymptomatic subjects. Design A cross-sectional study was carried out. Setting This study was conducted in a physiotherapy clinic located at School of Rehabilitation Sciences, Iran University of Medical Science and Health Services, Tehran, Iran. Subjects A convenience sample of 30 asymptomatic adults (15 males; 15 females; age range = 18–55 years) was recruited between August 2015 and December 2015. Methods Following a 2–minute warm-up, the subjects were asked to stand in a relaxed position and their skin was marked at the T12–L1 and S1–S2 spinal levels. From this position, they were asked to perform maximum lumbar flexion followed by maximum lumbar extension with their knees straight. Two blinded raters each used an inclinometer and the iPhone ® app to measure lumbar spine flexion–extension ROM. A third rater read the measured angles. To calculate total lumbar spine flexion–extension ROM, the measurement from S1–S2 was subtracted from T12–L1. The second (2 hours later) and third (48 hours later) sessions were carried out in the same manner as the first session. All of the measurements were conducted 3 times and the mean value of 3 repetitions for each measurement was used for analysis. Intraclass correlation coefficient (ICC) models (3, k) and (2, k) were used to determine the intra-rater and inter-rater reliability, respectively. The Pearson correlation coefficients were used to establish concurrent validity of the iPhone® app. Furthermore, minimum detectable change at the 95% confidence level (MDC95) was computed as 1.96 × standard error of measurement × \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$\sqrt{2}$\end{document}2. Results Good to excellent intra-rater and inter-rater reliability were demonstrated for both the gravity-based inclinometer with ICC values of ≥0.84 and ≥0.77 and the iPhone® app with ICC values of ≥0.85 and ≥0.85, respectively. The MDC95 ranged from 5.82°to 8.18°for the intra-rater analysis and from 7.38°to 8.66° for the inter-rater analysis. The concurrent validity for flexion and extension between the 2 instruments was 0.85 and 0.91, respectively. Conclusions The iPhone®app possesses good to excellent intra-rater and inter-rater reliability and concurrent validity. It seems that the iPhone® app can be used for the measurement of lumbar spine flexion–extension ROM. Level of evidence IIb.