Reliability Analysis of a Smartphone-aided Measurement Method for the Cobb Angle of Scoliosis

Study Design: A comparison between the smartphone-aided measurement method and the manual measurement method for the Cobb angle in adolescent idiopathic scoliosis. Objective: To evaluate the reliability and measurement error for the smartphone-aided Cobb angle measurement method and compare its reliability and measurement error with those of the manual method. Summary of Background Data: The development of smartphones has provided new opportunities that integrate mobile technology into daily clinical practice. Smartphone applications can provide quick assistance in the diagnosis and treatment of disease. Cobbmeter is a smartphone application designed for the measurement of Cobb angle on Apple iPhone smartphones. There is no study on the reliability and measurement error of this smartphone-aided measurement method. Methods: Fifty-three posteroanterior radiographs of adolescent idiopathic scoliosis patients with thoracic scoliosis were used for the standard Cobb method of measurement (manual set) and the smartphone-aided Cobb method of measurement (smartphone set). Five spinal surgeons measured the Cobb angle with the use of both the manual method and the smartphone-aided method. The measurement time was recorded for every measurement. The frequency and the cumulative percent distribution for intraobserver differences were tabulated, both for the individual examiners and for the overall results for the 5 examiners. The intraclass correlation coefficient (ICC) 2-way mixed model on absolute agreement was used to analyze measurement reliability. Summary statistics from analyses of variance calculations were used to provide 95% prediction limits for the error in measurements. A paired t test was used to compare the time consumed for the measurement between both sets. Results: The intraobserver and interobserver ICCs were excellent in the smartphone set and in the manual set. Both the intraobserver ICC and the interobserver ICC were better in the smartphone set than in the manual set. The mean Cobb angle of all measured x-rays was 29.3 degrees (range, 17-58 degrees) in the manual set and 29.1 degrees (range, 18-56 degrees) in the smartphone set. The mean time consumed was 13.7 seconds (range, 8.6-18.5 s) for the smartphone set, whereas it was 37.9 seconds (range, 30.1-46.9 s) for the manual set, and the mean time consumed for the smartphone set was significantly shorter than that of the manual set (P<0.05). Conclusions: Smartphone-aided measurement for Cobb angle showed excellent reliability and efficiency. It is suggested to popularize the use of this method in clinical practice.