Measuring the Cobb angle with the iPhone in kyphoses: a reliability study

Purpose

Smartphones have gained widespread use in the healthcare field to fulfill a variety of tasks. We developed a small iPhone application to take advantage of the built-in position sensor to measure angles in a variety of spinal deformities. We present a reliability study of this tool in measuring kyphotic angles.

Methods

Radiographs taken from 20 different patients' charts were presented to a panel of six operators at two different times. Radiographs were measured with the protractor and the iPhone application and statistical analysis was applied to measure intraclass correlation coefficients between both measurement methods, and to measure intra- and interobserver reliability

Results

The intraclass correlation coefficient calculated between methods (i.e. CobbMeter application on the iPhone versus standard method with the protractor) was 0.963 for all measures, indicating excellent correlation was obtained between the CobbMeter application and the standard method. The interobserver correlation coefficient was 0.965. The intraobserver ICC was 0.977, indicating excellent reproductibility of measurements at different times for all operators. The interobserver ICC between fellowship trained senior surgeons and general orthopaedic residents was 0.989. Consistently, the ICC for intraobserver and interobserver correlations was higher with the CobbMeter application than with the regular protractor method. This difference was not statistically significant.

Conclusion

Measuring kyphotic angles with the iPhone application appears to be a valid procedure and is in no way inferior to the standard way of measuring the Cobb angle in kyphotic deformities.