Validity and Reliability of an iPod ® Forearm Goniometer App

SIGNIFICANCE: Other health disciplines have begun to embrace smartphone technology. Occupational therapists should remain on the forefront of this trend and should be doing applied research to determine whether this software is clinically appropriate. Occupational therapists have a responsibility to correctly represent progress in documentation. By being able to improve reliability in quantifying improvements in physical capacity, third-party payers will be more inclined to continue to reimburse occupational therapists for their services.

INNOVATION: Research pertaining to smartphone apps in physical disability and rehabilitation within occupational therapy practice is especially limited. The use of smartphone apps in clinical practice is growing, as is the need for research to determine the usefulness of these tools. The Forearm Goniometer app eliminates the need for a consistent rater by allowing the client to handle the tool independently.

RESEARCH QUESTIONS: This study attempted to answer the following research questions: Does the app correctly measure the angle of two predetermined wedges? Does the app record similar numbers between the two trials? And do the measurements for full range of motion fall within the expected normal curve?

RATIONALE/BACKGROUND: Forearm pronation and supination are done during tasks such as eating food with a utensil, turning a doorknob, or using a screwdriver. The American Occupational Therapy Association highlights the widespread use of smartphones, stating that there are more than 70 million users in the United States alone.

METHOD: This study was a quasi-experimental design with a single group. The participants were a sample of 100 Keuka College students. A single iPod Touch^® device was used to gather all the measurements in the sample. The custom wedge was used to limit motion during predetermined angle trials. The research protocol was developed to provide uniformity among participants and to limit shoulder and elbow substitution. Each participant completed four measurements: two trials with the randomly selected predetermined angle and two trials using full range of motion.

A correlation analysis was used to determine test–retest reliability between trials. The predetermined angle measurements were analyzed with a one-sample, unpaired t test. The measurements for full range of motion were ranked into frequencies and were then compared to the expected measurements from a typical population.

RESULTS: The analysis revealed that the app did not accurately measure the predetermined angles. The p values for both predetermined angles were significantly different from the test angle. On average, the app measurement for pronation was 28° different from the expected measurement. The app did have high reliability between trials, with an overall correlation coefficient of .91. The app also measured full range of motion within the expected ranges, with 86% of the supination measurements and 61% of the pronation measurements falling between 80° and 100°.

CONCLUSION: This study shows that the Forearm Goniometer app has low validity with measuring angles below full range of motion. However, the high reliability of measurements with the device demonstrates the potential for this technology to increase consistency between therapists. Limitations of the study include not obtaining goniometric measurements to compare to the app measurements and the participants being from a convenience sample. The development of the gyroscope and motion sensor is promising for increasing the accuracy of this technology.