Assessing the concurrent validity and reliability of an iPhone application for the measurement of range of motion and joint position sense in knee and ankle joints of young adults

Abstract

Objective: To analyze the concurrent validity and reliability of an iPhone application for assessing range of motion (ROM) and joint position sense (JPS) in ankle and knee joints.

Design: Cross-sectional study.

Setting: Sport laboratory.

Participants: Twenty healthy and physically active volunteers.

Interventions: All participants performed a ROM and a JPS test in ankle and knee joints, which were simultaneously evaluated with photo-analysis and the iPhone application.

Main outcomes measures: A total of 80 angles were obtained with the iPhone app and the photo-analysis and compared for concurrent validity. Reliability was evaluated through re-scoring of images with the iPhone app by two different testers.

Results: Very high correlation was observed between both methods for ankle and knee ROM and knee JPS (r > 0.90), and high correlation for ankle JPS (r = 0.71-0.90), while Bland-Altman plots showed absolute agreement for all the variables. Inter- and intra-tester reliability was perfect for all the variables (ICC > 0.81), except for the inter-tester reliability of ankle JPS, which was substantial (ICC = 0.61-0.81).

Conclusions: This new iPhone application is valid and reliable for measuring ankle and knee ROM and JPS, although special attention is needed during ankle evaluation to avoid errors.