A novel method of producing a repetitive dynamic signal to examine reliability and validity of gait analysis systems

Gait dysfunction is a common functional complaint of clients who seek medical care. Gait dysfunction can be caused by musculoskeletal disorders such as osteoarthritis or fractures, or it can be caused by neuromuscular disorders such as multiple sclerosis or cerebrovascular accident. Decisions made by health care providers working with these clients could be enhanced by the availability of valid and reliable gait measurement. Valid and reliable gait measurement is possible with laboratory-based motion analysis systems, but these are not universally available. Several portable systems collect footfall data and provide a relatively inexpensive alternative to sophisticated motion analysis systems. However, data collected by these portable systems cannot be used with confidence because of the lack of verification of the validity and reliability of the data they collect about movement. This paper describes a novel method of examining test-retest reliability and concurrent validity that produces a signal with minimal variation. To produce repetitive distance and timing events, a cylindrical weight was rolled across the field of both the laboratory motion analysis system and the system to be evaluated. Measures of the weight's movement were taken simultaneously with both systems. A reference point was chosen to allow for comparison between the systems. The spatial measure that was compared between systems was the horizontal distance between successive repetitions of the reference point's vertical position. The temporal measure that was compared between systems was the time between successive repetitions of the reference point's vertical position. The method described in this paper provides a minimally variable repetitive signal that can be used to investigate concurrent validity of gait analysis systems.