Small Rotary Controls: Limitations for People with Arthritis

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Abstract
Improving access for persons with arthritis requires consideration of their basic abilities. This paper focuses on the design of knobs and how variations in key design factors can either create barriers or provide access for persons with arthritis. This information will provide input for human factor design guidelines that will promote universal access in home and workplace. Subjects for this study included 80 individuals with diagnosed rheumatoid or osteoarthritis, with an equal number in a control group. The test apparatus included a set of round knobs mounted on an apparatus for measuring static torque. We tested knobs of two diameters and varying surfaces and profiles. A pinch strength test was also conducted. Results showed individuals with arthritis applied significantly less torque to all control knobs than did control subjects and had relatively more difficulty with the larger knobs. The pinch test results correlated well for each subject with their applied torque on the rotary controls.