The design of products that are intended for individuals with arthritis should be guided by anthropometric data and by an understanding of the functional limitations associated with arthritis. Arthritis is a term used to describe painful inflammation of the joint or joints. The disability has many causes, and there are over 100 types of arthritis. Inflammation causes a reduction in tactile sensation and range of movement with a corresponding loss of dexterity and mobility. Arthritis is the greatest contributor to mobility and dexterity limitations, the largest category of functional limitations. As noted by TIA Access (1996), "Individuals have difficulty reaching things and doing complex or compound manipulations such as pushing while turning or pressing several buttons simultaneously. Twisting motions may be especially difficult. For individuals with arthritis, controls that require pinching or rotating are difficult to operate. In addition, individuals who are functionally limited are unable to exert as much force on controls as individuals without functional limitations. Individuals with poor muscle control may find it difficult to make fine motor movements with their fingers and may be restricted to gross movements with their hand(s)."
Anthropometric data might provide useful guidance for the design of containers for users with arthritis. There exists only a limited amount of anthropometric data on individuals with arthritis. However, hand dimensions may not differ significantly between individuals with and without arthritis (Fraser et al, 1999), except for instances in which arthritis causes deformation of the bones and joints (e.g., rheumatoid arthritis). These deformities may prevent a user's hand from fully encircling a cap or bottle. The table below shows anthropometric data for individuals without arthritis. The data were compiled from several sources (DTI, 2002; Ergonomics for Schools, 2008; RoyMech, 2008). These include measurements from British adults aged 19-65 years (Ergonomics for Schools, 2008), and from British adults of unspecified age (DTI, 2002; RoyMech, 2008).
|Dimension||Gender||5th percentile (mm)||50th percentile (mm)||95th percentile (mm)|
|Index finger length||Male||64||72||79|
The table below shows maximum grip diameters for individuals with and without dexterity disabilities (DTI, 2002). Maximum grip diameter is defined as the maximum diameter of a cylinder that a person can grasp with contact between the thumb and middle finger.
|Gender||5th percentile (mm)||50th percentile (mm)||95th percentile (mm)|
Maximum grip diameter is of particular importance for usage of containers. Users with arthritis may experience considerable pain when forcibly grasping an object with a wide grip, in great excess of their maximum grip diameter. Hand breadth should also be taken into consideration when designing the height of a container. If the container spans the entire breadth of the hand (or more), then the user can distribute gripping force across the whole palm and all four fingers.