The importance of reducing the incidence of secondary injuries related to manual wheelchair (MWC) propulsion is undisputed. Based on several research studies, approximately 50% of manual wheelchair users (MWU) report symptoms of repetitive strain injury (RSI) related to the demand on the upper extremity during propulsion and transferring tasks. A substantial effort has gone toward understanding and trying to reduce the incidence of RSI through improved wheelchair technology, training, and clinical practice. Despite these efforts, it is still argued that all long-term (>15yrs) MWU are likely to acquire a RSI. Technical advances, such as lighter and more adjustable wheelchairs have helped reduce the risk factors for RSI by decreasing the average propulsion force and increasing the stroke length during propulsion. By decreasing overall risk for RSI, these technical advances make progress, but more can and should be done to help preserve the mobility independence of MWU. A persistent problem during manual wheelchair propulsion is the difficulty while propelling over sloped terrain. Outdoors, sloped terrains are unavoidable-running-slopes (in the direction of travel) are necessary to transitions from one grade to another, and cross-slopes are required for water drainage. Although the ADA accessibility guidelines place upper limits on the allowable angle of these slopes these limits are often not followed, and any sloped surface can be burdensome to a MWU and increase the risk of an RSI, especially the cross-slope angle. Research findings suggest that a cross-slope angle of 2 degrees requires a 30% greater effort than propelling on flat ground. Additionally, based on perceived comfort, a one degree increase in cross-slope is equivalent to a 3.6 degree increase in running slope. Other research has demonstrated that an 80% increase in propulsive forces is necessary when propelling over a 6 degree cross-slope. The underlying mechanism causing the increased propulsion demand and decreased comfort is the tendency of the wheelchair to drift down the slope. This is due location of the center of gravity (which is forward of the rear axle) and the unconstrained rotation of the caster wheels. The goal of this project is to finalize the development and testing of the PathLock system, which biases the caster to maintain a strait path. Our Phase I prototype was positively received by clinicians and WCUs and valuable feedback was gathered about design modifications. Year 1 of this proposal will be to finalize the design and testing of the PathLock for TiLite TR wheelchairs, and Year 2 will be devoted to adapting the PathLock to other varieties and classifications of MWCs.

Public Health Relevance

The goal of this project is to finalize the design and development of the Pathlock system, which biases a wheelchair caster to help the user maintain a straight path during propulsion. This can be helpful if a user is carrying an object in one hand, is traveling over a cross-slope, or has unilateral functional deficit (such as hemiplegia).

National Institute of Health (NIH)
Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD)
Small Business Innovation Research Grants (SBIR) - Phase II (R44)
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Special Emphasis Panel (ZRG1-MOSS-F (15))
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Shinowara, Nancy
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Accessible Designs, Inc.
San Antonio
United States
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