The importance of reducing the incidence of secondary injuries related to manual wheelchair 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. Consequently, this uneven terrain can and increase the risk of an RSI, and decrease the likelihood that a MWU will go out and participate in society. 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. Shifting the center of gravity location rearward has largely been discarded as a solution because it can lead to instability, and solutions to address instability (such as anti-tip mechanism) limit independent mobility. The alternate solution, of locking the caster orientation has been developed, but current designs are impractical because they require the MWU to either lock/unlock the caster frequently, or perform wheelies to turn. The goal of this research is to evaluate the feasibility of a caster system which biases the caster system orientation to counteract drift on a cross-slope, but does not impair the ability for the MWU to make a desired turn. We have prototyped a bench-top version of this design, and have performed preliminary testing to quantify the bias necessary to counteract the down-slope drift. The goal of this research is to (1) prototype a caster system which can be fit to a manual wheelchair, (2) test the feasibility of the device in focus groups with MWU and clinicians, and (3) test the product durability using ANSI/RESNA wheelchair standards.
Wrist and shoulder complications are prevalent among wheelchair users due to the repetitive strain on the upper limb during manual wheelchair propulsion. Evidence suggests that propulsion over a surface with a cross-slope can result in an 80% increase in require push-rim force, increasing the risk of upper limb injury. Our goal it to determine the feasibility of a caster system which would reduce or eliminate these increased forces while propelling over sloped terrain and help increase community participation and quality of life.
