During typical wheelchair pushrim propulsion, significant forces must be applied by the wrist, arm and shoulder, despite the fact that they are not in optimum positions. Not surprisingly, pushrim wheelchair propulsion is associated with several common injuries. The most common are shoulder injuries and carpal tunnel syndrome (CTS). Surveys of manual wheelchair users show the prevalence of shoulder pain to be between 31% and 73% and of CTS to be between 49 and 73%. It is the specific aim of this proposed research program to build and test a wheelchair employing a lever drive mechanism with improved kinematics. The improved kinematic design will allow loading the wrists and shoulders through their normal range of motion and eliminating wrist flexion under load. There is reason to believe that straightening the wrists during loading may reduce the incidence of CTS. We have developed a lever drive concept that has the potential to reduce injuries and to deliver improved efficiency while overcoming the shortcomings of past lever drive systems. Our concept provides a continuously variable drive ratio, power delivery on both the push and pull strokes and straight line or arced powers strokes with a locked wrist.
Wheelchairs are in widespread use throughout the world. In the US alone, there are around 1.5 million wheelchair users. Of those, it is estimated that one half will eventually develop CTS and/or shoulder injuries such as rotator cuff tears. A wheelchair that could reduce the number of these injuries or allow injured users continued mobility would find broad acceptance.
