Studies have shown that manual wheelchair propulsion efficiency is between 5% and 18% depending upon the style of the wheelchair and the fit to the user (Bayley et al., 1987; Curtis et al., 1995; Nichols et al., 1979). The low efficiency of manual wheelchairs make them ineffective for some individuals to use during activities of daily living. Manual wheelchair users also experience a high incidence of upper extremity pain and joint degeneration. Between 25% and 80% of long-term manual wheelchair users are reported to have injuries to the wrist, elbow or shoulder (Boninger et al., 1999, 2001). The risk of injury tends to increase with age, while cardiovascular fitness tends to decrease (Boninger et al., 2003a).
The Smart™1661 kinetic measurement system was developed to study wheelchair propulsion and to improve clinical assessment of manual wheelchair propulsion (Cooper et al., 1997b, 1998b; Asato et al., 1993). The SMART™16618 provides a method for analyzing pushrim force that has proven critical to assess injury mechanisms (Cooper, 1997c, 1999; Boninger et al., 1997). Upper extremity models have been created in order to determine motion as well as net joint forces and moments (Koontz et al., 2002; Boninger et al., 1998b; Robertson et al., 1996). It has been shown that wheelchair pushrim forces are related to nerve conduction studies (NCS) variables (Boninger et al., 2000). NCS are used to diagnose carpal tunnel syndrome (CTS) a common condition that causes pain for wheelchair users. This study found that when controlling for subject weight, NCS was correlated with the cadence of propulsion and the rate of rise of the resultant force. Of particular importance was that the body mass of the wheelchair user was significantly correlated with NCS. Changes can be made to the wheelchair that alter the biomechanics and offer the potential for intervention (Boninger et al., 2000). Research has shown that individuals who sit low and behind the rear wheels had lower propulsive forces and stroke frequency, both shown to be associated with CTS (Cooper and Boninger, 1999).
In a series of magnetic resonance imaging (MRI) and X-ray imaging results for people with paraplegia, a high prevalence of osteolysis of the distal clavicle was revealed (Boninger et al., 2001). Investigations of the propulsive stroke concluded that the recovery phase is an important and modifiable parameter that can impact injurious biomechanics (Shimada et al., 1998; Boninger et al., 2002). A propulsion stroke during which the hand drops below the pushrim results in a greater push angle and lower stroke frequency, both of which likely protect against injury. The way an individual with paraplegia propels a wheelchair at baseline can predict progression of MRI findings 2 years later. Specifically, a large force directed towards the hub (radial force) was correlated with a higher MRI change score over time. Interestingly, almost all of the individuals with progression of MRI findings were women. Women use a larger radial force and are at greater risk of injury. This could be related to wheelchair set up or other gender differences (Boninger et al., 2003a).
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