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What comes to mind when you think about a power wheelchair's performance? Speed, electronics, turning radius, battery life, positioning components, and power seat functions may be considered, and all of those functions are great. However, the wheelchair may not perform as intended if the suspension is not considered. What is suspension? Let's look at a car's suspension as a good comparison. Suspension is a system of shock-absorbing components to help ensure a smooth and safe ride by absorbing energy from various road bumps and other kinetic impacts (Hawley, 2021). Sounds like something that is important for an individual who utilizes a power wheelchair, too, right?
Reviewing the research
The Sunrise Medical Clinical Educators recently completed a search on the impact of power wheelchair suspension on a rider's health and quality of life. There continues to be limited applicable research available. According to Candiotti et al., we know that wheelchair users are exposed to whole body vibration, especially when driving on sidewalks and in urban areas, but there is limited research pertaining to driving during daily activities (Candiotti et al., 2022).
What we did find was DiGiovine et al. completed a qualitative design focus group on the effect of whole-body vibration on power wheelchair mobility, including individuals with disabilities who utilize a power wheelchair and rehab professionals who have experience providing seating and mobility services (DiGiovine et al., 2015).
- It was identified that vibration, shock (single event and repeated), and motion have a significant effect on the health and quality of life for individuals who utilize a power wheelchair for mobility.
- Rehab professionals specifically identified individuals who utilize a power wheelchair that are most often affected by vibration, shock, and motion have the following diagnosis: SMA, MD, MS, ALS, SCI, CP, spina bifida, stroke, lower extremity amputations, Friedreich's ataxia, and brain injury. The clinicians also identified individuals aging with a disability or living in a rural setting are impacted and regardless of diagnoses, individuals with a startle reflex, spasticity, and hyper/hypo-tonicity are greatly affected.
- Both groups also identified adverse effects of whole-body vibration, shock, and motion include increased pain, discomfort, fatigue, and apprehension.
- Riders within the focus group had concerns with an increase in numbness and spasms. Traveling over thresholds, brick, potholes, pavers, decking, and curbs were some of the surfaces that triggered the above symptoms (DiGiovine et al., 2015).
Mohamed and colleges analyzed the impact of whole-body vibrations on the wheelchair user's health, comfort, and probability of vibration perceptions. Results showed the potential risks to riders' health due to prolonged driving of a power wheelchair on terrains such as tiled concrete and pavement bricks. Ultimately, Mohamed et al. recommend against usage of a power wheelchair for commuting and identified that the tendency for risk increased whole body vibration with lightweight riders as compared to heavyweight riders that may dampen low vibrations.
Even though there is little research directly relating power wheelchairs and the impacts of vibration on the human body, we found the International Organization for Standardization (ISO) 2631.1. This standard identifies what is determined to be acceptable frequency range for whole body vibration and the potential effects of vibration on health and comfort, as well as on perception and the incidence of motion sickness. In addition, a directive by the European Parliament and Council for safety and health at work (Occupational Safety and Health Administration, 2002) that lays down minimum requirements for the protection of workers from risks to their health and safety arising or likely to arise from exposure to mechanical vibration during the 8-hour workday.
- They identified harmful risks with hand-arm vibration including vascular, bone or joint, neurological, or muscular disorders.
- Those that have exposure to "whole-body vibration" are at an increased risk for lower-back morbidity and trauma of the spine (OSHA, 2002).
It should be noted that the European workers were monitored closely, and modifications were made to reduce risks with vibration for workers in an 8-hour day. Often, individuals who utilize wheelchairs for primary mobility are in their wheelchairs for much longer. Also, consider that these guidelines are likely for healthier individuals in the workplace. Consider the probable increased impact of the already compromised health systems of individuals who utilize power wheelchairs.
Considerations for manufacturers' suspension design
Of additional interest is how manufacturers derive the suspension they have on their wheelchairs. In the May 2023 eBook edition of Mobility Management, there was a discussion on how funding impacts power wheelchair design. When looking at suspension and power wheelchairs, it should be known that:
- Group 2 power wheelchairs are not required to have suspension, but Group 3 power wheelchairs are required.
- Medicare does not consider outside-the-home needs when funding power wheelchairs.
- CMS does not prohibit those power wheelchairs from being used outside.
Though funding is based on indoor use, it is important to recognize the challenges of designing a quality power wheelchair that will meet the needs of the rider and allow them to participate in activities that they need and want to do, both indoors and outdoors.
QUICKIE power wheelchair suspension
QUICKIE has made several improvements in pursuit of the best rider experience. Dan Critchfield, one of our Technical Educators, highlighted some key points about QUICKIE's power wheelchair suspension:
- The QUICKIE Q300 M Mini, Q500 M, and Q700 M are true mid-wheel drive power chairs. The weight distribution is 60% on the drive wheels, 20% on the front casters, and 20% on the rear casters. The advantage of true mid-wheel drive is a tighter turning radius and more intuitive driving due to the rider's head being positioned in the center of the chair's turning circle. Other manufacturers bias the drive wheel in front of the true mid position, which creates more of a front-wheel drive experience.
- Because QUICKIE chairs are truly mid-wheel drive, the drive wheel creates a kind of teeter-totter effect. To achieve maximum stability, the front and rear caster arms would need to be completely rigid. However, this would create a high-centering condition, where the drive wheels lose traction on uneven terrain. If the front and rear caster arms have upward movement, the high-centering behavior would be eliminated, but then the chair would want to pitch forward during deceleration or while going down a slope.
- To create a suspension that is both stable on slopes and capable across uneven terrain, the suspension needs to adjust automatically. This is what is called "active suspension."
- The Q300 M Mini and Q500 M suspension uses a simple friction roller to provide a stiffer suspension on flat or downward slopes. Once the chair encounters an uneven surface, the suspension loosens to provide maximum traction. It actively adjusts based on the driving conditions.
- The Q700 M's ProGrip suspension uses a progressive damping spring. This suspension is able to "sense" when the chair is decelerating quickly (i.e., stopping quickly or descending a slope) and provides a stiffer suspension that supports the chair to provide outstanding stability. When the chair encounters an uneven surface (i.e., small bumps/cracks), the suspension is more compliant in order to provide maximum traction and a softer, more comfortable riding experience.
What do you need to know as a therapist/supplier?
Therapists assessing for power wheelchairs, along with the supplier and rider need to take suspension into consideration. They need to have an understanding of how driving a wheelchair for extended periods of time and over varying terrains can impact a person's tolerance, positioning, health, and safety. When researching, a group of healthcare professionals including Choi, Davies, Sommerfeld, and McAlpine (2021) understood the impact and have developed a website focused on wheelchair vibration and how it impacts the health and daily function of riders: wheelchairvibration.wordpress.com.
Don't forget to educate the primary care providers so the correct wheelchair can be prescribed to optimize health status and prevent further complications. In the article, "A Primary Care Provider's Guide to Wheelchair Prescription for Persons with Spinal Cord Injury," Michael et al. included indicators for suspension including: spasticity (moderate to severe), need to leave home and traverse challenging terrain/distance/climate to perform mADLs, neck and/or back pain, as well as excessive muscular fatigue in someone who travels extensively in the power wheelchair (Michael et al., 2020). Providers also benefit from education on what can be a result of an improperly fitting wheelchair, so the appropriate referral to a seating specialist can be written for optimal outcomes for the rider.
Therapists and suppliers should also be aware of the different types of suspension systems used on Group 3 and 4 power wheelchairs from the different manufacturers, educate the riders, and take it all into consideration when making final recommendations with the rider.