Choosing The Right Power Chair Configuration

When choosing the power wheelchair drive configuration that best fits a client’s needs, which statement is true?
• Regardless of other considerations, a client’s personal comfort with the way the power base moves and responds is critical.
• Understanding a client’s many different environments is mandatory to choosing a good power base.
• Long-time power chair users can usually adapt to a different type of base – but don’t expect them to initially embrace the change!
• Certain lifestyle changes can warrant changing power bases.
Today’s power wheelchair technology has given rehab technology suppliers, clinicians and clients a range of power base choices, namely front-wheel, mid- or center-wheel, and rear-wheel drives. Making the right choice for a particular client, however, remains a highly personal matter of considering diagnosis, prognosis, lifestyle, environment and client adaptability, in addition to considering each drivetrain’s strengths and trade-offs.
So yes, it was a trick question, because according to the experts, all of those statements can be true.

Defining the Drivetrains: Front-Wheel Drive

A front-wheel drive power base, as its name suggests, has its drive wheels in front of the seat, which creates a kind of pulling effect and facilitates such acts as curb-climbing. As such, Permobil, for instance, says its front-wheel-drive C500 base “tackles obstacles with unmatched power and maneuverability.”

A SpinLife.com article by Susan Johnson Taylor, OTR, describes the front-wheel-drive configuration as “a very stable setup for uneven terrain, up and down hills. Out of the three types (of configurations), it climbs forward over small obstacles well also. Most of the chair is in back (of) you, so when turning, you have to be aware of what is behind you.”

Johnson adds, “The overall speeds are slower (about 5 to 5.5 mph) because the front-wheel drive tends to ‘fish-tail’ at higher, more reactive speeds.”
Some clients also benefit from the front-wheel-drive chair’s lack of front casters – casters that, on other configurations, can interfere with foot placement and positioning.

Defining the Drivetrains: Mid- & Center-Wheel Drive
The most prevalent power bases in mobility and rehab today are center- and mid-wheel drives. Considered a kind of evolution of earlier systems, the center-/mid-wheel-drive system might be thought of as technology’s answer to the real-world challenges of today’s power mobility users.

“Mid-wheel drive offers the smallest turning radius,” says Quantum Rehab’s Cody Verrett. He adds that the small turning radius — the ability for the chair to turn completely around in basically its own space just as we can turn around within our own two footprints — makes the base easy for clients to learn to drive.
“It’s very similar to the way we move through space,” Verrett says, “so (for) an individual who is a new injury or suffering from a chronic, progressive diagnosis who’s new to power mobility, it pivots and maneuvers very similarly to the way we ambulate. It’s extremely helpful and very intuitive for those individuals to learn how it operates — pivoting in their own space. Absolutely, it’s the same characteristics they’ve experienced (when walking).”

Invacare Corp.’s Julie Jackson says center-wheel drive is “the best for indoor driving. It’s really ideal for tight doorways, getting in and out of a door jam. Also, when you’re going down a narrow hallway with your center-wheel-drive chair, all you have to do is turn on a dime. You don’t have to consider what’s in front of you or what’s behind you. You know that if you can easily turn on your own axis, you’re going to make that turn.”

A possible concern with mid- and center-wheel-drive systems in the past has been that the bases are not able to offer the same obstacle-climbing ability or smooth ride that other drive configurations do, due to the placement of the drive wheels in the middle or center. But some of today’s generation of mid-/center-wheel-drive systems compensate by incorporating additional technology to answer those concerns.

Jackson says, for instance, of Invacare’s center-wheel-drive technology: “The reason why a lot of people prefer rear-wheel for a very small child first going into power is because it’s very caregiver friendly. Especially when they’re trying to go over a curb, it’s very easy for a parent to just push down on the back canes, tilt the chair up and climb over that obstacle. With a center-wheel-drive chair, it would be impossible for a caregiver to do that. That’s why it’s important for us to build SureStep into our products so they have the ability to climb obstacles on a center-wheel base.”

Quantum Rehab developed a Mid-Wheel 6 configuration that “offers six-wheel ground contact with the wheels, so we have four casters as opposed to two that we have in mid-wheel drive,” Verrett says. “That provides better stability on uneven terrain and different surfaces for individuals with more advanced diagnoses or more stability requirements. It adds significant stability enhancement while mirroring that turning within your own space, superior maneuverability and the pivoting/turning radius that mid-wheel drive provides. It’s the best of both worlds.”

Defining the Drivetrains: Rear-Wheel Drive

If center- and mid-wheel-drive platforms are “where it’s at” today, technology wise, then rear-wheel drive is the venerable equivalent of “where it came from.”
“As power chairs developed over time,” Verrett explains, “their history spawned out of a manual chair. (Manufacturers) basically took a manual chair and put motors on them, so it was always initially a rear-wheel-drive environment and market. So that created a large number of consumers that have a preference for the way that it drives and a feel for it that they don’t want to sacrifice for anything else.”

Rear-wheel-drive configurations, Jackson says, tend to excel outdoors.
“People who drive their chairs outdoors a lot, so they’re outside all the time — and they drive through aggressive terrain, high grass, gravel, very uneven terrain — they really like the rear-wheel-drive chairs, just due to the nature of the drive wheels being in the back,” she notes. “It’s going to get you through any aggressive outdoor terrain. It’s also considered to be the most stable on all terrains, and it offers you the best suspension options. You also get some of your fastest speeds with your rear-wheel-drive as well.”

Verrett concurs that rear-wheel drive systems can perform very well outside: “It’s quick; a lot of consumers appreciate a little bit higher speed, especially really active individuals. They appreciate being able to get across intersections along with the pedestrians and so forth. From a safety and access point, rear-wheel drive caters to those individuals who prefer a little more outdoor speed.”

Rear-wheel-drive trade-offs: “You have your largest possible turning radius,” Jackson notes. “It’s not the most intuitive driving platform that there is.”
Nevertheless, rear-wheel drive has plenty of loyal fans, particularly among long-time power chair users.
“Because most chairs developed years ago were all rear-wheel drive, for most people who went into chairs 20, 30 years ago, that’s what they knew,” Jackson says. “That’s what they became comfortable with. So now when they’re looking to purchase a new chair, it’s very hard for them to go to a center-wheel-drive chair, and they mainly would prefer to stick with rear-wheel drive.”

Center- vs. Mid-Wheel Drive

In many power chair discussions, “center-wheel drive” and “mid-wheel drive” are used almost interchangeably. So what is the difference between the two configurations?

Says Invacare Corp.’s Julie Jackson, “Center-wheel drive means the distance from your footplate to the middle of your drive tire and from the middle of the drive tire to the rear caster is the exact same distance. Mid-wheel drive just means that center-wheel-drive tire is somewhere in between the front and the rear. It doesn’t mean it’s directly in the center.” While Jackson says center-wheel drive is “more intuitive” for someone new to the configurations, she adds, “They’re very similar (to learn).” The “feel” of mid-wheel-drive can vary a bit from chair to chair and manufacturer to manufacturer, Jackson contends, because the drive wheels aren’t equidistant from front to back. For instance, she says, “If your drive tires (on a mid-wheel-drive chair) are closer to the front, it can feel a little bit like a front-wheel-drive product.”

Environmental Impacts on Power Bases
If a power chair’s seating system is all about meeting the client’s clinical needs, you could say the power base is much more about meeting the needs of the physical environments that the client navigates every day.
That may sound simple enough, but today’s typically active client requires a lot of versatility from a single power chair base.
“It’s really imperative that a variety of the most common environments that the user will encounter be carefully evaluated for access,” Verrett says. “Not just indoors, but also the surrounding property and the home, their work environment, transportation both public and personal, and other places they might visit on a common basis, like school or church, medical visits, that sort of thing. It’s really important that the user environments are determined and really well laid out.”

A basic checklist of environmental questions for a provider to ask a client could include the following:
• Home: How much turning room is there for a wheelchair indoors? How are doorways and entryways laid out? What is the outdoor property like, e.g., the distances and terrains to reach mailboxes, gardens, parking areas, etc.?
• Main daytime environments, such as work or school: How much floor space is there for turning around?
• Frequently visited locations in the community, including houses of worship, medical offices, homes of friends and family.
• Surrounding areas for all of the above: How far away are parking or drop-off areas from the buildings? Is the terrain between the parking areas and the buildings uneven, unpaved, etc.?
• Automotive transportation, either private or public, and other public transportation: What sizes of power chairs can be accommodated?
­­Verrett knows first hand how much a client’s environment can impact drivetrain choice.
“I have a (young client) who I did a power wheelchair for a long time ago when I was a provider in the Atlantic,” he recalls. “He had come from a rear-wheel-drive environment. We moved him to mid-wheel drive because he needed better accessibility to his vehicle and also his home. It was a slow transition for him, but once he committed to it and his family really adapted to the differences, it made accessibility much better for him when he moved to mid-wheel drive. His mom would let him in the kitchen because he wouldn’t smash up the cabinets, he was able to use the van that was donated to them, so mid-wheel drive really became a necessity for this particular individual, and they made that transition. It just took some time.”

Changing Power Bases Along the Way

That client example brings up another question: Over time, perhaps as a condition progresses or natural aging takes place, should clients consider changing drivetrain configurations?

“We typically don’t see that (too) much, where someone goes from one drive configuration to another,” Jackson says. “What we typically see as their disease progresses is that it’s usually addressed with different seating, not so much with the base…. What we do see is that if you go into center-wheel drive, you stick with center-wheel drive. If you go into rear-wheel drive, you stick with rear-wheel drive. Typically, even as the disease progresses, they’re not changing their frame design.”

Very young clients, Jackson adds, can be exceptions. Because many caregivers find rear-wheel-drive chairs easier to maneuver when their assistance is needed over curbs and obstacles, Jackson says, “When it comes to pediatrics (and) a child who is first going into a power chair, there actually is a lot of discussion out there” as to whether a rear-wheel-drive chair may be preferred.

“But then maybe later, as they get older and they’re going to school and then off to college, they may want to switch to a center-wheel drive,” she says.
For other clients, Jackson says, “Most of the times, when you go to a clinic, they are bringing out the center-wheel-drive chairs first. But every so often you see them bring out the rear-wheel or the front-wheel based upon the client’s home and where they’re going to be driving the chair, and then ultimately, what they feel the most comfortable is.”

Once clients find that “comfort zone,” most are quite reluctant to transition to another configuration, largely because the different power base types do drive differently and therefore “feel” different to the operator.

“A lot of children with muscular dystrophy, Duchenne’s, individuals from the VA, that population has come from rear-wheel drive, and that’s what they prefer,” Verrett says. “They continually look for that. Actually, when we try a different platform such as mid-wheel or front-wheel, they feel very out of sorts. It’s so different.”

That’s not to say that clients can’t learn to drive — and appreciate — a different drive configuration than the one they currently have. But the transition will take time and patience on the part of everyone involved, from client to provider to clinician to family members and other people in the environment.

“It’s been my experience that kids are more able to adapt to change depending on the situation they’re potentially faced with,” Verrett says.
Jackson says the transition time varies from child to child “from what I’ve heard from therapists. Some kids will just gravitate to it and make the change within a day; others can take a couple of weeks. But I think it is a change that someone does need to get used to and get accustomed to.”

A Very Individual Choice

There are definite tendencies related to today’s drivetrain choices: Center-/mid-wheel drive is the most prevalent power base, environment is key, clients don’t like changing configurations once they’ve grown accustomed to what they have. But as with any rehab equipment selection, a client’s overall needs and lifestyle need to be considered — which can make the situation very complex indeed.

“I was in Charlotte just a few weeks ago, and I saw a gentleman who’s probably about 30 going into a power chair for the first time,” Jackson says. “I was surprised actually to see him going into a rear-wheel drive. And so I asked the provider why they had fitted him for a rear-wheel over center-wheel, because you usually see new injuries going into center-wheel.

“He agreed with me, but he said this client was very unique in that he has a lot of pain, and he can feel any kind of a bump while he’s driving his chair. The rear-wheel drive had better suspension than the center-wheel drive, especially for being outdoors. So that’s why they selected the rear-wheel drive.”

Verrett adds that funding issues also have to be carefully considered, which can require providers to do some strategic forecasting: “You have to be able to see around corners and really envision what’s going to happen to this product over its lifespan and provide the most functional accommodations possible. You have to think those things through. As a provider, they have to communicate very well on a high level with the consumer they work with so the expectations of both are mutually understood.”

Since funding sources typically expect power chairs to last three to five years or more, providers may have to predict not only how the client will grow or change, but also how the chair’s environment may change as a result.

“If I were evaluating someone today who was 15 or 17 years old, we would have to consider the possibility that they might go to college,” Verrett says as anexample. “What would they need on a college campus environment? (Then) prepare the product for the lifespan of the funding cycle and its maximum ability to meet that individual’s needs.”

In the end, the “right” drivetrain choice can largely come down to what the client deems the most comfortable — physically, environmentally, emotionally.
“It really starts with the needs and requirements of the individual,” Verrett says of the assessment process. “That’s where I would start.”

All-Terrain Drivetrains: More Configuration Choices

While power chair drivetrain talk usually revolves around the three major choices – center-/mid-wheel, front-wheel and rear-wheel drives – there are other choices.

Manufacturers of all-terrain wheelchairs boast their products can go where other power chairs cannot, including treacherous and uneven terrains.
For instance, Innovation In Motion’s Extreme 4x4, aka X4, is “a true four-wheel-drive wheelchair that utilizes four independent motors and four low-pressure knobby tires,” says the company’s Rick Michael. “The X4 steers more like a car than a conventional wheelchair.” He adds that the four-wheel-drive chair is capable of “traversing sand, snow, mud and other soft terrains that conventional wheelchairs cannot.”

Tracabout’s IRV 2000, on the other hand, uses a track system that can run “in full flat position for snow or mud, and half track for normal running in sand or grass,” according to the company’s product information. IRV 2000 also features a “three-point mode suitable for smooth surfaces and carpet.”
And Independence Technology’s iBOT can operate in “Standard” function as a rear-wheel-drive chair, or in “4-Wheel” function, during which “the caster(s) are lifted off the ground and the four drive wheels are all placed on the ground, which acts more like a mid- or center-wheel chair,” says Independence Technology’s Sandy Salerno. The chair’s “Balance” function keeps the back two wheels on the ground while the other wheels rise; in the “Stair” function, the front two drive wheels rotate over the back drive wheels to enable the chair to climb stairs or steps. In the two-wheel formation, the iBOT uses gyroscopes to stay upright.

These “other” drive configurations have a couple of things in common, including clients who are active, particularly outdoors.
“The common denominator for all X4 users is not male/female, young/old, nor rural/urban,” Michael says. “The common denominator is that our users are active. They are parents that want to participate in family functions like sports, picnics on the beach, or just family time in the backyard; college students on campus; owners of landscaping, construction, and other such demanding businesses; and yes, disabled farmers, hunters and other active users that don’t live on a slab of concrete!”

Another commonality: Funding for these off-the-beaten path drivetrains can be challenging.
“The X4 was coded as a K0004 before the new wheelchair codes came out,” Michael says. “Now the minimum speed requirement for a Group 4 wheelchair is 6.5 mph, and the X4’s maximum speed is 5 mph. Without coding, Medicare/Medicaid and many insurance companies are not covering even a portion of the X4.” Michael says, however, that workers’ compensation, the Veterans Administration and vocational rehab have all purchased his all-terrain chairs.

Said Salerno about the iBOT, “In addition (to private insurance), other sources like the workers’ compensation (and) vocational rehabilitation agencies and non-profit organizations have all purchased the iBOT Mobility System for consumers.”


This article originally appeared in the September 2008 issue of Mobility Management.

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