Broadening the Base

Functional mobility for individuals needed extra durability or high stability

(reprinted with permission)

By Phil Mundy P. Eng.


Margaret used to fall out of her wheelchair. Regularly. This kind of problem shows up all too frequently for people with cerebral palsy, Huntington's disease, brain injury, psychiatric disorders, and a variety of other diagnoses affecting physical stability.

The trouble is, it is very hard to provide functional mobility for someone who doesn't move the way most people do. With so many wheelchair products to choose from, finding one that is hard to tip over should not be an issue. But it is.

Margaret lives in Vancouver, Canada, in a long-term care center. After overturning her traditional wheelchair several times, sometimes injuring herself, Margaret progressed through a variety of trial chairs until she was finally "manageable" in a chair that looked more like a recliner than wheelchair. The only thing that seemed to work involved lots of straps to ensure she was not able to fling herself around, getting enough momentum to do serious damage. There were two straps to keep her shoulders back, a big strap across her chest, and two crotch straps to keep her from slipping out the front. The chair had lots of padding since Margaret was in constant motion, banging against anything she could reach. To ensure stability, the base of the chair was considerably larger than a wheelchair and weighed about 50 percent more than normal. While the chair provided a safe environment, Margaret was not mobile. Her level of agitation increased dramatically with the passage of time.

Early in 1997, PDG Product Design Group was contacted about options the company might be able to offer. PDG manufactures wheelchairs for specific kinds of applications, including chairs for obese individuals and specialty manual tilt wheelchairs. The company had embarked on a project to providing a mobility base for people who need extra stability.

In Margaret's case, an equipment trial was arranged so that she could try using one of PDG's new Bentley wheelchairs for a week. Nancy Balcom, a kinesiologist with PDG assisted in setting up the device for Margaret to try.

In configuring Margaret's trial system, several key ideas were implemented as part of the equipment set-up. First, the chair was adjusted to provide a low seat-to-floor height, allowing Margaret to "walk" along while seated. To reduce the potential for tipping, the Bentley base is designed to allow the rear wheels to be positioned for an extra wide, extra long footprint. However, to ensure the chair can still be easily maneuvered through doorways, the rear wheels can be quickly repositioned so that the chair is approximately the same size as a standard adult wheelchair. Finally, the wheelchair was provided with an adjustable tilt mechanism so that Margaret could be tilted back as much as 25 degrees. Unlike any other tilt in space wheelchair, the Bentley tilt is accomplished while maintaining a constant seat-to-floor height. This allows Margaret to move around via foot propulsion even while in the tilted position.

A change in Margaret was almost immediate. Her level of agitation dropped dramatically. Instead of constantly struggling in her wheelchair, Margaret began to move around, still in constant motion, but not as violent as when using the previous wheelchair. When Margaret did lunge unexpectedly, the extra long and wide wheelbase provided dramatically improved stability. Care staff were soon satisfied that Margaret might no longer be likely to tip the chair over.

Padding and cushioning were dramatically reduced. The new system required only a basic modular seat cushion and padded lap belt to maintain good postural positioning. The adjustable tilt mechanism added to Margaret's level of comfort and independent mobility since she was immediately able to spend more time up and about.

Margaret is not the first person to need a wheelchair like this. The Bentley'began as project to provide independent mobility for a similar group of people living at Riverdale Hospital in Toronto, Canada.

Motion Specialties, a firm specializing in custom mobility, began the project in 1995. Motion answered a request to provide a wheelchair for a man in his forties living at Riverdale Hospital. Mr. R. was a resident with Huntington's disease, a hereditary degenerative neurological disorder. Usually beginning in mid-life, cells in the caudate nucleus of the brain begin to die, causing a relentless deterioration of intellectual ability, emotional control, balance and speech. Chorea, or involuntary movements, is nearly always a symptom as well.

There are three characteristic clinical features:

  • Loss of the ability to control bodily movements.

  • Loss of ability to think and to act quickly, to learn and to remember.

  • Apathy and severe depression, often resulting in suicidal behavior.

Those with Huntington's also exhibit poor social judgment and may be irritable and aggressive.

A meeting with the therapy team working with Mr. R. revealed he had already tried at least four heavy-duty wheelchairs unsuccessfully, either overturning or falling out of each one. During the initial clinic visit, Mr. R. arrived strapped into a wheelchair with plenty of padding and belts. Nursing and attendant care staff felt unable to provide a workable living environment. The challenge was to provide a wheelchair that would keep him safe, prevent falling or tipping the chair over, facilitate foot propulsion, and meet the facility's restraint free policy.

Over the next six months, four differently configured wheelchairs were constructed from scratch by Motion Specialties technician, Brian Bentley. Each successive attempt brought the team closer to a workable solution, but failed to meet the clinical team goals for various reasons.

Finally, a wheelchair was constructed that worked. The wheelbase was wider toward the rear of the chair, therefore resisting side tipping. The base was nearly 12 inches longer than most wheelchairs so that it would resist tipping to the rear. It had a low seat-to-floor height so that Mr. R could foot-propel. The low seat-to-floor height also lowered his center of gravity so that he would be less likely to tip over when he lunged one way or the other. The chair was set-up with a tilt mechanism so that when he became more agitated, the seat could be adjusted to increase stability and reduce the tendency for him to slide out the front. Finally, both the back and seat section of the seat frame were supported on springs so that when he rocked or lunged, the chair absorbed impact without injuring the user.

Now, three years after the first Bentley wheelchair was fabricated, these unusual wheelchairs are gaining acceptance with individuals needing something special. The following excerpts of letters from Care-Givers best describe what makes this mobility device so different;

Client Diagnosis: Post encephalitis brain damage

"...The special feature, and adjustable tilt base, allows Christina to rock forward safely while using her legs to propel herself. Unfortunately, this lady previously flung herself forward and injured herself after falling in a regular wheelchair. She was then placed in a geriatric chair, which totally restricted her movements. The base of the Bentley provides stability for aggressive or agitated patients while allowing them a certain degree of freedom to move."

J.W., Occupational Therapist
Fort McMurray, Alberta

Client Diagnosis: Cerebral palsy

"...We love it! We are currently using it to seat an adult Cerebral Palsy client. We were having an extremely hard time seating him safely and comfortably.... He was constantly leaning over to one side, would jackknife forward and be unable to reposition himself, often caused by his attempts to propel himself using his upper extremities. A year ago he managed to topple his wheelchair over and brake a femur in the process. He would not accept a recliner because it restricted him from propelling himself. This is the only independence he now has and it is very important for him to maintain it..."

M.L., Physiotherapist
Parksville, BC

Client Diagnosis: Severe developmental disability, epilepsy, behavior motor disfunction

"...I am happy to report to you that this chair is working out very well for Anita. She has not been able to tip it at all and she maneuvers it around independently much to her satisfaction and ours. We are thrilled that you have designed such an amazing and safe chair...."

K.B., Councilor
Val Therese, Ontario

While the efforts of PDG and Motion Specialties have produced tremendous progress in meeting the mobility needs of individuals like Margaret and Mr. R, there are still a few challenges to address when providing equipment for agitated individuals. A few people who are supposed to use the chair to prevent injuries associated with falling still get up and walk along corridors, dragging the wheelchair behind them. Seemingly tiny clients have been known to bend double reinforced components which were designed to withstand constant stress and strain as clients attempt to destroy or overturn the chair.

After months of struggle, Margaret can finally be left alone, safe, secure, and independent. When I visited her recently, about a year after her Bentley was first provided, I found Margaret happily sitting with a companion, moving continuously, but not restrained. In fact, when I noticed her lap belt was not fastened, her companion indicated "she knows just how to undo it, so we don't bother with it anymore."

Margaret's new wheelchair was set-up so that she could move around while in the tilted position. The freedom to move seems to reduce agitation while providing functional mobility. A year after starting to use her Bentley manual wheelchair, Margaret is still in constant motion. She has yet to figure out how to get it to tip over, but she's working on it...

Phil Mundy is president of PDG Product Design Group. He has worked in adaptive seating and positioning from almost 20 years, is a past board member of RESNA and current board member of the Canadian Adaptive Seating and Mobility Association. 

This is a home page devoted to Huntington's Disease information. The site is managed by Robert Laycock, Toronto, Ontario, Canada, E-mail:
This home page is supported by the Department of Neurology at the Kansas University Medical Center and by the Huntington's disease support groups
Mail contact:

Brian Bentley, David Harding, Lori Zoras, Motion Specialties, Toronto, Canada.

Creative Solutions; An Up-to-Date Look at Custom Design and Fabrication of Mobility Devices, David Harding, Rehab and Community Care Management, Fall 1998