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The Frame Game

Reprinted from PN June 2011

When it comes to manual-wheelchair frame materials, the choice should rest with users and therapists.

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Too often we take the path of least resistance. In the area of assistive technology (AT), especially that of manual wheelchairs, this means going with what is considered “standard.”

Unfortunately, what is considered standard is not always the best option for any given individual. This is because what becomes the standard is often determined by what is most likely to receive funding rather than by the intrinsic qualities of the technology.

What is best for an individual should be determined by that person and his or her therapist. Yet, if options are limited by funding or by too quickly defaulting to what is considered standard, the thoughtful process of choosing what is right is undermined.

Within the area of manual wheelchairs, one of the best examples of this is the choice of material for the chair’s frame. Less expensive chairs, made of aluminum, are typically funded. For some people, aluminum may be the best choice; for many others, it may not be. Yet, if alternatives are not considered, the ability to truly make the best choices is hindered.

Frame Material

Material selection is a central pillar of wheelchair design, along with function and aesthetics. Materials matter because they differ. Frame materials have different properties and ride characteristics, and they interact differently across varying designs and environments. The wheelchair industry, like the bicycle and aerospace industries, recognizes this fact and has offered a choice of materials to meet individual preferences and needs.

When the pursuit of lighter-weight wheelchairs took off more than three decades ago, lightweight aircraft-grade aluminum quickly became the dominant material because of its wide availability, user-friendly characteristics with respect to bending and shaping, and low cost. As the demand for better performance and durability and even lighter-weight frames increased, titanium was introduced. The unique properties of titanium make it an ideal material for premium wheelchair frames. But because titanium is difficult to refine and requires expertise and precision in welding and bending, it is a more expensive material.

Despite some price differences (and differences in likelihood of funding), end-users and therapists have an important role to play in ensuring they know their options in frame materials. Someone might ask if the “average” wheelchair user even cares about or can tell the difference between frame materials.

But who is average? Am I average? Are you average?

Assumptions about what may or may not matter to the “average user” are dangerous because in the end everyone ends up settling for less because the best options get underplayed or overlooked entirely. We don’t want to shoot for “average”—we want to consider all the best options knowing no one aspires to be “average.”

Choices such as frame material really matter! Consider that wheelchair users push on their handrims an average of 2,000–3,000 times a day, and every push and movement in the wheelchair is impacted by the chair’s design and material.

Titanium’s Advantages and Benefits

Titanium has three critical advantages that have driven its strong demand for more than a decade.

First, it has unparalleled strength and a high strength-to-weight ratio (Donachie, 1988; Welsch & Collings, 1994; Holt & Ho, 1996). This means less titanium material can be used while still building a stronger frame. Using less material leads to a lighter frame. Thus, titanium frames are stronger and lighter. Importantly, because less material is used, material expenses are reduced, and the price difference between titanium and aluminum is reduced as well.

Second, titanium has unique dampening qualities (e.g., Wolf, et al., 2007) so less vibration is transmitted to the user as he or she goes about activities of daily living. The resulting smooth ride benefits the rider by minimizing bumps and jolts, reducing fatigue, and increasing comfort. This benefit is incredibly important for active, long-term wheelchair users. Any reduction in vibration on a daily basis over years of use is simply invaluable.

Finally, titanium is a remarkably durable material. It does not rust or corrode, and its strength, toughness, and fatigue resistance means a titanium frame can withstand a pounding without failing. While other metals start to fatigue with repetitive use, titanium does not show signs of wear even after years of use.

For all these reasons and more, in an article that appeared in PN in 2005, renowned researcher and professor Dr. Rory Cooper listed the “expanded use of titanium” as #2 in his “Top 10 Advances” in manual wheelchairs over the past decade. If you prefer titanium’s strength, ride, and durability, these unique qualities directly translate into value and cost-effectiveness.

Aluminum: Still Important

With all the advantages of titanium, there are still very important reasons why someone may choose aluminum. It is a lightweight material, and because it is easy to work with, it lends itself to frame design and construction. Aluminum can be bent and welded in a variety of shapes. Thus, some people may prefer the fit they get from aluminum.

Also, while titanium is an excellent dampening material, some individuals may still prefer aluminum’s ride characteristics. Because aluminum is a stiffer material, it results in a stiffer ride some people find to their liking. In fact, many would consider a stiffer ride an advantage when rolling over or climbing up smooth terrain.

And then, of course, there is price. As noted above, because of its availability and ease of use, aluminum is less expensive. For some people, even if they are aware of alternatives, price can be a key factor that drives a preference for aluminum.

Going Beyond the Standard: Offer Choice

Whatever the choice is, it must be a thoughtful one informed by an awareness of the available options. When choices are taken away because what receives funding or is considered standard are the only options offered, it’s like letting someone else decide for us.

For decisions as critical as these, it is always worth going beyond what has been considered the standard. Especially given the meaningful differences between titanium and aluminum, it is surely worth being aware of and discussing these alternatives so whatever choice is made is a fully-informed one.

Manufacturers, for their part, will serve clients and therapists best by offering these options. This will leave the choice right where it should be: in the hands of end-users and their therapists.

Contact: David@3rivers.com.  

References

Boyer, R, Welsch, G, & Collings, EW (Eds). 1994. Materials Properties Handbook: Titanium Alloys. ASM International, Materials Park, OH.

Cooper, RA. 2005. “Top 10 Advances.” PN magazine. Vol. 59:3, 49-50.

Donachie, MJ, Jr. 1988. Titanium: A Technical Guide. ASM

International, ISBN 0871703092, Metals Park, OH.

Holt, JM, & Ho, CY. (Eds). 1996. Structural Alloys Handbook,

CINDAS/Purdue University, West Lafayette, IN.

Wolf, E., Cooper, RA, Pearlman, J, Fitzgerald, SG, & Kelleher, A. 2007. “Longitudinal Assessment of Vibrations During Manual and Power Wheelchair Driving Over Select Sidewalk Surfaces.” Journal of Rehabilitation Research & Development. Vol. 44:4, 573–580.

 

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The Frame Game

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