Canes Analysis and Recommendations for Improvement

Melanie Diez

In a country where life expectancy has increased dramatically since Colonial America (1) and the birth rate has seen a steady decline, perhaps it is not surprising that almost 13% of the population is age 65 or older. That number is predicted to reach 22% by 2030 (about 66 million people) (Howell 1997). With America getting older, we are faced with new social implications that force us to re-evaluate our current attitudes toward the more mature subgroups of our population.
One way to improve the quality of life for our elders is to examine how manufacturers design products for them. All too often products are presented to consumers without basic research into the design of the product. During the few cases where studies are performed to introduce "new ergonomic designs," the anthropometric data used is invalid for the following reasons:

i) the sample size is too small, or not representative of the aged population, which tends to be more dominated by females as age increases.

ii) the age brackets for older people encompass a larger population, oftentimes ranging over several decades, as opposed for younger populations which tend to be grouped in 5-, or 10-year intervals

iii) older people show greater variation in the amount of physical change their bodies experience over time due to nutrition, illness, level of activity, etc. (adapted from Kroemer 1997).

Another factor to consider is that products designed for disabled people are not necessarily well-designed for elderly people (Fernie 1997). For instance, a disabled person who has spent much of their life adapting to their unique circumstances will have a much better chance at operating a cane or other walking device as they grow older. Contrast this with an aging individual who is experiencing minor arthritis, slower memory recall, diminished balance, strength, and hearing and who is told, at the age of 65, that they must now incorporate an ugly metal walking aid into their lifestyle.

In a survey done on Americans using assistive devices to accommodate physical impairment, the largest category of users (approximately 5 million) was canes and crutches (LaPlante et al., 1992). The reasons for using a cane are as varied as there are types of canes. One of the most common reasons is to provide additional support to those who have compromised strength or balance in their lower limbs. Some conditions that may cause this are strokes, surgeries, and arthritis. In fact, the American Association of Retired Persons states in its 1992 AARP Product Report that, "The predominant medical condition among cane users is arthritis" and that, "almost 75 percent of users in one survey said they use a cane because of this condition." They later go on to mention that "with a third point of contact as much as 25 percent of your body's weight can be shifted away from lower limbs."

Keeping these facts in mind, it is disturbing to find out that an informal survey of the canes in today's market shows they lack the most basic principles of ergonomic design. Little research could be found supporting the designs behind the canes; indeed, most canes launch a practical assault on the hand and wrist.

While there are several aspects to the design of a cane (handle, shaft, base, tip), this study will concentrate on the handle designs. First, I will present a brief overview of the commonly accepted ergonomic design principles involved in handle design, followed by several examples of common cane handles.

Fraser (1980) states that the handle of a tool should conform to the natural holding position (neutral position) of the hand. In short, this means that the handle should maintain a straight wrist with minimal flexion, extension, or deviation. This can be done by incorporating an angle of 19 E" 5 E into the handle, as suggested by Emmanuel, Mills, and Bennett (1980). By reducing the angle through which the wrist itself must bend, injuries such as carpal tunnel syndrome can be minimized. Furthermore, grip strength has been shown to be maximized when the wrist is in neutral position (Terrell & Purswell, 1976).

The shape of a handle should be generally cylindrical, or shaped like a truncated cone to accommodate the different degrees of flexion exhibited by each finger. Pressure from the device must not be concentrated in a small area, or along pressure-sensitive areas of the palm and fingers. Sanders and McCormick (1993) suggest a large contact surface to reduce tissue and/or nerve compression. Repetitive finger action as well as vibration exposure should also be minimized.

Appendix 1 presents several examples of cane handles I encountered in medical supply catalogs (adapted from AARP Product Report 1992). Most, if not all of these designs violate several of the general guidelines listed above. The crooked cane, for instance, forces the fingers into unnatural flexion patterns with the little finger and index finger extended out further than the middle and fourth finger. The ball-topped cane concentrates the majority of the force directly into the palm, and forces the wrist into severe dorsiflexion when weight is applied. The T-shaped handle, the straight handle, and the shovel handle all focus the force along the crease of the hand and neglect the meatier, more-padded regions of the palm.

Appendix 2 shows an excerpt from a medical supplier. Once again, most of the handles follow a simple, horizontal bar-shaped design. Pictures of "patients" using the canes show the wrist undergoing dorsiflexion as the weight of the body flattens the hand against the handle.
In an effort to better understand the problems associated with cane usage, I spent a day walking around campus with a Lumex offset-style aluminum cane which I rented from the Finger Lakes Independence Center, an extension of the American Red Cross. The handle resembles the "straight" handle, except that it rests directly overhead the shaft. I experimented with different heights and observed the physical sensations caused by constant use.

I noticed several problems within the first five minutes. My triceps were quickly fatigued as they worked to hold my weight up. As a result, my scapula elevated to relieve the triceps, putting strain on my rotator cuff. This "shrugging" effect could be somewhat offset by lowering the height of the handle below my waist, which served to extend the arm and reduce the amount of elevation in the shoulder.

The handle of the cane was designed in such a way that the grip increased in broadness from the neck of the handle to the end, providing a wider, flatter surface where the palm would rest. Unfortunately, the result was not a more comfortable feel, but rather a terrible dorsiflexion combined with ulnar deviation in the wrist and a bruised hamate bone where the weight was concentrated. I felt tweaks of pain all day long in my wrist and shoulder which continued into the night, long after I had ended my experiment.

Aside from design problems, there were several functional problems as well. For instance, each step was accompanied by a jarring vibration which was transferred up the entire length of the arm every time the rubber cane tip struck the concrete. The swing of the cane often had to be initiated by a flick of the wrist, resulting in a constant repetitive oscillation between ulnar and radial deviations. Furthermore, adjusting the cane to the correct height was difficult due to a simultaneous push of a button and pull of the shaft requiring relatively dexterous fingers; arthritic hands would be pitifully ineffective.

While my experience is not meant to be taken as stereotypic of all cane-users, (and one could certainly argue that my problems would be reduced as soon as my muscles became attuned to their new actions), it should serve as a general description of the possible issues cane-users must face. I am young and physically fit; any problems I experienced using a cane would probably be augmented in a disabled or elderly individual.

It should be pointed out that many cane-users are older patients who have suffered strokes and other nervous disorders requiring extra stability.

Often these patients are in a weakened state with pain in their joints, or an inability to grasp (2 ). Furthermore, many elderly people experience a forward shift of their center of mass. A cane that requires too much strength from weak fingers could give a false sense of security and cause more falls than it prevents. Any assistive device that may increase a person's risk for a second injury due to poor design should be examined. The AARP stated that as much as 25% of a person's body weight could be shifted to the cane; imagine the dangerous effects this extra burden must place on a weakened person's wrist.

In an effort to approximate the changes in pressure within the wrist during cane-walking, I conducted an informal survey of 10 subjects. I presented them with the Lumex cane which I had used during my experiment and asked them to take a few moments to become familiar with it by walking around with it. I adjusted the height for them so that the handle came to their wrist when they stood erect and their arms were relaxed.

I then asked them to hold the cane in the position they felt most comfortable with while they were walking with it. Using a goniometer, I measured the angle their hand made with their wrist and calculated the intercarpal tunnel pressure (mmHg) according to a polynomial equation provided by Dr. Alan Hedge.

Appendix 3 shows the parabolic curve described by this equation (3 ). The average angle found in my ten subjects was approximately 58 E which corresponds to a pressure of approximately 110 mmHg. Compare this to the neutral position which experiences a pressure of about 26 mmHg. Given that nerve compression starts around 30 mmHg, this particular cane puts the user at an extremely compromising angle.

What do the manufacturers have to say regarding their products? It was extremely hard to get in touch with anybody who could answer questions about the design of canes. A survey of several catalogs and physical therapy units revealed that the prominent suppliers of canes were Lumex, Tem-Co, Invacare, Guardian, PCP, and API. Of these six, Lumex and Invacare faxed some general information to me (including the AARP report). API told me they had one engineer on the premises, and he was too busy to speak to me. In fact, most of the companies referred me to their engineers or "technical specialists." None of them could connect me with an ergonomist.
A representative from PCP offered to spare me a few minutes, but whined that he was "trying to run a business here and couldn't take a lot of time answering surveys all day long." After putting me on hold twice to take other calls, he finally admitted to me that their cane designs had been used for 30 years and there wasn't much need for re-design since "a cane is a cane". He did add that the grips had been changed occasionally, but when I asked him what circumstances elicited the change and what research was done to improve the design, he had no idea and in fact seemed annoyed that I had asked. Representatives from Guardian and Tem-Co were unavailable for comment and/or never returned my messages.

Does this mean that there is absolutely no scientific foundation for the cane handles we see today other than the whimsy of one or two engineers or the fact that they have always been designed that way? What about the new and improved designs that brand themselves as "ergonomically-designed"? In fact, one brand which advertised its ergonomic-grip handle boasted about its indentations for the fingers- an expressly undesirable characteristic in ergonomics which limits the range of users to only a handful (no pun intended)!

It appears that there is a general lack of research behind the designs of canes on the market today. Indeed, many of the designs have not been changed for several decades. What can be done to identify the areas where improvement is most needed?

One option is to improve the available data on older populations by conducting better surveys of aging people. This includes using smaller age ranges (i.e., 65-70, 70-75,etc. instead of 65+), and taking into account disabilities which may come with age. New designs for canes should then be based on the anthropometric results of intended users.

Another option is to go to the laboratory and design the canes based on the movements involved in cane walking. Fernie (1997) describes the advantages of motion analysis systems which use markers attached to the subject to record the different motions the joints and limbs experience. Such analyses are a vital addition to anthropometric data as they reveal the otherwise unknown biomechanics of the motion.

Of course, the most important key to developing better canes and other assistive devices is to incorporate consumer input. It is vital to remember that elderly individuals have special needs that may push them into the 5%ile that is sacrificed in order to accommodate the rest of the population. The common problem of avoiding or delaying the use of an assistive device should not be augmented by a an ugly and embarrassing, or uncomfortable design.

From my experience alone, I would suggest experimenting with ways to reduce the amount of fatigue in the triceps as well as the resultant elevation in the scapula. One way to do this is to lower the height of the cane so as to straighten the arm. This reduces the angle in the arm and thus the amount of force the triceps must exert to hold the body up. Cramping in the hand is also a problem, since the finger muscles are small and not well-designed for extended periods of flexion. Vibration dampers might be worth checking into. The repetitive striking of the pavement became annoying as well as painful after a day of use. The handle should also be designed so that the maximum force is applied to the meaty part of the hand, not the bony part.

In conclusion, I found that the canes available today show little attempt to be designed according to basic ergonomic principles. In addition, the designs available today are the same designs used decades ago, with a few alterations in the handle. While some of these "new and improved" grips are advertised as "ergonomically-designed", many of them actually go against basic design principles. Furthermore, there is absolutely no consideration for the fact that elderly consumers differ in their needs from the disabled and other populations. This is a direct result of the lack of anthropometric data on the elderly.

Finally, I would recommend the following steps to improve the current situation. First, expand the anthropometric data by conducting new studies that are sensitive to the changes that occur to the body after age 65. Second, couple these statistics with laboratory studies of motion analysis that shows the movements of the limbs during cane-walking. Third, incorporate consumer input into the redesign of a new handle. Obviously these three recommendations will not necessarily guarantee a perfect cane, however they will open up the avenues of communication between manufacturer and user, thus hopefully precipitating change a little more often than once every 30 years.

References

American Association of Retired Persons. 1992. Product Report Vol. 2, No. 3. Washington, DC: AARP.

Committee on an Aging Society (Ed.) 1987. The social and built environment on an older society. Washington, DC: National Academy Press.

Fernie, G. 1997. Assistive Devices. In A.D. Fisk & W. A. Rogers, eds. Handbook of Human Factors and the Older Adult. San Diego: Academic Press.

Fisk, A.D., and Rogers W.A., eds. 1997. Handbook of Human Factors and the Older Adult. San Diego: Academic Press.

Fraser, T.M. 1980. Ergonomic Principles in the Design of Hand Tools. Occupational Safety and Health Series No. 44. Geneva: International Labor Office.

Howell, W.C. 1997. Foreword, Perspectives, and Prospectives.

Kermis, M.D. 1984. Psychology of human aging. Boston, MA: Allyn & Bacon.

Kroemer, K.H.E. 1997. Anthropometry and Biomechanics. In A.D. Fisk & W. A. Rogers, eds. Handbook of Human Factors and the Older Adult. San Diego: Academic Press.

LaPlante, M.P., Hendershot, G.E., & Moss, A.J. 1992. Assistive technology devices and home accessibility features: Prevalence, payment, needs, and trends. Advance Data: Centres for Disease Control, 217, 1-11.

Sanders, M.S., and McCormick, E.J. 1993. Human Factors in Engineering and Design, 7th Ed. McGraw-Hill, Inc.

Terrell, R., and Purswell, J. 1976. The influence of forearm and wrist orientation on static grip strength as a design criterion for hand tools. Proceedings of the Human Factors Society 20th Annual Meeting. Santa Monica, CA: Human Factors Society, pp. 28-32.