The Balancing Act: Are Amputees Falling for It?

By Phil Stevens, MEd, CPO

Balance is a complex thing, relying on visual, vestibular, and proprioceptive inputs—and that's for people without limb loss. For many prosthetic patients, it's a function that they struggle to relearn with various degrees of success. Because of its importance to rehabilitation, it's worth taking a closer look at. Along the way, we'll review some of the research that has been done to tease out the various components of this balancing act.

In 1990, Alexander C.H. Geurts and his research team in the Netherlands began to probe the question of balance among the amputee population.1 They open their research report with the following broad statement: "Although an amputation is primarily a peripheral disorder, a central reorganization within the sensorimotor system must take place as a reaction to the altered peripheral constraints."

In other words, even though it's the patient's leg that is missing and there are a variety of issues regarding the maturation of the residual limb post amputation, the changes experienced by the amputee are not limited to the involved extremity. There are other adaptations within the central nervous system that must occur as the patient assimilates the incoming information from a much-altered extremity and then employs new compensatory adaptive movements. The authors describe this process as the "reorganization of postural control."

To evaluate this reorganization process, the authors had to quantify balance. One method of doing so involves using force plates to examine how much an individual's center of mass moves in a defined plane and in a defined time period. The more sway recorded, the more the balance of the individual can be considered compromised. This was the approach Guerts' team used to determine the postural control of ten healthy control subjects and ten unilateral amputees who had just received their first prosthesis following their amputations.

The researchers hypothesized that while postural control is relatively automatic prior to an amputation, its post-amputation reorganization likely requires more concentration, or, as the researchers phrase it, "attentional load." A second objective of their research was to examine the impact of attentional load on balance and the dynamics of attentional load throughout rehabilitation. Essentially, what happens if a new amputee can't devote his or her full attention to maintaining balance, and do these attentional demands change as an amputee gains experience with his or her altered body and prosthesis?

Stroop Test

So in addition to having their balance assessed during quiet standing, the subjects were also tested while performing something called a modified Stroop test. In this standardized exam, subjects are shown 25 colored words representing color names that are randomly incongruent with the printed colors. For example, the word "BLUE" might be printed in the color red. Subjects are asked to name the colors of the ink as quickly as possible, all the time suppressing the tendency to simply read the words. These assessments were conducted on two occasions. The first was within the first few days of training with their new prosthesis. The second was just before the completion of therapy, three to eight months later.

The results were not far from what you would expect. First of all, the amputees demonstrated a lot more sway in both quiet standing and under "attentional load" than their age-matched control subjects. Second, when the quiet standing condition was examined at the beginning and conclusion of rehabilitation, though there were no "statistically significant" differences, there was a slight tendency toward improved balance among the amputees. Third, while the addition of the cognitive task had no appreciable impact on the balance of the able-bodied control subjects, balance efficiency decreased significantly when amputees were tested under the cognitive load of the Stroop test. Finally, the balance efficiency during cognitive loading was significantly better at the conclusion of rehab than at its onset. Thus, the postural control of the amputees appeared to become more automatic and less cognitively demanding by the end of training.

This was one of the first glimpses into the "reorganization of postural control" among patients following amputation. Further attempts would follow. A team from Israel reaffirmed the trend toward decreased postural sway among amputees following their formal prosthetic rehabilitation. They also examined balance in both an "eyes open" and "eyes closed" condition at the beginning and end of rehabilitation and found that amputees became less reliant on visual feedback as they gained prosthetic experience.2 Their conclusions were strengthened a short time later by Guerts' Dutch team, which conducted very similar research and observed the same decreased visual dependence, presumably the result of their subjects' post-amputation postural reorganization.3 A fourth study that was conducted in Sweden using the same force-plate techniques found that while the sway values of traumatic amputees were greater than those of healthy controls, they were less than those of vascular amputees.4

More recently, researchers from the United Kingdom examined postural-sway values among several cohorts of patients with diabetic neuropathy. Subjects with neuropathy alone acted as controls against cohorts with secondary foot complications, including ulceration, partial foot amputation, and transtibial amputation.5 As might be expected, these researchers found that neuropathy alone is associated with compromised balance when compared to historical data from healthy controls. Furthermore, the excursion values for the center of pressure were significantly higher among all three of the cohorts with secondary foot compromise relative to the control group that had neuropathy only. Somewhat surprisingly, the excursion values observed among the cohorts with foot ulceration, partial foot amputation, and transtibial amputation did not vary significantly.

Scott Moltzan. Photograph ©2010 Otto Bock HealthCare, Minneapolis, Minnesota.

Such studies are somewhat instructive as to the processes that might be going on as a new amputee adjusts to life with a prosthesis. However, all they really tell us is what happens when a subject attempts to stand for 30 seconds in a controlled laboratory environment with the medial sides of their heels 8.4cm apart and with each foot toed out nine degrees from the sagittal midline. Of greater interest are the abilities of amputees to dress and transfer independently, engage in social activities, and work around the house. To what extent does balance affect such real-world activities?

A paradigm shift in the understanding of real-world balance came about not in a study of subjects with amputations, but in a study involving the elderly. In one important paper, Mary Tinetti, MD, and her colleagues gathered a wealth of information about activities of daily living (ADL) among more than 1,000 senior citizens.6 Included were ADL assessments on tasks such as grooming, dressing, and transferring; assessments of social activity such as employment, volunteering, and attending events; and assessments of physical activity such as light and heavy housework, yard work, and involvement in recreational sports. For each subject, the researchers collected information on falls, reported fear of falls, and fall-related efficacy.

The information on fall-related efficacy is of particular interest. Efficacy, as described by Bandura,7 began as a concept in behavioral psychology and refers to an individual's perception of his or her ability to perform in various domains. Creating an instrument called the Falls Efficacy Scale, the Yale researchers asked their patients to rate their confidence level in doing ten specific activities that might present a challenge to maintaining balance, such as simple shopping and reaching into cabinets or closets. Rather than rating the subjects on their ability to perform a given task, patients were asked to report their confidence or level of concern in completing these tasks.

Lo and behold, after all the numbers were tallied, it was not fall history or the reported fear of falling, but rather the idea of self-efficacy or self-confidence that correlated the closest with the seniors' ability to perform ADL, engage socially, and participate in physical activities. Thus, in addition to all the factors outlined earlier—vision, proprioception, and vestibular reflexes—actual day-to-day behavior is also dependent on an individual's perception of his or her capabilities. In fact, these self-appraisals appear to impact activity and function regardless of whether or not they are accurate.

Would this idea of self-confidence play out in the amputee population as well? This is the question that William Miller, PhD, and his colleagues from the University of British Columbia, Canada, have taken a close look at. In a recent study, the authors administered a newer falls-efficacy survey instrument to 435 unilateral amputees in the Ontario region.8 The assessment survey, known as the Activities-Specific Balance Confidence (ABC) Scale, was created as a more informative version of Tinetti's Falls Efficacy Scale.9

In addition to the ABC scores, the researchers collected information on fall history and fear of falling. They also collected certain balance-related "quality-of-life scores," assessing mobility capability, mobility performance, and social activity. They then performed the necessary statistics to determine which of the fall/balance factors correlated with enhanced function and societal participation among amputees.

The results make it clear that the idea of an individual's balance confidence is both a prevalent and important consideration. The researchers found that while 52 percent of unilateral-amputee study participants had fallen in the past year, and 49 percent reported a fear of falling, a full 65 percent had low balance-confidence scores. Furthermore, fall history had no relation to the subjects' quality-of-life indicators in any of the three domains, and the fear of falling demonstrated only a weak correlation. In contrast, the ABC scores of each subject's balance confidence correlated very strongly with mobility capability and performance, as well as with the subjects' social involvement.

Thus, it appears that in addition to the variables the researchers analyzed in labs using force plates, an important part of an amputee's ability to maintain his or her balance throughout the day seems to be his or her confidence in the ability to do so. What's more, a follow-up study further underscored just how much of a concern balance confidence is among lower-limb amputees. Among a large cohort of lower-limb amputees with a mean age of 62, the average ABC score was 64 (where 100 points represents complete balance confidence across all defined tasks in the scale).10 By comparison, a cohort of similar age that was described as "having no health problems" reported an average ABC score of 91.11 Thus, there appears to be a considerable disparity between lower-limb amputees and their age-matched peers. For amputees whose amputations occurred within the past three years, whose amputations were vascular in origin, who were over 70 years of age, or who used mobility devices for indoor ambulation, the disparities are particularly striking, with each of these subpopulations reporting mean ABC scores of 56 or lower.10

With the balance deficits associated with lower-limb amputation now identified across these various domains, the question that naturally follows is this: "Can we improve our patients' balance through components, training, or other means, and would those improvements ultimately correlate to an improved quality of life?" It's a concept worth pondering. What elements make up the balancing act, and are our patients falling for it?

Phil Stevens, MEd, CPO, is in clinical practice with Hanger Prosthetics & Orthotics, Salt Lake City, Utah. He can be reached at

References

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