The Balancing Act: Scene 2

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By Phil Stevens, MEd, CPO

The first installment of our discussion of balance among individuals with lower-limb amputations examined various techniques that have been developed to quantify balance in this population, and some of the broad influences that can affect balance, such as visual inputs, cognitive loads, and balance confidence (The O&P EDGE, May 2010). That discussion concluded with the following question: "Can we improve our patients' balance through training, alignment, or components?" This article addresses that question through a literature-based discussion, which examines various modalities that appear to improve amputee balance—including a discussion of specific prosthetic components, socio-demographic influences, and increased physical activity.

Components

Feet

Variflex foot-one of the many different types of Flex feet. Photograph courtesy of Ossur.

Numerous studies have looked at various prosthetic-foot types in terms of their resultant biomechanics, addressing such issues as gait velocity, kinematics, and energy efficiency. By comparison, very little has been done to address questions of balance and stability. Recent literature on the subject is limited to a single study comparing the properties of the Flex foot to those of the SAFE foot.1 While the paper is focused primarily on questions of resultant kinetics, the researchers also asked their subjects to rate their perceived stability when wearing each type of prosthetic foot on a number of different surfaces. The results were not far from what you might expect. The subjects reported little difference in perceived stability for standing and walking on flat surfaces. However, as walking terrains became increasingly demanding, subjects reported an increasingly stronger preference for the Flex-foot condition.1 Thus, it appears that prosthetic-foot choice may influence a patient's perceived stability, particularly when ambulating across challenging surfaces.

Ankles

Researchers at the Northwestern University Prosthetics Research Laboratory, Chicago, Illinois, recently evaluated the effects of prosthetic-ankle mechanisms on the gait characteristics of subjects with bilateral amputations.2-3 Much like the foot study cited earlier, both of these investigations were focused primarily on kinematics and other laboratory-derived observations. But once again, the inclusion of self-report questionnaires throughout the study protocols provided some insight on issues of stability and balance.

A small cohort of experienced prosthesis users with bilateral transfemoral amputations, using either polycentric or Mauch SNS knee joints, were fit with Seattle LiteFoot 2 prosthetic feet two weeks before the subsequent addition of Endolite Multiflex ankle mechanisms.2 Following two additional weeks of acclimation, subjects reported on their perceptions with both the new prosthetic feet and with the subsequent inclusion of the ankle mechanisms. Increased comfort was reported by all but one subject. Likewise, all but one subject reported that the ankle units made it easier to walk on uneven ground.2

Endolite Multiflex ankle. Photograph courtesy of Endolite

The researchers later recruited a much larger cohort of subjects with bilateral transtibial amputation.3 In this investigation, subjects experienced four test conditions, each separated by a two-week acclimation period prior to data collection. Test conditions included the following: (1) bilateral Seattle LiteFoot 2 prosthetic feet only; (2) the inclusions of either Endolite Multiflex ankle units or Otto Bock torsion adapters according to randomized assignment; (3) the replacement of the preceding prosthetic-ankle mechanisms with the other ankle joint type; and (4) the "combined configuration" in which both flexion and torsion units were used simultaneously. Relative to balance concerns, statistically significant findings included the reported perception that walking on uneven terrain was made easier with the inclusion of each of the three possible ankle interventions when compared to the baseline assessments. Similarly, the presence of flexion units at the ankle made the negotiation of inclined surfaces easier than that experienced in each of the two configurations lacking the flexion unit at the ankle.3

Thus, there is preliminary evidence to suggest that the functions associated with flexion and torsion ankle mechanisms may facilitate ease of ambulation across uneven ground and inclined surfaces among patients with bilateral amputations where sound-side limb compensations are not possible.

Knees

Ironically, with respect to questions of balance and stability, studies have thus far been limited to the two prosthetic knee types, each representing the opposite extremes of technology, complexity, and cost. Studying a cohort of unilateral dysvascular amputees between the ages of 61 and 80, a team of researchers from Toronto set out to determine the differences experienced with the use of free-swinging versus locking knee joints.4 For the purposes of the study, only those subjects were recruited who actively walk in their community with a free-swinging, single-axis, stance-control prosthetic knee joint. Baseline data was collected while subjects were using their articulating knee joints. Subjects then received locking knee joints, used these in the community for one week, and returned for further study. Of the 14 study subjects, 11 reported a preference for the locking knee joint. Additionally, two-minute walk-test scores found that irrespective of knee preference, subjects walked, on average, 21 percent faster in the locked-knee condition. Prosthetic use also appeared to be greater in the locked-knee condition. Although the small number of study subjects precluded rigid statistical analysis, the three subjects who preferred the articulate knee joint were younger than those who preferred the locked-knee condition, with average ages of 63 and 71, respectively. Also, these three subjects walked substantially faster in the articulate-knee condition than their peers in the study. The reasons offered by those who chose the locked knee over the articulating knee related to improvements in balance, with subjects citing improved security, less concentration during walking, and an improved ability to climb stairs and walk outdoors.4

Otto Bock C-Leg. Photograph courtesy of Otto Bock HealthCare.

On the opposite end of the spectrum of prosthetic knee joints lies the complexity of microprocessor-regulated technologies. These knee joints, most notably the Otto Bock C-Leg, have been the subject of research inquiries for more than a decade. However, it has only been in the last several years that researchers have delved into the effects of this component choice on amputee balance. Prosthetic Research Study, Seattle, Washington, conducted the first of these efforts. Venturing outside of the strict laboratory environment, Hafner, et al., examined the effects of this knee-joint technology on tasks and challenges more consistent with those encountered in daily life.5 While many of their findings are beyond the scope of this discussion, several of them are quite relevant. For example, throughout a pre-defined schedule in which subjects transitioned between sessions of extended use in their previous knee units and C-Legs, they were asked several questions regarding such issues as confidence, concentration, stumbles, and falls. The cumulative responses to five of these questions yielded statistically significant improvements when subjects were using C-Legs compared to baseline responses. The nature of these five questions suggest the potential clinical impact of this knee-joint technology on questions of balance: "Over the past four weeks, how often have you had a 'stumble,' a 'semi-controlled fall,' or an 'uncontrolled fall'?" "How difficult has it been to complete a task while walking, such as talking or reading?" "How frustrated have you been with the amount of falls you have taken?"

The following year, a group of Florida-based clinicians reported on a convenience sample of 19 transfemoral amputees as they transitioned from their existing conventional knee joints to C-Legs.6 As part of their research protocols, subjects were asked on two separate occasions how many times they had stumbled or fallen in the past 60 days. The first was after a 90-day baseline observation period with their existing knee joint and the second following 90 days of C-Leg use. Importantly, decreases in the number of both stumbles and falls were reported with the use of the microprocessor-regulated technology, further strengthening the position that knee-joint selection can dramatically impact the balance and stability of individuals with lower-limb amputations.

As suggested in the initial discussion on the topic, balance among the amputee population can be studied at several levels. Patient reports on stumbles, falls, and multitasking while walking represent one line of inquiry. However, the conclusions drawn from these types of observations are strengthened when balance is further investigated with more objective, quantifiable techniques. In the case of microprocessor-regulated knee joints and their effects on balance, this strict laboratory validation was performed by researchers from the Mayo Clinic.7 In their investigation, researchers used computerized dynamic posturography to assess balance on differing knee-joint technologies. The technique in question evaluates the visual, somatosensory, and vestibular inputs of balance by recording a patient's center-of-mass excursions while varying the visual and support-surface conditions. Fifteen transfemoral patients underwent this form of objective balance assessment in both conventional hydraulic knee units and microprocessor-regulated units. The researchers observed significant improvements in the equilibrium scores across all of the various balance domains as well as a significant improvement in the composite equilibrium score.

Thus, recent literature supports the idea that, as with prosthetic-foot and ankle components, the balance of individuals with lower-limb amputations can be affected by the choice of prosthetic-knee mechanism. With these early investigations into both simple locking knees and more elaborate microprocessor-regulated knee joints having established this precedent, it can be hoped that similar investigations evaluating the effect of other component changes on patient balance may soon appear.

Confidence and Lifestyle

In addition to the possible effects of prosthetic component selection on balance, some literature seems to suggest that certain socio-demographic and lifestyle situations may also play a role. For example, having established its reliability and validity among the lower-limb amputee population, a team of researchers from Vancouver British Columbia administered the Activities-specific Balance Confidence (ABC) Scale to 435 community-dwelling, unilateral amputees. The researchers categorized their data according to a number of different factors, identifying mean balance-confidence scores for a number of different demographics.8 It is not possible to modify some of these factors. For example, patients above the age of 71 reported balance-confidence scores roughly 30 percent below their younger peers (ages 23-55), female subjects reported scores roughly 20 percent below their male peers, and patients with vascular amputations reported scores nearly 30 percent below those patients with nonvascular-related limb loss.8

Other reported factors are modifiable but raise intriguing questions as to whether potential modifications to a given factor would actually affect balance. For example, patients who noted an education level less than the 12th grade reported balance-confidence scores 22 percent below their peers with higher education levels. Similarly, subjects who noted an annual income of less than $20,000 reported balance-confidence scores 22 percent lower than subjects who noted an annual income of $40,000. Additionally, amputees who identified with depressive symptoms reported confidence scores roughly 25 percent below their peers who lacked these symptoms.8 While some of these factors may have some indirect bearing on balance, it is more likely that they reflect the general confidence of the individual, highlighting one of the potential limitations of patient-generated data.

Are there other modifiable lifestyle factors that could more directly affect patient balance? If so, could their effects on balance be objectively measured without the filtering of patient perceptions? These questions serve as an interesting backdrop to a recent paper that would seem to suggest that regular sports participation may improve the general balance of individuals with unilateral lower-limb amputations.9 Specifically, researchers from the Turkish Armed Forces Rehabilitation and Care Center examined the possible effects of playing amputee soccer. In the paper in question, the authors identified 12 subjects who had played on an amputee soccer team for at least six months. Control subjects were then selected from a cohort of unilateral amputees who did not actively engage in sports but were similar in age, body mass index, cause and level of amputation, general health, and limb dominance.

Among the numerous outcome techniques examined, researchers quantified the single-leg balance of all subjects on their sound-side limb using the Kinesthetic Ability Trainer (KAT) balance system. The amputee athletes demonstrated significantly better balance than their matched controls. Didactic questioning about fear of falling and fall rates appeared to support a difference in the overall balance of the two cohorts. For example, only three of the 12 athletes reported a fear of falling, compared to ten of their 12 non-athlete peers. Similarly, the athletes reported an annual fall rate of less than one, while the reported rate of the non-athletes was just over five.9

The relationship observed in this paper is one of correlation, leaving questions of causation to inference. While it seems likely that participation in sports improved balance for the amputee athletes, it is also possible that those subjects with better balance were more drawn to sports. However, the notion that such lifestyle alterations might affect balance is not without precedence. As a notable example, the introduction of Tai Chi has been found to improve functional balance and reduce fall rates among the elderly.10-12 Similar phenomena might be expected with the introduction of sport and recreation activities within the amputee population.

Conclusion

The restoration of balance and stability following amputation remains a challenging undertaking. What little evidence we currently have in this area seems to suggest that prosthetic component selection may play an important role. Furthermore, there is preliminary evidence to suggest that changes in lifestyle and participation levels may also be beneficial. However, our current understanding is limited. To the extent that clinicians and manufacturers alike make balance an important consideration in their interactions with their patients, we can anticipate continued improvements to the "balancing act" of individuals with lower-limb amputations.

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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