Of primary interest in the current study was the issue of whether patients could improve their energy expenditure by walking more symmetrically. When patients were given RTVF, there were significant improvements with each type of display and for each energy-related variable measured (Table 2). In addition, the actual symmetry for the three forms of feedback improved for all subjects, indicating that the statistically significant improvements were not attributable to a placebo-type effect (i.e., when patients knew they were supposed to walk more symmetrically) but were associated with quantitative improvements in gait symmetry.
EFFECT OF SEGMENT LENGTH
Based on clinical parameters, such as lowest palpable pulse, skin temperature, and bleeding during surgery, amputations are performed proximal to the level of irreparable damage or infected tissue. Surgeons keep as much length as possible while removing enough of the limb so that proper healing will occur at the distal end and future amputations are not necessary. Gonzalez et al. 10 reported that transtibial amputation with at least 9 cm of tibia preserved would result in performance far superior to that of knee disarticulation and transfemoral amputations.
Publications during the past 30 years have reported that as amputation level increases, energy cost of ambulation with a prosthetic device increases and self-selected walking speed decreases. The pathology underlying the need for an amputation is also a factor in rehabilitation. For instance, it has been shown that traumatic transtibial amputees are able to walk at faster speeds than are patients with transtibial amputations related to vascular disease. 5,11–13 Waters et al. 5 reported that the through-knee amputees had a self-selected walking speed falling between those of transtibial and trans-femoral amputees. However, the O2 consumption of a through-knee amputee was the highest of these three groups. Ankle disarticulation amputees were found to choose a walking speed higher than that of transtibial amputees, but the two groups were found to have the same metabolic cost for ambulation. Based on these findings, it is of interest to review the data shown in Figure 4, where our findings suggest that transtibial vascular patients require less oxygen per meter traveled. Closer inspection of our data showed that the vascular transtibial patients had longer residual limbs (23 cm or 12.4 percent segment length) than did the traumatic amputations (17.8 cm or 10.4 percent segment length). Thus, in our cohort, it is likely the additional segment length compensated for the underlying reason for amputation.
Gonzalez et al. 10 reported the average self-selected walking speed of 64 m/min at an energy expenditure of 13.06 mL/ kg·minute for transtibial amputations caused by peripheral vascular disease. Pagliarulo et al. 12 reported that 15 vascular transtibial patients ambulated at 71 m/minute with an oxygen consumption of 15.5 mL/kg·minute. Gailey et al. 14 conducted a study in which 39 nonvascular transtibial patients walked an average pace of 67.1 m/minute and had a metabolic energy expenditure of 12.9 mL/kg·minute. In the current study, vascular transtibial individuals had an average self-selected speed of 61.7 m/minute at an energy cost of 9 mL/kg·minute, and nonvascular transtibial amputee subjects had a speed of 65.8 m/minute at 11.2 mL/kg·minute.
EFFECT OF GAIT SPEED, AGE, AND SUBJECT MASS
Oxygen consumption (expressed as mL/kg/minute) during gait exhibits a linear relationship with the speed of walking according to the following equation 15:
In the current study, the coefficient was 0.082 (as opposed to 0.1 in the above equation), but this value was not statistically significant (p >.05). With regard to the effects of age, during a 22-year span, the regression coefficient was 0.055, although as with body mass, this was not statistically significant (p >.05).
Oxygen consumption is also a function of body mass, and investigators have shown that there is a significant positive correlation during walking between oxygen consumption and body weight. 16 Thus, oxygen consumption often is normalized to an individual’s body mass when investigating weight-bearing activities. Other factors, such as certain pathologies, also may influence oxygen consumption. Non–insulin-dependent diabetes mellitus and chronic lesions of the foot, two pathologies associated with limb amputation, have been shown to affect energy expenditure. Individuals with non–insulin-dependent diabetes mellitus have demonstrated, relative to healthy control subjects, a reduced rate of increase in oxygen consumption during increasing work loads, suggesting limitations in oxygen delivery. 17 With regard to lesions of the foot, rigidity of the talocalcaneal joint has been shown to result in a 5 percent to 20 percent increase in oxygen consumption, thus indicating increased energy expenditure. 18
REAL-TIME VISUAL FEEDBACK
The problem of gait asymmetry has been examined by a number of researchers. Bach et al. 6 developed a computer simulation to minimize energy cost or maximize symmetry. He found that through optimizing the prosthetic limb’s mass distribution there was a significant increase in gait symmetry and a decrease in energy expenditure. Furthermore, previous work by our group 7 showed that RTVF could lead to improvements in gait symmetry, even when the patients had been exposed to the computer displays for only 2 minutes.
In the current study, both symmetry and energy demands (as assessed by oxygen consumption and heart rate) were compared before and after patients received RTVF. The results showed that across all types of feedback, tidal volume had the most dramatic improvement (22 percent), compared with 6 percent and 3 percent improvements in VO2 and heart rate, respectively. Subjectively, patients tended to prefer the “butterfly plot”; although in two of the subjects, there were some technical difficulties that prevented data for this form of feedback from being collected. Nevertheless, of the remaining nine subjects, six showed an improvement in symmetry when this form of feedback was used. For the percent stance time and push-off force displays, there were symmetry improvements in seven and eight subjects, respectively.
There are certain limitations of the study that need to be recognized. First, this study required that patients wear a respiratory mask while walking on a treadmill. Although the patients seemed to cope well with both the oxygen measurement system and the treadmill, it is possible that the instrumentation constrained their walking patterns. Second, to have patients perform the full battery of tests (i.e., walking without feedback as well as three different feedback modes), only patients who could walk for the required length of time were accepted for this study. This limitation restricted the initial sample size, and it also means that the results should not be extrapolated to patients who have poorer locomotion capabilities. Third, patients were diverse in both their reasons for having an amputation and their type of prosthetic limb, leading to added variability in their gait mechanics and consequently in their energy expenditure. This limitation was partially addressed by having subjects serve as their own controls. Finally, these results, although encouraging, must be interpreted with caution because it is not yet clear that these changes in gait symmetry and oxygen consumption would result in long-term learning of a more symmetrical gait pattern. Because the primary goal of this project was to determine if amputee patients could respond positively to real-time visual feedback (i.e., use less energy during gait), and because this was shown to be the case, the questions of long-term gait-training effects are left to future research.
In summary, this study used three visual displays while patients walked on a treadmill, and all three were associated with significant improvements in energy consumption (Table 2). This suggests that even for patients who have had a suboptimal level of amputation, there may be forms of rehabilitation that can greatly increase the likelihood that they could walk more efficiently and have a higher level of daily mobility.
The authors thank Dean Frazier for graciously assisting with patient selection. This work was funded in part by Grant EEC 9820538, provided by the National Science Foundation.
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Keywords:© 2004 American Academy of Orthotists & Prosthetists
amputee gait; biomechanics; lower extremity; residual limb length