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Comparison of Effort Between Below-Knee Amputee and Normal Children

The purpose of this preliminary investigation was to compare physiological and biomechanical measures of effort for walking of below-knee-amputee (BKA) and normal children. For this investigation effort was evaluated utilizing three measurements: oxygen uptake (V02), heart rate and vertical displacement of a marker approximating the whole body center of mass. Three children acted as subjects for this investigation, two as controls. One of the BKA children wore a flex foot terminal device as a part of his prosthesis and the remaining two wore a SACH foot terminal device. The subjects walked for two minutes at up to four different treadmill speeds, including their preferred speed. The results for V02 and vertical displacement of the COM seemed to separate subjects into two groups. The first group consisted of BKAs wearing a SACH foot terminal device and the second group consisted of normal children and the child with the flex foot terminal device. The first group generally displayed greater effort for all walking speeds when compared to respective values in the second group.

Introduction

The gait of below-knee-amputee (BKA) children is different from that of normal children.2,5 The differences noted, in particular the asymmetries, might naturally be expected since the structure of the prosthetic limb is different from that of the nonprosthetic limb. However it is presently unknown whether the differences in gait are beneficial, detrimental or inconsequential with respect to the long and short term health of BKA children. In the long term, chronic higher loading in the nonprosthetic limb may increase the risk for future degenerative joint disease.1,4 In the short term, it may require greater effort for BKA children to walk and run when compared to the effort required by normal children. This greater effort may prevent BKA children from having the same typical experiences as those of normal children and may result in a reduced quality of life.

Effort can be evaluated from both physiological and biomechanical perspectives. Physiologically effort has been evaluated by measuring oxygen uptake (V02 ml/kg/min.) and heart rate. Pagliarulo et al.,7 determined the effort of 15 unilateral BKA adults with no pre-existing vascular disease. Subjects walked with a prosthesis and with crutches at various speeds, including their freely chosen speed. Results indicated that while the average freely chosen speed for both methods of gait were not significantly different, the heart rate and V02 were significantly different. Walking with a prosthesis was accomplished with lower heart rates and lower VO2 values than walking with crutches. In addition, V02 increased when subjects walked faster or slower than their freely chosen speed under either walking condition. It was concluded that the use of the prosthesis should be encouraged over walking with crutches.

Nielsen et al.,6 measured the heart rate and V02 of seven adult unilateral traumatic BKAs during various walking speeds. Three subjects walked with both SACH and flex foot terminal devices. Results indicated that the freely chosen walking speed for the flex foot was generally higher than for the SACH foot. V02 was similar for both terminal devices at slower speeds, while at faster speeds slightly less oxygen was consumed when the subjects wore the flex foot compared to the SACH foot. However the differences in the values of V02 between these terminal devices were never greater than the differences between either device and the lower VO2 values of normal subjects. These same trends were also displayed for heart rate.

From these investigations it may be concluded that: 1) although prosthetic gait requires less physiological effort than crutch walking, it nevertheless requires greater effort than walking with two intact lower limbs and 2) the differences with respect to effort for two different terminal devices may be small. Whether BKA children display the same or greater physiological effort for walking as adult BKAs has not been reported.

Physiological measurements can provide valuable information to evaluate the effort of BKAs under varying walking conditions, however they cannot offer an explanation as to why greater effort is required. In contrast, biomechanical measures may offer a mechanical explanation for greater effort. Utilizing both physiological and biomechanical measurements, a relationship may be established to consider a cause and effect interaction for effort. The purpose of this preliminary investigation was to compare physiological and biomechanical measures of effort of BKA and normal children during walking.

Methods

Five children volunteered to participate in this investigation. Three of the children were BKAs and two had normal intact lower limbs. One of the BKA children wore a flex foot terminal device as a part of his prosthesis and the remaining two wore a SACH foot terminal device. The physical characteristics of the subjects are presented in Table 1 .

After the procedures of the study were explained to the children and parents and informed consent forms were signed, the children were permitted to walk on a treadmill for 3-5 minutes. In addition, the children were given time to practice breathing with a small mouthpiece. The purpose of this step was to make each subject comfortable with the technicians and to familiarize them with the testing equipment and environment.

Prior to the data collection, each subject was asked to choose his/her preferred speed of walking on the treadmill. This was achieved by having each subject increase or decrease the speed of the treadmill by verbal communication with the treadmill operator until he/she felt comfortable. With the freely chosen speed selected, the treadmill was stopped and the child was prepared for data collection. The subjects then walked for two minutes at each of the following treadmill speeds: 1) preferred, 2) 0.7 m/s, 3) 0.9 m/s, 4) preferred, 5) 1.1 m/s, and 6) preferred.

For this investigation, effort was evaluated utilizing three measurements: heart rate, VO2 and vertical displacement of a surface marker approximating the whole body center of mass (COM). Heart rate was monitored with a PE 3000 Sport Tester and VO2 was measured using a Horizon metabolic cart. A sensor unit was attached to the chest of the child to monitor the heart rate and headgear and mouthpiece were placed on the child to allow for determination of VO2 It had been determined in a preliminary experiment that two minutes was adequate for these children to reach a steady level of heart rate and VO2. Thus while VO2 and heart rate were monitored every 30 seconds only the final value was used in the analysis. Vertical locations of the reflective surface marker placed on the sacrum were determined for 7-10 step cycles at both 45 and 90 seconds into data collection with a Motion Analysis video system. Vertical displacements of the surface marker were determined for each step cycle. Displacements were normalized by dividing by subject height and then an average value was determined. Since only five subjects were involved in the preliminary investigation statistical treatment could not be performed to determine significant differences between variables.

Results

Freely Chosen Speeds

The means and standard deviations (sd) for speed, heart rate, VO2 and displacement of COM for the preferred walking speed are presented in Table 2 . The results for the preferred speed did not generally deviate substantially from the beginning to the end of testing for any given subject. The consistency of these results provided a measure of testing reliability and the results for the fixed speeds were viewed as being reasonable.

Fixed Speeds

The results for heart rate at the fixed speeds are presented in Figure 1 . For each subject the heart rate was greatest at the fastest speed and with one exception was lowest at the slowest speed. At the two greater speeds the two BKAs with a SACH foot had the highest heart rates and at the fastest speed, all three BKAs had the highest heart rates. VO2 results for fixed speeds are shown in Figure 2 . For every subject, as the speed increased the VO2 also increased. Except for the slowest speed, the two BKAs with the SACH foot had the greatest values. For this exception Normal2 had a slightly greater VO2 value than SACH2. The BKA with the flex foot had VO2 values that were closer to those values of Normal1 than to the other BKAs and the values for Normal1 were the lowest for the entire group. The results presented in Figure 2 suggest a tendency towards two distinct groups of subjects, particularly at the fastest speed tested. The first group emerging appeared to be the BKA children wearing the SACH foot terminal device. The second group appeared to consist of the normal children and the BKA child wearing the flex foot terminal device. The results for the average vertical displacement of the COM are presented in Figure 3 . The results presented in this figure clearly suggested two distinct groups of subjects. The first group and the ones that had the greatest vertical displacement of the COM were again the BKAs with the SACH foot. The second group, displaying a smaller vertical displacement of the COM, consisted of the two normal children and the BKA with a flex foot. At any given speed the differences separating the members within the groups was always less than those differences separating the values between the groups.

The physiological measure of VO2 and the biomechanical measure of vertical displacement of the COM were plotted for the three fixed speeds (Figure 4 ). As with the data presented in Figure 3 , the results displayed in this figure showed the same two distinct groups. However in this figure the effect of the walking speed was disregarded. The mean for the vertical displacement of the COM of the SACH group were 0.044 0.005 respectively and for the other group were 0.025 0.005 respectively. The mean for the range (i.e., average maximum-average minimum) of VO2 in the SACH group was 5.3 ml/kg/min and in the other group 2.9 ml/(kg.min). The mean and sd for VO2 values in the SACH foot group was 17.4 2.6 ml/(kg.min) and in the other group 14.5 1.7 ml/(kg.min) respectively.

Discussion

It should be noted that the results which have been presented represent information collected from only three subjects and two controls. Interpretation and discussion of the results should be viewed with due consideration to that limitation. Pagliarulo et al.,7 and Nielson et al.,6 reported an average speed for walking with a prosthesis of about 1.2 to 1.4 m/s. The BKA children with the SACH foot averaged 0.8 m/s and the BKA child with the flex foot had a freely chosen walking speed of 1.3 m/s. The average heart rate at the freely chosen speed in the Pagliarulo investigation was 106 b/m (sd = 10) and was not reported by Nielson. The average heart rate of 116 b/m in the present investigation was slightly higher than the subjects reported by Pagliarulo. Finally, the V02 for the two previous investigations was about 15 to 16 ml/(kg.min) while the VO2 for the BKA children in the present investigation was 16.5 ml/(kg.min).

A comparison for VO2 can be made between the fixed speeds of the Nielson investigation and those in the present investigation. The VO2 for BKAs and normals of the Nielson ranged from 11 to 16 and 7.5 to 11 ml/(kg.min) respectively, for the three fixed speeds utilized in the present investigation. No difference existed between subjects with the different terminal devices at the 0.7 mills speed and about a 2 ml/(kg.min) difference existed at the 1.1 m/s speed. The values for the VO2 of the BKA and normal children in the present investigation were very similar to those values presented by Nielson.

While physiological measures for effort have been documented for BKA adults they have not been previously reported for BKA children. This investigation reported the measures for heart rate and VO2 of BKA children and found that they were consistent with those found for BKA adults.

A slightly greater consumption of oxygen by BKA children wearing the SACH foot terminal device was observed when compared to that of normal children and the child with the flex foot terminal device (Figure 2 ). This relationship also existed for the results of vertical displacement of the COM. A separation of subjects into a SACH foot group and normal and flex foot group appears reasonable (Figures 3 ,4 ). Hence, for the physiological variable of VO2 and the biomechanical variable of vertical displacement of the COM, the average values for the SACH foot group were higher than those of the normals and child with the flex foot. This result appears to be different from those reported by Nielson. The differences separating SACH and flex foot values for VO2 in their investigation were never greater than the differences separating either of those values and the values for normals. The small sample numbers in both investigations prevents resolving this issue.

The results of the physiological measurement of VO2 may provide an appropriate method for measuring differences in required effort for BKA and normal children and differences in required effort between terminal devices for BKA children. However, VO2 does not provide a potential explanation for these observations. The results of this investigation suggest that the approximation of the vertical displacement of the COM presented in Figure 3 may provide a partial explanation for the higher metabolic cost of ambulation in BKA children with a SACH foot. The BKA children wearing the SACH foot terminal device were shown to have a greater vertical displacement of their COM during walking when compared to the two normal children and the BKA wearing the flex foot. This greater vertical displacement generally means that the weight of the body of the BKAs must be traveling through a greater range of vertical motion than that of the normals and the child with the flex foot. It would seem reasonable to suggest that the greater range of vertical motion may require greater physiological effort for the BKA children wearing the SACH foot.

Conclusions and Recommendation

The following tentative conclusions are made as a result of this investigation. 1) The freely chosen walking speed, heart rate, and VO2 for BKA children appear to be in general agreement with similar measurements for BKA adults. 2) The VO2 and vertical displacement of the COM seemed to separate subjects into one group consisting of BKA wearing a SACH foot terminal device and a second group consisting of normal children and a child with a flex foot terminal device. The first group generally displayed greater effort for all walking speeds when compared to respective values of the second group. In terms of the physiological and mechanical measures used for determining effort, the BKA children wearing the SACH foot terminal device were different from the normal children; while the BKA child wearing the flex foot terminal device was similar to the normal children. Additional study is required to determine if these preliminary data are statistically valid.

Acknowledgment

Funding provided by the Variety Club of Southern Alberta-Tent 61, through the Alberta Children's Hospital. The authors would like to acknowledge the help of A. Godfrey, K. Pritchard and M. Rodberg in the collection of this data.

Human Performance Laboratory, The University of Calgary, 2500 University Dr. N. W

Calgary, Alberta, Canada, T2N 1N4

References:

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  2. Engsberg JR, Tedford KG, Harder JA: Timing Changes for Stance, Swing and Double Support in a Recent BelowKnee-Amputee Child. Pediatric Exercise Science in press, 1990.
  3. Engsberg JR, Lee AG, Patterson JL, Harder JA: External Loading Comparisons between Normal and Below-Knee-Amputation Children during Walking. Arch Phys Med Rehabil Submitted, 1990.
  4. Hungerford DS, Cockin J: Fat of the Retained Lower Limb Joints in Second World War Amputees. Proceedings and Reports of Universities, Colleges, Councils and Associations 57-b(1):111, 1945.
  5. Lewallen R, Dyck G, Quanbury A, Ross K, Letts M: Gait Kinematics in Below-Knee Child Amputees: A Force Plate Analysis. J. Pediatric Orthopedics 6:291-298, 1986. 6. Nielson DH, Shurr DH, Golden JC, Meier K: Comparison of Energy Cost and Gait Efficiency during Ambulation in Below-Knee Amputees Using Different Prosthetic Feet-A Preliminary Report. J. Prosth and Orthot 1(1):24-31, 1989.
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