Results

The results show no indication that physical exertion has an influence on amputee gait symmetry measured by an overall symmetry index, or that there is a significant interaction effect of exertion and subtle alignment perturbation. It could not be shown that there are significant differences when evaluating gait symmetry based on only kinematics parameters and based on only kinetics parameters. The combined gait asymmetry indices (overall, kinematics, kinetics) met the normality assumption and where therefore analyzed by RMANOVA. For most of the isolated asymmetry variables, the normality assumption was found to be violated, and statistical tests were subsequently conducted using non-parametric methods, such as the Friedman test for repeated measures analysis, and the Wilcoxon Signed Ranks test for post-hoc comparisons of conditions. No adjustments were made to account for multiple comparisons.

Univariate comparisons suggest that asymmetry in the parameter “step length” was different across conditions (² =7.8, p=0.05). Post hoc tests showed that a statistically significant

difference existed between conditions PRE/NORM and PRE/PF (z= 1.960, p=0.050), with

asymmetry being higher in the PRE/NORM condition. A statistically significant difference existed also between conditions PRE/PF and POST/PF (z= 2.380, p=0.017), with asymmetry being higher in the POST/PF condition (figure 7). This translates into the finding that asymmetry in step length improved initially after increasing the foot plantar-flexion, but decreased significantly when subjects had reached a higher level of exertion and were asked to walk with the same alignment of increased plantar-flexion.

Other differences in bilateral symmetry measured in isolated variables were not found to be significant at the 0.05 threshold.

Figure 6: Step length asymmetry means and standard deviations over the four tested walking

conditions. Differences between PRE/NORM and PRE/PF, as well as between PRE/PF and POST/PF are significant at the .05 level.

In comparing gait variables within the same leg across conditions, it was found that “maximal knee flexion” (² =8.2, p=0.042), “maximal knee moment” (² =9.0, p=0.029), and “maximal dorsiflexion moment” (² =8.5, p=0.037) were significantly different.

Post hoc tests were conducted to determine the nature of those differences. The “maximal knee flexion” was significantly higher in condition POST/PF compared to PRE/PF (z=2.275, p=0.023). The “maximal knee moment” was higher in condition POST/NORM compared to PRE/NORM (z=2.511, p=0.012) and compared to PRE/PF (z=2.275, p=0.023). The “maximal dorsiflexion moment” was higher in condition PRE/NORM compared to POST/NORM (z=2.353, p=0.019).

Findings on the three investigated asymmetry indices, as well as on asymmetry in individual variables are listed in tables 3 and 4. Leg-wise effects of the interventions are listed in table 5 for the prosthetic legs, and table 6 for the respective sound legs.

Table 3: Effect sizes of exertion, increased ankle plantar-flexion, and interaction effects on indices of gait asymmetry. Asymmetry has been computed for each gait variable by dividing the bilateral differences with the bilateral mean. Combined indices were normally distributed over the sample of 8 unilateral amputees, and were statistically compared by RMANOVA. (PRE – low exertion, POST – strong exertion, NORM – initial alignment, PF – 2 deg plantar flexion)

Asymmetry

Table 4: Group mean and standard deviation of asymmetry values for isolated gait variables. Asymmetry has been computed for each gait variable by dividing the bilateral differences with the bilateral mean. The majority of the asymmetry values were not normally distributed over the sample of 8 unilateral amputees. Shapiro-Wilk tests of normality were conducted, and respective p-values are reported (where p<0.05 indicates a violation of the normality assumption). For consistency, all variables were statistically compared by Friedman tests.

Asymmetry indices PRE/NORM PRE/PF POST/NORM POST/PF pShapiro-Wilk ^ pFriedmann

max knee flex 0.064 ± 0.053 0.062 ± 0.062 0.072 ± 0.047 0.061 ± 0.072 0.001 1.050 0.789

Table 5: Group mean and standard deviation of unilateral variability values for isolated gait variables. Variables have been computed for every prosthetic leg and every condition. The majority of the values were not normally distributed over the sample of 12 prosthetic legs evaluated for this analysis.

Shapiro-Wilk tests of normality were conducted, and respective p-values are reported (where p<0.05 indicates a violation of the normality assumption).

For consistency, all variables were statistically compared by Friedman tests.

Gait variable PRE/NORM PRE/PF POST/NORM POST/PF pShapiro-Wilk ^ p_Friedmann

max knee flex (deg) 65.079 ± 5.007 63.782 ± 7.495 66.688 ± 8.878 66.858 ± 8.045 0.021 8.200 0.042*

% time of max 72.333 ± 2.188 74.250 ± 3.019 72.750 ± 2.527 73.083 ± 3.728 0.036 2.235 0.525 max dorsiflex (deg) 15.172 ± 4.408 13.753 ± 4.552 15.418 ± 5.060 16.248 ± 6.248 0.333 5.700 0.127

% time of max 53.333 ± 6.415 53.667 ± 7.165 52.667 ± 7.177 53.833 ± 8.441 0.000 1.473 0.688 max plantarflex 1 (deg) -7.060 ± 2.795 -8.645 ± 3.451 -8.436 ± 4.526 -7.562 ± 6.020 0.030 2.000 0.572

% time of pflex 1 8.167 ± 1.403 9.917 ± 1.379 8.333 ± 1.969 9.250 ± 3.621 0.187 7.619 0.055 max pflex 2 (deg) -4.954 ± 9.675 -6.851 ± 9.909 -3.899 ± 9.274 -8.402 ± 18.089 0.012 3.900 0.272

% time to 2nd pflex 68.667 ± 3.257 70.000 ± 3.954 68.000 ± 2.730 71.083 ± 5.712 0.014 1.750 0.626 max knee moment (Nm) 0.966 ± 1.070 0.942 ± 0.989 1.502 ± 1.283 1.424 ± 1.301 0.005 9.000 0.029*

% time of max 41.750 ± 30.221 36.833 ± 23.288 31.917 ± 22.857 35.500 ± 28.315 0.003 4.282 0.233 max dflex moment (Nm) 1.623 ± 0.859 1.096 ± 0.468 0.902 ± 0.614 1.290 ± 1.233 0.000 8.500 0.037*

% time of max 52.083 ± 16.681 48.417 ± 5.744 44.167 ± 10.853 51.250 ± 14.536 0.000 1.964 0.580 max pflex moment (Nm) -0.406 ± 0.512 -0.228 ± 0.135 -0.298 ± 0.248 -0.164 ± 0.124 0.000 2.500 0.475

% time of max 13.333 ± 17.510 21.083 ± 22.581 21.917 ± 25.486 34.417 ± 37.157 0.000 5.081 0.166 STP % of cycle 64.129 ± 2.285 65.304 ± 2.528 64.327 ± 4.033 64.604 ± 4.623 0.265 1.084 0.781 step length (cm) 70.568 ± 9.682 70.183 ± 8.003 74.816 ± 12.104 69.396 ± 12.117 0.001 1.800 0.615

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Table 6: Group mean and standard deviation of unilateral variability values for isolated gait variables. Variables have been computed for the contralateral (sound) leg of all participating unilateral amputees for every condition. The majority of the values were not normally distributed over the sample of 8 sound legs evaluated for this analysis. Pelvis obliquity and pelvis tilt, although not attributable to one leg side or the other are included because these variables were evaluated for the same 8 subject sample of unilateral amputees. Shapiro-Wilk tests of normality were conducted, and respective p-values are reported (where p<0.05 indicates a violation of the normality assumption). For consistency, all variables were statistically compared by Friedman tests.

Gait variable PRE/NORM PRE/PF POST/NORM POST/PF pShapiro-Wilk ^ p_Friedmann

max knee flex (deg) 66.692 ± 5.536 63.304 ± 3.803 63.482 ± 3.324 62.952 ± 4.203 0.075 5.100 0.165

% time of max 72.125 ± 1.553 72.625 ± 2.669 72.750 ± 2.053 71.750 ± 2.053 0.155 1.671 0.643 max dorsiflex (deg) 12.412 ± 5.327 11.621 ± 7.079 13.948 ± 6.360 14.441 ± 6.419 0.282 3.000 0.392

% time of max 49.000 ± 7.521 48.875 ± 6.010 50.875 ± 3.182 48.500 ± 4.106 0.001 1.303 0.729 max plantarflex 1 (deg) -7.110 ± 3.212 -7.145 ± 3.290 -6.505 ± 2.392 -6.199 ± 2.187 0.088 0.450 0.930

% time of pflex 1 9.750 ± 1.389 10.375 ± 1.188 9.250 ± 1.982 8.750 ± 2.053 0.024 1.732 0.630 max pflex 2 (deg) -11.462 ± 10.606 -12.047 ± 11.846 -11.261 ± 10.810 -9.913 ± 9.980 0.127 1.800 0.615

% time to 2nd pflex 67.500 ± 3.071 68.625 ± 1.598 69.125 ± 4.764 67.875 ± 2.100 0.014 4.027 0.259 max knee moment (Nm) 0.729 ± 0.626 0.725 ± 0.715 0.663 ± 0.521 0.835 ± 0.903 0.005 0.150 0.985

% time of max 27.875 ± 19.172 33.125 ± 21.027 27.250 ± 17.895 31.000 ± 18.974 0.001 3.164 0.367 max dflex moment (Nm) 1.374 ± 0.373 1.326 ± 0.315 1.351 ± 0.472 1.313 ± 0.413 0.360 2.850 0.415

% time of max 49.000 ± 2.390 49.125 ± 2.696 48.625 ± 2.264 47.125 ± 4.257 0.127 1.446 0.695 max pflex moment (Nm) -0.315 ± 0.151 -0.312 ± 0.151 -0.285 ± 0.146 -0.256 ± 0.176 0.144 0.750 0.861

% time of max 10.500 ± 4.986 10.125 ± 5.617 14.250 ± 19.009 13.250 ± 15.782 0.000 2.015 0.569 STP % of cycle 63.490 ± 2.586 63.374 ± 2.481 62.821 ± 2.533 62.305 ± 1.353 0.021 2.468 0.481 step length (cm) 73.939 ± 6.719 73.348 ± 4.929 75.118 ± 7.380 73.921 ± 7.199 0.000 1.050 0.789 max pelvis obliquity (deg) 2.486 ± 3.820 2.308 ± 4.179 3.372 ± 3.824 3.676 ± 3.478 0.072 7.050 0.070 max pelvis tilt 22.534 ± 11.686 20.592 ± 10.086 20.808 ± 10.580 20.039 ± 10.837 0.282 0.150 0.985

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A comparison on individual asymmetry indices is given in figure 8. The respective tables of extracted data are attached in Appendix B. Figure 9 visualizes the averaged asymmetry indices.

Figure 7: Individual asymmetry indices for all 8 subjects. Perfect bilateral symmetry would be represented by an index value of 0. Indices are comprised of gait variables as defined in table 2. One step per subject and condition was analyzed.

Figure 8: Comparison of asymmetry indices, averaged over all 8 subjects. Perfect bilateral symmetry would be represented by an index value of 0. Indices are comprised of gait variables as defined in table 7. Error bars illustrate the variance over the sample

Main contributor to the bilateral asymmetry in trans-tibial amputee gait were variables related to the ankle angle, with regard to the magnitude and time of the maximal plantar-flexion during the step cycle. Figure 10 shows the respective graphs pertaining to one subject. There is no ankle plantar-flexion in the prosthetic leg during the push-off phase. Instead, the maximal such ankle motion occurs at the beginning of the stance phase where the plantar flexion resembles that of the sound leg. As this curve is represented by two variables (maximal plantar-flexion 1 and maximal plantar-plantar-flexion 2), the different timing and magnitude of the absolute maxima of ankle plantar-flexion on prosthesis and sound leg is accounted for.

Figure 9: Ankle flexion angle curves for prosthetic and sound leg over one step cycle for one subject (number 8), measured by conventional gait analysis. Steps have been normalized to the step cycle duration and offset values corrected for comparability. To illustrate the 2x2 design matrix, the PRE condition of low exertion is displayed in the top row, POST condition of “strong” exertion below, normal alignment in the left column, altered alignment in the right.