The derived variables related to moments in this study include the amplitude of ankle and hip joint moments changes in the direction of the pulling perturbations (flex/extension moments) in both lower limbs, the peak value of these moments, as well as the amplitude and maximum magnitude of the sum of moments in the sagittal plane. The moments in the coronal plane (abd/adduction moments) were very small, thus are not presented. The magnitudes of all moments were normalized to the mass of the participants in kilograms.
5.3.2.2.1 Ankle Flex/Extension Moment
The ankle moments in the back-pulling test are presented in Figure 5.19. The positive and negative values were, respectively, the dorsi-flexor and plantar-flexor joint moments.
A
B
Figure 5.19 Changes of ankle moments in sagittal plane during back-pulling sessions, A: Non-Amputees, B: Amputees. -ve indicates plantar flexor moments.
There was a negative moment (plantar-flexor moment) in both groups and in both sides during the whole of the test. The load release was associated with a rapid increase in a plantar-flexor moment, which remained once balance was retained. In the amputee group, a similar trend was observed, but the moments were generally smaller in the prosthetic ankle.
As is seen in Table 5.21, the amplitude of the ankle moment changes during back-pulling perturbation for the IL of amputees was more than five times larger than their prosthetic side, and it was also larger than in the non-amputees.
Table 5.21 Amplitude of ankle moment in sagittal plane during standing balance against back/front pulling loads
Prturbation condition Balance against back
pulling load (BB)
Balance against front pulling load (FB)
Limb Moment (Nm/kg) SD Moment (Nm/kg) SD
Amp ute e s S1 (n=11) Intact 0.401 0.086 0.393 0.119 Prosthetic 0.079 0.031 0.091 0.051 S2 (n=11) Intact 0.401 0.109 0.392 0.113 Prosthetic 0.078 0.038 0.093 0.046 Follow-up (n=3) Intact 0.400 0.067 0.384 0.057 Prosthetic 0.096 0.017 0.105 0.070 Non -Amp ute e s S1 (n=14) Right 0.263 0.094 0.245 0.072 Left 0.265 0.092 0.223 0.066 S2 (n=14) Right 0.282 0.109 0.296 0.087 Left 0.299 0.106 0.294 0.082 Follow-up (n=11) Right 0.276 0.088 0.282 0.053 Left 0.323 0.060 0.277 0.073
S1: without insoles, S2: with insoles, Follow-up: after at least 4 weeks of using insoles
Figure 5.20 shows the ankle moment in the sagittal plane during front-pulling perturbation. In non-amputees and the intact side of amputees, the moment was initially plantar-flexor, which reduced rapidly and, in some cases, became a dorsi-flexor moment at load release, but then returned to a plantar-flexor moment, though smaller than the initial moment, once balance was retained. The initial moment in the IL and in the non- amputees was larger when compared to the back-pulling sessions. This moment was close to zero in the prosthetic side in amputees throughout, indicating that the prosthetic ankle contributed little to balance stability in these tests. As seen in Figure 5.20, the amplitude of the prosthetic ankle moment in the front-pulling sessions was a little more than in the back-pulling and was approximately one-quarter of the moments in the IL. There was a significant difference between group amplitudes of the sagittal plane’s ankle moment changes during standing balance (Pillai's trace = 0.834, F(3, 20) = 33.604, p<0.001, partial eta squared effect = 0.834), and between the intact and prosthetic side of amputees (Pillai's trace = 0.832, F(3, 20) = 33.002, p<0.001, partial eta squared effect = 0.832.) Insole use did not affect either group (p = 0.084) or the results of the two perturbation sessions (p = 0.699). When comparing the three sessions of insole use in the non-amputee group (without insoles, using insoles and after at least for weeks of use), there was a significant increase in the amplitude after using the insoles (F = 3.981,
p = 0.044, partial eta squared effect = 0.285). However, no difference was found between the perturbation sessions and right/left data (p = 0.47).
A
B
Figure 5.20 Changes of ankle moments in sagittal plane during front-pulling sessions, A: Non-Amputees, B: Amputees. -ve indicates plantar flexor moments.
Table 5.22 presents the absolute maximum sagittal plane ankle moments of each limb of the participants in both groups. All peak values among the non-amputees and in the IL of amputees were plantar-flexor moments, but five moments in S1 and four moments in S2 were dorsi-flexor for the prosthetic side. The amount was more than 2.5 times larger in the IL compared to the prosthetic side.
Table 5.22 Peak value of ankle moment in sagittal plane during standing balance against back/front pulling loads
Prturbation condition Balance against back
pulling load (BB)
Balance against front pulling load (FB)
Limb Moment (Nm/kg) SD Moment (Nm/kg) SD
Amp ute e s S1 (n=11) Intact 0.483 0.129 0.297 0.097 Prosthetic 0.181 0.137 0.147 0.138 S2 (n=11) Intact 0.489 0.135 0.305 0.119 Prosthetic 0.173 0.164 0.118 0.114 Follow-up (n=3) Intact 0.362 0.025 0.322 0.088 Prosthetic 0.219 0.178 0.179 0.051 Non -Amp ute e s S1 (n=14) Right 0.358 0.160 0.245 0.111 Left 0.353 0.163 0.215 0.111 S2 (n=14) Right 0.389 0.160 0.247 0.099 Left 0.398 0.178 0.229 0.087 Follow-up (n=11) Right 0.370 0.144 0.274 0.085 Left 0.380 0.145 0.242 0.093 S1: without insoles, S2: with insoles, Follow-up: after at least 4 weeks of using insoles
All peak magnitudes among the non-amputees, except one in S1, were plantar-flexor moments in the front-pulling perturbation, but the direction of peak values was more variable among the prosthetic ankle and IL data for the amputee group. For the IL, four moments in S1 and three moments in S2 were dorsi-flexor, while four moments in S1 and five moments in S2 were dorsi-flexor for the prosthetic ankle. The amount was more than two times larger in the IL compared to the prosthetic side; however, the magnitudes were smaller than in the back-pulling sessions.
There was a significant difference between the groups’ peak value of ankle moment in the sagittal plane (Pillai's trace = 0.542, F(3, 20) = 7.886, p = 0.001, partial eta squared effect = 0.542;) and between the perturbation sessions and the intact/prosthetic side of the amputees (Pillai's trace = 0.768, F(3, 20) = 22.116, p<0.001, partial eta squared effect = 0.768). Insole use did not affect either group (p = 0.422) or the results of the two perturbation sessions (p = 0.718). When comparing the three sessions of insole use in the non-amputee group (without insoles, using insoles and after at least four weeks of use), the use of insoles did not change the peak moment (p = 0.58).
5.3.2.2.2 Hip Flex/Extension Moments
The positive and negative values are, respectively, flexor and extensor joint moments. Figure 5.21 indicates that a positive moment (hip flexor moment) was prominent in the non-amputee group, while the moment for the IL of amputees was a large hip extensor and in the prosthetic side an alteration of around zero. These moment changes have a sinusoidal pattern: initially, a small flexor moment appears in reaction to the load release which, in a short time, converts to an extensor moment and, again, to a flexor moment to retain balance in both legs. The changes here were sharper and happened over a shorter time in the non-amputees compared to the IL, particularly in the prosthetic side of the amputees.
As seen in Table 5.23, the amplitude of the sagittal plane hip moment changes during back-pulling perturbation for the IL of the amputees was 2-3 times larger than their prosthetic side; it was also larger than in the non-amputees. Similar to the back-pulling perturbation, Table 5.23 also shows the amplitude of the sagittal plane hip moment changes during front-pulling perturbation for the IL of amputees was 2-3 times greater than their prosthetic side; it was also greater than in the non-amputees.