Journal of NeuroEngineering and Rehabilitation

well-adapted, traumatic, K3-K4 amputees: transfemoral amputees using a restricted set of mechanical knees (TFM), transfemoral amputees using the C-leg (TFC), transtibial amputees using energy-storage-and-return feet (TT). A additional group of healthy control subjects ( “ Controls ” in short), was also included to highlight general trends. Methods Subjects Sixty K3-K4 lower-limb amputees participated in the study after signing an informed consent: 12 mechanical knee users (TFM, 46 ± 10 y.o.), 25 C-leg users (TFC, 48 ± 13 y.o), 23 transtibial amputees (TT, 44 ± 14 y.o.), with no statistically significant differences in term of age (ANOVA, p > 0.62). Ten controls were also included (28 ± 2 y.o.). All amputees had completed a 3-week, intense gait training program at the same specialized prosthetic & rehabilitation center, with the support of the same rehabilitation team. The clinical center has ISO 9001 treatment pathways for amputees and provides over 800 transfemoral and 1200 transtibial prostheses every year. Following training, all patients had been successfully using their prostheses for at least 1 month at the time of testing. The components provided to patients are summarized in Table 1 . Almost 92% of patients used either the Variflex or Variflex LP foot. Mechanical knees were selected to match the activity level of the C-leg, and are consistent with knees selected for comparison with the C-leg in previous studies [ 31 , 32 ] . Measurements After standing still for 10 s, subjects walked along a long indoor hall at self-selected speed, that was noted. During this trial, the GRF was measured on each side through instrumented insoles (Pedar-X, Novel, D), sampling at 100 Hz [ 33 , 34 ] . Data processing For each subject, GRF data were export to MATLAB. Based on the 10 s ’ orthostatic posture, body weight was calculated. Assuming a foot-floor contact threshold at 10% body weight, we detected heel-strike and toe-off events for the two sides. We isolated the steady state condition by considering the central 10 strides. Calculation of temporal symmetry For each stride, we calculated the step and stance duration. Then, for each couple of consecutive sound-affected gait cycles, we calculated the following indexes of symmetry: – Step Symmetry (SPS): Step Duration SOUND / Step Duration AFFECTED – Stance Symmetry (SNS): Stance Duration SOUND / Stance Duration AFFECTED For Controls, ratios were right over left side. A value of 1 represents perfect symmetry. For each index of symmetry, we calculated the subject ’ s median value over the trial. Finally, we obtained the distribution of the median values for the two indexes over TFM, TFC, TT and Controls. Calculation of loading symmetry For each gait cycle, the integral over the stance period of GRF was calculated, i.e. the impulse of GRF , as previously reported by [ 2 ] . Then, for each couple of consecutive sound-affected gait cycles, we calculated the index of symmetry: – Impulse Symmetry (IMS): Impulse SOUND / Impulse AFFECTED A value of 1 represents perfect symmetry. Right over left side was used for Controls. Afterward, the GRF profile of each gait cycle was checked to verify the presence of the first peak within the 0 – 40% of the gait cycle, and of a second peak within the 60 – 100%. Subjects reporting both peaks in more than half of the trials formed the “ Two-Peaks ” subgroup. For the subjects in Two-Peaks we operated as follows. For each couple of consecutive sound-affected gait cycles, we calculated the following index: – First Peak Symmetry (P1S): First peak SOUND / First peak AFFECTED P1S provides a measure of peak force asymmetry at loading response, while IMS provides a measure of the asymmetry in cyclic loading. These are two different mechanism of osteoarthritis development [ 10 , 35 – 37 ] . For each index of symmetry, we calculated the subject ’ s median value over the trial. Finally, we obtained the distri- bution of the median values for the two indexes over TFM, TFC, TT and Controls. Table 1 Prosthetic components used and associated quantities TFM TFC TT Foot Variflex LP: 10 1C40: 2 Variflex LP: 25 Variflex: 18 Variflex LP: 2 Truestep: 1 Esprit: 1 1C40: 1 Knee TotalKnee 2100: 5 3R60: 2 Mauch: 2 C-leg: 25 Cutti et al. Journal of NeuroEngineering and Rehabilitation 2018, 15 (Suppl 1):61 Page 31 of 72