## 2 Materials and Methods
### Plantar Pressure and Gait Analysis
#### 2.5.2 Inertial Sensors  
Inertial measurement units (IMUs) are small, lightweight sensors that consist of an accelerometer, gyroscope and magnetometer able to measure gait characteristics and to compute spatial-temporal and specific kinematic parameters. Figure 2: Graphical visualization of plantar pressure parameters shown in software. The IMUs used in this study were Wiva Science IMUs by Letsense(r) (Letsense group, Bologna, Italy). A sensor was positioned on the patient's waist (L5 level) with a special belt that does not affect mobility; in this way, the patient could walk freely [10; 31]. Ankle joint mobility measurements were performed with a sensor placed on the dorsum of the foot (II-IV metatarsal level). Joint range analysis was conducted passively by the operator with the patient sitting. At the end of the gait and joint mobility analysis, the parameters calculated during the tests were displayed to the software Biomech Studio 2018(r). The following parameters were evaluated:  
* Walking speed [m/min], normal values: 77.4 m/min for men; 71.4 m/min for women [32]. * Cadence [steps/min]--number of steps per minute, normal values: 52.8 steps/min for men; 55.8 steps/min for women [32]. * Stride length [m]--distance between two consecutive heels strikes of the same foot, normal values: 1.46 m for men; 1.28 m for women [32]. * Stride duration [s]--the time between two consecutive heel strikes of the same foot, normal values: 1.14 (\(\pm\)0.08) s for men; 1.08 (\(\pm\)0.08) s for women [32]. * Step length [m]--between the ipsilateral and contralateral heel strikes. The parameter is expressed as a percentage value considering the stride length; normal values: 50% left; 50% right [32]. * Step duration [s]--the time between ipsilateral and contralateral heel strikes. The parameter is expressed as a percentage value considering the duration of the step cycle (symmetry ratio); normal values: 50% left; 50% right [32]. * Stance duration [% of gait cycle]--the foot support phase, i.e., from heel strike to toe off of the same foot, duration as percentage of gait cycle, normal values: 60.31 (\(\pm\)1.7)% [32]. * Swing duration [% of gait cycle]--the foot swing phase, i.e., from toe-off to heel strike of the same foot, duration as percentage of gait cycle, normal values: 39.6 (\(\pm\)1.9)% [32]. * Double support duration [%]--the duration of the phase of support on both feet as percentage of gait cycle, normal values: 9.4 (\(\pm\)2.3)% for men; 9.6 (\(\pm\)4.6)% for women [32]. * Variability [% of the affected foot gait duration]--the coefficient variation in the duration of the gait of the foot considered. Indicates the reproducibility/repeatability of a step-in time; the lower the value, the more the step is repeatable. Therefore, it undergoes fewer variations during the cycle of the walk. * Symmetry--the ratio between the swing duration of the right foot and the swing duration of the left foot. It is an index used to evaluate the difference between the two steps during the gait. The ratio of maximum symmetry is when the index is equal to 1. The trunk or pelvis movements' kinematic data are presented on the sagittal, frontal and transverse planes, and are defined, respectively, as tilt angle, obliquity and rotation. * TILT (sagittal plane) [\({}^{\circ}\)] (Figure 3) is defined as the rotation of the pelvis around its transverse axis. The angle is defined as positive of anterior bending and negative the rear bending. * OBLIQUITY (frontal plane) [\({}^{\circ}\)] (Figure 3): on the frontal plane each \"hemi-pelvis\" rises during the support phase (stance) and descends in the swing phase of the corresponding leg. Positive angle values (Up) are defined with the lifting of the right pelvis during foot support of the corresponding foot, while negative angle values (Down) are defined with the lowering of the right pelvis resulting in lifting the left pelvis during support of the corresponding foot. * ROTATION (transverse plane) [\({}^{\circ}\)] (Figure 3): each \"hemi-pelvis\" rotates internally to the side of the dominant leg.