Uses of Phantom Sensations Induced by Global and Local Modifications of the Prosthetic Socket as Somatosensory Feedback During Walking in Lower Limb Amputees

A composite assessment of phantom limb sensations will be conducted via a semi-structured interview. Data collected will include:

• Type of sensation (e.g., tingling, pain, movement).
• Location (toes, heel, calf).
• Intensity (Mild, Strong, Very Strong).

The participant's average walking speed, measured in meters per second (m/s). The measurement will be collected using inertial measurement units (IMUs) and/or a Vicon motion capture system while the participant walks on hard ground or on a treadmill at their self-selected speed.

Gait symmetry will be calculated based on the stride length of the affected (or corresponding) limb and the healthy limb. The symmetry index is a unitless ratio (or percentage) that quantifies the difference between the two limbs. A value of 1 (or 100%) indicates perfect symmetry. Measured using inertial measurement units or the Vicon system.

The total surface area capable of triggering phantom sensations will be measured. For each type of stimulation (brush, pressure, point, electrical), the number of 3x3 cm areas causing a sensation will be counted. The total surface area (in cm²) will be calculated by multiplying this number by 9. A map will be generated for each stimulation modality.

When each reactive area is stimulated, the participant will rate the intensity of the phantom sensation perceived on a 6-point Numerical Rating Scale (NRS), ranging from 0 (no sensation) to 5 (maximum intensity imaginable). The average intensity of the reactive areas will be calculated for each type of stimulation.

The recorded EEG activity will be used to model and locate the source of the maximum cortical response. The primary outcome measure will be the coordinates (e.g., in the MNI or Talairach atlas) of the center of activation in the somatosensory cortex. The objective is to compare the source localization obtained during ecological gait after each demanding walking situation.

At the end of the four test sessions, participants will be asked to rank the four conditions (rigidity A/B, with/without focal pressure) from most to least conducive to walking. The primary outcome will be the condition ranked first by the largest number of participants.

Several key walking parameters (speed in m/s, cadence in steps/min, step symmetry index) will be measured using inertial sensors during the outdoor walk. The analysis will compare the average values of these parameters between the four socket conditions.

The number of steps per minute (steps/min) when walking at a comfortable speed. Measured using inertial measurement units or the Vicon system.

The electrical activity of key muscle groups (e.g., quadriceps, hamstrings, glutes, paravertebral muscles) will be recorded using surface electromyography (EMG). The analysis will focus on the timing and amplitude of muscle activation to assess motor coordination.

The maximum force exerted on the ground with each step, measured in Newtons (N) or as a percentage of body weight (%BW). The measurement will be taken using force platforms (AMTI), pressure insoles (Loadsol), or an instrumented mat (Zeno).

The cognitive load perceived by the participant will be assessed using the NASA Task Load Index (NASA-TLX) self-report questionnaire. The total score, ranging from 0 to 100, will be calculated. A higher score indicates a greater perceived cognitive load.

Electroencephalographic (EEG) activity will be recorded via a headset. Cognitive load will be quantified by analyzing the power ratio in specific frequency bands at the frontal electrodes.

The average walking speed (in m/s) measured using inertial measurement units and pressure soles (Loadsol) during a predefined outdoor route including various difficulties (stairs, slopes, etc.).

Participants' verbal descriptions of the nature of the interaction (facilitating, hindering, neutral), the evolution and characteristics of phantom sensations during walking will be collected via a structured interview at the end of the session. The data will be analyzed thematically.

For the subgroup of participants with an amputation of less than 6 months at inclusion, the intensity of phantom sensations will be re-assessed using the 3-point ordinal scale.

For the subgroup of participants reporting interaction between sensations and focal stimulation after various stimulations using a rubber tip (pressure), a brush, and a needle. The change in sensation intensity (rated on a scale of 0 to 5). The result will be categorized as "increase," "decrease," or "no change."

Perceived mental workload will be assessed using the NASA-TLX questionnaire immediately after each walking session. The total score will be compared between the four socket conditions.

The overall comfort perceived for each condition will be assessed at the end of each session using a Numerical Rating Scale (NRS) ranging from 0 (very uncomfortable) to 10 (very comfortable). The average score will be compared between the four conditions.

For each condition, a structured description of the sensations reported (type, location, intensity, perceived usefulness for walking) will be collected through an interview. The data will be analyzed thematically to compare the sensory experience.