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

Condition(s) studied

Investigational drug(s) / intervention(s)

Gait analysis: Participants with unilateral amputations and a control group will undergo a comprehensive walking analysis. In a lab setting (on a treadmill or floor), their gait will be recorded using inertial sensors, EMG, force plates, and motion capture, while an EEG cap and a NASA-TLX questionnaire will assess cognitive load. Capable participants will also perform a walking test on a real-world outdoor course with varied terrain. The data will be analyzed to compare walking patterns between groups (amputees vs. controls, and amputees with vs. without phantom limbs). Finally, participants will describe any interactions they perceived between their phantom sensations and walking during the tests.

Mapping of referred sensations.: Participants reporting referred sensations in gait analysis phase will undergo further testing. The study will investigate whether prosthesis pressure or a specific socket interaction causes these sensations. A 3x3 cm grid will be drawn on the residual limb to systematically map referred sensations using various stimuli (brush, pressure tip, electrical stimulation). Participants will rate the intensity and describe the location of any resulting phantom sensations. This mapping will be repeated after 6 months to assess the stability of these sensations over time, with the ultimate goal of potentially using them to provide sensory feedback for prosthesis users. The session will last approximately 2 hours.

Exploration of the areas of the brain activated during referred sensations: Unilateral transfemoral amputees with detailed referred sensation maps will have their brain activity recorded using a 64-electrode EEG cap. Non-invasive stimuli will be applied to four specific sites: an area on the residual limb that elicits a referred sensation, the corresponding location on the intact foot, a neutral area on the residual limb, and its corresponding location on the intact thigh. This process, involving 400 total stimulations, will be repeated after 6 months to track cortical changes. Non-amputee participants will also be tested as a control group to check for symmetry in brain responses to thigh stimulation. Each session lasts about 2 hours.

Evaluation of the effects of socket modifications on phantom sensations and walking: This phase will evaluate how socket modifications affect phantom sensations and walking in 10 transfemoral amputees. First, the best material to comfortably induce referred sensations will be determined in a small sub-study. Then, each participant will be tested under four conditions: their usual socket and a socket with different rigidity, both with and without a specific local pressure point added inside. The location of this pressure point is based on the user's sensation map. Participants' walking will be analyzed in both lab and real-world environments for each condition, and they will provide feedback on their sensations and which setup they find most helpful. The evaluation involves 4 sessions over 2-3 months

Phantom limb interview: A semi-structured interview will be conducted to ask participants to describe their phantom limb sensations (type, location, intensity) under three conditions: without their prosthesis, while standing with it, and while walking with it. This aims to identify factors influencing these sensations. Additionally, a brief physical examination of the residual limb will be performed to see if touch in specific areas triggers any referred sensations.

Study summary

Following lower-limb amputation, the loss of somatosensory information from the missing limb renders walking less automatic, more cognitively demanding, and often asymmetric, which can lead to secondary pathologies.

Hypothesis: This study is based on the hypothesis that phantom limb sensations (PLS), when coherent with the prosthetic device's movements and the phases of the gait cycle, can compensate for the loss of somatosensory feedback and thereby improve locomotion for individuals with amputation. It is further hypothesized that it is possible to artificially induce these coherent and useful sensations, notably through "referred sensations" elicited by stimulation of the residual limb (e.g., via the prosthetic socket).

Objectives: The project aims to:

* Determine whether the natural presence of phantom limb sensations during walking impacts gait parameters.
* Confirm in a larger patient population that modifications to the prosthetic socket can induce or enhance phantom sensations that are perceived as useful for walking.
* Investigate whether these perceptual changes (induced or enhanced) are associated with objective, measurable improvements in gait quality.

Eligibility

Primary outcome measure(s)

• Characterization of phantom limb sensations — The first day of the study
  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).
• Walking speed under laboratory conditions — The first day of the study for the control group and the second day of the study for participants with amputation
  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.
• Step length symmetry index. — The first day of the study for the control group and the second day of the study for participants with amputation
  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.
• Changes in the surface area of sensory maps referred to the residual limb — 2nd or 3rd day of the study depending on whether the participant with an amputation was included in phase 2 or not and during the 6-month follow-up visit.
  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.
• Change in the average intensity of reported phantom sensations. — 2nd or 3rd day of the study depending on whether the participant with an amputation was included in phase 2 or not and during the 6-month follow-up visit.
  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.
• Localization of the cortical source of somatosensory evoked potentials (SEPs) during stimulation of referred sensation areas — The second day of the study for participants with amputation
  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.
• Participant's subjective preference for one of the four socket conditions tested. — Day 7 of the study
  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.
• Change in the spatiotemporal parameters of walking in ecological situations — Days 4 to 7 to the study
  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.

Trial sites (1)

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