Clinical Investigation to Validate the Safety and Performance of Integrating Functional Electrical Stimulation Into the ABLE Exoskeleton

This is a pre-post, single-centre, quasi-experimental study with an estimated duration of 16 weeks. The study will be conducted at therapy2people GmbH (Vienna, Austria). A minimum of 15 participants (5 per subgroup: spinal cord injury, acquired brain injury, multiple sclerosis) will be recruited within a period of up to 8 weeks.

After providing informed consent, participants will undergo a screening visit to confirm eligibility based on predefined inclusion and exclusion criteria. At the latest, one week after screening, participants will complete a baseline assessment.

The intervention will consist of 8 gait training sessions with the ABLE Exoskeleton with Functional Electrical Stimulation integration(ABLE FES), performed twice per week over 4-5 weeks. Each session will last approximately 60 minutes and include donning/doffing, walking training, and safety/performance assessments. Electrode placement and stimulation parameters will be adapted to the participant's neurological condition.

Outcome measures will focus on device safety (adverse events, serious adverse events, withdrawals) and clinical performance (donning/doffing time, walking distance, number of steps, standing time, therapist assistance, gait parameters, and motor torque). Additional measures will include lower limb spasticity, pain, perceived exertion, user satisfaction, and tolerance to FES.

For safety monitoring during sessions involving functional electrical stimulation (FES) with the exoskeleton, vital signs including heart rate and blood pressure will be measured before, during, and after the intervention sessions.

At the latest, one week after the last training session, a post-training assessment will be conducted. Two weeks later, participants will return for a follow-up visit to record any adverse events since the end of training.

This study will provide valuable evidence on the safety, feasibility, and potential rehabilitation benefits of integrating functional electrical stimulation into a robotic exoskeleton for patients with neurological gait impairments.

Inclusion criteria

• 18 to 80 years old
• Diagnosis of acquired brain injury, spinal cord injury (neurological level between C5 and L2, AIS B to AIS D), or multiple sclerosis
• Currently undergoing physiotherapy treatment, either as an inpatient or outpatient at the investigating center
• Ability to provide informed consent

Exclusion criteria

• Significant osteoporosis that may increase the risk of fracture
• Unresolved fractures in the pelvis or limbs, or a history of fragility fractures in the lower limbs within the past 2 years
• Spinal instability (or use of spinal orthoses, unless medically approved)
• Deterioration >3 points of the total in the motor score of the International Standards for the Neurological Classification of Spinal Cord Injury (ISNCSCI) in the last 4 weeks. Loss of sensation and/or motor activity above the level of injury detected that has not been evaluated by a doctor.
• Severe spasticity: Level 4 on the Modified Ashworth Scale
• Orthostatic hypotension: Inability to tolerate at least 10 minutes in an upright position
• Uncontrolled autonomic dysreflexia
• Medical instability
• Unstable cardiovascular condition, hemodynamic instability, untreated hypertension (SBP > 140 mmHg, DBP > 90 mmHg), deep vein thrombosis (DVT), or uncontrolled autonomic dysreflexia
• Severe comorbidities, including any condition deemed inappropriate by the investigator for using the ABLE Exoskeleton or for completing the study
• Pressure ulcers Grade I or higher (as defined by the European Pressure Ulcer Advisory Panel - EPUAP) in areas that will be in contact with the device
• Anthropometric measurements incompatible with the ABLE Exoskeleton, specifically height outside the 1.5-1.9 m range or weight exceeding 100 kg
• Anatomical constraints (such as leg length differences, users unable to position themselves inside the device) that are incompatible with the device
• Range of motion restrictions preventing normal gait or sit-to-stand transitions, including: Ankle: ability to achieve at least neutral (0°) position; Knee: ability to extend to at least -10°; Hip: bilateral hip flexion of at least 100° and extension of at least 0°
• Heterotopic ossification
• Pregnant or breastfeeding women
• Cognitive impairment that results in the inability to follow simple instructions, particularly psychological or cognitive problems that do not allow a participant to follow study procedures
• Requires assisted ventilation.
• Scoliosis >40-50º Cobb angle.
• Presence of pacemakers, defibrillators, or other non-compatible electronic implants.
• Open wounds, infections, or active irritation at the electrode placement sites.
• Severe dermatological conditions in the stimulation area.
• Uncontrolled active epilepsy.
• Malignant tumors in the area of application.
• Severe loss of sensation in the areas where electrodes are to be placed.
• Medical conditions where electrical stimulation is contraindicated by physician recommendation.
• Inability to communicate pain, discomfort, or adverse reactions during stimulation.
• Venous thrombosis, thrombophlebitis, or severe arterial obstruction.
• Chronic venous insufficiency with significant varicosities.
• Hemophilia.
• Ongoing infectious process or fever.
• Presence of metallic implants in the flow area between the electrodes