Spinal Cord Injury: 4 People Walk Again with Neurostimulation Controlled by Trunk Movement

4 people with chronic, functionally complete thoracic spinal cord injury, who were unable to voluntarily contract the muscles of their lower limbs, were able to maintain a standing position and walk with a walker thanks to a new method of controlling epidural electrical stimulation of the spinal cord.

The strategy uses a very simple movement: a slight voluntary extension of the trunk. This movement is enough to modify the response to stimulation and facilitate the transition from leg extension, which is necessary to support body weight, to the coordinated flexion of the hip, knee, and ankle needed to take a step forward. In this way, the patient actively contributes to controlling locomotion through trunk movement.

These are the findings of a study published in Med - Cell Press, conducted as part of the MINE laboratory (Modular Implantable Neuroprostheses), established through a collaboration between Vita-Salute San Raffaele University and the Scuola Superiore Sant’Anna, and based at IRCCS Ospedale San Raffaele.

The research team was led by Professor Pietro Mortini, Director of the Neurosurgery and Gamma Knife Radiosurgery Unit at IRCCS Ospedale San Raffaele and Full Professor of Neurosurgery at Vita-Salute San Raffaele University, and Professor Silvestro Micera, Professor of Bioengineering at the Scuola Superiore Sant’Anna.

Epidural electrical stimulation of the spinal cord is one of the most promising strategies studied in recent years to promote the recovery of certain motor functions in people with spinal cord injury. The most advanced experimental approaches have achieved important results using, for example, brain-spinal cord interfaces, neural signal decoding algorithms, and purpose-built devices.

This time, however, the MINE laboratory team took a different approach, starting from an observation made during stimulation: as the intensity effectively perceived by the neural structures changes, the response of the lower limbs also changes, shifting from knee extension, which is necessary to support body weight, to the coordinated flexion of the hip, knee, and ankle that makes it possible to take a step forward.

The researchers therefore discovered that this transition can be triggered by the patient through a slight voluntary extension of the trunk (an average of about 9 degrees), without changing the stimulator settings. The authors call this principle trunk-mediated control (TMC): the underlying hypothesis is that trunk movement temporarily alters the anatomical relationship between the neural structures and the electrodes, thereby changing the effect of the stimulation.

The strategy was evaluated in the first 4 participants enrolled in the study, all of whom had a chronic traumatic spinal cord injury between T4 and T7, classified as AIS A or B and functionally complete from a motor perspective, with no ability to voluntarily contract the muscles of the lower limbs.

After implantation of a commercially available spinal cord stimulator and 4 months of intensive rehabilitation, all 4 participants were able to:

• maintain a standing position;
• walk with a walker, without manual assistance or body-weight support systems.

The WISCI II score, used to assess walking ability in people with spinal cord injury, increased in all participants from 0 to 9; one participant walked 132 meters during 42 minutes of continuous walking, and all were able to walk while navigating turns, slopes, and uneven outdoor surfaces. 3 participants also became able to maintain a standing position while supporting themselves with one hand, using the other for simple daily activities.

The rehabilitation program played a central role: participants followed daily, progressive training guided by physiotherapists to learn how to use the stimulation increasingly effectively while standing and walking. The program began with trunk control exercises and lower-limb activation with neurostimulation, before gradually progressing to standing, weight shifting, and finally walking with a walker.

“The result comes from integrating spinal cord stimulation with an innovative, intensive, progressive, and individualized rehabilitation program designed to transform the motor responses evoked by stimulation into functional abilities: from standing to activities of daily living performed while upright, through to walking,” says Dr. Sandro Iannaccone, Director of the Department of Rehabilitation for Neurological Cognitive-Motor Disorders at IRCCS Ospedale San Raffaele.

“The most clinically interesting aspect is that we are not talking about recovery of the ability to voluntarily contract the leg muscles: that ability remained absent in all 4 participants. Instead, we found a way to use a preserved voluntary function, trunk movement, to control the effects of stimulation and allow the person to actively participate in generating the step,” emphasizes Professor Pietro Mortini.

“From a neuroengineering perspective, the key finding is that the body itself becomes part of the control interface. We do not need to decode a brain signal or add external sensors: we exploit the interaction between a preserved voluntary movement, body biomechanics, and nervous system stimulation to generate the command required for stepping. It is a simple principle, but precisely this simplicity could make it particularly interesting from a translational perspective,” concludes Silvestro Micera, Professor of Bioengineering at the Scuola Superiore Sant’Anna.

The researchers emphasize that none of the 4 participants recovered voluntary contraction of the leg muscles during the study: lower-limb movement was therefore generated by the stimulation. No adverse events related to dysautonomia were observed.

The study was funded by Vita-Salute San Raffaele University, Boston Scientific Spa, Fondazione Cariplo, Fondazione Bertarelli, #NextGenerationEU (NGEU), and the Italian Ministry of University and Research (MUR).