Four people with complete spinal cord injury walk again thanks to trunk movement-controlled neurostimulation

The study, published in Med – Cell Press by physicians and researchers from the MINE Lab of Università Vita-Salute San Raffaele, IRCCS Ospedale San Raffaele and Scuola Superiore Sant’Anna, shows that small voluntary trunk movements can modulate electrical stimulation of the spinal cord, enabling people with paraplegia due to a complete thoracic spinal cord injury to control their steps. The strategy uses a commercially available spinal cord stimulator, without the need for brain implants, external sensors or decoding algorithms

Four people with chronic, functionally complete thoracic spinal cord injury, with no ability to voluntarily contract their lower-limb muscles, were able to stand and walk with a walker thanks to a new method for controlling epidural electrical stimulation of the spinal cord.
The strategy relies on a very simple movement: a slight voluntary extension of the trunk. This movement is sufficient 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 required to take a step forward. In this way, through trunk movement, patients themselves contribute to controlling locomotion.

The findings come from a study published in Med – Cell Press, conducted within the MINE (Modular Implantable Neuroprostheses) Laboratory, established through a collaboration between Università Vita-Salute San Raffaele and 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 Università Vita-Salute San Raffaele, and Professor Silvestro Micera, Professor of Bioengineering at Scuola Superiore Sant’Anna.

Using trunk movement to regain control of stepping 

Epidural electrical stimulation of the spinal cord is one of the most promising strategies investigated 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-spine 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 effective intensity of stimulation experienced 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 then discovered that this transition can be triggered by patients themselves through a slight voluntary extension of the trunk — approximately 9 degrees on average — without changing the stimulator settings. This is the principle the authors define as trunk-mediated control (TMC): the underlying hypothesis is that trunk movement temporarily alters the anatomical relationship between the neural structures and the electrodes, thereby modifying the effect of stimulation.

Study results 

The strategy was evaluated in the first four participants enrolled in the study, all of whom had chronic traumatic spinal cord injuries between T4 and T7, classified as AIS A or B and functionally motor complete, with no ability to voluntarily contract their lower-limb muscles.

Following implantation of a commercially available spinal cord stimulator and four months of intensive rehabilitation, all four participants were able to stand and walk with a walker, without manual assistance or body-weight support systems. Their WISCI II score, used to assess walking ability in people with spinal cord injury, increased from 0 to 9 in all four participants; one participant covered 132 metres during 42 minutes of continuous walking, and all were also able to walk while negotiating turns, slopes and uneven outdoor surfaces. Three participants were also able to remain standing while supporting themselves with just one hand, leaving the other free to perform simple activities of daily living.

Rehabilitation played a central role: the participants underwent daily, progressive training, guided by physiotherapists, to learn how to use the stimulation increasingly effectively while standing and walking. The programme began with trunk-control exercises and neurostimulation-assisted activation of the lower limbs, 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 individualised rehabilitation programme designed to transform the motor responses evoked by stimulation into functional abilities: from standing to performing activities of daily living while upright, and ultimately to walking,” says Dr Sandro Iannaccone, Director of the Department of Rehabilitation for Neurological and Cognitive-Motor Disorders at IRCCS Ospedale San Raffaele.

“From a clinical perspective, the most interesting aspect is that we are not talking about a recovery of the ability to voluntarily contract the leg muscles: that ability remained absent in all four participants. Instead, we found a way to use a preserved voluntary function — trunk movement — to control the effects of stimulation and enable the person to actively participate in generating each step,” emphasises 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 harness the interaction between a residual voluntary movement, the biomechanics of the body and nervous system stimulation to generate the command required for stepping. It is a simple principle, but this very simplicity could make it particularly interesting from a translational perspective,” concludes Silvestro Micera, Professor of Bioengineering at Scuola Superiore Sant’Anna.

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

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