A nine-degree lean of the torso, and four paralysed patients walked

Four people with complete thoracic spinal cord injuries — three men and one woman, from Umbria, Marche and Lombardy — walked again at Ospedale San Raffaele in Milan. None had felt a voluntary contraction in their legs since the day they were injured. One of them covered 132 metres in a single continuous walk.

The method is called trunk-mediated control, and it came out of the joint MINE laboratory — Modular Implantable Neuroprostheses — run by Università Vita-Salute San Raffaele with the Scuola Superiore Sant'Anna in Pisa. It is led by the neurosurgeon Pietro Mortini and the bioengineer Silvestro Micera. The implant delivers epidural electrical stimulation to the spinal cord; the patient's own trunk decides when and how it fires.

That inversion is the point. Earlier systems asked patients to press buttons on a tablet or a handheld remote, or ran preset gait programmes a technician had chosen in advance. Here the deliberate lean of the torso shifts the stimulated response from a simple extension of the leg into a coordinated flexion — a walking motion, initiated by the person doing the walking.

It took four months of intensive rehabilitation to learn the coordination. Afterwards the four could stand, walk with a walker, and handle what a laboratory corridor never offers: curves, slopes, irregular ground outdoors. The results appeared in the Cell Press journal Med, funded in part by Fondazione Cariplo, Fondazione Bertarelli and Italy's NextGenerationEU programme.

The hardware itself has an unlikely history. Paddle electrodes of this class have been slid into the epidural space since the 1970s, to block chronic back and leg pain — tens of thousands are implanted each year in the United States alone. Researchers repurposed them after noticing that stimulation below a lesion could wake the spinal circuits that generate stepping, with nothing arriving from the brain at all.

From there the line runs through Louisville, the Mayo Clinic and Lausanne, where Grégoire Courtine and Jocelyne Bloch had patients taking steps within a day of the implant being switched on, and later linked a cortical implant to the spinal stimulator so a Dutch patient could walk by thought.

The nerves were not repaired. A gesture of the torso was translated into motion instead.

Roughly 20 million people worldwide were living with spinal cord injury in 2019. For those whose injuries were classified complete and irreversible, what the Milan team has shown is narrow but concrete: a repeatable path back to walking that begins with something the patient can still do.