One of medicine's oldest dreams has just taken a big step closer to reality. Three people whose spinal cord injuries left them largely paralyzed below the waist for at least four years used an electrical pulse generator implanted in their spine and crutches or frames to walk again.

Ever since scientists established that instructions from our brains to our limbs are transmitted as electrical signals through the spinal cord, people have wondered whether we could bypass the damage caused in accidents. Putting the idea into practice has been much harder, but several labs have been able to get rats with severed spinal cords walking again.

Now Lausanne University Hospital has announced a similar achievement in humans. Dr Jocelyne Bloch inserted implants into three patients to activate leg muscles. "All the patients could walk using body weight support within one week. I knew immediately that we were on the right path,” Bloch said in a statement. 

The work is not just a matter of providing a path that carries the electrical signals from the brain to the legs. “The targeted stimulation must be as precise as a Swiss watch,” Bloch said. 

Bloch and colleagues mapped the parts of the spinal cord responsible for each movement that combines to allow us to walk, and established the sequence of electrical pulses that would make these occur. They then used messages coming from the brain down the undamaged part of the spinal cord to trigger the necessary signals below the injury.

The triggering of neglected nerves encourages the building of connections to replace those that were lost.

The work has been published in Nature with an accompanying paper in Nature Neuroscience on some of the challenges overcome in the process.

There have been previous announcements of outwardly similar achievements, but this work has a crucial difference from its predecessors. Participants in other trails who started walking through the use of electrical stimulation slipped backwards once intensive therapy stopped. Two of the three participants in the Lausanne trial, however, held onto the gains they had made when left to continue alone.

Trials by other researchers, two of which were published in September this year, also usually required longer periods of concerted training to achieve their benefits. For people with spinal injuries and limited access to rehabilitation facilities, these difference will matter.

So far none of the participants are walking more than a few meters unaided, and all three had residual movement prior to the operation. One had previously been able to shuffle, while another could move one leg but not the other. All three showed major improvements afterward, but the greatest test of the technology will be whether it will benefit those with no current leg movement.