science gets miracles that seem biblical: partially restore the sight of a blind woman or, more recently, that three quadriplegic people walk again thanks to the implantation of some electrodes. They are still imperfect advances. In the case of the woman, she was able to recognize shapes and letters; in that of the three men who managed to walk, they did so in a rudimentary way and without control of their movements. But they are real first steps in restoring mobility to patients with spinal cord injuries. From the Hospital for Paraplegics in Toledo, Andrés Barriga (Cáceres, 50 years old), from the Spanish Spine Society, views this progress with hope and also with caution. There are years left, he says, before it can become widespread among patients.
Ask. What are the implants?
Answer. They are commonly used to treat neuropathic pain, for example in spinal surgeries that have not gone well. The novelty of these electrodes is that they stimulate the lumbar nerve roots that control the muscles of the legs. They are placed over the dura (the covering of the spinal cord and nerves in the cauda equina) in a specific place to stimulate each muscle. For example: the psoas is stimulated and the hip is flexed and if we do it in the quadriceps, the knee is extended. Each one must be in the exact place to move each muscle. But it is not voluntary mobility, it is achieved by a computer program that regulates the serial contraction of the different muscles that simulate walking. The patient is implanted a stimulator under the skin of the abdomen or back, which is like a small flask, similar to a heart pacemaker
P. When you say you don’t do it voluntarily, do you mean that the patient doesn’t activate those electrodes with their brain?
R. No, you can’t. That would be the next milestone, but for that we would also have to connect the brain with each electrode through the injured area of the spinal cord. Now, if the patient wants to walk, he activates that mode and the sequence of stimuli, after intensive training and rehabilitation, reproduces the human gait. The patient walks, but without controlling every movement with his brain.
P. How far is that next step from controlling that entire sequence with the brain?
R. There is already technology such as that used with electrodes that are placed on the head and are capable of detecting stimuli from the brain to give simple orders, such as turning a light on or off through home automation systems. But it is necessary to ensure that this technology, which exists for very simple commands, is capable of sending stimuli for something as complex as walking. This is a matter of bioengineering, a capability that can surely be developed in the near future.
P. When do you think they can be applied routinely or when can they arrive in Spain?
R. It will take a few years. Many tests are needed. This could come if we were invited to participate in the experimental project with our patients. We are probably the monographic hospital for spinal cord injuries with the most patients in Europe. We have the surgical and rehabilitation experience, the patients and the means to carry it out.
P. Will it be expensive to implant it in each person?
R. This is an experimental prototype that is priceless right now. But it shouldn’t be too expensive. In fact, epidural electrode technology is already commonly used in the National Health Service throughout Spain. But, logically, these new electrodes have been developed by a company that will patent the invention.
P. What other research is there in parallel to restore the ability to walk to quadriplegic people?
R. There’s a lot. On the one hand, engineering lines like this one. There are others that try to make the neurons grow from one side of the spinal cord to the other, that is, they can bridge the injured area by connecting both sides. In our hospital we participate in one that aims to join the two healthy parts of the bone marrow through multiple carbon microfibers. Because the axons of the neurons grow back, but they encounter the glial scar that forms in the injured area and prevents them from continuing to grow and connect with the other healthy area of the spinal cord. With these microfibers we try to make this connection happen. After a promising first phase in rats, we have developed it in a pig model. The main problem is that in our experimental model, the scar forms again and again, despite the multiple drugs and products that we have tried to eliminate it. We continue to investigate the formula that prevents the formation of the scar, which is the main problem, because the marrow is healthy on both sides.
P. That would be a more structural solution.
R. We are also participating in a trial with other hospitals with cells implanted in patients who have just had a spinal cord injury. Therefore, there are several lines of investigation and in the end the solution will surely be the conjunction of all of them. Because each spinal cord injury has a different injury. Depending on each one, an à la carte treatment will have to be designed.
P. What is stem cell research?
R. What the stem cells try to do is to form neurons in the injured area that can regenerate the marrow. At the moment they are still promising tests, which first have to give good results in animals to later reach the human clinic.
P. And so far, these electrodes are the furthest you’ve come to walk again?
R. Yes, this makes it possible for the patient to walk, even if it is a computer that does it for him. Walking, cycling or different movements, depending on the program that is activated. We have seen great progress, but there is still a long way to go before all those with spinal cord injuries can walk again.
P. I suppose that in your hospital both doctors and patients are waiting for each advance like this.
R. All the doctors at the hospital are involved in research and we are also attentive to what may come from outside. And the paraplegic patient wants to try anything. But the first thing in any new treatment is to check that it is safe for the patient. There are therapies that can cause more damage than you already have or be dangerous.
P. They will have to manage the expectations of the patients, so that they do not think that they will be walking tomorrow.
R. Yes, any news makes patients ask if there is a cure for their paralysis. It is normal. Although you have to take precautions and inform them well. It has happened with several novel therapies. First with growth hormone, which seemed to improve the spinal cord injury and everyone wanted to put it on. They came from all over Spain asking. A rigorous and well-designed study was carried out, proving that it had no use. There was another Portuguese surgeon who stated that with a technique that he performed, patients improved. There were many who underwent spinal surgery for nothing. Then came the boom of stem cells with inconclusive results so far. The electrodes do really work, but it will be necessary to test them in selected cases.
P. Selected based on what?
R. For example, depending on muscle capacity. A young patient will have more ability to use the upper limbs to move than an 80-year-old patient, who finds it much more difficult to walk and support himself. Many paraplegic patients walk with bimotors or with exoskeletons, but because they have a lot of them, they have more non-atrophic musculature that can regenerate again. 80% of paraplegics are men, because they are the ones who have the most traffic or sports accidents, there are more male bikers than female bikers… That young patient has better chances. And then you also have to take into account the level of injury. It is not the same as having had a cervical injury that also affects the arms or not.
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