For someone who has lost an extremity, any kind of prosthetic limb can make a huge difference—but having a bionic device fitted, giving the user intuitive function, can be transformational. We spoke to Prof Oskar Aszmann, director of the Christian Doppler Laboratory for the Restoration of Extremity Function at the Medical University of Vienna, about the latest developments in connecting robotic limbs to the human body.
MedicalExpo e-magazine: How did you become interested in bionic prosthetics?
Prof Oskar Aszmann: I am a plastic and reconstructive surgeon with a focus on neurological surgery (peripheral nerve) surgery. My specific interest in bionic reconstruction came from a patient 15 years ago who had lost both arms. We started to think about how we could reconstruct extremities when they were gone and realized the way forward was to connect the nerves to a technological device.
MedicalExpo e-magazine: Can you explain how your system works?
Prof Oskar Aszmann: There are different avenues as to how neurosignals can surface and be picked up so they can operate the prosthesis. There is the option of picking up brain activity with a brain-machine interface, which is being pursued by some very prominent researchers but the problem here is that the connectivity of the central nervous system is so complex it is difficult to get clear reliable signals without a lot of background noise. The other option is to pick up signals directly from the nerve, but the problem here is that the signals are very small—we are talking about nanovolts. So, we have chosen to go to the muscle. For us, this is a translator of neural information: it can naturally translate the information into functional control signals. It is also an amplifier because whereas a neural signal is in nanovolts, the muscle activity is in macrovolts and that is something we can pick up not only directly on the muscle but also through the skin with sensors.
MedicalExpo e-magazine: How does the bionic limb connect to the body?
Prof Oskar Aszmann: We have worked out how to get the brain into the machine but the other big problem in prosthetic management is how we get the prosthesis onto the skeleton. We are pursuing osteointegration, meaning we implant a titanium device into the bone, wherever the limb was lost. This allows the patient to have a very quick release attachment of the prosthesis directly to the implant, so they do not need a harness. There is also then the possibility of getting the biosignals through the bone into the prosthesis.
MedicalExpo e-magazine: What are the benefits to the user of a bionic prosthesis?
Prof Oskar Aszmann: I recently saw a patient who lost an entire arm in a road traffic accident and now has both arms that he is able to use intuitively. That would not have been possible without the technology we have developed in recent years. Pain is a very complex issue, but generally, if a patient goes through a restorative process with a bionic arm, their pain levels drop.
MedicalExpo e-magazine: Who might be a suitable candidate for a bionic limb?
Prof Oskar Aszmann: From a biological point of view, anyone who has a need could have this type of procedure done and could come to our clinic. However, these prostheses are expensive devices. They cost in the region of £150,000 and are often paid for by insurance companies. The limits may therefore be more financial than biological.
MedicalExpo e-magazine: What do you predict for the future of this field?
Prof Oskar Aszmann: With all probability, within the next five years we will have a system ready that will be able to provide signals wirelessly from the brain to the machine. Also looking ahead, the more widely used these technologies become then hopefully prices will drop. While numbers of amputees are low, when we think that patients with a brain stroke who have lost the use of a limb might also benefit from a bionic prosthesis, then the numbers are much higher. If we can make good use of this type of technology for these other kinds of patients, then prices will drop.