For a number of years, Erasmus MC trauma surgeon Oscar van Waes has been placing a new type of prosthesis in the bone of some people after a leg amputation. This prosthesis is directly clipped to a stem anchored in the bone, also called osseointegration or click prosthesis. Compared to a socket prosthesis this has advantages: it causes less pain and walking is easier. Every year about 100 people in The Netherlands qualify for osseointegration.
Van Waes has heard from his patients with a click prosthesis that they stumble less often. ‘I can imagine, because with such a prosthesis you experience the unevenness of the ground much better.’ He sought collaboration with the Biomechanical Engineering department at TU Delft. This collaboration between Van Waes and Jaap Harlaar, professor of clinical biomechanics at TU Delft, gave rise to the idea for the stumble meter: an objective way to measure whether click prosthesis wearers actually stumble less. ‘After an extensive analysis of his clinical findings, I thought: this stumbling, I can do something with that’, says Harlaar.
Dylan den Hartog, at the time a Master’s student in Mechanical Engineering at TU Delft, developed the stumble meter as a graduation project. The meter, the size of a matchbox, measures acceleration and rotation of the leg. To set up the device, Den Hartog attached it to the lower leg of ten healthy volunteers. They were then tripped up by unexpected obstacles on a treadmill (wearing a safety harness, of course).
Using the data from the stumbling experiment, Den Hartog developed an algorithm that could correctly detect 273 of the 276 tripping events. To do this, he used machine learning, a form of artificial intelligence. ‘In addition to distinguishing between tripping and daily movements such as climbing stairs, we were also able to distinguish between two types of reactions to tripping.’
Van Waes is very pleased with the stumble meter. ‘This device is immediately applicable for research.’ The next step is to use the meter on people with a standard socket prosthesis and a click prosthesis and measure the difference. In doing so, Van Waes hopes to demonstrate that people with click prostheses actually stumble less than people wearing a socket prosthesis.
Technicians and medics
The collaboration between the technicians and medics has gone very well for both of them. Van Waes: “Prosthetics is becoming more advanced. With TU Delft we want to develop more expertise in the field of sensors and feedback between the prosthesis and the nerves in the stump.’ Conversely, it is interesting for technologists to come up with solutions to questions from the clinic, adds Prof. Harlaar, who is also affiliated with the Orthopaedics Department at Erasmus MC. They are certain: the collaboration has a great future ahead of it.
The stumble meter is one of the first results of the collaboration between Erasmus MC and TU Delft, called Convergence Health & Technology.