Tasked with developing intelligent prosthetic knee joints that are capable of detecting early failure before a patient suffers, a team of scientists at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland developed sensors that are integrated into the polyethylene part of the prosthesis.

Once a knee replacement has been performed, and the surgical site is closed, the only feedback is the patient’s qualitative and subjective assessment. If the prosthesis is misaligned or if it unseals, which can occur in about 20 percent of cases, the researchers say, the patient can experience significant pain, which is difficult to quantify. The sensors can diagnose the interior of the joint, and, in some cases, help patients avoid having a new operation.

Arash Arami of the Laboratory of Movement Analysis and Measurement devoted part of his thesis to the question of unsealing in the prosthesis. He chose the knee because it is a complex joint that is often injured. With an algorithm he developed, he could precisely calculate the micro-movements of the prosthesis and detect, via vibration, any loosening. Then, using sensors implanted in a prosthesis mounted on a mechanical knee simulator, he could demonstrate how it how it reacts to applied forces.Even if it is possible to see the problems of sealing or alignment using an x-ray coupled with a bone scan, doctors still really have no way to detect the cause.

Five EPFL laboratories have joined in a project funded by the National Science Foundation. To help the industry integrate new tools into smart prostheses, the scientists decided to put these sensors in the middle part, which is the polyethylene insert. This material is common to all knee prostheses, regardless of manufacturer.

Since these inserts have more or less the same shape and volume, the researchers say that if it can be instrumentalized without touching the femoral or tibial part, it will be easier for the industry to implement. But first, they must prove how the sensors represent a real benefit for both patients as well as doctors and the industry.