Artificial knees get smarter

A patient has been fitted with an artificial knee replacement with a new generation of sensors, to provide a wealth of information on twisting, bending, compressive and shearing loads across the human knee.

The data is transmitted wirelessly and will help scientists and clinicians analyse the forces at work during activities such as walking or rising from a chair.

The benefits may include design improvements for artificial knees, better surgical instrumentation, and better postoperative physical therapy. Historically, knee implants have been designed using predictions based largely on theoretical data.

A custom titanium alloy total knee replacement is the basis for the device, which has been fitted to a patient at the Scripps Clinic in the US.

The tibial component accepts standard, commercially available high molecular weight polyethylene inserts. The stem portion is hollow – and this hollow space houses wireless strain gauge electronics developed by MicroStrain. A polyethylene cap is threaded onto the distal end of the stem, and protects the hermetically sealed radio antenna. The electronics, including the sensing elements, are fully contained within the implant, which is hermetically sealed using laser-welding techniques. The finished, sealed implant is tested for hermeticity using fine helium leak-detection methods, the same methods that are used to test advanced pacemakers.