For the first time ever, a patient was implanted with an investigational full artificial knee replacement that wirelessly transmitts “digital, 3 dimensional torque and force data back to computers,” according to MicroStrain Inc., a Williston, Vermont-based company.
From the company’s press statement:
In-depth analysis can now be undertaken of forces and torques transmitted across the knee joint during normal human activities such as stair climbing, rising from a chair and walking. The results of this analysis can be used to develop design improvements, refine surgical instrumentation, guide postoperative physical therapy and potentially detect the individual activities that would overload the implant…
The micro-miniature, micro-power nature of their wireless transmitter electronics and innovative multi-channel strain measurement technology has enabled this breakthrough. Batteries are completely eliminated by using an integral miniature coil within the implant, to harvest energy from an externally applied alternating field, which powers the implant. The remote powering coil is secured to the outside of the patient’s shin, away from the knee. Using a wireless antenna, the implant transmits digital sensor data to a computer in a readable format. The twelve strain gauges are input to a computer, which uses a stored calibration matrix to convert the raw strain data into 3-D torques and forces about the knee…
A custom titanium alloy total knee replacement was provided as the basis for the device. The tibial component accepts standard, commercially available high molecular weight polyethylene inserts. The stem portion is hollow — and this hollow space is used to house MicroStrain’s wireless strain gauge electronics. 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. The array of twelve sensitive piezoresistive strain gauges were embedded within the implant’s custom designed tibial component. The strain gauged knee was precalibrated prior to implantation. For the first time, orthopaedic researchers now have the tools to measure 3-D forces and torques in live human knees. As the recipient of this smart implant progresses during rehabilitation, 3-D load and torque data will be collected, for the first time, by Dr. D’Lima and his staff at Scripps Clinic during activities
of daily living, including walking, climbing stairs, running, etc.
Press release (.pdf)…
(hat tip: gizmag)