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Machine Design

Orthopedic Implants Keep Getting Smarter

A patient has had a full artificial knee replacement that can wirelessly report, 3-D torque and force data back to computers.

Julie Kalista
Online Editor

The results can be used to develop design improvements, refine surgical instrumentation, guide postoperative physical therapy, and potentially detect activities that would overload the implant.

This second generation implant handles 12 channels of strain data. Batteries are completely eliminated by using a miniature coil within the implant to harvest energy from an externally applied alternating field that powers the implant. The remote powering coil is secured to the outside of the patient's shin. Using a wireless antenna the implant transmits digital sensor data to a computer in a readable format.

A custom titanium alloy total knee replacement with a hollow stem portion houses the wireless strain gauge electronics. A polyethylene cap is threaded onto the distal end of the stem and protect the sealed radio antenna. The sensors are fully contained within the implant this is sealed using laser welding. The sealed implant is tested using fine helium leak detection.

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