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The Department of Health & Human Services (DHHS), through the National Institute of Arthritis and Musculoskeletal Diseases (NIAMS) has awarded a Phase I SBIR grant to MicroStrain Inc for the development of a tiny, implantable microsensor, capable of detecting micro-motion of hip replacement stems within the human femur in vivo.

Over 250,000 hip replacements are inserted annually in the USA and loosening of the replacements is the greatest source of long-term failure. However, femoral component subsidence measured on plane radiographs (accuracy 2-3 millimeters) is not typically evident before five years. Therefore, very sensitive motion measurement techniques are needed to be able to predict the success or failure of an implant design in the early stages.

Radiostereometry (RSA) can sensitively (100-500 micrometers) track implant position and is the present gold standard for detecting early excessive subsidence, which is a predictor of ultimate clinical failure. However, implementation of RSA requires custom components and complex radiographic equipment, which are not widely available. Furthermore, RSA can only measure the static (unmoving) position of the implant relative to bone.

The new sensors to be developed by MicroStrain engineers will overcome these limitations, providing researchers and clinicians with a new tool to detect early implant micro-motion as well as providing insight into the dynamic behavior of hip implants in vivo. The new system will track micro-motion at update rates of 200 samples per second. The implanted microelectronics will include non-volatile memory and bi-directional wireless communications, allowing the plug to measure and maintain a record of settling (or "subsidence") over time.

"Eventually, we expect that the sensor plug will be used for pre-clinical trials and post-market surveillance of new uncemented femoral components", said Steven Arms, MicroStrain's President. "However, the technology developed under this SBIR program will find its way into a number of advanced Starter Kits, which will harvest magnetic field energy to sense, record, and report data from within the body".

About MicroStrain

MicroStain, Inc. currently produces a range of wireless sensing instruments, including microprocessor based, multichannel, programmable transmitters that are compatible with a wide range of sensors, including: thermocouples, strain gauges, accelerometers, displacement sensors, and capacitive sensors. MicroStrain is a privately held corporation based in Burlington, Vermont USA.

Contact: Lynne McMinn, VP Marketing lmmcminn@together.net MicroStrain Inc Tel: (802) 862 6629 Internet hyperlink: http://www.microstrain.com/news.cfm?nid=136

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