Recent innovations in computer-assisted surgery are pushing the boundaries of modern medicine to new and exciting frontiers. As conventional surgical instrumentation continues to give way to advanced console- and camera-based systems, surgeons are able to operate on patients with exceptional precision.

As the patient’s knee is put through a full sweep of motion, the surgeon using the KneeAlign 2 System relies on the positioning and dynamics captured by the ADI IMU to quickly determine the precise orientation of the femoral cutting block.

The design team at OrthAlign is taking this innovation trend one step further with the recent introduction of its KneeAlign 2 System, a palm-sized surgical navigation system for precise tibial and femoral alignment during total knee arthroplasty (TKA), a surgical procedure in which pieces of the knee are replaced with artificial parts. Rather than employ camera-based navigation, which adds significant expense and size to a surgical navigation system, OrthAlign’s design team counts on an ADI iSensor IMU (inertial measurement unit) to enable an orthopedic surgeon to determine, within seconds, the center of rotation of a patient’s femur and calculate the precise angles to cut the bone during knee replacement surgery.

“ADI’s iSensor inertial measurement technology plays a critical role within our KneeAlign 2 System, and equipped our design team to achieve aggressive precision, form factor, and cost targets,” said Darius Kharabi, vice president of Corporate Development, OrthAlign Inc.

The ADI iSensor IMU designed into the KneeAlign 2 System provides six-degrees-of-freedom measurement via three accelerometers and three gyroscopes that sense linear motion and angular motion, respectively. The iSensor IMU is capable of precisely tracking an instrument’s motion on all axes, even during demanding operating conditions. The compact IMU device provides access to both calibrated and dynamically compensated sensor data over a standard digital SPI interface, and offers the ability to digitally tune the sensor filtering and processing to adapt to multiple application scenarios. The availability of precise inertial data over a simple digital interface, out of the box, allowed the OrthAlign design team to save years of development time in bringing this revolutionary product to market.

With the ease of use available from traditional instrumentation, OrthAlign’s KneeAlign 2 System has received 510(k) clearance from the FDA as being substantially equivalent to camera-based, large-console computer-assisted surgery systems for tibial and femoral measurement.

With U.S. demand for TKAs expected to climb 673% from 2005 to 2030, OrthAlign’s continued innovation in the field of knee surgery, enabled in part by ADI’s iSensor technology, is significant for surgeons and patients alike.

The palm-sized KneeAlign unit and its associated cutting instrumentation are compatible with all implant systems used in total knee arthroplasty. According to figures available from the Agency for Healthcare Research and Quality, approximately 675,000 Americans underwent knee replacement surgery in 2009. That figure is expected to be dwarfed in subsequent years as it is estimated the surgery will be performed on 3.5 million people in 2030.*

Currently, an estimated 30% of all TKA procedures result in poor implant alignment.** By using an ADI iSensor IMU, the KneeAlign 2 provides alignment precision comparable to the larger, significantly more expensive camera-based navigation systems, which have been shown to result in knee replacement alignment outcomes of 91% accuracy, compared to only 68% accuracy using conventional mechanical surgery.**

In September 2011, OrthAlign completed its limited use release of approximately 50 TKA surgeries using the KneeAlign 2 for both femoral and tibial navigation in highly regarded knee surgery centers across the United States and the results were extremely encouraging. According to OrthAlign, it plans to launch the KneeAlign 2 System in the first quarter of 2012, while continuing clinical studies at the Hospital for Special Surgery in New York, Scripps Green Hospital in California, and other centers of excellence.

References
* The Journal of Bone and Joint Surgery, “Projections of Primary Revision Hip and Knee Arthroplasty in the United States from 2005 to 2030,” Steven Kurtz, PhD; Kevin Ong, PhD; Edmund Lau, MS; Fionna Mowat, PhD, and Michael Halpern, MPH, MD, PhD.

** The Journal of Arthroplasty, “Meta-Analysis of Alignment Outcomes in Computer-Assisted Total Knee Arthroplasty Surgery,” J. Bohannon Mason, MD; Thomas K. Fehring, MD; Rhonda Estok, RN, BSN; Deirdre Banel, BA; and Kyle Fahrback, PhD, Vol. 22 N. 8 2007.

Bob Scannell, MSCE, BSEE, is a business development manager for Inertial MEMS Products for Analog Devices Inc. He can be reached at bob.scannell@analog.com.