Medical MEMS tackles knee replacement
R Colin Johnson
9/23/2011 5:34 PM EDT
PORTLAND, Ore.—Currently, more than 30 percent of knee replacement surgeries suffer from misalignment problems caused by the "fog of surgery"–where the precise orientation of internal bones is difficult to determine. By adding a complement of Analog Device Inc.'s high-precision MEMS sensors to track the alignment and motion of a patient's knee during the surgery, OrthAlign Inc. (Aliso Viejo,Calif.) aims to dramatically increase precision.
"The high-precision of Analog Devices' IMU enables our KneeAlign system to perform as well as optical systems that cost $400,000 or more," said Darius Kharabi, OrthAlign’s vice president of corporate development. "Now surgeons can now get a much higher degree of precision with an easy-to-use device that costs a fraction of the price."
The stakes are huge, since more than 675,000 knee replacements are performed every year in the U.S. alone, with trends indicating that as many as 3.5 million Americans will have the procedure performed by 2030, according to the Agency for Healthcare Research and Quality (Rockville, Md.).
Unfortunately, today most knee replacements are performed using antiquated mechanical alignment tools which are imprecise, resulting in a success rate of less than 70 percent, according to according to studies in the Journal of Arthroplasty (Mason, 2007) . Until now, the only alternative was purchasing an optical alignment system to increase success rates. But the instruments are bulky, hard-to-use and expensive, resulting in less than 5 percent of knee procedures performed using them.
The OrthAlign medical device uses three-axis gyroscopes and accelerometers in an Analog Devices' inertial measurement unit (IMU) to guide the surgeon's scalpel for knee replacements.
The new OthAllign MEMS-based instrument, on the other hand, is small enough to hand hold, cheap enough to throw away after a single use, works in just a few seconds, and is as precise as the optical systems costing hundreds of thousands of dollars more, according to OrthAlign.
OrthAlign was founded in 2008 and has already demonstrated a MEMS-based knee-surgery alignment tool for performing one part of the total knee arthroplasty (TKA) procedure. The company received Food and Drug Administration clearance earlier this year for its second-generation KneeAlign instrument, which guides the surgeon when making both the top and bottom severances necessary to remove the natural knee and insert the mechanical one during TKA.
The IMU from Analog Devices was chosen for its high-precision use of three-axis gyroscopes and accelerometers to track knee orientation in real time, according to OrthAlign. After attaching the IMU-bearing module to the natural knee, the surgeon merely moves the natural knee threw its normal range of motion—a procedure that takes less than 30 seconds—after which algorithms uses the precision motion tracking data from the MEMS sensors to calculate the positioning of the cutting instrumentation on the knee. A display on the front panel of the KneeAlign instrument shows surgeons the real-time positioning of their cutting instrument to help ensure precise alignment for the artificial knee.
OrthAlign's MEMS-based KneeAlign instrument is currently being used by the Hospital for Special Surgery (New York) and the Scripps Green Hospital (San Diego), but will be available to hospitals in select geographies in the first quarter of 2012.