At University of Florida, Virtual Knees Get Wear & Tear.

Business Editors/Health/Medical Writers

GAINESVILLE, Fla.--(BUSINESS WIRE)--Nov. 13, 2002

Knee replacement surgery is performed on more than 250,000 Americans annually, yet less technology is brought to bear on this issue than on the development of common household appliances.

"More engineering analysis goes into the washing machine in your home than into the artificial knee joints implanted in people," says Dr. B.J. Fregly, assistant professor in the Department of Mechanical and Aerospace Engineering at the University of Florida.

Fregly is addressing that problem by taking technologies traditionally used for mechanical engineering and extending them to the human body. Though the study is still in the early stages, Fregly and his team believe that a greater understanding of the factors that contribute to joint failure will lead to longer-lasting artificial knee designs and better surgical procedures.

Problems related to wear typically limit the life span of knee implants to 15 or 20 years - possibly less for more active patients. As younger patients are diagnosed with knee joint problems, the restricted life span and functional limitations of artificial knees are becoming an increasing concern.

"We want knee implant recipients to be able to resume all their favorite activities - playing a game of tennis or going on long walks - without limitations or fear of wearing out their new knees prematurely," says Fregly. "With this research, we aren't just hoping to prolong the life span of artificial knees; we are hoping to prolong the patient's enjoyment of life."

Fregly, whose previous work has been published in Journal of Biomechanics and Journal of Biomechanical Engineering, leads a group of researchers who are evaluating and testing artificial knee designs by simulating a real-world environment specific to individual patients.

His team begins the process by placing reflective markers on the patient's skin and clothing during treadmill walking and stair-rise activities. The patient's motion data is captured by LCD devices and stored in a computer database.

Dr. Scott Banks of the Biomotion Foundation in West Palm Beach, Fla., augments the motion capture data with a dynamic x-ray procedure called fluoroscopy. Fluoroscopy accurately measures knee joint motion for natural or artificial knees.

When studying artificial knees, Banks obtains computer-aided design (CAD) models of the implant components from the manufacturer. He then uses custom software to match the 3D CAD models to each 2D fluoroscopic image as though he were orienting an object to a photograph of its shadow. The image-matched components are used to quantify the 3D motion of the patient's knee under real-life loading conditions, such as walking and climbing stairs.

The process for studying natural knees is more difficult, since CAD models of the bones are not readily available. To create models of natural knees, Fregly's team uses CT scans, which produce static 2D image slices of a patient's leg. The CT data are imported into sliceOmatic image-processing software from TomoVision (www.tomovision.com), where the 2D slices are stacked to create a 3D model. The range of data in this 3D model is collected in coordinates known as "point clouds."

Researchers then use Geomagic Studio software from Raindrop Geomagic (www.geomagic.com) to automatically generate accurate 3D computer models from the point cloud data. The team uses polygon models from Geomagic Studio for shape-related tasks such as image matching. The polygonal models are then converted into highly accurate mathematical surface models for contact stress analysis.

Once the researchers have developed contact stress predictions from the movement data, the final comprehensive wear model is created with help from Dr. Greg Sawyer, a University of Florida friction and wear specialist. Combining accurate knee motion data with contact stress predictions creates a wear model that pinpoints the exact places where an artificial knee is likely to fail.

Eventually Fregly and Dr. Rafi Hafka, an optimization specialist in the Mechanical and Aerospace Engineering department, will be able to fine-tune a full-body model to reproduce movement data collected from the patient prior to surgery. The surgeon and research team will then perform the surgery on the computer model to predict which surgical parameters or implant designs will produce the best outcome for a particular patient. Patients will be followed long-term and re-measured in the movement lab following surgery to assess the model's predictions.

By developing a better understanding of how and where stress and movement produce wear, Fregly, Banks, Sawyer and Haftka hope advances can be made to extend the life span and functionality of artificial knees.