Mow has developed software that creates 3-D computer models from magnetic resonance images (MRI) of a patient's knee. The models can aid doctors in planning more effective surgical treatment of knee injuries or guide physical therapists to better rehabilitate patients.

Sitting in front of his desktop computer at Columbia University, Mow, Ph.D., the Stanley Dicker Professor of Biomedical Engineering and Orthopedic Bioengineering, can call up a precise physiologic model of the human knee and, with a click of the mouse, make the knee flex and move. As it moves, pressure points within the knee joint change color in proportion to the stress acting on the knee during motion. "You can't see stress acting within the human knee," says Mow, "but now you can with this computer model."

Mow's computer knee model is not simply an animated cartoon. It is a true dynamic engineering model, with the precise geometry and all the mathematical equations and physical laws built in to represent true-to-life forces and anatomy. "We are concerned with the whole area of mechanics and in determining the most appropriate stress and strain laws for these complex tissues," says Mow.

He first defined the appropriate laws in 1980, earning high recognition in the bioengineering research community. Then he and other researchers developed a set of algorithms that incorporated the complex anatomies of the joint surfaces and the material properties.

To acquire MRI pictures of the knee, Mow worked with researchers in Columbia's Radiology Department. Over the last five years, they have developed a method that gives 200-micron accuracy over the surface of the knee, roughly three times the thickness of a human hair.

The MRI models then were calibrated using a method known as stereophotogrammetry, "and they are extremely accurate," says Mow.

It is like taking pictures of a planet and using them to map its topography mathematically. But instead of using a photographic image to make a map, Mow used the MRI images to make a model of the joint. "We borrowed the methodology, although we wrote all the programs," he says. Once the MRIs were calibrated from cadaver specimens, Mow went on to calibrating real patient data.

That is the point at which the software becomes the most valuable, says Mow. Just as it is too crude to characterize leg bones as perfect cylinders, it would be almost useless to consider that the same bone in one person is exactly the same shape as in different persons. "Joints come in an infinite variety of shapes and sizes, just as the human face does," says Mow, so individual models are essential.

Accurately describing the material properties and behavior of human cartilage in a patient's knee is also where the current challenge lies, says Mow. "When this is done, the doors will be wide open to analyzing many important clinical problems, including those of tissues engineered to replace damaged ones."

Presently, it is unknown if any of the biologic replacements from tissue engineering can withstand or function in the knee. "If tissue-engineered cartilage cannot withstand the high stresses and strains within a joint, then they are of no use," says Mow. With his models, Mow can calculate not only the stresses and strains within the biologic tissues, but also fluid flow and ion transport through the tissues, cartilage and bone.

"But few studies of this type have ever been undertaken," says Mow. "It is a grand challenge for the field of tissue engineering in the next decade."

Once there is enough patient data calibrated, Mow says he will be confident in writing programs for simulated surgery for specific patients. Generic programs for several surgical procedures of the knee are now being written.

In anticipation of that day, Mow is already working with radiologists and knee surgeon J. Richard Steadman, M.D., chief U.S. Olympic ski team surgeon in Vail, Colo. Mow and Steadman hope to develop a telemedicine system that can transport the MRI data electronically between them.

"In the future," says Mow, "we could create these models from clinical MRIs transmitted electronically from anywhere in the world and provide expert consultation for those surgeons who might be unsure as to the most appropriate procedure for a specific patient."

In a successful future scenario, a skier who falls on a slope and injures a knee could be taken to a nearby hospital and have MRI images taken. The images and other information would then be sent to a biomedical engineer, where a precise computer model of the injured knee would be created using Mow's software. This model could then be sent to any number of specialized surgeons, such as Steadman, who could try out different techniques on the model and advise the doctors attending the injured skier what the best procedure would be. Mow would eventually like to put a computer screen right in the operating room so the model can be viewed during surgery.

Several hurdles remain before the scenario can become reality. "MRI systems from place to place are different," says Mow, "and manufacturers have their own protocols." He adds that the quality and capacity of data transmission lines and connections also must improve.

But the hurdles haven't discouraged Mow or his colleagues from applying to the National Institutes of Health for funding to develop the first computer-aided surgical planning system for orthopedics. "Nothing like this has ever been done in biomedical imaging," Mow says. "It's unique. It's multidisciplinary. It brings together the best of medicine, radiology, surgery, engineering, computer vision and so much more."

Under a Whitaker Foundation Special Opportunity Award, Mow, who is also director of the Center for Biomedical Engineering, is developing a new biomedical engineering department at Columbia that will emphasize biomechanics, cell and tissue engineering, and biomedical imaging.