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Dr. William Mihalko of InMotion and Campbell Clinic performs computer-assisted surgery on a patient

When orthopedic surgeons first began doing knee replacements, the prostheses they implanted were made of heavy stainless steel, and the surgeon used manual guidelines to cut the bones and fit the joint into place. Today, computer-assisted navigation systems are enabling surgeons to do these implants with a higher degree of accuracy, and the joints used are being made from lighter, more durable alloys.

Such strides in technology require millions of dollars in research, as well as doctors with the facility to work as both clinicians and researcher scientists. William Mihalko, MD/PhD, along with John Williams, PhD, is a physician who was hired to do research for InMotion Musculoskeletal Institute, a not-for-profit orthopedic research lab in Memphis which specializes in translational research.

Mihalko is currently the only orthopedic surgeon in Memphis doing computer-assisted surgery. The navigation software utilizes infrared signals to make a more accurate map of the knee for implant surgery. As an associate professor with the University of Tennessee Health Science Center (UTHSC) and a practicing orthopedic surgeon with Campbell Clinic, Mihalko will do basic science inquiry with the aim of interfacing his research with UTHSC, Campbell Clinic, and medical device manufacturers in Memphis to bring new technology to market.

While Mihalko is working on joint alignment, Williams is refining kinematic computer modeling tools that simulate motion, predicting what kind of movement or range of motion an individual will have in six months after receiving a joint prosthesis. The aim is to better understand and predict how an implant will work for each individual to improve outcomes in all patients.

Computer imagery enables Mihalko to look at the knee in 3D. From that image, he can measure distances, angles, determine cutting planes on the bone, and look at the body's alignment for implant positioning. When it comes to full knee replacements, "There's a lot we don't know. We get it right about 85 percent of the time," said Mihalko. "But the knee, mechanically, is more complex than a hip. The hip is like a ball and socket (whereas) the knee has rotational slide and glide with two joints. There are more moving parts, more places for things to go wrong."

While surgeons have traditionally used manual instruments to gauge cuts on the tibia and fibula, and determine joint alignment, the computer-assisted system, explained Mihalko, "is like a car navigation system, it gives markers in the bone to tell the computer where bones are in space. The surgeon puts in anatomical landmarks, then we know how to align the knee."

Having the best alignment possible means an implant that might last 15, 20, even 30 years. Using manual guides, the knee's alignment with the body generally falls between 5 to 7 degrees. With computer imaging, it's more likely to be within 2 or 3 degrees. Even with a 3 degree alignment, however, a prosthesis can fail in some patients within five to 10 years, thus requiring a second surgery.

Still, said Mihalko, "Computer imaging gives a more accurate way to cut the bone and information on how to balance soft tissue. The computer can also tell a surgeon how loose or tight ligaments around the knee are. Before the physician felt to determine how balanced you are. Now the computer can tell."

"The long-term result is where the pay back comes," noted InMotion President and Executive Director Dick Tarr. "We want to lower revision surgeries. That's more expensive and it takes longer, also the results aren't quite as good because the bone has been damaged. We can get optimal results with revisions, but we don't want to have to do it."

Jeff Almand, MD, an orthopedic surgeon with the Mississippi Sports Medicine and Orthopedic Clinic in Jackson, Miss., has been doing computer-assisted surgery for the past two years. He took classes offered by DePuy Orthopaedics, a device manufacturer, and does an estimated 500 knee and hip replacements annually.

"Anyone who's using it and has done a lot of replacements will tell you they're doing a better job. The computer does it more accurately and perfectly than manual instruments. The question is, does it matter over the long haul, and the answer is yes, particularly for younger patients who will be using a prosthesis longer. If they are younger, then they would rather be assured that it's put in properly and accurately."

The problem is, computer-assisted surgery is still in its infancy. Experts estimate that only five percent of surgeons use the technology in the U.S., compared to roughly 30 percent in Europe, which means not enough empirical data has been amassed to show its long-term effectiveness. The cost of the computer equipment can also be prohibitive, particularly if hospitals don't have high enough volume to offset surgery costs. Medicare has begun reimbursing for the procedure but some private payers, like Blue Cross, are still waiting to see if the long-term outcomes warrant reimbursement.

With millions of Baby Boomers marching toward retirement, the demand for hip and knee replacements will continue to rise. In 2006, 193,000 Americans had knee replacements, 39 percent of all such surgeries nationally, according to the American Academy of Orthopedic Surgeons. That number is expected to mushroom as boomers age. So too, will the demand for implants that last longer and can be implanted while patients are still more active. Doctors at InMotion hope to capitalize on the expertise available in Memphis to make greater contributions and improve knowledge in the field.

Tags:

Campbell Clinic, computer-assisted surgery, InMotion, knee replacement, orthopedic surgery

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