A new computer-driven ?navigation system? at Rogue Valley Medical Center helps orthopedic surgeon Steve Chamberlain determine the exact placement of a prosthetic knee joint. (Photo by Denise Baratta) — — —

A three-dimensional map pinpoints the site for an artificial joint

A new computerized navigation system helps surgeons at Rogue Valley Medical Center confirm proper alignment for prosthetic knees.

Accurate placement is a critical aspect of joint replacement surgery. If an artificial knee isn't aligned with the leg bones above and below, the new joint may wear out sooner or make walking feel unnatural.

In the knee you've got to get it exactly right, said Dr. Steve Chamberlain, a Medford orthopedic surgeon who has been using the equipment for about six weeks.

The system uses wireless technology to create a three-dimensional map of the knee, and surgeons use the landmarks it identifies to determine where to put the replacement joint. Chamberlain said the mapping tools work much like the global positioning systems that hunters use to find their way in the woods

We map various points in the knee to get the lay of the land, he said.

— The computer replaces the jigs, gauges, X-ray images and other tools that surgeons have used for years to position artificial knees. Surgeons also relied heavily on their own experience to know where to place an artificial joint.

The more you did it, the better you got, Chamberlain explained.

Knee replacement is complex surgery because there are six degrees of freedom in the joint. A knee moves forward and backward, up and down, and left and right.

The navigation system, manufactured by Michigan-based Stryker Corp., collects data about the patient's leg movements before any bones are cut. The information helps the surgeon decide where to cut the leg bones to position metal plates that form the top and bottom of the replacement joint.

The computer doesn't perform the surgery, Chamberlain stressed. It assists the surgeon.

The computer also allows a surgeon to make a smaller incision, because the computer can see details that a surgeon could only see with his eyes by making a larger opening in the leg and exposing more interior structure.

You couldn't do a minimally invasive knee without this, said Rob Patterson, a physician assistant who works with Chamberlain.

Knee replacement has become increasingly popular as people in their 50s and 60s seek to stay physically active. More than 250,000 TKRs (total knee replacements) are performed in the United States every year. RVMC alone did 340 in 2005.

Replacing a knee is a highly personal decision, Patterson said.

It comes down to how you define yourself as a person, he said. When you're unhappy with your quality of life, that's what tells us you're ready for surgery. We see lots of patients for years and years before they have their joints replaced.

While the procedure has a high rate of success, it's not something most people rush into. Post-surgical physical therapy can go on for months, and the surgery is expensive. A total knee replacement at RVMC costs about &

36;30,000 based on an average hospital stay of three to four days. (RVMC's cost estimate also includes post-operative physical therapy.)

RVMC spent &

36;222,500 to acquire the Stryker navigation system, said Scott Kelly, RVMC vice president for planning, marketing, and business development.

Patterson said learning to trust the computer was one of the most difficult aspects of incorporating the equipment into a procedure that the surgical team had done many times.

We had to develop a sense of faith in the computer, he said. We put the (measuring) jig on (the patient's knee to verify the computer data) until we established trust in the machine and got a feel for the instructions it was giving us.

The same equipment eventually will be used to assist hip replacement surgery. Chamberlain said the computer system will be most useful for surgeons who perform relatively few knee replacements.

The computer, if they use it, will help them get better, he said. The number one thing this tool does is bring all the orthopedists more consistent results.

Search and replace"bkettler@mailtribune.com.