Photos by Carl Costas / Sacramento Bee Physical therapist Bobby Natividad measures the flexibility of Charlesetta Stalling's left leg two days after her total right-knee replacement at Methodist Hospital in Sacramento. Dr. Stephen Howell helped design the custom-fit OtisMed knee.

SACRAMENTO — Charlesetta Stalling likes to call herself "62 years young." She is vigorous and healthy; her life is packed with plans, trips and stories still to be spun.

Unfortunately, Stalling's 62-year-old knees have told a different tale.

Plagued with degenerative arthritis, also called osteoarthritis, Stalling has been sidelined on and off with pain and, even worse, difficulty doing the gardening, cha-cha dancing and traveling she yearns to do.

A total knee replacement surgery in 2004 got her back on track, but the education consultant and popular storyteller knew it was only a matter of time before her other knee would meet the same fate.

That happened last month, when orthopedic surgeon Stephen Howell replaced Stalling's other knee in an operation at Methodist Hospital in Sacramento.

This time, however, Howell used a new method, aided by special three-dimensional imaging and computer software. The technology aims to customize each new knee, preserve more of the patient's bone and ligaments and shorten recovery time.

The method, marketed by Fremont-based OtisMed, was developed by Howell, known in the orthopedics world for his improvements in surgical techniques for anterior cruciate ligament tears.

With an aging population and the rise in joint-pounding obesity, knee replacement surgeries are multiplying. The American Academy of Orthopaedic Surgeons reports that in just seven years, the number of knee replacement surgeries has almost doubled, from 266,000 in 1998 to 455,000 in 2004.

In that time, however, few innovations have been made in knee replacement.

The problem with conventional knee replacement surgery, Howell said, is that one of five patients is unhappy with the result, either because of enduring pain or a general lack of mobility.

Achieving a better fit

"I can do three surgeries in the same day and have one patient who loves me, one who had an arduous recovery and a third not that happy at all," Howell said. "And yet, I think I have done the same operation. What we don't account for is the individuality of the patient's geometry and anatomy of the knee. Everyone is a little different."

To achieve a better fit, Howell starts with an MRI of the patient's knee, which allows him to see the knee in parallel slices, like a tomato perfectly cut into equally sized rounds with a Cuisinart.

The images are used with specially developed software that reassembles the slices into a three-dimensional model of the knee's bones and cartilage, leaving out muscles and tendons.

Of course, like the patient's real knee, the model appears misshapen because of arthritis, the breakdown of cartilage that works as a cushion between the bone and joint.

"We convert that arthritic knee into a virtual, naturally aligned, normal knee," Howell said. "Where there are areas that are worn, we fill in the gap, realign the leg and end up with a knee that may have existed 15 years ago."

After that, a computerized 3-D image of the replacement parts to be used in the surgery is matched to the virtual model.

That information is used to create plastic guides that fit on the end of the femur and tibia and tell the surgeon exactly where to cut the bone for the implant.

Stalling's most recent knee crisis occurred when she stood up quickly from a seated position on the floor of her home.

Tests showed a torn meniscus, arthritis behind the knee and a total lack of cartilage in the front of the knee. The diagnosis forced her to cancel a scheduled trip with a friend to Uruguay, where they'd hoped to start a library for women.

60 minutes to complete

The custom knee procedure appealed to Stalling, she said, because it promised a quicker recovery. Translation: Her trip to Hawaii in two months would go as planned.

"And this knee will be more like the one I have, but new and improved," she said.

Stalling's operation required far fewer instruments and took about 60 minutes to complete.

After removing fatty tissue from around the knee, Howell drilled the guides into the bones, then slipped his saw into the guide to shape the bone and ready it for the implant.

Like a woodworker with a block of pine, he then chiseled out any excess bone to smooth the platform for the prosthesis, which is then fixed into place with cement.

Three hours later, Stalling was raising her leg out of bed on her own.

A computer-generated model of Charlesetta Stalling's knee made before her replacement surgery shows how it was projected to look after the procedure in a Sacramento hospital.

The next day, she was gingerly taking steps with the help of a walker. Two days later, she confidently tackled a set of stairs and showed off the near-normal flexion she'd already achieved.

"We always used to hope and pray for 90-degree flexion," said Stephanie Rogers, who supervises inpatient physical therapy at Methodist. Like others who have had the new knee surgery, Stalling already could bend her knee to 110 degrees.

"I've been doing this for 12 years," Rogers said. "You see such a difference. It has made our job a lot easier."

Dr. Amir Jamali, an orthopedic surgeon at the UC Davis Medical Center familiar with the OtisMed technology, is cautiously optimistic about its future.

"It's a new way to look at the problem," Jamali said. "There is a chance that you would have a more stable knee."

But Jamali, who uses a different surgical method involving anatomical landmarks and computer calculations, cited some concerns, as well.

Because the surgeon relies on guides made by technicians prior to the procedure, he said, "the potential downside is that the surgeon has very little control over what happens in surgery."

More research needed

UC Davis mechanical engineer Maury Hull, who has worked with Howell for 15 years on various innovations and helped refine the new knee replacement technology, said additional research needs to be done before orthopedic surgeons are convinced that the OtisMed knee approach is a significant improvement over older techniques.

But Hull is confident the technology's benefits will prove overwhelming.

"I think it's going to revolutionize knee replacement surgery," he said. "I think it will catch fire soon."

Stalling is pretty certain, too. "I don't know when," she said, "but I'll be dancing."