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One hip doc

DN Staff

February 23, 2004

8 Min Read
One hip doc

Point Man: Engineer and medical doctor Tony DiGiola developed the first computer-based planning and navigation system for hip-replacement surgery. It uses optical sensors, infrared camers, computers and special software.

Pittsburgh, PA-Getting an appointment to see Dr. Anthony DiGioia can be a long process. Unless you have hip, knee, or other joint problems. Then, the engineer-turned-orthopedic surgeon clears his calendar and sees you right away.

Luckily, I don't have any of those problems-yet-so it took me over a year to meet with him. Never mind that my reason was to tell him that he was a top candidate for the Design News/Phillips Plastics Special Achievement Award for his invention of the multi-patented Hip-Navigation System, a computer-based planning and guidance tool for surgeons, and for the strides he has been making to advance minimally invasive surgery and surgical tools.

It's not that he didn't feel honored, he assured me. But there were patients to see and surgeries to perform, and he wouldn't re-schedule any of them just to receive an award. I would have to wait.

That's typical, DiGioia's colleagues say.

In an age where many people act as if "it's all about me," Tony DiGioia seems on the surface to be all about them-his patients. But, it's not just on the surface, says Chris Hendrickson, head of the department of civil engineering at Carnegie Mellon University, where DiGioia got his engineering degree: "He really wants to help people; that's what turns him on."

And that's also what turned him toward a medical career-and his eventual development of the Hip-Nav, and later, Knee-Nav surgical-navigation systems.

Hip and knee surgery are commonplace in the U.S. today. There are nearly 250,000 hip replacements and 300,000 knee replacements annually. The vast majority are successful, with about 90 percent of the joint replacements lasting some 10 years. Moreover, only about 2-to-5 percent of hip implants get dislocated within a year after initial surgery. So why devote your career to improving something that's already very good by most standards? The simple answer is that 90 percent isn't good enough by DiGioia's standards. The failure rates, as small as they are, add millions of dollars to the nation's medical costs. But, far more important to DiGioia is the pain and inconvenience to patients. He vowed to improve that record, and, says Jim Osborn, director of Carnegie Mellon University's Medical Robotics Technology Center, "his steadfast insistence on finding improvements has made a big difference."

Indeed! In the last 13 years since DiGioia and his team introduced Hip Nav to the surgical world, it has been responsible for cutting the one-year dislocation rate to less than 1 percent.

And there's more. Hip Nav-and DiGioia's evangelizing-have helped convince the implant industry to direct some of its engineering efforts toward development of products for minimally invasive surgery, which should cause less tissue trauma, shorter hospital stays, and faster patient recovery. Implant manufacturers Zimmer and Stryker Howmedica Osteonics, for example, are working with DiGioia and other physicians on new implants and surgical tools.

Technology Tour de Force

The Hip-Nav system, the first computer-based system for hip-replacement surgery, and its younger cousin, Knee Nav, use an array of optical sensors, infrared cameras, computers, and special software to develop a blueprint for surgery that improves implant placement. Hip Nav has three components: a preoperative planner, a range-of-motion simulator, and an intraoperative navigational system that helps the surgeon measure and place the implant in the right spot.

One of the keys to Hip Nav-and a feature that distinguishes it from all other computer-based surgical-navigation tools-is the use of computed tomography (CT) scans as a guide for correlating implant size, position, and orientation in relation to the pelvis prior to surgery. Critics say that CT scans are too expensive, especially for routine surgery. But DiGioia and his team insist they may be a better surgical investment than traditional X-rays, given the trend toward less and minimally invasive techniques. CT scans provide a complete 3-D view of the joint.

Surgeons compare the 3-D geometry of the pelvis and femur to 3-D models of prostheses provided by implant manufacturers to help them select the right size and fit. Additionally, the Hip-Nav system generates models of the pelvis and femur for visualization and range-of-motion studies, which help surgeons find the best position for the implant.

"There isn't much freedom in how you position an implant, but this planner lets us play with different variables to see how they would affect the joint mechanism," says Branislav Jaramaz, Ph.D. and scientific director of the Institute of Computer-Assisted Orthopaedic Surgery (ICAOS) at Pittsburgh's Western Pennsylvania Hospital, which DiGioia founded. A computer scientist and civil engineer, Jaramaz has been at DiGioia's side since the early '90s and leads the team that writes the codes that drive Hip Nav.

One of the other keys to Hip Nav is an optical tracking system to keep tabs on the implant, pelvis, and surgical tools during surgery. Hip Nav uses an infrared camera to determine the location of markers through the use of light-emitting diodes attached to the markers. The markers act as motion sensors. Surgeons collect surface points on the bone to relate the position of the pelvis to the CT scan and preoperative plan.


The son of a well-known Pittsburgh civil engineer, DiGioia got a B.S. in civil engineering from Carnegie Mellon University in 1979 and an M.S. in civil/biomedical engineering at the same school three years later. His advisor in graduate school was William "Red" Whittaker, famed expert and pioneer in field robotics and a previous Design News Special Achievement Award winner.

A weight lifter and football standout at CMU, DiGioia, whom Civil Engineering Dean Hendrickson remembers as a "vicious" blocker, always had a keen interest in the mechanics of the human body. So it seemed natural when he took a part-time job in graduate school designing hip implants in an orthopaedic research lab. That's when he decided to go to medical school. "He had been studying classical civil engineering, but he was restless," recalls Whittaker.

His move toward a medical career surprised many, including his family. But Whittaker, a restless engineer himself who at the time was looking for ways to do more with his professional life, was among those who encouraged him to pursue his goals. "I told him orthopaedics was a wonderful world of mechanics and that civil engineering was applicable there," he says.

He followed his passion at Harvard Medical School, where he graduated with honors in 1986.

The mid-to-late 80s were watershed years in medical technology. In 1986, researchers at IBM, working with others at the University of California at Davis, developed Robodoc, a robotic milling machine that could mill a cavity in the femur for placement of a hip implant and shape the cavity for precise fit and positioning. DiGioia began using it at Pittsburgh's Shadyside Hospital.

"It became clear to us that surgeons weren't quite ready for an active robotic system like Robodoc," DiGioia recalls. So he teamed up with Jaramaz, who was completing his Ph.D. work at the time, and Takeo Kanade, former director of the CMU Robotics Institute and co-founder of the medical robotics program at the school. They applied for and received a grant from the National Science Foundation to develop a passive, computer-based navigation system that surgeons could use while still maintaining control of the surgery itself.

But there were important engineering problems to overcome first: finding a way to track the motion of the surgical tools and the bones. DiGioia and Jaramaz found the solution at Northern Digital Inc. The company had developed an optical localization system equipped with light-emiting diodes that they knew could be used for tracking the position of the bone and surgical tools.

DiGioia's new passion is minimally invasive surgery. Last year, he, Jaramaz, and others published a report in The Journal of Arthoplasty summarizing the results of a study of less invasive surgeries he performed with Hip Nav using a mini-incision technique. The study reviewed the progress of 33 patients who received total hip replacements using a mini-incision (7-13 cm) surgical technique with 33 patients whose surgery employed the traditional 25-to-35-cm incisions. While the average surgical time for the mini-incision group was slightly longer (20 minutes), that group showed significantly more improvement in limp, stair climbing, and distance walking in the six-month follow-up examination.

Retired contractor Barry Douglas, of Ligonier, PA is a believer. Last year, DiGioia replaced his hip using Hip Nav and minimally invasive surgical techniques. He threw away the cane within three weeks. "Of all my medical experiences over the years, the DiGioia experience was the most blessed," he says.

Apparently hundreds of other patients agree. And DiGioia returns the compliment. Douglas says DiGioia invited him to a "patient-appreciation day" in Pittsburgh recently. "There were about 1,000 present and former patients there at the Carnegie Science Center, and it was a great time."

Great accolade for one hip doc.

National Editor Paul E. Teague can be reached at[email protected].

Web Resource

For additional information on Hip Nav
Go to http://rbi.ims.ca/3845-559

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