Dr. William Bargar is an old hand at hip replacement. Like any orthopedic surgeon, he routinely hacks the damaged ball off the end of a patient's thighbone and installs a metal substitute. It's a tricky operation, but as Bargar is now busy demonstrating, M.D.s are not uniquely qualified to perform it. In the midst of a recent hip replacement, Bargar stepped back at a critical point and let an assistant take over. The assistant was a 250-pound robot. The machine, known as Robodoc, did nothing heroic; its role was limited to carving a recess in the end of the thighbone to make way for the implant. But the operation was the first ever performed, even in part, by an automaton-and the frontier it opened could extend far beyond hip surgery.
What Robodoc brings to the operating room is not assembly-line efficiency but greater surgical precision. Engineers can now fabricate nearly perfect replicas of a patient's hip. The standard prosthesis consists of two pieces: a plastic socket, which fits into the pelvic bone, and a metal pin that goes into the top of the thighbone. The pin has a ball on the end which protrudes from the thighbone an fits into the plastic socket. Unfortunately, there's never been an elegant way to hollow out the thighbone to make way for the pin. The traditional method, which involves banging on a spike with a mallet, creates such a jagged recess that only 20 percent of the pin ends up touching the bone. Because the bone grows to the pin only at points of contact, the whole hip is compromised.
Bargar and veterinarian Hap Paul, both of the University of California, Davis, developed Robodoc to address that problem. Their system includes a CT scanner to generate three-dimensional images of the thighbone, a robotic arm to drill the hole and a computer program that lets the surgeon mediate between the two. First the surgeon calls up a live image of the patient's thighbone and uses a "mouse" (an electronic pointer) to designate an ideal cavity. Then, after opening the patient and guiding the robot to the bone, he gives a go-ahead, and the robot mills the hole with a high-speed drill.
In tests on cadavers and ailing dogs, Robodoc has handily outperformed the spike and mallet, achieving 96 percent contact between bone and implant. But Nov. 7 marked the machine's first encounter with a living person. The operation, performed on a 64-year-old arthritis patient at the Sacramento, Calif, Sutter General Hospital, came off without a hitch. If nine additional operations show similar success, Robodoc will get a larger trial run and, with luck, a license from the FDA.
Hip replacement is a big industry. U.S. surgeons perform nearly a quarter million operations annually, and one out of 10 is to replace an existing implant. "If we can do a better job at the front end," says Bargar, "it will save money and prevent a lot of pain later on." Hip surgery is just the beginning. With minor adjustments, Robodoc could bring greater precision to other joint operations and ultimately to eye, ear and brain surgery. Doctors needn't worry, though: unlike an assembly-line android, this one will always need close supervision.