May 21, 2002
Hip and knee replacement surgeries are done every day in hospitals across the country. Joint replacement is an effective and common way to treat severe arthritis in large joints. But up until recently, those with arthritis in their fingers or other small joints were simply out of luck. That changed last fall when the U.S. Food and Drug Administration approved the first workable artificial finger joint, the "Ascension MCP PyroCarbon Total Joint."
It's the invention of Stephen Cook, professor of orthopedics, and Jerome Klawitter, a former member of the Tulane faculty. Their finger joint succeeds where others have failed because it's made of pyrolytic carbon. This material, which is used to make mechanical heart valves, is extremely biocompatible and its rigidity is very similar to bone.
"In contrast, metal is many times stiffer than bone, so you have a mismatch of materials," Cook said. "That's not as much of a problem in the hip, where the bones are big and thick. But in the hands, the bones have very small, thin cortices, and the stress transfer of the prosthesis to the bone is critical. So implants made of metal and other types of traditional orthopedic materials have never worked in the hand."
Cook, who has been at Tulane since arriving as an undergraduate in 1970, began working on the finger joints with his mentor Klawitter in the late 1970s. They first implanted them in baboons at the primate center. When that experiment was successful, the two began working with surgeons at the Mayo Clinic to make custom finger joints for their patients.
Eventually, 151 of these were implanted in 53 patients between 1979 and 1987. Those implants worked well, but orthopedics companies showed little interest in developing them for the marketplace. The demand for artificial hips and knees was growing quickly at the time, and manufacturers seemed content to focus on that market.
In 1992, the Joe W. and Dorothy Dorsett Brown Foundation gave Cook and Klawitter a grant to do a follow-up study of the finger joints that had been implanted at the Mayo Clinic and to examine their commercial viability.
"Dorothy Brown had arthritis and had to give up crocheting and other things later in her life," Cook said. "So the trustees thought this would be a good use of their money."
They found that the implants were holding up well. About 70 percent of them still functioned beautifully without revision after 16 years. And even those that had to be revised showed no signs of wear or deformity.
"Another interesting thing about this carbon material is that it doesn't wear. It approaches a diamond in terms of wear properties," Cook said.
Cook and Klawitter founded a company called Ascension Orthopedics in order to pursue FDA approval for the finger joint and to manufacture and market it and other joints made with pyrolytic carbon. The joint that was just approved is meant to replace the knuckle, or metacarpophalangeal joint, which is the joint most commonly affected by rheumatoid arthritis.
Additional devices are in the works for other small joints in the fingers, thumb, elbow and toes. Now the challenge they face is that of educating rheumatologists, surgeons and arthritis sufferers that there is now a way to restore function in the finger joints. But at least one surgeon has gotten the message. Kathleen Robertson, an assistant professor of orthopedics, hopes to begin implanting the finger joint this month.
Heather Heilman may be reached at firstname.lastname@example.org.
Tulane University, New Orleans, LA 70118 504-865-5000 email@example.com