In the years that followed, design and manufacturing technology advanced rapidly. All-ceramic implants were used with great success throughout Europe and Japan—but not in the U.S. For this technologically advanced country, one bad experience was enough to spoil the entire market.
In 1990, the FDA gave approval for ceramic heads to be used with polyethylene cups, opening the U.S. market to both alumina and zirconia balls. But ceramic cups could not be used. As of press time, the situation was unchanged. Despite the widely documented successes in other countries with all-ceramic designs, the FDA had yet to give approval for these systems in the U.S.
“The advantages of the all-ceramic designs are well documented,” says Ian C. Clarke, Ph.D., a research professor of orthopedic surgery at Loma Linda University School of Medicine (LLUMC) in Loma Linda, Calif., and a key proponent of the all-ceramic bearing. “Why should American patients be denied this beautiful bearing? We can use ceramic balls, but we cannot use ceramic cups, and we cannot use ceramic knee-joints, even though the Japanese have been using ceramic knee-joints for about 20 years. The FDA is supposed to be helping patients in the U.S., but in this case they’re actually handicapping them.”
Despite scientific evidence proving the viability of the all-ceramic designs, U.S. patients must cope with inferior metal and plastic bearing materials, and a vast potential market for ceramic manufacturers remains untouched.
“Alumina-on-alumina is over 1000 times more wear resistant than the polyethylene bearings,” says Dr. Clarke. “We have successfully run alumina-on-alumina bearings in serum for 20 million cycles, which is equivalent to 20 years in a patient. And they performed beautifully.”
Positive results have also been seen with zirconia ceramic—a material that was previously taboo in these applications due failures in prior lab experiments. “We started investigating and discovered that there is nothing wrong with the ceramic—it was the way it was being tested,” says Dr. Clarke. “The zirconia ceramic bearings were being tested in water or in a salt solution, and that doesn’t make sense. We don’t test our other bearings in those solutions. Physicians who are using the zirconia ceramic in France and Germany are puzzled why researchers are saying that it’s very bad when their results in actual implants have been very good. It was the testing system that was flawed.”
Dr. Clarke and his associates at LLUMC discovered that when tests were conducted using a protein-containing bovine serum with low protein concentrations, which closely replicates the joint fluid in the human body, the performance of the zirconia bearings was far greater than that of the polyethylene bearings and equal to that of the alumina bearings.
Other ceramic materials are also emerging that could lend even greater strength and durability to an all-ceramic hip or knee implant. For instance, CeramTec in Germany recently introduced a new alumina-delta material (an Al-Zr composite) that shows a great deal of promise in these applications. And Crystaloy®, a new bioceramic with reinforced fibers manufactured by Industrial Ceramic Technology Inc. in Ann Arbor, Mich., has shown excellent results in wear studies.
In August 2000, an Orthopedic Panel comprising researchers, surgeons and industrial consultants representing the orthopedic industry and ceramic manufacturers recommended that the FDA approve all-alumina hip joints with modular ceramic heads. While the FDA has been slow to respond, Dr. Clarke and others think that approval is forthcoming.
“The performance benefits of ceramic are very clear,” Dr. Clarke says. “We are diligently trying to get the word out so that everyone understands the results of the studies. So far we’ve presented this data in over 10 countries in the last few years to try to spread the word about the advantages of the all-ceramic designs. And the FDA will continue to be pressured by industry and organizations to approve these designs. We are hopeful that the FDA will announce its approval sometime this year.”
When that happens, Clarke says, the opportunities will be endless. “FDA approval of all-ceramic bearings will open the floodgates to ceramic innovation in the U.S.,” Clarke says.
And that would be good news for both patients and manufacturers.