Has the time come to ease the restrictions on ceramics?

After nearly 20 years, the debate still rages over whether the FDA is doing the right thing in keeping ceramic implants sidelined.

Issue: February 2003

ORLANDO, Fla. — It has been nearly 20 years since the Food and Drug Administration pulled its approval of ceramic hip replacement systems. In that span, the advances in ceramics technology have been slow, but they have been steady.

Some orthopedic surgeons, such as Douglas A. Dennis, MD, clinical director of the Rocky Mountain Musculoskeletal Research Laboratory in Denver, feel that the progress has been substantial and that the Food and Drug Administration must note the lack of restrictions placed on ceramic implants in other parts of the world.

Dennis and William J. Maloney, MD, chief of orthopedic surgery service at Barnes-Jewish Hospital in St. Louis, discussed the issue during a debate at the 19th Annual Current Concepts in Joint Replacement Winter 2002 meeting.

Work in progress

“I think that every total hip that we look at using ceramics is a work in progress,” Dennis said. “I do not think that we have nearly the worldwide experience with it and I think we’re on our learning curve, but I think that it’s got some potentially exciting advantages as far as low wear. As we’re putting hip replacements in people that have three or four decades to live, I think that we have to look for better materials.”

Maloney said, however, that 30 years of searching has not convinced him that ceramics will ever be the answer.

“If you take John Callaghan’s data on the Charnley hip arthroplasty and if you match it age for age with the French data on ceramic-on-ceramic articulations, the Charnley looks better, with less revisions at 20 years and less revisions at 15 years,” Maloney said. “So to date, even if it is a lower wear articulation, they have not solved their fixation problem. They have cemented the cups. They have screwed in the cups, they have put in press-fit cups with a bioactive backside and still the loosening rate is no better than with any other articulation. Plus, they are continuing to break.”

Progress has been made

The first ceramic implant was put in by Frenchman Pierre Boutin, MD, in the early 1970s. The first generation implants often failed due to loosening and early fractures. Dennis emphasized that those early problems were caused by the use of poor low-density material with large grain size.

“We did not know how to correctly manufacture the components,” Dennis said. “There were large porosity deviations and mismatches in both diametral clearance and taper tolerances.”

Dennis said that those early problems have been solved, as have some of the early mechanical processing woes. Today’s ceramic implants are stronger — up to four times as hard as current metal implants — and harder than ever before with a significantly reduced grain size.

That has led, Dennis said, to wear rates as low as 0.016 mm per year. Additionally, he said that ceramic implants allow for the use of larger femoral heads than metal-on-polyethylene articulations, which leads to greater stability. The material is also relatively bioinert.

Addressing the infrequent reports of osteolysis in ceramic articulations, Dennis pointed to a study by Petit et al that compared macrophage response to alumina ceramic and polyethylene debris in identical particulate size and volume. The authors measured amounts of tumor necrosis factor- (TNF-) and found that although ceramic particles cause TNF- release, they do so at a rate 8-to-10 times less than that observed with polyethylene.

Another study has shown that polyethylene particles induce a significantly greater release of TNF- compared with alumina.

“Ceramic-on-ceramic hip replacements have had excellent long-term results in Europe with very low wear,” Dennis said. “The hardness resists three-body wear debris and I personally think that the osteolysis risk is extremely low if properly manufactured.”

Primary foundations

Maloney focused on four of the primary foundations among ceramic implant supporters — the articulation’s low wear rate, scratch resistance, inertness of the wear particles and low breakage rate — and attempted to find faults with each.

First, he pointed to a report by Bragdon et al that examined four different ceramic femoral heads, finding that all had in vivo surface damage, multidirectional scratches, crater formation and grain separation.

Next, Maloney looked at a study by Walter et al, published in 1992, that examined 48 total hip arthroplasties and found considerable wear in the ceramic heads with cup malpositioning. A high abduction angle led to the highest wear rates. And while wear is extremely low in a well-functioning ceramic articulation, surgeons need a lot of expertise to guarantee a good articulation, Maloney said.

“In this country, the majority of cases are done by surgeons who do 10 or less hips per year,” he said. “With ceramic hip articulations there are limited femoral neck lengths and there are no elevated liners, both of which increase the importance of preoperative planning. If you don’t do it right [implant positioning], you’re going to get more dislocations. And dislocation, as we all know, is related to surgical volume.”

To demonstrate the bio-inert qualities of ceramic implants, Maloney showed results from a laboratory experiment done at his center. A study was done of poor-performing ceramic-on-ceramic articulations and after seven years in vivo, there was osteolysis around the femur in some cases. Ceramic particles stimulated bone-resorbing cytokines.

“There is no question that ceramic particles are not bio-inert,” Maloney said.

Finally, Maloney pointed to the experience in Japan with a cementless total hip ceramic-on-ceramic articulation with a polyethylene layer introduced by Kyocera (Kyoto, Japan). The product had to be recalled due to an early fracture rate of about 2%.

“These modular acetabular components are part of an ongoing human experiment,” Maloney said. “And as you saw from the Kyocera experience and other recent reports, the fracture risk is real and I think that it’s going to continue to present a problem.”

For your information:

Maloney W. Ceramic-ceramic: Sands in time! In the affirmative. #3. Presented at the 19th Annual Current Concepts in Joint Replacement Winter 2002 Meeting. Dec. 11-14, 2002. Orlando, Fla.

Dennis D. Ceramic-ceramic: Sands in time! In opposition. Presented at the 19th Annual Current Concepts in Joint Replacement Winter 2002. Dec. 11-14, 2002 Meeting. Orlando, Fla.