New generation of cementless implants show promise for tibial fixation in TKR

Issue: July 2010

A new generation of cementless, ultraporous metal ingrowth materials may allow for more durable fixation of a knee implant to the bone in cases where biologic fixation has historically achieved less than optimal outcomes, according to an orthopedic investigator at the 2010 Current Concepts in Joint Replacement Spring Meeting, in Las Vegas.

“Today, the patients we perform total knee replacement on with end-stage arthritis of the knee are younger, more active, heavier and harder to mend,” said Matthew J. Kraay, MD, a professor of orthopedic surgery at Case Western Reserve University School of Medicine in Cleveland. “And although cemented knee replacement works well, it may not be as durable as we would like it to be in this subset of patients.”

Ingrowth potential

Kraay noted that there are various ultraporous metal implants for hips and knees available on the market. “It seems to have a very reliable ingrowth potential compared to previously used cementless devices,” he told Orthopedics Today. “For example, results of cementless knees from the 1980s showed that ingrowth was variable; hence, clinical outcomes and performance of those devices were variable, and not as reliable as they should have been.”

His experience has been with trabecular metal (Zimmer, Inc.), which has been in use for approximately 10 years. “The bone seems to grow in more reliably, more extensively and more predictably,” Kraay said. “Therefore, I think it is going to end up being more durable, along with a lower early failure rate and a lower late failure rate.”

‘Dealer’s choice’

He noted that research over the past 25 or 30 years in knee replacement has shown that both cementless and cemented femoral components “work quite well, so it is really dealer’s choice.” “You cement the femur or you treat the femur without cement. The real difficulty is that if the knee replacement fails with cement, it tends to fail on the tibial side. So is there a better, more durable way of attaching the implant to the bone?”

Among younger, higher-demand patients, who are increasingly being treated with knee arthroplasty, “I think going cementless on the tibial side will provide for more durable fixation on the tibia,” said Kraay, who spoke on reverse hybrid fixation in total knee arthroscopy (TKA) at the meeting. Treating this subset of patients with tibial component fixation without cement when using these new ultraporous materials “will probably in the long run turn out to be superior.”

To enhance results, however, the surgical technique “has to be meticulous,” Kraay said. “You need to have a well-aligned cut on the tibia and a perfectly flat tibial cut.” Patient selection is important as well. “You want to make sure the patient has good bone,” he said. A proper implant design also helps.

Most patients he chooses for the cementless procedure are men who are under the age of 55 years. “As the population becomes heavier and heavier, we are seeing more patients who are candidates,” Kraay said. “The interfaces also seem to be improving with time after insertion.” In contrast, cemented components “seem to have more evidence of potential aseptic loosening,” based on radiostereometric analysis (RSA).

“Results have been great,” Kraay said of the approximately 50 patients treated with the ultraporous metal implants on which he has follow-up data. “There have been no loosenings. And hopefully, this is something that will last several decades vs. 10 to 15 years for the gold standard of implant fixation with acrylic bone cement.” – by Bob Kronemyer

Reference:

Kraay, MJ. Reverse hybrid fixation in TKA: dealer’s choice. Paper 45. Presented at the 11th Annual Current Concepts in Joint Replacement Spring Meeting. May 23-26. Las Vegas.

Matthew J. Kraay, MD, 11100 Euclid Ave., Cleveland, OH 44106; 216-844-8371; e-mail: matthew.kraay@uhhospitals.org. He receives grant and/or research support from Zimmer, Inc.