Not all patients may benefit from knee arthroplasty prosthesis design innovations

Lisa G. Suter

Innovations in prosthetic design may not equally benefit everyone who undergoes total knee arthroplasty, according to Yale School of Medicine researchers.

Their findings, published in the New England Journal of Medicine, noted while the FDA has approved more than 35 new total knee arthroplasty (TKA) systems or components annually for the past 10 years, the approval process for such devices may be lacking.

“Oversight of device innovation is currently under scrutiny,” Lisa G. Suter, MD, and colleagues wrote in the article. “Safety concerns have been raised over total joint components and other devices approved through the FDA’s 510(k) clearance process, whereby devices perceived as posing a low risk of complications are approved for marketing without clinical trials.”

One concern, Suter and colleagues cited is the focus of regulatory approval on the similarity of a device to previously approved devices — a factor they wrote that could encourage producing more devices offering only minor improvements over their predecessors but might be associated with higher implant costs.

“The trade-offs between incremental improvement and the additional costs and technical complexity of the required procedure are poorly understood and seldom investigated rigorously,” Sutter and colleagues wrote.

Methods and findings

To investigate, the researchers ran the Osteoarthritis Policy Model to compare clinical outcomes of hypothetical implants with those of existing implants in cases of knee osteoarthritis, which examined life expectancy and implant survival using standard and “innovative” implants for both young and older TKA patients with and without illness.

“We used a range of values for the potential reduction in the likelihood of long-term implant failure with hypothetical innovative implants and estimated the proportion of each patient cohort that would remain alive with their original (standard or innovative) implant intact 20 years after surgery,” the researchers wrote.

They reported that the model found that by 20 years postoperatively, 19% of the healthy TKA patients aged 50 years to 59 years at the time of their procedure would have died. That mortality increased to 86% for patients aged 70 years to 79 years with coexisting conditions at surgery. After 20 years, 65% and 11% of the groups, respectively, would still be alive with their original implant.

These findings — among others discussed in the article — suggest older patients or those with multiple co-existing conditions may not live long enough to benefit from “small, incremental” gains in the durability of the implant.

No one-size-fits-all approach

“Our findings suggest that there can be no one-size-fits-all approach to the use of innovative devices,” the investigators wrote. “Given the low annual failure rate of existing implants, even significant reductions in long-term failure rates would have little effect on overall implant survival in older, sicker patients.”

The findings have greater impact when taking into consideration that newer “innovative” implants have demonstrated greater short-term failure rates. Further, these more advanced implants are often more expensive — and the increase in cost may not be worth the small benefits seen in certain cases.

Reference:

Suter LG, Paltiel AD, Rome BN, et al. Medical device innovation — Is “better” good enough? N Engl J Med. 2011; 365:1464-1466.

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