CHICAGO - Posterior-stabilized (PS) bearings used in total knee arthroplasty (TKA) may increase the risk of revision compared with bearings of other design, new data suggest.
That possibility has previously been reported in studies outside the United States, and now an analysis of more than 300,000 cases in the American Joint Replacement Registry (AJRR) suggests it’s the case in the United States as well.
Principal investigator Ryland Kagan, MD, of the department of orthopedic surgery at Oregon Health & Science University in Portland, told this news organization, “What’s unique about our experience in the U.S. is our overall high use of PS implants.”
Dr. Ryland Kagan
More than half of TKAs in the United States use the PS bearings; in comparison, in Australia and European countries, PS use is closer to 20%, he said. Because of this disparity, previous studies have not been seen as generalizable to the United States, he said.
Researchers used AJRR data from 2012 to 2019 and identified all primary TKA procedures performed during that period. Cases were linked to supplemental Centers for Medicare & Medicaid Services data to find revision procedures that may not have been included in the AJRR database.
Jamil Kendall, MD, an orthopedic resident at OHSU, was first author on the study. The team evaluated patient demographics, polyethylene characteristics, procedure dates, and cause for revision in the 305,279 cases.
Of those cases in which implant characteristics were reported, 161,486 (52.9%) patients received PS bearings, and 143,793 (47.1%) received minimally stabilized bearings.
The researchers compared three minimally stabilized implants (cruciate retaining [CR], anterior stabilized [AS], or pivot bearing designs) with each other for risk and then compared minimally stabilized options as a group with the PS bearings.
They found no significant differences among the three minimally stabilized options.
But revision risk was higher when they compared the minimally stabilized implants with the PS bearing implants. Use of PS bearings had a hazard ratio of 1.25 (95% confidence interval, 1.2-1.3; P < .0001) for all-cause revision and an HR of 1.18 (95% CI, 1.0-1.4; P = .02) for infection.
Among the patients with minimally stabilized bearings, 1,693 (1.2%) underwent revision for any cause, and 334 (0.2%) underwent revision for infection. For patients with PS bearings, 2,406 (1.5%) underwent revision for any cause, and 446 (0.3%) underwent revision for infection.
Even a small difference significant
Dr. Kagan said, “The difference isn’t dramatic, but when you think of the total number of total knee arthroplasties done, you’re talking about millions of procedures. Even with a small increased risk, you’re going to see a large influence for a population.”
Richard Lynn Illgen, MD, director of the University of Wisconsin-Madison joint replacement program, told this news organization this work identifies a trend, but he pointed out that registry-based studies have important limitations.
“They cannot establish causality,” he said. “There are many potential confounding variables and potential selection biases that could affect the study. Specifically, the study did not control for degree of deformity or medical comorbidities. Although some surgeons routinely use PS designs for all primary TKAs, others use PS designs for patients with more severe deformities. It is possible that PS designs were used more frequently in patients with a greater degree of deformity, and this could introduce a selection bias.”
He added that no data were included to enable stratification of groups according to medical comorbidities.
“It is possible that selection bias exists comparing the relative degree of medical comorbidities between patients in the PS TKA and minimally constrained TKA groups,” Dr. Illgen said.
He said further prospective, randomized studies are needed to eliminate selection bias and to better determine whether the observed pattern of increased risk of revision holds up, compared with the minimally supported versions.
The authors acknowledged those limitations, but Dr. Kagan said the high percentage of PS procedures in the United States helps mitigate potential bias.
Dr. Illgen serves as a consultant and developer for Stryker, is chair of the AAOS AJRR Research Projects Subcommittee, and is a member of the AJRR Steering Committee. Dr. Kagan receives research support from KCI, Ortho Development, and Smith & Nephew, where he is also a paid consultant. Dr. Kendall reports no relevant financial relationships. Another coauthor of the study is a paid consultant for 3M, Heraeus, Immunis, Smith & Nephew, Zimmer Biomet, and Total Joint Orthopedics and has stock or stock options in Joint Development.
A version of this article first appeared on Medscape.com.