Posterior-Stabilized Bearing Design Ups Revision Risk

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 possiblity 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 US as well.

Principal investigator Ryland Kagan, MD, assistant professor of orthopedic surgery at Oregon Health and Science University (OHSU) in Portland, told Medscape Medical News, "What's unique about our experience in the US is our overall high use of PS implants."

More than half of TKAs in the US 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 US, he said.

Researchers used AJRR data from 2012–2019 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 (HR) of 1.25 (95% CI, 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, 1693 (1.2%) underwent revision for any cause, and 334 (0.2%) underwent revision for infection. For patients with PS bearings, 2406 (1.5%) underwent revision for any cause, and 446 (0.3%) underwent revision for infection.

Even a Small Difference Significant

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."