"Thicker" Polyethylene Bearings Are Not Associated With Higher Failure Rates in Primary Total Knee Arthroplasty

Despite improvements in polyethylene bearing surface properties, only 1 previous study has examined the results of larger thickness bearings. The purpose of this study was to determine whether polyethylene thickness influenced patient outcomes and implant survival following modular total knee arthroplasty.

A retrospective review was performed of patients undergoing primary total knee arthroplasty from 2003 to 2014 in a single practice database. Patients were separated into "thin" and "thick" polyethylene groups based on manufacturer polyethylene bearing sizes of 14 mm or less compared to those greater than 14 mm, respectively. Patient clinical outcomes, need for revision surgery, and overall implant survival rates were evaluated.

A total of 6698 primary knee arthroplasties were included, and a thin bearing was used in 96.5% of these cases. Preoperatively, patients with a thick bearing had significantly lower Knee Society clinical scores (P < .01), a trend toward lower functional scores (P = .06), and more significant coronal plane deformity. Postoperatively, patients with thick bearings exhibited better Knee Society clinical and pain scores as well as similar functional scores and University of California at Los Angeles activity scores. The overall reoperation rate and 10-year survivorship free of revision were similar between thick and thin bearings (1.7% vs 2.3%; 98.2% vs 96.1%). Patients with thin bearings were twice as likely to require a manipulation under anesthesia postoperatively (P = .02), while there were no failures in the thick bearing group due to aseptic loosening or instability.

Patients with thick polyethylene bearings performed similarly or better in multiple clinical outcomes and survivorship compared to those with thin bearings.