Knee Wear Measured in Retrievals: A Polished Tray Reduces Insert Wear
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Polyethylene wear is often cited as the cause of failure of TKA. Rotating platform (RP) knees show notable surface damage on the rotating surface raising concerns about increased wear compared to fixed bearing inserts.
We therefore addressed the following questions: Is wear in RP inserts increased compared to that in fixed bearing inserts? Does the surface roughness of the tibial tray have a measurable impact on in vivo wear of modular knees? And does wear rate differ between posterior stabilized (PS) and cruciate retaining (CR) knees?
We compared wear in two series of retrieved knee devices: 94 RP mobile bearings with polished cobalt-chrome (CoCr) trays and 218 fixed bearings with both rough titanium (Ti) and polished CoCr trays. Minimum implantation time was 0.4 months (median, 36 months; range, 0.4–124 months) and 2 months (median, 72 months; range, 2–179 months) for the RP and fixed bearing series, respectively.
Wear rate was lower for RP inserts than for fixed bearing inserts. Backside wear rate was lower for fixed bearing inserts mated to polished CoCr trays than for inserts from rough Ti trays. Inserts against polished trays (RP or fixed bearing) showed no increase in wear rate increase over time. Wear rate of PS knees was similar to that of CR knees.
We found mobile bearing knees have reduced wear rate compared to fixed bearings, likely due to the polished CoCr tibial tray surface. Fixed bearing inserts in polished CoCr trays wear less than their counterparts in rough Ti trays, and the wear rate of inserts from polished CoCr trays does not appear to increase with time.
The authors thank the surgeons who have collaborated with our institutions by sending retrieved devices for analysis. We also thank DePuy Orthopaedics, Inc, for providing the design and manufacturing data for the implants studied in this investigation, without which this type of clinical retrieval analysis is not possible.
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