Dissociation of polyethylene insert from the tibial baseplate following revision total knee arthroplasty.

Dissociation of a modular tibial insert from the metal baseplate is a rare complication after revision total knee arthroplasty. We herein report an unusual presentation of a polyethylene insert failure that occurred in a posterior-stabilized constrained total knee arthroplasty. The polyethylene insert was posteriorly displaced, which has never been reported in the literature. The assumed mechanism is disengagement of the locking screw after repetitive motion. During knee full extension while standing from a chair, a sudden downward force on the anterior half of the insert caused posterior lift-off of the insert from the tibial baseplate and promoted a sliding force to push the insert posterior when the locking mechanism failed. This unique complication in a fully constrained posterior-stabilized implant should be considered as a cause for implant failure.