“Backside” polyethylene deformation in total knee arthroplasty

The clinical importance of polyethylene deformation between the tibial insert and base plate (“backside”) is unclear. We used a semiquantitative scoring system to compare clinical and radiographic factors with articular and backside deformation of 106 retrieved polyethylene tibial inserts. Backside deformation was associated with polyethylene thickness and type of locking mechanism. Deformation of the articular surface correlated with femoral osteolysis (P=.05). The mean backside deformation score was 33% greater for implants from patients with osteolysis than for implants from patients without osteolysis (P=.07). Our study may be biased based on the types of implants available for study, but for this group of implants, we cannot conclude with 95% certainty that backside polyethylene deformation was clinically important as a cause of periprosthetic osteolysis or implant loosening.