Distinctive Polyethylene Damage in Rotating-Platform Total Knee Arthroplasty: A Comparative Retrieval Study in Patients Revised With Clinical Instability

Abstract

Background

Biomechanical studies suggest mobile-bearing rotating-platform total knee arthroplasty (TKA-RP) has limited tolerance of asymmetric flexion gaps, and improper balancing may result in polyethylene insert instability. We sought to identify a distinctive pattern of polyethylene insert damage associated with clinical failure of TKA-RP.

Methods

There were nine patients who had an index TKA-RP and underwent a revision for symptomatic flexion instability (clinical cohort) from 2013 to 2019. There were 30 TKA-RPs (registry cohort) that were randomly selected from an all-cause revision retrieval database with archived clinical and demographic data. Based on prior biomechanical testing, we hypothesized a distinctive pattern of polyethylene damage would occur on the postero-lateral articular surface with dynamic instability. Polyethylene inserts were inspected by three experienced reviewers using the modified Hood method and categorized according to clinical instability and damage pattern. Each registry implant was dichotomized with damage either consistent or not, with that observed in the clinical cohort.

Results

Of the nine, seven clinical cohort inserts exhibited a consistent pattern of polyethylene damage on the postero-lateral articular surface, ranging from localized loss of machine lines on the insert margin to gross deformation of the articular surface lip with loss of peripheral wall contour. In five of these seven knees, both components were secure at revision. Of the 30 registry cohort patients, nine reported mechanical symptoms of clinical instability. There were eight inserts that exhibited a polyethylene damage pattern similar to that observed in the “clinical cohort”; only two knees had both components secure at revision.

Conclusions

The majority (15 of 18) of retrieved TKA-RP inserts associated with clinical instability exhibited a distinctive pattern of postero-lateral articular surface polyethylene damage, suggesting posterior condyle subluxation over the peripheral insert wall as predicted by cadaveric testing. Concomitant aseptic loosening did not preclude this hallmark damage pattern.

Level of evidence

Level IV.