Is Wear Still a Concern in Total Knee Arthroplasty With Contemporary Conventional and Highly Crosslinked Polyethylene Tibial Inserts in the mid- to Long-Term?

Abstract

Background: Modern literature has brought into question if wear of tibial inserts made from conventional or highly crosslinked polyethylene (HXL PE) is still a factor limiting longevity of total knee arthroplasty (TKA) in the mid- to long-term. It is the objective of this study to determine: 1) most common causes of mid- to long-term TKA failure, 2) the prevalence of delamination, and 3) the medial/lateral linear wear rates of conventional and HXL PE tibial inserts retrieved in the mid- to long-term.

Methods: A tibial insert retrieval cohort of 107 inserts (79 conventional, 28 HXL PE) with a minimum time in situ of 6.5 years (mean 11.7 ± 4) was studied. Failure causes were determined from chart-review, delamination presence was assessed microscopically, and medial/lateral linear wear was determined by minimal thickness changes measured with a dial-indicator.

Results: The most common mid-to long-term etiologies for failure were instability (44.9%), PE wear 15%), aseptic loosening (14%), and infection (13.1%). Delamination occurred in 70% of inserts (72.1% conventional, 64.3% HXLPE). Gross material loss due to delamination appeared to be the underlying reason for at least 33.3% of cases exhibiting instability. Of the cases removed for infection, 75% exhibited no histopathological hallmarks of acute infection. The medial/lateral wear rates were 0.054/0.051 (conventional) and 0.014/0.011 (HXL) mm/y, respectively.

Conclusions: Polyethylene wear still appears to be a major primary and secondary cause for TKA revision in the mid- to long-term. Wear may manifest as destabilizing delamination or as continuous release of fine wear particles potentially resulting in inflammatory responses and subsequent failure.

Keywords: Delamination; Highly crosslinked; Polyethylene; Tibial inserts; Total knee arthroplasty; Wear.

Figure 1

Photographs illustrating characteristic features of various degrees of delamination: (a) The PE bearing surface exhibits characteristic wear features such as polishing, scratches, striated patterns, and pitting; however, no delamination was noted. (b) Subsurface cracks can be seen on the bearing surface characterized by a ‘milky’ surface appearance, but there is no significant material loss. (c) Gross material loss associated with delamination on the bearing surface. Note that delamination scores 1 and 2 can vary in the number of affected locations and overall area.

Figure 2

Measuring rig used for thickness change evaluation as a proxy measure for linear wear.

Figure 3

Illustration of the main reason for mid- to long-term failures associated with this tibial insert cohort and breakdown by type of polyethylene.

Figure 4

Distribution of delamination for tibial inserts grouped by the major reasons for failure in this cohort.

Figure 5

Scatter plots illustrating linear wear over time in situ on the (a) medial and (b) lateral side.