Surface analysis of retrieved bilateral UHMWPE tibial inserts under varus malalignment condition

Abstract

Failure analysis on a retrieved ultra-high molecular weight (UHMWPE) knee tibial inserts of bilateral total knee replacement (TKR) was performed due to aseptic loosening detected after 16 years (left) and 12 years (right) in vivo services. Despite long implantation time, the effect of varus malalignment present on a 71 years old female patient (body mass index, 35.1) with a non-active lifestyle will be considered as a factor towards the TKR failure. We, therefore, determined whether implant malalignment was associated with increased surface damages in both retrieved tibial inserts. Surface damage morphology was assessed using a 3D laser microscope and Scanning Electron Microscope (SEM). ATR-Fourier Transform Infra-Red (ATR-FTIR), Differential Scanning Calorimetry (DSC) and Gel-Permeation Chromatography (GPC) were used to measure changes of chemical and physical properties of retrieved inserts. Results show left-16 years insert possesses more severe wear degradation (crater and cracks) compare to wear on right-12 years insert (delamination, multidirectional scratches, and ripple). The surface roughness on the medial compartment seems to be higher than the lateral side for both inserts which can be affected by uneven load distribution contribute by the varus deformity. Higher crystallinity of left-16 years insert (66.99%) compare to right-12 years insert (56.52%) were an indicator of major mechanical changes happen on left insert which was contributed by oxidation with respect to implantation time of both inserts. Our findings revealed that in vivo oxidation is a main contributing factor to the failure of implants, but not varus malalignment. The material properties in the oxidized layer are significantly altered, including a very substantial reduction in molecular weight displayed by both inserts.