Backside wear in total knee replacement: A new quantitative measurement method and a comparison of polished cobalt-chromium tibial trays with titanium tibial trays

Abstract In modular total knee replacements, polyethylene backside wear can occur due to micro-motion between the tibial tray and polyethylene insert. Tibial trays manufactured from a cobalt-chromium alloy with highly polished surfaces are increasingly used to prevent backside wear. However, there is no quantitative evidence for this supposed wear advantage because previous evaluations only considered the subjective assessment of surface damage and changes without any information about the characteristics of the generated wear products. The validity about a true wear in the form of material removal is often missing. Therefore, this study used a new method to quantitatively investigate the possible wear advantage of polished cobalt-chromium tibial trays. Total knee replacements with titanium and polished cobalt-chromium tibial trays (SIGMA® DePuy Synthes & Johnson&Johnson, USA) were tested in a physiological knee wear simulator according to ISO-14243-1 for 3 x 106 cycles. The articulation side was hermetically separated from the backside of the insert. The serum was analyzed separately by particle analysis according to ASTM-F1877. With polished cobalt-chromium tibial trays, significantly (p = 0.003) less backside wear particles was generated. The backside wear particles differ significantly in size and morphology from the articulating particles. In this study, backside wear was measured quantitatively and its wear particles were characterized for the first time. We demonstrated that even with modern inlay locking mechanisms and polished surfaces, wear particles on the backside can account for 15–33% of total wear. With polished cobalt-chromium trays, significantly less backside wear particles was generated. [Display omitted] •New method to isolate polyethylene backside wear particles from articulated wear.•Quantitative measurement and characterization of polyethylene backside wear particles.•Unexpectedly high proportion of backside wear relative to total wear.•The backside wear particles are smaller than the articulating wear particles.