Abstract
Introduction
The purpose of this multicenter study was to assess the oxidative stability, mechanical behavior, wear and reasons for revision of 2nd generation sequentially annealed HXLPE, X3, and compare it to 1st generation XLPE, Crossfire. We hypothesized that X3 would exhibit similar wear rates but lower oxidation than Crossfire.
Methods
182 hip liners were consecutively retrieved during revision surgeries at 7 surgical centers and continuously analyzed over the past 12 years in a prospective, multicenter study. 90 were highly crosslinked and annealed (Crossfire; Implanted 4.2±3.4 years, max: 11 years), and 92 were highly crosslinked and annealed in 3 sequential steps (X3; Implanted 1.2±1.5 years; max: 5 years). Oxidation was characterized in accordance with ASTM 2102 using transmission FTIR performed on thin sections (∼200μm) from the superior/inferior axis. Mechanical behavior was assessed via the small punch test (ASTM 2183).
Results
The liners were revised predominantly for loosening, instability, and infection. No differences were detected in linear penetration rates rates between the X3 and Crossfire liners (p=0.40), independent of head size. Oxidation was comparable between the Crossfire and X3 cohorts at the bearing surface, backside, and locking mechanism (p>0.05). At the rim, X3 liners exhibited lower oxidation than Crossfire (p<0.001). Ultimate strength of the HLXPE was not significantly different between X3 and Crossfire (p=0.996).
Discussion
This ongoing study continues to evaluate the polyethylene properties and reasons for revision among clinically relevant HXLPEs used in total hip replacement. Both Crossfire retrievals, implanted for up to 11 years, and X3 retrievals, implanted up to 5 years, have thus far proven effective at reducing wear rates. Mechanical behavior oxidative stability has been preserved at the bearing surface of the retrievals for both materials. The oxidative stability of Crossfire and X3 at the rim face of the liners, however, is formulation dependent. With respect to oxidation, it is clear that sequential annealing reduced rim oxidation when compared with first-generation annealing.
