Mechanical Properties, Oxidation, and Clinical Performance of Retrieved Highly Cross-Linked Crossfire Liners After Intermediate-Term Implantation

Abstract

Sixty Crossfire (Stryker Orthopaedics, Mahwah, NJ) liners were consecutively revised after an average of 2.9 years (range: 0.01 – 8.0 years) for reasons unrelated to wear or mechanical performance of the polyethylene. Femoral head penetration was measured directly from 42 retrievals implanted for over 1 year. Penetration rate results (0.04 mm/y, on average; range: 0.00-0.13 mm/y) confirmed decreasing wear rates with longer in vivo times. Overall, we observed oxidation levels at the bearing surface of the 60 liners (0.5, on average; range: 0.1-1.7) comparable to those of non-implanted liners (0.5, on average; range: 0.3-1.1) and preservation of mechanical properties. We also measured elevated oxidation of the rim (3.4, on average; range: 0.2-8.8) that was correlated with implantation time. Rim surface damage, however, was observed in only 3/60 (5%) cases. Retrieval analysis of the three rim-damaged liners did not reveal an association between surface damage and the reasons for revision.

Do First-generation Highly Crosslinked Polyethylenes Oxidize In Vivo?

“…Previous studies have reported lower oxidation of the bearing surface for annealed and gamma inert sterilized highly crosslinked liners [7,18] as compared with the rim and may explain the general preservation of wear properties seen in clinical studies [9,18,28]. However, in the case of a malfunctioning hip such as chronic instability with dislocation, rim oxidation may contribute to localized delamination or rim fracture [18]. Previous studies of remelted liners, including shortterm retrievals, demonstrated low levels of oxidation [5,30].…”

“…Many clinical studies of firstgeneration highly crosslinked polyethylenes have reported superior wear performance of both annealed and remelted materials in the first decade of use [4, 9-14, 16, 24, 28] when compared with controls. Comparatively few studies have explored their long-term oxidative stability in vivo [8,18,20,30].…”

“…For annealed and gamma inert sterilized highly crosslinked components, in vivo oxidation occurs preferentially at the rim of the liner, which has the greatest exposure to oxygen-containing body fluids and tissues [17]. Previous studies have reported lower oxidation of the bearing surface for annealed and gamma inert sterilized highly crosslinked liners [7,18] as compared with the rim and may explain the general preservation of wear properties seen in clinical studies [9,18,28]. However, in the case of a malfunctioning hip such as chronic instability with dislocation, rim oxidation may contribute to localized delamination or rim fracture [18].…”

Vitamin E diffused, highly crosslinked UHMWPE: a review

“…The free radicals were reduced by annealing but this implant was also terminally gamma sterilised, which introduced additional free radicals. In the long-term, there was significant oxidation in irradiated and annealed UHMWPE in vivo [21,35,72]. Despite this at intermediate follow-up (up to eight years), the penetration rates of highly crosslinked annealed UHMWPE are less than those for conventional UHMWPE [43,64], and the clinical effects of this elevated oxidation have yet to manifest themselves [35].…”

“…In the long-term, there was significant oxidation in irradiated and annealed UHMWPE in vivo [21,35,72]. Despite this at intermediate follow-up (up to eight years), the penetration rates of highly crosslinked annealed UHMWPE are less than those for conventional UHMWPE [43,64], and the clinical effects of this elevated oxidation have yet to manifest themselves [35]. One study showed fatigue damage at the oxidised rim of explanted irradiated and annealed UHMWPE acetabular liners although none were revised due to rim damage [21].…”