Crack Initiation in Retrieved Cross-Linked Highly Cross-Linked Ultrahigh-Molecular-Weight Polyethylene Acetabular Liners

Background Radiation-crosslinked UHMWPE has been used for joint implants since the 1990s. Postirradiation remelting enhances oxidative stability, but with some loss in strength and toughness. Vitamin E-stabilized crosslinked UHMWPE has shown improved strength and stability as compared with irradiated and remelted UHMWPE. With more active phenolic hydroxyl groups, natural polyphenols are widely used in the food and pharmaceutical industries as potent stabilizers and could be useful for oxidative stability in crosslinked UHMWPE. Questions/purposes We asked whether UHMWPE blended with polyphenols would (1) show higher oxidation resistance after radiation crosslinking; (2) preserve the mechanical properties of UHMWPE after accelerated aging; and (3) alter the wear resistance of radiation-crosslinked UHMWPE. Methods The polyphenols, gallic acid and dodecyl gallate, were blended with medical-grade UHMWPE followed by consolidation and electron beam irradiation at 100 kGy. Radiation-crosslinked virgin and vitamin E-blended UHMWPEs were used as reference materials. The UHMWPEs were aged at 120°C in air with oxidation levels analyzed by infrared spectroscopy. Tensile (n = 5 per group) and impact (n = 3 per group) properties before and after aging as per ASTM F2003 were evaluated. The wear rates were examined by pin-on-disc testing (n = 3 per group). The data were reported as mean ± SDs. Statistical analysis was performed by using Student's t-test for a two-tailed distribution with unequal variance for tensile and impact data obtained with n C 3. A significant difference is defined with p \ 0.05. Results The oxidation induction time of 100 kGy UHMWPE was prolonged to 144 hours with 0.05 wt% dodecyl gallate and 192 hours with 0.05 wt% gallic acid compared with 48 hours for 0.05 wt% vitamin E-blended UHMWPE. Accelerated aging of these polyphenol-blended UHMWPEs resulted in ultimate tensile strength of 50.4 ± 1.4 MPa and impact strength of 53 ± 5 kJ/m 2 for 100 kGy-irradiated UHMWPE with 0.05 wt% dodecyl gallate, for example, in comparison to 51.2 ± 0.7 MPa (p = 0.75) and 58 ± 5 kJ/m 2 (p = 0.29) before aging. The pin-on-disc wear rates of 100 kGy-irradiated UHMWPE with 0.05 wt% dodecyl gallate and 0.05 wt% gallic acid were 2.29 ± 0.31 and 1.65 ± 0.32 mg/million cycles, comparable to 1.68 ± 0.25 and 2.05 ± 0.22 mg/million cycles for 100 kGy-irradiated virgin and 0.05 wt% vitamin E-blended UHMWPE. Conclusions Based on the sample numbers tested in this study, polyphenols appear to effectively enhance the oxidation stability without altering the mechanical properties or pin-on-disc wear rate of radiation-crosslinked UHMWPE. Clinical Relevance Crosslinked UHMWPE with natural polyphenols with improved oxidative stability and low wear may find clinical application in joint implants.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Natural Polyphenols Enhance Stability of Crosslinked UHMWPE for Joint Implants

Shen

Gao

Liu

2015

“…Although polyethylene wear and aseptic loosening were important reasons for failure of CPE inserts, these were not seen with the XLPE inserts (Table 2). We found no evidence of an increased propensity for rim fracturing or cracking with the XLPE liners, which has been reported in some previous studies [16,17,35]. We also specifically evaluated the damage scores in the peripheral zone of the liner that contacts with the locking mechanism in the shell.…”

Section: Discussionmentioning

confidence: 52%

Backside Wear Is Not Dependent on the Acetabular Socket Design in Crosslinked Polyethylene Liners

Bali

McCalden

Naudie

et al. 2016

Background Although it is understood that backside damage occurs in polyethylene acetabular liners, the effect of highly crosslinked polyethylene, which has completely replaced conventional polyethylene, has yet to be examined. Questions/purposes The purpose of this study was to answer the following questions: (1) With conventional polyethylene (CPE), did the acetabular design make a difference in backside wear? (2) Is there a difference in backside damage between CPE and crosslinked polyethylene (XLPE) liners? (3) With XLPE, is the difference in backside wear between designs still present? (4) Is there any difference in backside damage in various zones on backside of individual liners? Methods This single-institution retrieval analysis involved visual damage scoring on the backside of 233 polyethylene liners implanted between 2002 and 2011. The liners were retrieved from either polished/dovetail cups (PD) or roughened/wire cups (RW) made by two different manufacturers. The inserts were divided into four groups: PD-CPE (n = 105), PD-XLPE (n = 16), RW-CPE (n = 99), and RW-XLPE (n = 13). Aseptic loosening and polyethylene wear were the predominant reasons for revision of CPE liners, whereas instability and infection were the common reasons for revision of XLPE liners. The time in situ (TIS) was shorter for the XLPE liners as compared with the CPE liners (PD-CPE: 8.5 years [SD 4.4]; ; ; ). The backside of each liner was divided into five zones and graded initially from a scale of 0 to 3 for seven different damage modes by one observer. There was substantial interobserver (kappa 0.769) and intraobserver (0.736) reliability on repeat scoring. To compare the effects of crosslinking, a subset of the conventional polyethylene liners was matched to the crosslinked liners based on TIS,

“…While reports of clinical fracture or crack-related failures remain rare for crosslinked UHMWPE implants, clinically retrieved components have been reported involving catastrophically fractured bearings [4,15], intact components containing initiated subcritical cracks [6], and bearing surfaces exhibiting extensive apparently brittle surface cracking [5]. Crosslinked formulations of UHMWPE provide an excellent wear-resistant bearing surface in total joint arthroplasty, but the long-term resistance to crack-related damage phenomena in these materials is unclear.…”

Section: Introductionmentioning

confidence: 99%

“…A relative decrease in K incep generally shifts the stable crack propagation uniformly to lower values of stress intensity [3,8,12], and such a shift is known to accompany crosslinking in UHMWPE [3,8,12]. The reduced toughness and crack propagation resistance of crosslinked formulations of UHMWPE are of interest for clinical applications, particularly in light of recently reported cases of brittle damage or catastrophic fracture of highly crosslinked THA bearings [4][5][6]15].…”

Section: Introductionmentioning

confidence: 99%

Crack Propagation Resistance Is Similar Under Static and Cyclic Loading in Crosslinked UHMWPE: A Pilot Study

Furmanski

Rimnac

2011

Self Cite

Background Recent work suggests crack phenomena (eg, crack initiation and propagation) in UHMWPE do not depend on cyclic damage mechanisms. Materials for which crack phenomena occur in static (noncyclic) mode should exhibit similar crack propagation behavior under static and cyclic loading conditions. Questions/purposes Do cracks in UHMWPE stably propagate from acute notches under static loading with a velocity dependent on crosslink density? Are materialranking evaluations for crack propagation resistance similar under static and cyclic loading conditions? Does time to failure for a notched specimen under static loads yield the same material rankings as crack propagation data? Methods Notched compact tension specimens were machined from UHMWPE gamma-irradiated with a 0-, 50-, 75-, or 100-kGy dose and subsequently remelted. Static loads were applied until failure occurred or 2 weeks had elapsed. Crack propagation rates and time to failure were recorded and compared to data from cyclic experiments. Results Static and cyclic loading both produced stable crack propagation and similar performance rankings of material groups, except in the case of the unirradiated material, which did not fail under static loads. Normalized measures of crack propagation velocities generally showed quantitative agreement between the two methods. Normalized time to failure under static loading also agreed well with crack propagation velocity. Conclusions Crack propagation under static loading produced qualitatively and quantitatively similar performance results as those under cyclic loading. Time to failure under static loads corresponded closely with the crack propagation velocity and may itself be a robust metric of crack propagation resistance. Clinical Relevance Total joint arthroplasties may experience superficial cracking in the UHMWPE bearing surface or catastrophic fracture. Quantifying resistance to crack phenomena in UHWMPE is important to design engineers and to clinicians using crosslinked UHMWPE materials under challenging mechanical conditions.