Majority of ultra-high molecular weight polyethylene (UHMWPE) medical devices used in total joint arthroplasty are crosslinked using gamma radiation to improve wear resistance. Alternative methods of crosslinking are urgently needed to replace gamma radiation due to rapid decline in its supply. Peroxide crosslinking is a candidate method with widespread industrial applications. Oxidative stability and biocompatibility, which are critical requirements for medical device applications, can be achieved using vitamin-E as an additive and by removing peroxide by-products through high temperature melting, respectively. We investigated compression molded UHMWPE/vitamin-E/di-cumyl peroxide blends followed by high-temperature melting in inert gas as a material candidate for tibial knee inserts. Wear resistance increased and mechanical properties remained largely unchanged. Oxidation induction time was higher than most of the other clinically available formulations. The material passed the local-end point biocompatibility tests per ISO 10993. Compounds found in exhaustive extraction were of no concern with margin-of-safety values well above the accepted level, indicating a desirable toxicological risk profile. Peroxide crosslinked, vitamin-E stabilized, and high temperature melted UHMWPE has recently been cleared for clinical use in tibial knee inserts. With all the salient characteristics needed in a material that can provide superior long-term performance in total joint patients, peroxide crosslinking can replace gamma radiation crosslinking of UHMWPE for use in all total joint replacement implant including acetabular liners

The April 2023 Hip & Pelvis Roundup³⁶⁰ looks at: Do technical errors determine outcomes of operatively managed femoral neck fractures in younger adults?; Single-stage or two-stage revision for hip prosthetic joint infection (INFORM); Fixation better than revision in type B periprosthetic fractures of taper slip stems; Can you maximize femoral head size at the expense of liner thickness?; Plasma D-dimer for periprosthetic joint infection?; How important is in vivo oxidation?; Total hip arthroplasty for HIV patients with osteonecrosis.

HXLPE acetabular liners were introduced to reduce wear-related complications in THA. However, post-irradiation thermal free radical stabilization can compromise mechanical properties, leave oxidation-prone residual free radicals, or both. Reports of mechanical failure of HXLPE acetabular liner rims raise concerns about thermal free radical stabilization and in vivo oxidization on implant properties. The purpose of this study is to explore the differences in the mechanical, physical and chemical properties of HXLPE acetabular liner rims after extended time in vivo between liners manufactured with different thermal free radical stabilization techniques. Remelted, single annealed and sequentially annealed retrieved HXLPE acetabular liners with in vivo times greater than 4.5 years were obtained from our implant retrieval laboratory. All retrieved liners underwent an identical sanitation and storage protocol. For mechanical testing, a total of 55 explants and 13 control liners were tested. Explant in vivo time ranged from 4.6 – 14 years and ex vivo time ranged from 0 – 11.6 years. Rim mechanical properties were tested by microindentation hardness testing using a Micromet II Vickers microhardness tester following ASTM standards. A subset of 16 explants with ex vivo time under one year along with five control liners were assessed for oxidation by FTIR, crystallinity by Raman spectroscopy, and evidence of microcracking by SEM. No significant difference in in vivo or ex vivo was found between thermal stabilization groups in either set of explants studied. In the mechanically tested explants, there was no significant correlation between in vivo time and Vickers hardness in any thermal stabilization group. A significant correlation was found between ex vivo time and hardness in remelted liners (r=.520, p = .011), but not in either annealed cohort. ANCOVA with ex vivo time as a covariate found a significant difference in hardness between the thermal free radical stabilization groups (p 0.1) was found in retrieved remelted (25%), single annealed (100%) and sequentially annealed (75%) liner rims. Crystallinity was increased in the subsurface region relative to control liners for both annealed, but not remelted, liner rims. Hardness was increased in oxidized rims for both annealed cohorts but not in the remelted cohort. Microcracking was only found along the surface of one unoxidized remelted liner rim. Mechanical properties were reduced at baseline and worsened after in vivo time for remelted HXLPE liner rims. Rim oxidation was detected in all groups. Oxidation was associated with increased crystallinity and hardness in annealed cohorts, but not remelted liners. Increased crystallinity and oxidation do not appear to be directly causing the worsened mechanical behavior of remelted HXLPE liner rims after extended in vivo time

Introduction. HXLPE acetabular liners were introduced to reduce wear-related complications in THA. However, post-irradiation thermal free radical stabilization can compromise mechanical properties, leave oxidation-prone residual free radicals, or both. Reports of mechanical failure of HXLPE acetabular liner rims raise concerns about thermal free radical stabilization and in vivo oxidization on implant properties. The purpose of this study is to explore the differences in the mechanical, physical and chemical properties of HXLPE acetabular liner rims after extended time in vivo between liners manufactured with different thermal free radical stabilization techniques. Material and Methods. Remelted, single annealed and sequentially annealed retrieved HXLPE acetabular liners with in vivo times greater than 4.5 years were obtained from our implant retrieval laboratory. All retrieved liners underwent an identical sanitation and storage protocol. For mechanical testing, a total of 55 explants and 13 control liners were tested. Explant in vivo time ranged from 4.6 – 14.0 years and ex vivo time ranged from 0 – 11.6 years. Rim mechanical properties were tested by microindentation hardness testing using a Micromet II Vickers microhardness tester following ASTM standards. A subset of 16 explants with ex vivo time under one year along with five control liners were assessed for oxidation by FTIR, crystallinity by Raman spectroscopy, and evidence of microcracking by SEM. Results. No significant difference in in vivo or ex vivo time was found between thermal stabilization groups in either set of explants studied. In the mechanically tested explants, there was no significant correlation between in vivo time and Vickers hardness in any thermal stabilization group. A significant correlation was found between ex vivo time and hardness in remelted liners (r=.520, p=.011), but not in either annealed cohort. ANCOVA with ex vivo time as a covariate found a significant difference in hardness between the thermal free radical stabilization groups (p<.0005, η. 2. = 0.322). Post hoc analysis revealed hardness was significantly lower in the retrieved remelted group compared to both the single annealed (p=.001) and sequentially annealed (p<.0005) cohorts. Hardness was significantly higher in the retrieved remelted liners compared to controls (p=.007), with no different in either annealed cohort. Detectable subsurface oxidation (OI > 0.1) was found in retrieved remelted (25%), single annealed (100%) and sequentially annealed (75%) liner rims. Crystallinity was increased in the subsurface region relative to control liners for both annealed, but not remelted, liner rims. Hardness was increased in oxidized rims for both annealed cohorts but not in the remelted cohort. Microcracking was only found along the surface of one unoxidized remelted liner rim. Conclusion. Mechanical properties were reduced at baseline and worsened after in vivo time for remelted HXLPE liner rims. Rim oxidation was detected in all groups. Oxidation was associated with increased crystallinity and hardness in annealed cohorts, but not remelted liners. Increased crystallinity and oxidation do not appear to be directly causing the worsened mechanical behavior of remelted HXLPE liner rims after extended in vivo time. For any figures or tables, please contact authors directly

Alpha Lipoic Acid (L.A.) is an effective natural antioxidant discovered in the human body in 1951 from L.J. Reed and I.C. Gunslaus from liver. It is inside broccoli, spinach and red meats, especially liver and spleen. Actually it is largely used as antioxidant in antiaging products according to the low toxicity level of the product. The present study take into consideration the possibility to reduce oxidation of medical irradiated UHMWPE GUR 1050, mixing together polyethylene powder and Alpha Lipoic Acid powder. The study is composed of two parts. Part 1 Thermostability of alpha lipoic acid during polyethylene fusion Part 2 detection of oxygen level in artificially aged irradiated polyethylene. Solid pieces were made with Gur 1050 powder (Ticona Inc., Bayport, Tex, USA) and mixed with Alpha Lipoic Acid (Talamonti, Italy, Stock 1050919074) 0,1%-­‐0,3%-­‐0,5%-­‐1%-­‐2% and gamma ray irradiated with 30 kGy (Isomedix, Northborough, MA). An owen (80° Celsius) was used to produce an aging effect for 35 days in the doped and control samples (Conventional not doped polyethylene). This process simulate an aging effect of 10 years into the human body. Part 1 : THERMAL STABILITY : a Fourier Transfer Infra Red (FTIR) test was made in pieces molded in a cell at 150° and 200°Celsius and pressure of 200 MPa comparing to the UHMWPE powder mixed with alpha lipoic acid. The presence of Alpha Lipoic Acid in the polyethylene was found at any depth in the manufacts. Part 2 : OXIDATION OF THE SURFACE : After 5 weeks at 80° Celsius in a owen (ASTM standard F-­‐2003-­‐02)A FOURIER TRANSFER INFRA RED TEST (FTIR) was made in the superficial layer and deeper on the undersurface of doped 0,1% and conventional UHMWPE. The antioxidation limit is defined as the ratio of the area under 1740cm/−­‐1 carbonyl and 1370 cm/−­‐1 Methylene absorbance peaks. In conventional UHMWPE oxidation is detected on the surface and decreases in the deeper layers down to zero under 1500 Micron. In the doped UHMWPE, FTIR demonstrate a very low oxidation limit on the surface and at any depth, comparing to conventional UHMWPE. The examples show that Lipoic Acid is effective as antioxidant in irradiated UHMWPE and it is stable with respect to thermal treatment. For any figures or tables, please contact authors directly

Introduction. In vivo, UHMWPE bearing surfaces are subject to wear and oxidation that can lead to bearing fatigue or fracture. A prior study in our laboratory of early antioxidant (AO) polyethylene retrievals, compared to gamma-sterilized and highly cross-linked (HXL) retrievals, showed them to be more effective at preventing in vivo oxidation. The current analysis expands that early study, addressing the effect of:. manufacturing-variables on as-manufactured UHMWPE;. in vivo time on these initial properties;. identifying important factors in selecting UHMWPE for the hip or knee. Methods. After our prior report, our IRB-approved retrieval laboratory received an additional 96 consecutive AO-retrievals (19 hips, 77 knees: in vivo time 0–6.7 years) of three currently-marketed AO-polyethylenes. These retrievals represented two different antioxidants (Vitamin E and Covernox) and two different delivery methods: blending-prior-to and diffusing-after irradiation cross-linking. Consecutive HXL acetabular and tibial inserts, received at retrieval, with in vivo time of 0–6.7 years (260 remelted, 170 annealed) were used for comparison with AO-retrievals. All retrievals were analyzed for oxidation and trans-vinylene index (TVI) using a Thermo-Scientific iN10 FTIR microscope. Mechanical properties were evaluated for 35 tibial inserts by uniaxial tensile testing using an INSTRON load frame. Cross-link density (n=289) was measured using a previously published gravimetric gel swell technique. Oxidation was reported as maximum ketone oxidation index (KOI) measured for each bearing. TVI was reported as the average of all scans for each material. Cross-link density and mechanical properties were evaluated as a function of both TVI and oxidation. Results. Minimal increase in oxidation was seen in these AO-retrievals, out to almost 7 years in vivo. In contrast, HXL-retrievals showed increasing KOI with time in vivo (annealed-HXL = 0.127/year, remelted-HXL = 0.036/year, p<0.001). HXL oxidation rate was higher in knees (0.091/year) than in hips (0.048/year), p<0.001. Cross-link density (XLD) correlated positively with TVI for both HXL (Pearson's correlation=0.591, p<0.001) and AO (Pearson's correlation=0.598, p<0.001) retrievals. AO-materials had higher TVI for the same or similar XLD than did HXL polyethylene. XLD correlated negatively with KOI for HXL retrievals (Pearson's correlation=−0.447, p<0.001). Mechanical properties varied by material across all materials evaluated, with tensile toughness correlating negatively with increasing TVI (Pearson Correlation=−0.795, p<0.001). Discussion. Irradiation cross-linking has been used effectively to improve wear resistance. Residual free radicals from irradiation are the target of AO-polyethylene, to prevent loss of UHMWPE XLD, resulting from in vivo oxidation of free radicals as seen in HXL retrievals, and toughness, resulting from oxidation or initial remelting. Despite different manufacturing variables, AO-polyethylene retrievals in this cohort had minimal oxidation and no change in XLD or toughness due to oxidation. However, toughness did vary with irradiation dose as did cross-link density. To achieve the same level of cross-linking as HXL-polyethylene required a higher irradiation dose in blended AO-polyethylene. AO-polyethylenes evaluated in this study had toughness that decreased with irradiation dose, but avoided loss of toughness due to remelting. Because AO-polyethylenes did not oxidize, they did not show the decrease of cross-link density, and potential loss of wear resistance, seen in HXL-polyethylene. For any figures or tables, please contact authors directly

Aims

The aim of this study was to identify the effect of the manufacturing characteristics of polyethylene acetabular liners on the survival of cementless and hybrid total hip arthroplasty (THA).

Introduction. HXLPE acetabular liners were introduced to reduce wear-related complications in THA. However, post-irradiation thermal free radical stabilization can compromise mechanical properties, leave oxidation-prone residual free radicals, or both. Reports of mechanical failure of HXLPE acetabular liner rims raise concerns about thermal free radical stabilization and in vivo oxidization on implant properties. The purpose of this study is to explore the differences in the mechanical, physical and chemical properties of HXLPE acetabular liner rims after extended time in vivo between liners manufactured with different thermal free radical stabilization techniques. Material and methods. Remelted, single annealed and sequentially annealed retrieved HXLPE acetabular liners with in vivo times greater than 4.5 years were obtained from our implant retrieval laboratory. All retrieved liners underwent an identical sanitation and storage protocol. For mechanical testing, a total of 55 explants and 13 control liners were tested. Explant in vivo time ranged from 4.6 – 14.0 years and ex vivo time ranged from 0 – 11.6 years. Rim mechanical properties were tested by microindentation hardness testing using a Micromet II Vickers microhardness tester following ASTM standards. A subset of 16 explants with ex vivo time under one year along with five control liners were assessed for oxidation by FTIR, crystallinity by Raman spectroscopy, and evidence of microcracking by SEM. Results. No significant difference in in vivo or ex vivo was found between thermal stabilization groups in either set of explants studied. In the mechanically tested explants, there was no significant correlation between in vivo time and Vickers hardness in any thermal stabilization group. A significant correlation was found between ex vivo time and hardness in remelted liners (Δ=.520, p=.011), but not in either annealed cohort. ANCOVA with ex vivo time as a covariate found a significant difference in hardness between the thermal free radical stabilization groups (p<.0005, η. 2. = 0.322). Post hoc analysis revealed hardness was significantly lower in the retrieved remelted group compared to both the single annealed (p=.001) and sequentially annealed (p<.0005) cohorts. Hardness was significantly higher in the retrieved remelted liners compared to controls (p=.007), with no different in either annealed cohort (figure 1). Detectable subsurface oxidation (OI > 0.1) was found in retrieved remelted (25%), single annealed (100%) and sequentially annealed (75%) liner rims (figure 2). Crystallinity was increased in the subsurface region relative to control liners for both annealed, but not remelted, liner rims. Hardness was increased in oxidized rims for both annealed cohorts but not in the remelted cohort. Microcracking was only found along the surface of one unoxidized remelted liner rim. Conclusion. Mechanical properties were reduced at baseline and worsened after in vivo time for remelted HXLPE liner rims. Rim oxidation was detected in all groups. Oxidation was associated with increased crystallinity and hardness in annealed cohorts, but not remelted liners. Increased crystallinity and oxidation do not appear to be directly causing the worsened mechanical behavior of remelted HXLPE liner rims after extended in vivo time. For any tables or figures, please contact the authors directly

Introduction. While advances in joint-replacement technology have made total ankle arthroplasty a viable treatment for end-stage arthritis, revision rates for ankle replacements are higher than in hip or knee replacements [1]. The questions asked in this study were (1) what retrieved ankle devices demonstrate about ankle arthroplasty failures, and (2) how do these failures compare to those seen in the hip and the knee?. Materials and Methods. An IRB-approved retrieval laboratory received retrieved polyethylene inserts and surgeon-supplied reason for revision from 70 total-ankles (7 designs, including five currently-marketed designs) from 2002 to the present. All retrievals were rated for clinical damage. Polyethylene inserts received six months or less after retrieval (n=45) were analyzed for oxidation using Fourier Transform Infrared (FTIR) spectroscopy, reported as maximum ketone oxidation index [2]. Insert sterilization method was verified using trans-vinylene index [3]. Oxidation measured in the 45 ankle inserts versus their time in vivo was compared to oxidation rates previously published for gamma-sterilized hip and knee polyethylene retrievals [6]. Statistical analysis was performed using IBM SPSS v.22. Results. The ankle devices were retrieved most commonly for loosening (n=22) followed by polyethylene fracture (n=9). These failure modes occurred after statistically different in vivo time (loosening: mean=4.4±3.6 years; polyethylene insert fracture: mean=9.5±4.1 years; p=0.002). Presence of clinical fatigue (cracking and/or delamination) was identified in 24 of the 70 retrieved inserts, and its presence correlated with in vivo time (Spearman's rho =0.449, p<0.001). Thirteen of these fatigued inserts were analyzed by FTIR. TVI analysis confirmed the sterilization method of the fatigued inserts: 12 gamma, 1 non-gamma sterilized. All 13 fatigued inserts had maximum ketone oxidation index (KOI) of 1.2 or higher. Presence of fatigue correlated with measured oxidation (Spearman's rho =0.685, p<0.001). Six of the 9 inserts that fractured in vivo were analyzed by FTIR. All were gamma-sterilized, and all had oxidation of 1.2 or higher. Oxidation rate determined for most of the 45 ankle inserts was at or above oxidation rates previously published for gamma-sterilized hip and knee polyethylene retrievals [6]. Discussion. This retrieval study concurs with the ankle arthroplasty literature that loosening is the most common reason for ankle revision [4]. Ankle inserts retrieved as a result of implant loosening had lower oxidation and no fatigue damage resulting from their shorter in vivo time. Fatigued and/or fractured inserts were in vivo for longer times, allowing more oxidation to occur. The effect of oxidation on polyethylene tensile strength and ductility has been reported for tibial inserts [5]. Oxidation above the critical value [5] has a dramatic effect on the ability of the polyethylene to resist fatigue damage and fracture, since the toughness of the polyethylene drops to near zero. All fatigued and fractured ankle inserts had oxidation that exceeded this critical oxidation. Most ankle inserts, whether gamma or non-gamma sterilized, oxidized at or above the oxidation rates previously published for gamma-sterilized hip and knee polyethylene retrievals [6]

Introduction

Cobalt chrome femoral head has been used widely in total hip arthroplasty and has shown favorable outcome. However, there is still of concern of potential metal toxicity from the wear debris. In the other hand, titanium is well known for its biocompatibility but it is not used in bearing surface of arthroplasty due to its brittleness. Recently, coating of the prosthesis using plasma electrolytic oxidation (PEO) has shown favorable surface protection. Thus, in this study, we tried to find out whether the PEO coating on the titanium surface would provide surface protection.

Introduction. Oxidation of ultrahigh molecular weight polyethylene (UHMWPE) can lead to failure of implants used in total joints. Cyclic loading is postulated to be one mechanism of in vivo oxidation in UHMWPE components as one previous study has shown [1]. We developed an accelerated aging test that incorporated compressive cyclic loading that the UHMWPE components would be exposed to in vivo. Surgeons are moving towards larger femoral heads in hip arthroplasty and removing less bone in knee arthroplasty necessitating thinner UHMWPE components. We hypothesized that, in this accelerated aging test, thinner UHMWPE components would be more susceptible to oxidation caused by the cyclic loading due to higher stresses in the material. Materials and Methods. All samples tested in this study were Conventional PE: GUR1050 was machined into test specimens, vacuum packaged and gamma sterilized. Test samples were blocks 100 mm × 89 mm in cross-section with 3 different thicknesses: 1 mm, 3 mm, and 10 mm (n=3 each). Three cylinders were cored out of each test sample to serve as controls (Fig 1a) that were physically separated and thereby isolating the oxidation attributable to an applied compressive cyclic load. The controls were placed back into the holes from where they were cored during testing. Compressive loading was administered by a 12.5 mm diameter applicator affixed to a hydraulic test frame (Fig 1b), and all testing was done at 80°C in air. A sinusoidal compressive cyclic stress between 1 and 10 MPa was applied at 5 Hz for 7 days. Microtomed thin films from all samples were analyzed via Fourier Transform Infrared Spectroscopy (FTIR) to quantify oxidation [2] after testing. Oxidation was measured through the thickness of the sample at targeted points along the length from directly underneath the center of the load applicator to 10mm away (Fig 1a). Oxidation was also measured through the thickness of the cylindrical controls. Results. The oxidation profiles of each sample at 0.0mm (Fig 2a) and 3.0mm (Fig 2b) from the center point of load application showed that as one decreases the thickness of the test sample the oxidation levels of the sample increase. Both locations showed increased oxidation over the control samples. Discussion. Cyclic loading increased the rate of oxidation of gamma sterilized UHMWPE. The oxidation also increased with decreasing thickness of the UHMWPE samples. This oxidation could potentially accelerate the long term oxidative instability and could contribute to the delamination failure of tibial inserts. For figures/tables, please contact authors directly.

Introduction. The optimum UHMWPE orthopaedic implant bearing surface must balance wear, oxidation and fatigue resistance. Antioxidant polyethylene addresses free radicals, resulting from irradiation used in cross-linking, that could oxidize and potentially lead to fatigue damage under cycles of in vivo use. Assessing the effectiveness of antioxidant (AO) polyethylene compared to conventional gamma-sterilized or remelted highly cross-linked (HXL) polyethylene is necessary to set realistic expectations of the service lifetime of AO polyethylene in the knee. This study evaluates what short-term antioxidant UHMWPE retrievals can reveal about: (1) oxidation-resistance, and (2) fatigue-resistance of these new materials. Methods. An IRB-approved retrieval laboratory received 25 AO polyethylene tibial insert retrievals from three manufacturers with in vivo time of 0–3 years. These were compared with 20 conventional gamma-inert sterilized and 30 HXL (65-kGray, remelted) tibial inserts of the same in vivo duration range. The retrievals were. (1) analyzed for oxidation and trans-vinylene index (TVI) using an FTIR microscope, and (2) inserts of sufficient size and thickness were evaluated for mechanical properties by uniaxial tensile testing using an INSTRON load frame. Oxidation was reported as maximum oxidation measured in the scan from the articular surface to the backside of each bearing. TVI was reported as the average of all scans for each material. Average ultimate tensile strength (UTS), ultimate elongation (UE), and toughness were the reported mechanical properties for each material. Results. Maximum oxidation values differed significantly across material types (p=0.018, Figure 1). No antioxidant retrieval exhibited a subsurface oxidation peak, in contrast to conventional gamma-sterilized (55%) and highly cross-linked (37%) retrievals that exhibited subsurface oxidation peaks over the same in vivo time (Figure 2). Trans-vinylene index (TVI) correlated positively with nominal irradiation dose (p<0.001). Mechanical properties varied by material, with tensile toughness correlating negatively with increasing TVI (p<0.001, Figure 3). Discussion. AO polyethylene was developed to address the problem of free radicals in polyethylene resulting from irradiation used in cross-linking or sterilization. Each manufacturer used a different antioxidant or method of supplying the antioxidant. However, all of the antioxidant materials appeared to be effective at minimizing oxidation over the in vivo period of this study. The antioxidant materials prevented in vivo oxidation more effectively than both conventional gamma-sterilized and remelted HXL polyethylene, at least over the in vivo period represented. The toughness, or ability of the material to resist fatigue damage, decreased with increasing irradiation cross-linking dose (increasing TVI). The AO polyethylenes evaluated in this study had lower toughness than conventional gamma-sterilized polyethylene, but they avoided the loss of toughness due to remelting. Clinical relevance. Antioxidant polyethylene tibial retrievals showed superior oxidation resistance to conventional gamma-inert and remelted HXL inserts. Material toughness varied with the irradiation dose used to produce the material. Comparison of antioxidant retrieval tensile properties can be used as a guide for clinicians in choosing appropriate materials for the applications represented by their patients

Introduction

The longevity of highly cross-linked polyethylene (XLPE) bearings is primarily determined by its resistance to long-term oxidative degradation. Addition of vitamin E to XLPE is designed to extend in vivo life, although it has unintended consequences of inducing higher frictional torque and increased wear when articulating against metallic femoral heads.^1–3 Conversely, lower friction was observed when oxide ceramic heads were utilized.³ Previous studies suggest that oxide ceramics may contribute to XLPE oxidation, whereas a non-oxide ceramic, silicon nitride (Si₃N₄), might limit XLPE's degradation.⁴ To corroborate this observation, an accelerated hydrothermal ageing experiment was conducted using static hydrothermal contact between XLPE and commercially-available ceramic femoral heads.

INTRODUCTION. Multiple sources have consistently reported oxidation indices less than 0.1 with Marathon® inserts implanted up to 10 years. Understanding effects of oxidation level on UHMWPE wear in vivo is of great value. The objective of this study is to characterize the wear performance of Marathon® acetabular inserts at various levels of artificially induced oxidation, quantified using Bulk Oxidation Index (BOI) as determined per ASTM F2102, and to ascertain if wear rate is affected by progressive polyethylene oxidation. METHODS. GUR 1050 UHMWPE acetabular inserts, re-melted and cross-linked at 5.0Mrad (Marathon®, DePuy Synthes Joint Reconstruction, Warsaw, IN), were artificially aged per ASTM F-2003 in a stainless steel chamber at 5 atm. oxygen pressure and 70°C. Samples were maintained at temperature for 9, 10.4 and 11 weeks. After aging was completed, Fourier Transform Infra-Red (FTIR) spectroscopy was employed on one insert from each time point to evaluate the induced oxidation as a result of artificial aging. Resulting induced BOI values measured by FTIR were 0.195, 0.528 and 1.184. UHMWPE inserts had an inner diameter of 28mm and an outer diameter of 48mm and were articulated against 28mm diameter M-Spec® metal femoral heads (DePuy Synthes Joint Reconstruction, Warsaw, IN). Testing was conducted on a 12-station AMTI ADL hip simulator (AMTI, Watertown, MA) with load soak controls per ISO 14242-1:2014(E) in bovine serum (18mg/mL total protein concentration) supplemented with 0.056% sodium azide (preservative) and 5.56mM EDTA (calcium stabilizer). The UHMWPE inserts were removed from the machine, cleaned, and gravimetric wear determined per ISO 14242-2:2000(E) every 0.5 million cycles (MCyc) for 4.0 MCyc total. A two-tailed student's t-test was used (variance determined by F-test results) to analyze differences in wear rates between the three test groups. RESULTS. After 4.0 MCyc of wear testing, the average wear rate of the Marathon® UHMWPE acetabular inserts with OI levels of 0.195, 0.528 and 1.184 articulated against the CoCrMo femoral heads were 6.0 ± 4.2 mg/MCyc (±95% confidence interval), 8.7 ± 0.4 mg/MCyc and 15.3 ± 2.2 mg/MCyc, respectively (Figure 1). As BOI level increased, the wear rate also increased. Wear rates of inserts with BOI of 0.195 compared to 0.528 were not significantly different (p=0.11). Wear rates of inserts with BOI of 0.195 were significantly lower (p=0.00) compared to 1.184. Wear rates of inserts with BOI levels of 0.528 were significantly lower (p=0.00) compared to 1.184. DISCUSSION. This study aimed to characterize the wear performance of Marathon® acetabular inserts at three levels of oxidation created by accelerated aging. Artificially aged inserts with a BOI level similar to those reported from clinically retrieved Marathon® inserts (0.195) had a wear rate equivalent to non-aged inserts previously tested (data not shown), indicating the in vivo oxidation of this highly cross-linked UHMWPE has no effect on wear rate. Although not measured clinically, higher levels of oxidation may result in significantly higher wear rates in vivo

Background. Sequentially annealed, highly crosslinked polyethylene (HXLPE) has been used clinically in total knee arthroplasty (TKA) for over a decade[1]. However, little is known about the reasons for HXLPE revision, its surface damage mechanisms, or its in vivo oxidative stability relative to conventional polyethylene. We asked whether retrieved sequentially annealed HLXPE tibial inserts exhibited: (1) similar reasons for revision; (2) enhanced resistance to surface damage; and (3) enhanced oxidative stability, when compared with tibial inserts fabricated from conventional gamma inert sterilized polyethylene (control). Methods. Four hundred and fifty-six revised tibial inserts in two cohorts (sequentially annealed and conventional UHMWPE control) were collected in a multicenter retrieval program between 2000 and 2016. We controlled for implantation time between the two cohorts by excluding tibial inserts with a greater implantation time than the longest term sequentially annealed retrieval (9.5 years). The mean implantation time (± standard deviation) for the sequentially annealed components was 1.9 ± 1.7 years, and for the control inserts, 3.4 ± 2.7 years (Figure 1). Reasons for HXLPE revision were assessed based on medical records, radiographs, and examinations of the retrieved components. Surface damage mechanisms were assessed using the Hood method[2]. Oxidation was measured at the bearing surface, the backside surface, the anterior and posterior faces, as well as the post (when available) using FTIR (ASTM F2102). Surface damage and oxidation analyses were available for 338 of the components. We used nonparametric statistical testing to analyze for differences in oxidation and surface damage when adjusting for polyethylene formulation as a function of implantation time. Results. The tibial inserts in both cohorts were revised most frequently for loosening, infection, and instability. Instability was observed more frequently in inserts without a stabilizing post. In both cohorts, the most commonly observed surface damage mechanisms were burnishing, pitting, and scratching. Delamination was rare and only observed in 2 sequentially annealed inserts and 7 inserts in the control cohort. We observed six cases of posterior condyle fracture, which was always associated with instability (Figure 2). 5/6 of the fracture cases did not have a stabilizing post. Oxidation indices of the sequentially annealed inserts were, on average, low (ASTM oxidation index < 1) and not significantly different than the control inserts on the bearing surface and anterior/posterior face (Figure 3). Discussion. The findings of this study document the reasons for revision, surface damage mechanisms, and oxidative behavior of sequentially annealed HXLPE for TKA. We observed evidence of low in vivo oxidation in both retrieved sequentially annealed HXLPE and control tibial inserts. We found no association between the levels of oxidation and clinical performance of the HXLPE tibial components. However, because of the short-term follow-up, analysis of longer-term retrievals may be appropriate

INTRODUCTION. Highly cross linked polyethylenes (HXPE) have to be treated thermally after irradiation to eliminate residual free radicals. By adding vitamin E in the polyethylene powder a post-irradiation thermal treatment is not necessary. In this review the correlation between the intrinsic properties and the long-term stability of Vitelene® as a high performance material for artificial hip articulation will be displayed. MATERIALS & METHODS. Three different types of polyethylene (UHMWPE; GUR1020) were analyzed to compare mechanical properties as well as oxidative stability: PE. STD. (γ, 30 kGy, N. 2. ), HXPE. REM. (γ, 75 kGy, remelted, EO), Vitelene® (β, 80 kGy, 0.1% Vitamin E, EO). Artificial aging (ASTM F2003 − 70 °C, O. 2. at 5 bar) was used to simulate environmental damage. To evaluate the oxidation stability the Oxidation-Induction-Time (OIT) was measured by Differential Scanning Calorimetry (DSC - ASTM D3895) and the Oxidation Index (OI) was determined by Fourier-Transformation-Infrared-Spectroscopy (FTIR - ASTM F2102). The mechanical properties were analyzed by tensile- and impact investigations (ASTM D638 and ISO 11542-2) as well as by Small Punch Testing (SPT - ASTM F2183). The amount of wear was measured gravimetrically (ISO 14242-2). RESULTS. OIT [minutes], after 0, 14, 28, 42, 56 and 70 days aging, respectively 0.47, 0.41, 0.45, 0.42, 0.42 and not determined (nd) for PE. STD,. 0.46, 0.46, 0.47, 0.41, 0.41 and nd for HXPE. REM,. 12.09±0.50, 11.67±0.54, 10.78±0.25, 10.42±0.36, nd and 9.25±0.19 for Vitelene®. Cristallinity [%], after 0, 14, 28 and 42 days aging, respectively 55±2, 63±2, 79±4, 88±3 for PE. STD. , 47±2, 48±0, 50±1, 57±1 for HXPE. REM. , 52±1, 51±1, 53±14, 53±2 for Vitelene®. OI, after 0, 14, 28, 35 and 42 days aging, respectively 0.11±0.03, 0.67±0.15, 4.48±1.17 for PE. STD. , 0.07±0.05, 0.06±0.02, 0.09±0.02, 0.24±0.05, 0.69±0.36 for HXPE. REM. , 0.06±0.01, 0.08±0.01, 0.08±0.01, 0.09±0.01, 0.09±0.01 for Vitelene®. Tensile Strength [MPa], after 0 and 42 days aging, respectively 47.9±10, 0.7±0 for PE. STD. , 56.0±4.0, 25.0±2.0 for HXPE. REM. , 53.1±1.0, 52.0±4.3 for Vitelene®. Elongation [%], after 0 and 42 days aging, respectively 469±69 and 0 for PE. STD. , 343±14, 7±3 for HXPE. REM. , 372±11, 380±15 for Vitelene®. Impact Strength [kJ/m²], after 0 and 42 days aging, respectively 149±6, 4±1 for PE. STD. , 95±1, 5±1 for HXPE. REM. , 86±10, 91±7 for Vitelene®. SPT - Average Ultimate Load [N], after 0, 14 and 28 days aging, respectively 61.5±4.0, 56.3±5.3, 8.2±0.2 for PE. STD. , 71.4±2.2, 68.0±9.9, 64.4±8.2 for Vitelene®. Wear [mg/Mio cycles] (Ø36 mm Biolox® delta), after 0, 14 and 42 days aging, respectively 19.0±0.6, 30.3±3.1 and 365.8±37,2 for PE. STD. , 2.0±0.3, nd and 52.0±16.4 for HXPE. REM. , 2.5±0.5, nd and 2.3±0.7 for Vitelene®. CONCLUSION. The mechanical properties of Vitelene® are unchanged even after 42 days of artificial aging which is correlated to low wear in total hip arthroplasty. Vitamin E stabilization is effective in preventing oxidation and aging of the polyethylene after irradiation cross linking

Introduction. Thermally treated 1st generation highly crosslinked polyethylenes (HXLPE) have demonstrated reduced penetration and osteolysis rates, however, concerns still remain with respect to oxidative stability and mechanical properties of these materials. To address these concerns, manufacturers have introduced the use of antioxidants to quench free radicals while maintaining the mechanical properties of the HXLPE. Two common antioxidants are α-tocopherol (Vitamin-E) and pentaerythritol tetrakis (PBHP). These may be either mixed prior to consolidation, or diffused throughout the polymer after consolidation and irradiation. In vitrostudies have shown that these materials are oxidatively stable and have improved mechanical properties compared to 1st generation HXLPEs; however, few studies have investigated the in vivo performance of anti-oxidant stabilized HXLPE. The purpose of this study was to investigate the revision reasons, oxidation, and mechanical properties of retrieved short-term anti-oxidant HXLPE. Methods. Between 2010 and 2015, 73 anti-oxidant HXLPE components were collected as a part of an IRB approved, multi-institutional retrieval analysis program during routine revision surgery. Of the seventy-three components, 30 (41%) were acetabular liners, whereas, 43 were tibial inserts. The components were fabricated from three different materials: Vitamin-E Diffused HXLPE (n=30; E1, Biomet), Vitamin-E Blended (n = 41; Vivacit-E, Zimmer) and PBHP blended (n = 2, AOX, DePuy). The hip and knee components were implanted for 0.7 ± 0.8 years (Range: 0.0–2.25 years) and 0.8 ± 1.1 years (Range: 0.0–4.5 years), respectively. Implantation time, patient weight, age, gender, and activity levels were similar between hip and knee components (Table 1). For oxidation analysis, thin slices (∼200μm) were taken from medial condyle and central eminence of the tibial inserts or the superior/inferior axis from hip components. The slices were boiled in heptane for six hours to extract lipids absorbed in vivo. 3-millimeter FTIR line scans were taken perpendicular to the surface of interest, according to the ASTM F2102. Mechanical properties were assessed using the small punch test (ASTM F2183). Forty-three explants were available for destructive testing. Results. The predominant revision reasons were loosening, instability, and infection (Figure 1). Oxidation was low in both the hip and knee components (Mean OI≤0.1; Figure 2). For both tibial inserts and acetabular liners, there was no correlation between implantation time and oxidation indices (p>0.05). In the tibial inserts, the AP face had slightly higher oxidation indices than the articulating surface (Mean difference = 0.04; p=0.03). There was no difference in ultimate load between hips and knees at the surface (p=0.14) or the subsurface (p=0.38). Discussion. This study analyzed the revision reasons, oxidative stability, and mechanical properties of short-term retrieved 2nd generation HXLPE. The observations of this study show that anti-oxidant infused HXLPE exhibited low oxidative indices (Mean OI<0.1). There was no difference observed in the mechanical properties of these materials between hip and knee applications. However, this study is limited by short implantation times. This is unavoidable because the materials have only recently become clinically available. The data presented serves as a benchmark for future studies when longer-term retrieved implants become available

Introduction. Inradiation cross-linked and melted ultrahigh molecular weight polyethylene (UHMWPE) total joint implants, the oxidation potential is afforded to the material by by post-irradiation melting. The resulting cross-linked UHMWPE does not contain detectable free radicals at the time of implantation and was expected to be resistant against oxidation for the lifetime of the implants. Recently, analysis of long-term retrievals revealed detectable oxidation in irradiated and melted UHMWPEs, suggesting the presence of oxidation mechanisms initiated by mechanisms other than those involving the free radicals at the time of implantation. However, the effect of oxidation on these materials was not well studied. We determined the effects of in vitro oxidation on the wear and mechanical properties of irradiated and melted UHMWPEs. Materials and Methods. Medical grade slab compression molded UHMWPE (GUR1050) was irradiated using 10, 50, 75, 100, 120 or 150 kGy. The irradiated and melted UHMWPEs were accelerated aged at 70°C for 2, 3, 4, 6 and 8 weeks at 5 atm of oxygen. Oxidation profiles were determined by first microtoming 150 μm cross sections; these were then extracted by boiling hexane for 16 hours and vacuum dried for 24 hours. They were then analyzed on an infrared microscope as a function of depth away from the surface. An oxidation index was calculated per ASTM 2102 as the ratio of the area under the carbonyl peak at 1740 cm-1 to the area under the crystalline polyethylene 1895 cm-1 peak. The cross-link density was calculated as previously described (Oral 2010). The wear rate was determined using a custom-designed pin-on-disc wear tester against CoCr polished discs at 2 Hz and a rectangular path of 5 × 10 mm in undiluted bovine serum (Bragdon 2001). Tensile mechanical properties were determined using Type V dogbones according to ASTM D638. Results and Discussion. Oxidation increased as a function of aging duration for all UHMWPE samples. The cross-link density decreased non-linearly with increasing oxidation and the wear rate increased non-linearly. The dependence of wear on cross-link density was different for freshly irradiated, unoxidized samples in contrast to aged and oxidized samples (Figure 1). The elongation at break and the ultimate tensile strength decreased with increasing oxidation (Figure 2) and the modulus increased with increasing oxidation. There was an increase in the oxidation rates and oxidation levels of irradiated and melted UHMWPEs with increasing radiation dose (Figure 1), which suggested that regardless of the presence of residual free radicals, increased cross-linking made the material more prone to oxidation and oxidative degradation. The wear rate was not very sensitive to oxidation with an increase only observed at an oxidation index of 1 (Figure 3), suggesting a significant level of degradation and oxidative damage only at this level of oxidation. In contrast, the tensile strength and elongation-at-break were very sensitive to oxidation, showing severe degradation at low oxidation levels. Significance. This is the first study exploring the effects of simulated oxidation in irradiated and melted UHMWPEs without detectable free radicals known to cause oxidation. We have shown that when oxidation occurs, severe degradation may occur in irradiated and melted UHMWPEs

Introduction

In total hip arthroplasty (THA), polyethylene (PE) liner oxidation leads to material degradation and increased wear, with many strategies targeting its delay or prevention. However, the effect of femoral head material composition on PE degradation for ceramic-PE articulation is yet unknown. Therefore, using two different ceramic materials, we compared PE surface alterations occurring during a series of standard ceramic-PE articulation tests.

Background. Highly cross-linked polyethylene (HCLPE) was introduced to reduce wear and osteolysis in total hip arthroplasty (THA). There is no reported data regarding wear rates and clinical performance of Crossfire HCLPE (Stryker, Mahwah, New Jersey) in young and active patients. The purpose of this prospective study is to assess minimum 10-year wear rates and survivorship of Crossfire in young and active patients. Material and Methods. Between January 2001 to December 2003, 52 consecutive THAs (43 patients; 26 males and 17 females), 55 years and younger, with an average University of California Los Angeles activity (UCLA) score of 7.3 ± 1.5 (5 – 10) at the time of surgery were prospectively followed. The mean age of patients was 47.4 ± 7.8 years old (range 24 to 55 years). Indication for surgery included osteoarthritis in all cases. All operations were performed by the senior surgeon via a posterolateral approach. All components were non-cemented SecurFit femoral stem, 28 mm Cobalt-Chromium (Co-Cr) femoral head, and Trident PSL cup with Crossfire HCLPE acetabular liner (Stryker, Mahwah, New Jersey). At minimum 10-years follow-up (mean 11.5 ± 0.94 years), wear rates were assessed using the Roman software. Hospital for Special Surgery (HSS) scores and survivorship data were analyzed. Results. Good to excellent clinical results were seen with HSS score of 38.1 ± 4.7. The mean linear wear was 0.019 ± 0.018 mm/year (range 0 to 0.082). There were no revisions for osteolysis or loosening, periprosthetic infection or dislocation in this cohort. Kaplan-Meier survivorship was 100% for all failures. Conclusion. This is the first study to demonstrate that metal on Crossfire performs very well with excellent survivorship and wear rates at a minimum 10-year follow-up in young and active patients. Oxidation concern with Crossfire has not caused any clinical problems up to 10 years