Summary Statement. This study assesses oxidation, mechanical behavior and revision reasons of 2. nd. generation HXLPE used in total hip and knee arthroplasty. While oxidation was low for both X3 and E1 HXLPEs, oxidative regional variations were detected in the sequentially annealed cohort. Introduction. First generation highly crosslinked polyethylenes (HXPLEs) have proven successful in lowering both penetration and osteolysis rates. However, 1. st. generation annealing and remelting thermal stabilization have been associated with in vivo oxidation or reduced mechanical properties. Thus, 2. nd. generation HXLPEs were developed to improve oxidative stability while still maintaining material properties. Little is known about the in vivo clinical failure modes of these 2. nd. generation HLXPEs. The purpose of this study was to assess the revision reasons, wear, oxidative stability, and mechanical behavior of retrieved sequentially annealed Vitamin E diffused HXLPE in THA and TKA. Methods. 251 2. nd. Generation HXLPE hip and knee components were consecutively retrieved during revision surgeries and continuously analyzed in a prospective, IRB approved, multicenter study. 123 acetabular liners (Implanted 1.2y; Range 0–5.0y) and 117 tibial inserts (Implanted 1.6y; Range 0–5.8y) were highly crosslinked and annealed in 3 sequential steps (X3). Five acetabular liners (Implanted 0.6y; Range 0–2.0y) and six tibial inserts (Implanted 1.3y; Range 0.5–1.8y) were diffused with Vitamin E (E1). Patient information was collected from medical records. Linear penetration of liners was measured using a calibrated digital micrometer (accuracy: 0.001 mm). Surface damage of tibial components was assessed using the Hood method. Thin sections were taken from the acetabular liners (along the superior/inferior axis) and the tibial components (along the medial condyle and central spine) for oxidation analysis and analyzed according to ASTM 2102. Mechanical behavior was assessed via the small punch test (ASTM 2183). Results. The liners and tibial components fabricated from both HXLPEs were revised predominantly for loosening, instability, and infection. The average penetration rate for the Sequentially Annealed group was low (PR=0.045mm/yr). Pitting, scratching and burnishing were the predominant damage mechanisms of the tibial inserts within both material groups, with no evidence of delamination. Oxidation indices were low (Mean OI≤0.3) and similar between liners and inserts of the Sequentially Annealed components at the bearing and backside surface (p≥0.15). Oxidation was positively correlated with implantation time at the bearing surface of the Sequentially Annealed groups (Rho>0.29, p<0.005). The Ultimate Load of the Sequentially Annealed acetabular liners was statistically higher than the tibial components (p<0.001), however the mean difference was minimal (∼6N). Discussion. This study evaluated the properties of 2. nd. generation HXLPEs used in THA and TKA. Sequentially Annealed liners had penetration rates comparable with 1. st. generation HXLPEs. While oxidation was low for both sequentially annealed and Vitamin E HXLPEs, we were able to detect regional variations in the oxidative in the sequentially annealed cohort. Longer-term retrievals are necessary to fully assess the oxidative stability of Vitamin E diffused HXLPE used in TKA and THA

Summary Statement. Fretting and corrosion has been identified as a clinical problem in modular metal-on-metal THA, but remains poorly understood in modern THA devices with polyethylene bearings. This study investigates taper damage and if this damage is associated with polyethylene wear. Introduction. Degradation of modular head-neck tapers was raised as a concern in the 1990s (Gilbert 1993). The incidence of fretting and corrosion among modern, metal-on-polyethylene and ceramic-on-polyethylene THA systems with 36+ mm femoral heads remains poorly understood. Additionally, it is unknown whether metal debris from modular tapers could increase wear rates of highly crosslinked PE (HXLPE) liners. The purpose of this study was to characterise the severity of fretting and corrosion at head-neck modular interfaces in retrieved conventional and HXLPE THA systems and its effect on penetration rates. Patients & Methods. 386 CoCr alloy heads from 5 manufacturers were analyzed along with 166 stems (38 with ceramic femoral heads). Metal and ceramic components were cleaned and examined at the head taper and stem taper by two investigators. Scores ranging from 1 (mild) to 4 (severe) were assigned in accordance with the semi-quantitative method adapted from a previously published technique. Linear penetration of liners was measured using a calibrated digital micrometer (accuracy: 0.001 mm). Devices implanted less than 1 year were excluded from this analysis because in the short-term, creep dominates penetration of the head into the liner. Results. The majority of the components were revised for instability, infection, and loosening. Mild to severe taper damage (score ≥2) was found in 77% of head tapers and 52% of stem tapers. The extent of damage was correlated to implantation time at the head taper (p=0.0004) and at the stem taper (p=0.0004). Damage scores were statistically elevated on CoCr heads than the matched stems (mean score difference=0.5; p<0.0001) and the two metrics were positively correlated with each other (ρ=0.41). No difference was observed between stem taper damage and head material (CoCr, ceramic) (p=0.56), nor was a correlation found between taper damage and head size (p=0.85). The penetration rate across different formulations of HXLPE was not found to be significantly different (p=0.07), and therefore grouped together for further analysis. Within this cohort, penetration rate was not found to be associated with head size (p=0.08) though a negative correlation with implantation time was noted (ρ=−0.35). When analyzed along with taper damage scores, a correlation was not observed between head taper damage scores and HXLPE penetration rates (p=0.51). Discussion. The results of this study do not support the hypothesis that 36+ mm ceramic or CoCr femoral heads articulating on HXLPE liners are associated with increased risk of corrosion among HXLPE liners when compared with smaller diameter heads. A limitation of this study is the semi-quantitative scoring technique, heterogeneity of the retrieval collection and short implantation time of the larger diameter heads. Because corrosion may increase over time in vivo, longer-term follow-up, coupled with quantitative taper wear measurement, will better assess the natural progression of taper degradation in modern THA bearings

Highly cross-linked polyethylene (HXLPE) is now a common used bearing surface in total hip arthroplasty. Current studies report superior wear rates with the use of HXLPE in total hip arthroplasty. However, there are few studies to support its long term use. The aim of this study is to measure the long term wear of HXLPE and evaluate patient satisfaction at more than 10 years follow up. 44 total hip arthroplasties were performed through a direct lateral approach by a single surgeon. All patients received the same uncemented acetabular component, mean liner thickness was 6.91mm (SD= 0.68). 16 of the femur components were cemented. Outcomes analysed include wear rates, osteolysis, revision rates, SF12 and Oxford hip scores. Wear rate was calculated using computer software (Polyware®) using edge detection software. Mean age at surgery was 58.9 years (SD= 11.67). The mean follow up was 11.3 years (SD= 1.19). There was no evidence of osteolysis and none had undergone revision surgery. Mean two dimensional wear was 0.38mm (SD= 0.25) and mean wear rate per year was 0.03mm (SD= 0.02, range 0.009 to 0.078). Oxford hip score at last follow up indicated satisfactory joint function (mean= 42 SD= 6.2). Our results support the use of highly cross-linked polyethylene in primary total hip replacements. The absence of osteolysis and need for revision surgery over a mean of 11.3 years is very encouraging

Summary Statement. In the present hip simulator studies, bearings with the newest generation of HXLPE, stabilised with vitamin E, did not show increased wear under severe conditions, such as accelerated ageing, component mal-orientation and third body wear. Introduction. Unfortunately, acetabular hip components cannot always be implanted in optimal condition. Therefore, we performed hip simulator studies with cups made from highly cross-linked, vitamin E stabilised UHMWPE in i) artificially aged condition, ii) with an inclination angle corresponding to 80 ° in vivo and iii) with third bodies coming from the Ti coating of the acetabular cup. Methods. For these hip simulator studies, seleXys cup inlays, size 28/EE, and RM Pressfit samples 50/28 (Mathys Ltd Bettlach, Switzerland) were used. Standard PE parts and vitamys® inlays (highly cross-linked, vitamin E stabilised UHMWPE) were tested in the same series. PE cups were machined out of sintered GUR 1020 slabs, packaged and gamma-sterilised in inert atmosphere at 30 kGy. The vitamys® material was made in-house by adding 0.1 wt.-% of vitamin E (Merck KGaA, Darmstadt/Germany) to GUR 1020 powder from Ticona GmbH, Kelsterbach/Germany. Cross-linking used 100 kGy gamma-irradiation and the final sterilisation was gas plasma. Artificial ageing was done under pressurised oxygen at 70 °C according to ASTM F2003 for 14 days (standard PE) and 60 days (vitamys®), respectively. The hip simulator test protocol of ISO 14242 was kept for the artificially aged cups, but the inclination angle altered to 80 ° for the test with the steep cup position. In the third test, the test fluid (diluted bovine serum stabilised with sodium azide and EDTA) was altered by adding about 10 Ti particles to the bearing for the first million cycles. This test condition imitates third body wear by particles shed from the coating of the RM cups. All testing was conducted at the RMS Foundation (Bettlach / Switzerland) on a servo-hydraulic six-station hip simulator (Endolab, Thansau/Rosenheim, Germany) at a temperature of 37±1°C. At lubricant change interval of 500’000 cycles, the inlays were measured gravimetrically with an accuracy of 0.01 mg. Results. The wear rate of the standard UHMWPE in the condition aged for 14 days reached 45 mg/Mcycle, corresponding to a 57 % increase over non-aged cups. For the vitamys® cups, the wear rate was virtually unchanged even after 60 days ageing (5.8 mg/Mcycle vs. 5.9 mg/Mcycle). For standard UHMWPE tested with an inclination of 80°, wear was 16% lower than those of the inlays with 45° inclination. Whereas for the vitamys® inlays, the wear rate was about the same for both inclination angles (5.4 mg/Mcycle vs. 5.9 mg/Mcycle,). The addition of Ti particles increased the wear rate of standard UHMWPE to 35 mg/Mcycle. However, vitamys® was hardly affected by the third bodies: the wear rate stood at 7.8 mg/Mcycle. Conclusions. Based on the present simulator study, it seems that hip bearings with the newest generation of HXLPE, stabilised with vitamin E, are exempt from increased wear rate when subjected to severe conditions, such as accelerated ageing, component mal-orientation and third body wear

Summary Statement. In the most recent type of highly cross-linked UHMWPE, stabilised by vitamin E, the majority of this anti-oxidant cannot be leached out. Even more, the vitamin E molecules are grafted to the UHMWPE polymer backbone by an ether bond. Introduction. Today, highly cross-linked, vitamin E stabilised UHMWPE is clinically accepted as bearing material in joint replacements. Little is known about the chemistry of this antioxidant in the polymer after irradiation. The present investigation presents a model for the chemical nature of the trapping of vitamin E in PE. Method. UHMWPE type GUR 1020 (Ticona GmbH, Kelsterbach/Germany) was blended with 0.1 % vitamin E (Merck KGaA, Darmstadt/Germany), compression moulded at Mathys Ltd Bettlach in-house and cross-linked with γ-irradiation dose of nominally 100 kGy. To assess the extent of vitamin E leachable out, three 0.3 mm sections were cut from the centre of the samples. By extraction in heptane for 48 h at 98 °C, this amount of vitamin E trapped in the polymer was determined by Fourier transform infrared spectroscopy (FTIR) as relative vitamin E index (RVEI). The nature of the extracted substances was analysed by GC-MS. For solids, many of modern spectroscopic methods are not applicable. Therefore, 0.1 % vitamin E were dissolved in two model hydrocarbons (cyclohexane and n-octane) and irradiated at the same 100 kGy γ-dose. In order to determine the chemical bond vitamin E – hydrocarbon after irradiation, these liquid solution samples were analysed by different spectroscopic methods, such as GC-MS, MALDI-TOF-SIMS, HPLC and NMR. Results. Extraction experiments showed that only 23 % of the vitamin E could be extracted by heptane after irradiation whereas from a non-irradiated control sample, all vitamin E was extracted. GC-MS confirmed that the extracted vitamin E was chemically unchanged. Analysing the model hydrocarbons after irradiation, the GC-MS-chromatogram of the cyclohexane solution showed a single peak of the formal cyclohexene adduct of vitamin E. Illustrates this adduct, cyclohexyl-6-O-α-tocopherolether. Contrariwise, the same analysis of the n-octane solution revealed three formal octane adducts. By preparing references substances these three peaks could be attributed to ethers of vitamin E bonded at three different, but chemically equivalent CH. 2. positions on the eight carbon atom chain of n-octane. The single mass peak of the cyclohexane solution arises from the six chemically equivalent carbon atoms in this cyclic hydrocarbon. The 100 kGy γ-dose transformed 76 % of the vitamin E in the n-octane solution to the corresponding ethers and 68 % of the vitamin E in the cyclohexane to cyclohexyl ether. Therefore we postulate that in highly cross-linked, vitamin E stabilised UHMWPE the vitamin E is grafted to the polymer carbon backbone by an ether bond at the phenolic OH group of the vitamin E molecule. Conclusion. Upon irradiation, vitamin E is grafted to the UHMWPE polymer backbone to a large amount. This portion of antioxidant cannot leach out. Therefore, vitamin E stabilised HXLPE is protected from oxidation and ageing by a chemically grafted, quasi internal antioxidant

Summary Statement. In young, active patients cementless THR demonstrates excellent prosthetic stability by RSA and outstanding clinical outcomes at 5 years using a tapered titanium femoral stem, crosslinked polyethylene liners and either titanium or tantalum shells. Introduction. Early femoral implant stability is essential to long-term success in total hip replacement. Radiostereometric analysis (RSA) provides precise measurements of micromotion of the stem relative to the femur that are otherwise not detectable by routine radiographs. This study characterised micromotion of a tapered, cementless femoral stem and tantalum porous-coated vs. titanium acetabular shells in combination with highly cross-linked UHMWPE or conventional polyethylene liners using radiostereometric analysis (RSA) for 5 years following THR. Patients and Methods. This IRB-approved, prospective, double randomised, blinded study, involved 46 patients receiving a primary THR by a single surgeon. Each patient was randomised to receive a titanium (23) (Trilogy, Zimmer) or tantalum (23) (Modular Tantalum shell, Zimmer) uncemented hemispheric shell and either a highly-crosslinked or conventional polyethylene liner. Tantalum RSA markers were implanted in each patient. All patients had a Dorr A or B femoral canal and received a cementless, porous-coated titanium tapered stem (M/L Taper, Zimmer). All final femoral broaches were stable to rotational and longitudinal stress. RSA examinations, Harris Hip, UCLA, WOMAC, SF-12 scores were obtained at 10 days, 6 months, and annually through 5 years. Results. All patients demonstrated statistically significant improvement in Harris Hip, WOMAC, and SF-12 PCS scores post-operatively. Evaluation of polyethylene wear demonstrated that median penetration measurements were significantly greater in the conventional compared to the HXPLE liner cohorts at 1 year through 5 years follow-up (p<0.003). At 5 years, conventional liners showed 0.38 ± 0.05mm vertical wear whereas HXLPE liners showed 0.08 ± 0.02mm (p<0.003). Evaluation of the femoral stems demonstrated that the rate of subsidence was highest in the first 6 months (0.09mm/yr), with no other detectable motion through 5 years. Two outlying patients had significantly higher stem subsidence values at 6 months (0.7 mm and 1.0mm). One stem stabilised without further subsidence after 6 months (0.7mm), and the other stem stabilised at 1 year (1.5mm). Neither patient has clinical evidence of loosening. Evaluation of acetabular shells demonstrated less median vertical translation in tantalum than titanium shells at each time-point except at 3-years follow-up, however due to large standard errors, there was no significant difference between the two designs (p>0.05). These large standard errors were predominantly caused by two outliers, neither of which had clinical evidence of loosening. Discussion/Conclusion. In this RSA study of young THR patients, cementless tapered femoral stems, highly crosslinked polyethylene liners, and tantalum or titanium acetabular shells all demonstrated excellent performance through 5 years follow-up. Highly crosslinked polyethylene liners demonstrated significantly less wear than conventional liners. The femoral stem showed excellent stability through 5 years, with no clinical or radiologic episodes of failure. The small amount of micromotion seen is less than that previously reported for similar tapered, cementless stems and approaches the accuracy of RSA (0.05mm). Both acetabular shells demonstrated excellent stability with minimal micromotion at 5 years without significant differences in migration. All patients demonstrated significant clinical improvement in pain and function and additional RSA evaluation of these patients is planned