Introduction. Clinically relevant attributes of an orthopedic bearing material include its strength, oxidative stability, and wear resistance. Recent reductions in bearing wear and oxidation have been realized by crosslinking (HXLPE), and through the incorporation of α-tocopherol (VE). VE infusion has improved the oxidative stability of HXLPE in vitro [1] and in vivo (as evidenced by retrievals) [2]. However, concern has been raised that adding VE may increase the frictional torque of bearings, potentially increasing the risk of trunnionosis [3]. This study compares the 3D frictional torques of HXLPE vs Vitamin-E HXPLE, against 28 mm and 36 mm metal and ceramic heads. Methods. Samples were made from prints for commercially available Ringloc liners (Biomet, IN). The HXLPE group was made from ArCom XL, and the VE-HXLPE was made from E1 HXLPE (Biomet, IN). Femoral heads were of cobalt chrome (ASTM F1537), or ceramic (Biolox Delta™). Testing was performed at EndoLab®, Germany. An ISO 14242–1 compliant six-station simulator and 3D gait cycle was utilized. During the cycle, the abduction/adduction range was −4°/+7°, the flexion/extension was +25°/-18°, and the external/internal rotation was −10°/+2°. Testing was performed at 37±2 °C, at 1 Hz, and with a maximum dynamic load of 3.0 kN. Lubrication medium was calf serum, EDTA, and antibiotics diluted in DI water (30 g/l of protein). Measurements were averaged across 5 cycles after 120 completed cycles of motion, and after 200 cycles. Analysis was performed using Minitab with multiple 2-way ANOVAs, with a p=0.05 significance threshold. Results. There was a statistically significant effect from head size (p≤0.0005). 36 mm heads exhibited higher torque (4.25±0.31 Nm, 200 cycles) than the 28 mm heads (2.90±0.08 Nm). There was no statistically significant effect (p≥0.409, all outputs) from head type (metal vs ceramic). In the 36 mm groups, there was no statistically significant effect (p≥0.300, all outputs) from the liner material (HXLPE vs VE-HXLPE). Within the metal head groups, the inclusion of VE statistically significantly decreased (p≤0.018, all outputs) the average mean frictional torques by 8.07±4.6%. Conclusion. A larger head size increased the frictional torque. In the metal head groups the infusion of VE decreased the frictional torque, and VE did not statistically significantly change the torque in the ceramic groups. A previous report found that VE increased torque [3], but evidence herein does not support that conclusion. Limitations of the previous study include; use of a simplified rotation torque method, non-physiologic lubrication, lack of statistical analysis, unknown implant design, and unknown VE concentration and processing methods. Based on these results, no adverse clinical effects are anticipated due to VE-associated changes in frictional torque. Short-to-mid-term clinical results have not shown any adverse effects [4]

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. 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

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. The long-term wear performance of highly cross-linked polyethylene (HXLPE) in cemented total hip arthroplasty (THA) has rarely been reported. Here we report a prospective randomized comparative analysis of radiographic wear after a minimum follow-up of 10 years in cemented THAs with either HXLPE or conventional polyethylene (CPE), and assess its clinical relevance. Patients and Methods. From 1999 to 2001, we conducted 94 primary cemented THAs with a 22.225-mm head at our hospital as part of a prospective randomized trial. All surgeries were performed using a direct lateral approach with a trochanteric osteotomy (Dall's approach). The patients were divided into 4 groups. Twenty-six hips in group A were implanted with CPE sockets against zirconia heads and Charnley-type stems. HXLPE sockets (Aeonian, Kyocera Medical Corp) were implanted in all hips in the other 3 groups. Twenty-five hips in group B were implanted with zirconia heads and KC stems (Kyocera Medical Corp), 23 hips in group C with zirconia heads and distal cylindrical stems, and 20 hips in group D with stainless steel heads and C-stem (DePuy Inc). The sockets were highly cross-linked by gamma irradiation at a dose of 35 kGy, heat annealed at 110ºC, and sterilized with 25 kGy of gamma irradiation in nitrogen. For radiographic evaluation, anteroposterior radiograms were taken for each patient annually, and every two years postoperatively for wear analyses. Two-dimensional head penetration was measured on each postoperative radiogram using a computer-aided technique. Results. Wear measurements were performed for 59 cases followed up over 10 years. Linear wear rates were 0.138±0.074 (mm/year±SD) for group A, 0.010±0.015 for group B, 0.013±0.020 for group C, and 0.012±0.027 for group D. Linear wear rates differed significantly between group A and other groups, and no significant difference was found among groups B, C, and D. There were four revision cases. Among them, two sockets of group A were revised for aseptic loosening at 7 and 14 years postoperatively with linear wear rates of 0.749 and 0.153 mm, respectively. Two stems of group B and C were revised for aseptic loosening at 10 and 9 years postoperatively with linear wear rates of 0.007 and 0.041 mm, respectively. There were no other cases with aseptic loosening in any group. Osteolysis was found in 10 cases (group A: 7, group B: 1, group C: 1, group D: 1), and there was a significant difference in linear wear rates between the cases with and without osteolysis (0.157±0.083 and 0.030±0.053 mm/year±SD respectively). Discussion. The two revision cases of HXLPE did not have aggressive socket wear, and possibly cement fracture caused osteolysis and stem instability. The results of this study indicate that there is a significant difference in wear rate between CPE and HXLPE, and it was evident that PE wear was associated with osteolysis and aseptic loosening of the socket

The introduction of a new implant material is not without risk. A series of worst-case scenarios were developed and tested accordingly to answer questions such as: what will happen if the implant is not placed in a good orientation? What will happen to the material after a long implantation time, e.g. 20 or more years?. To reach a higher level of safety, a new approach for the preclinical testing has been taken. The vitamys® material (a novel vitamin-doped HXLPE) followed a severe pre-clinical testing protocol, including mechanical, tribological and biocompatibility testing. The testing includes a comparison of vitamys® vs. standard-UHMWPE and other HXLPE after accelerated ageing for periods equivalent to 20 and 40 years in-vivo. Hip simulator testing was done at inclination angles from 35° to 65° to assess the “forgiveness” of the material for mal-orientation. Comparing the test results to published data, it becomes evident that the vitamin addition and the sequence of the manufacturing steps both have a significant effect of the resulting mechanical, ageing and wear properties. In contrast to UHMWPE or HXLPE without antioxidant, the vitamys material behaves in a very “forgiving” manner: Hip simulator testing of vitamys at high inclination angles and even with severely aged material revealed no increase of wear rates. The vitamys material was first introduced in a monoblock polyethylene cup with a thin Ti-particle coating, the RM-Pressfit vitamys® acetabular cup (Mathys Ltd Bettlach, Switzerland). Its first implantation occurred in Sept. 2009. Since then, a total of nearly 500 implantations have been documented in a prospective multi-centre clinical study involving 11 clinics in 5 countries (CH, DE, FR, NL and NZ). Based on the pre-clinical testing and its first clinical experience, we have reason to believe that the RM-Pressfit vitamys® possesses interesting and unique features such as high elasticity (no stress-shielding), high ageing and wear resistance combined with clinically proven biological anchorage – making it theoretically suitable for a whole range of patients, including the young and active

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 (Table 1). 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 (Figure 1). The average penetration rate for the Sequentially Annealed group was low (PR = 0.045 mm/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 (Figure 2, 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

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 characterize 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; Figure 2) 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; Figure 3). 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 with taper damage scores, a correlation was not observed between head 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

Introduction. Highly crosslinked polyethylene (HXLPE) was clinically introduced approximately a decade and a half ago to reduce polyethylene wear rates and subsequent osteolysis. Clinical and radiographic studies have repeatedly shown increased wear resistance, however concerns of rim oxidation and fatigue fracture remain. Although short to intermediate term retrieval studies of these materials are available, the long-term behavior of these materials remains unclear. Methods. Between 2000 and 2015, 115 1st generation HXLPE acetabular liners implanted for 5 or more years were collected and analyzed as part of an ongoing, multi-institutional orthopaedic implant retrieval program. There were two material cohorts based on thermal processing (annealed (n=45) and remelted (n=70)). Each cohort was stratified into two more cohorts based on implantation time (5 – 10 years and >10 years). For annealed components, the intermediate-term liners (n=30) were implanted on average (±SD) for 7.3 ± 1.7 years while the long-term liners (n=15) were implanted for 11.3 ± 1.8 years. For remelted components, the intermediate-term liners (n=59) were implanted on average (±SD) for 7.2 ± 1.3 years while the long-term liners (n=11) were implanted for 11.3 ± 1.2 years. For each cohort, the predominant revision reasons were loosening, instability, and infection (Figure 1). Short-term liners (in-vivo <5ys) from previous studies were analyzed using the same protocol for use as a reference. For oxidation analysis, thin slices (∼200 μm) were taken from the superior/inferior axis and subsequently boiled in heptane for 6 hours to remove absorbed lipids that may interfere with the oxidation analysis. 3mm line profiles (in 100μm increments) were taken perpendicular to the surface at each region of interest. Oxidation indices were calculated according to ASTM 2102. Penetration was measured directly using a calibrated micrometer (accuracy=0.001mm). Results. The penetration rates for both the annealed and remelted cohorts were low and similar between the two material cohorts (Figure 2). There were several cases of fractured zirconia heads associated with a manufacturer recall that resulted in higher penetration rates. At the bearing and rim surfaces, the annealed liners had higher oxidation indices than the remelted components (p<0.001). For the remelted components, the intermediate-term liners had higher oxidation indices than the short-term liners (p=0.001). For the annealed liners, both the long-term and intermediate-term liners had higher oxidation indices compared with the short-term liners (p=0.007 and 0.001, respectively). Discussion. Thermally treated first generation HXLPEs were introduced to reduce polyethylene wear and prevent oxidative degradation. The results of this study suggest that both thermally treated HXLPEs demonstrate lower penetration rates than conventional polyethylene, however, the resistance to oxidation was formulation dependent. Specifically, the remelted components were more effective at preventing oxidation than the annealed liners. However, despite the lack of measurable free radicals, we were able to observe temporal changes in the oxidation of the remelted liners. Future work will include analysis of long-term 1stgeneration annealed HXLPE to fully assess its performance in the second decade of service

The purpose of this study was to evaluate the Mid-term results (minimum 5 year) of the use of 36 mm metallic femoral head coupled with 1st generation HXLPE in patients with the age of less than or equal to 50 years-old. This retrospective study included 31 cases sustained hip pain needed Total Hip Replace Arthroplasty. We used cementless stem(FMT, Zimmer, Warsaw, Indiana) at 28 cases and cement stem(Versys, Zimmer, Warsaw, Indiana) at 3 cases. We used Trilogy (Zimmer, Warsaw, Indiana) in all cases as an acetabular cup and Longevity (Zimmer, Warsaw, Indiana) in all cases as a HXLPE. Mean acetabular cup size was 52.88mm. Mean HXLPE liner thickness at 45o was 6.18mm [Fig.1]. Mean Harris hip score was 91(86–96) and all cases obtained more than 15 scores in Merle d'Aubigne and postel method at recent follow ups. All femoral stem showed stable fixation status. Mean acetabular cup Inclination was 50.6o and Anteversion was 23.1o. During follow ups, there was no complication including dislocation, osteolysis, infection and plastic fracture. Bedding-in wear rate was 0.079±0.034mm/yr. And Steady- state was 0.043±0.016mm/yr. In vitro study, 1stgeneration HXLPE showed negative mechanical property changes due to high dose radiation and remelting. So, concerns remained in using HXLPE to active patients. But we checked a good results in terms of functional scores and wear rates. And, there was no major complication during minimal 5 years check ups. So, the authors thought THRA with 36mm- metallic heads on 1st-Generation Highly Cross-linked Polyethylene as a bearing surface could be a good option in less than or equal to 50 years patients

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 1. st. 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

Introduction

There has been almost universal adoption of highly cross-linked polyethylene as the polyethylene of choice in metal-on-polyethylene articulations in total hip replacement (THR). Although wear of conventional polyethylene has been shown to be related to periprosthetic osteolysis, the relationship between wear of highly cross-linked polyethylene and osteolysis remains uncertain. Our aim was to determine the incidence and volume of periacetabular osteolysis at a minimum of seven years following primary THR with metal on highly cross-linked polyethylene articulations.

The benefits of HXLPE in total knee arthroplasty (TKA) have not been as evident as total hip arthroplasty (THA). A systematic review and meta-analysis to assess the impact of highly-crosslinked polyethylene (HXLPE) on TKA outcomes compared to conventional polyethylene (CPE) is described. All studies comparing HXLPE with CPE for primary TKA were included for analysis. The minimum dataset included revision rates, indication for revision, aseptic component loosening and follow-up time. The primary outcome variables were all-cause revision, aseptic revision, revision for loosening, radiographic component loosening, osteolysis and incidence of radiolucent lines. Secondary outcome measures included postoperative functional knee scores. A random-effects meta-analysis allowing for all missing data was performed for all primary outcome variables. Six studies met the inclusion criteria. In total, there were 2,234 knees (1,105 HXLPE and 1,129 CPE). The combined mean follow-up for all studies was 6 years. The aseptic revision rate in the HXLPE group was 1.02% compared to 1.97% in the CPE group. There was no difference in the rate of all-cause revision (p = 0.131), aseptic revision (p = 0.298) or revision for component loosening (p = 0.206) between the two groups. Radiographic loosening (p = 0.200), radiolucent lines (p = 0.123) and osteolysis (p = 0.604) was similar between both groups. Functional outcomes were similar between groups. The use of HXLPE in TKA yields similar results for clinical and radiographic outcomes when compared to CPE at midterm follow-up. HXLPE does not confer the same advantages to TKA as seen in THA

With the introduction of highly crosslinked polyethylene (HXLPE) in total hip arthroplasty (THA), orthopaedic surgeons have moved towards using larger femoral heads at the cost of thinner liners to decrease the risk of instability. Several short and mid-term studies have shown minimal liner wear with the use HXLPE liners, but the safety of using thinner HXPLE liners to maximize femoral head size remains uncertain and concerns that this may lead to premature failure exist. Our objective was to analyze the outcomes for primary THA done with HXLPE liners in patients who have a 36-mm head or larger and a cup of 52-mm or smaller, with a minimum of 10-year follow-up. Additionally, linear and volumetric wear rates of the HXLPE were evaluated in those with a minimum of seven-year follow-up. We hypothesized that there would be minimal wear and good clinical outcome. Between 2000 and 2010, we retrospectively identified 55 patients that underwent a primary THA performed in a high-volume single tertiary referral center using HXLPE liners with 36-mm or larger heads in cups with an outer diameter of or 52-mm or smaller. Patient characteristics, implant details including liner thickness, death, complications, and all cause revisions were recorded. Patients that had a minimum radiographic follow-up of seven years were assessed radiographically for linear and volumetric wear. Wear was calculated using ROMAN, a validated open-source software by two independent researchers on anteroposterior X-rays of the pelvis. A total of 55 patients were identified and included, with a mean age of 74.8 (range 38.67 - 95.9) years and a mean BMI of 28.98 (range 18.87 - 63-68). Fifty-one (94.4%) of patients were female. Twenty-six (47.7%) patients died during the follow-up period. Three patients were revised, none for liner wear, fracture or dissociation. Twenty-two patients had a radiographic follow-up of minimum seven years (mean 9.9 years, min-max 7.5 –13.7) and were included in the long-term radiographic analysis. Liner thickness was 5.5 mm at 45 degrees in all cases but one, who had a liner thickness of 4.7mm, and all patients had a cobalt-chrome head. Cup sizes were 52mm (n=15, 68%) and 50mm (n=7, 32%). Mean linear liner wear was 0.0470 mm/year (range 0 - 0.2628 mm) and mean volumetric wear was 127.69 mm3/year (range 0 - 721.23 mm3/year). Using HXLPE liners with 36-mm heads or bigger in 52-mm cups or smaller is safe, with low rates of linear and volumetric wear in the mid to long-term follow-up. Patients did not require revision surgery for liner complications, including liner fracture, dissociation, or wear. Our results suggest that the advantages of using larger heads should outweigh the potential risks of using thin HXLPE liners

Increased femoral head size reduces the rate of dislocation after total hip arthroplasty (THA). With the introduction of highly crosslinked polyethylene (HXLPE) liners in THA there has been a trend towards using larger size femoral heads in relatively smaller cup sizes, theoretically increasing the risk of liner fracture, wear, or aseptic loosening. Short to medium follow-up studies have not demonstrated a negative effect of using thinner HXLPE liners. However, there is concern that these thinner liners may prematurely fail in the long-term, especially in those with thinner liners. The aim of this study was to evaluate the long-term survival and revision rates of HXLPE liners in primary THA, as well as the effect of liner thickness on these outcomes. We hypothesized that there would be no significant differences between the different liner thicknesses. We performed a retrospective database analysis from a single center of all primary total hip replacements using HXLPE liners from 2010 and earlier, including all femoral head sizes. All procedures were performed by fellowship trained arthroplasty surgeons. Patient characteristics, implant details including liner thickness, death, and revisions (all causes) were recorded. Patients were grouped for analysis for each millimeter of PE thickness (e.g. 4.0-4.9mm, 5.0-5.9mm). Kaplan-Meier survival estimates were estimated with all-cause and aseptic revisions as the endpoints. A total of 2354 patients (2584 hips) were included (mean age 64.3 years, min-max 19-96). Mean BMI was 29.0 and 47.6% was female. Mean follow-up was 13.2 years (range 11.0-18.8). Liner thickness varied from 4.9 to 12.7 mm. Seven patients had a liner thickness <5.0mm and 859 had a liner thickness of <6.0mm. Head sizes were 28mm (n=85, 3.3%), 32mm (n=1214, 47.0%), 36mm (n=1176, 45.5%), and 40mm (n=109, 4.2%), and 98.4% were metal heads. There were 101 revisions, and in 78 of these cases the liner was revised. Reason for revision was instability/dislocation (n=34), pseudotumor/aseptic lymphocyte-dominant vasculitis associated lesion (n=18), fracture (n=17), early loosening (n=11), infection (n=7), aseptic loosening (n=4), and other (n=10). When grouped by liner thickness, there were no significant differences between the groups when looking at all-cause revision (p=0.112) or aseptic revision (p=0.116). In our cohort, there were no significant differences in all-cause or aseptic revisions between any of the liner thickness groups at long-term follow-up. Our results indicate that using thinner HXPE liners to maximize femoral head size in THA does not lead to increased complications or liner failures at medium to long term follow-up. As such, orthopedic surgeons can consider the use of larger heads at the cost of liner thickness a safe practice to reduce the risk of dislocation after THA when using HXLPE liners

Introduction. Highly crosslinked, ultra-high molecular weight polyethylene (HXLPE) acetabular liners inherently have a risk of fatigue failure associated with femoral neck impingement. One of the potential reasons for liner failure was reported as crosslinking formulations of polyethylene, increasing the brittleness and structural rigidity. In addition, the acetabular component designs greatly affect the mechanical loading scenario, such as the offset (lateralized) liners with protruded rim above the metal shells, which commonly induce a weak resistance to rim impingement. The purpose of the present study was to compare the influence of the liner offset length on the impingement resistance in the annealed (first generation) and vitamin E-blended (second-generation) HXLPE liners with a commercial design. Materials and Methods. The materials tested were the 95-kGy irradiated annealed GUR1020, and the 300-kGy irradiated vitamin E-blended GUR1050 HXLPE offset liners, which were referred to as “20_95” and “50E_300”, respectively. These liners had 2, 3, 4-mm rim offset, 2.45-mm rim thickness, and 36-mm internal diameter. Their rims were protruded above the metal rim at 2, 3, 4mm. Rim impingement testing was performed using an electrodynamic axial-torsional machine. The cyclic impingement load of 25–250N was applied on the rims through the necks of the femoral stems at 1Hz. The rotational torque was simultaneously generated by swinging the stem necks on the rims at 1Hz and its rotational angle was set at the range of 0–10˚. The percent crystallinity was analyzed on the as-received (intact) and impinged HXLPE acetabular rims by confocal Raman microspectroscopy. Results. The number of cycles to failure was dependent on the offset length (2, 3, 4-mm) in 20_95 and 50E_300 liners. Our results showed that the shorter the rim offset, the shorter the number of cycles to failure. In both HXLPEs, accumulation of impingement damages significantly decreased crystallinity in their near-surfaces, indicating the occurrence of crystallographic breakdown. In each offset length tested, the fracture always occurred much earlier in 50E_300 than 20_95. However, the magnitudes of the microstructural changes at the time of failure were much less in 50E_300 than 20_95. Conclusions. Although it is known that vitamin E blend into HXLPE can improve the fatigue resistance of HXLPE, the impingement resistance of 50E_300 was lower than vitamin-E free 20_95, indicating a larger negative contribution of high-dose radiation (300kGy) over a positive contribution of the vitamin E blend in 50E_300. Our results implied that the reduction of the protruded rim length in the offset liners may increase the neck-rim contact stresses at the time of impingement, causing a decrease in the fatigue durability. Therefore, if HXLPE offset liner is used, surgeons should take special care in maximizing the volume of the protruded lip section

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

Introduction. First-generation annealed HXLPE has been clinically successful at reducing both clinical wear rates and the incidence of osteolysis in total hip arthroplasty. However, studies have observed oxidative and mechanical degradation occurring in annealed HXLPE. Thus, it is unclear whether the favorable clinical performance of 1st generation HXLPE is due to the preservation of bearing surface tribological properties or, at least partially, to the reduction in patient activity. The purpose of this study was to evaluate the in vitro wear performance (assessed using multidirectional pin-on-disk (POD) testing) of 1. st. -generation annealed HXLPE with respect to in vivo duration, clinical wear rates, oxidation, and mechanical properties. Materials and Methods. 103 1. st. -generation annealed HXLPE liners were collected at revision surgery. 39 annealed HXLPE liners were selected based on their implantation time and assigned to three equally sized cohorts (n=13 per group); short-term (1.4–2.7y), intermediate term (5.2–8.0y) and long-term (8.3–12.5y). From each retrieved liner, two 9-mm cores were obtained (one from the superior region and one from the inferior region). Sixteen cores were fabricated from unimplanted HXLPE liners that were removed from their packaging and six pins from unirradiated GUR 1050 resin served as positive controls. Multidirectional POD wear testing was conducted against wrought CoCr disks in a physiologically relevant lubricant (20 g/L protein concentration) using a 100-station SuperPOD (Phoenix Tribology, UK). Each pin had its own chamber with 15mL lubricant maintained at 37±1°C. An elliptical wear pattern with a static contact stress of 2.0 MPa was employed. Testing was carried out to 1.75 million cycles at 1.0 Hz and wear was assessed gravimetrically. POD wear rates were calculated using a linear regression of volumetric losses. In vivo penetration was measured directly using a calibrated micrometer. Oxidation was assessed on thin films obtained from superior and inferior regions of the liners (ASTM 2102). Mechanical properties were assessed using the small punch test (ASTM 2183). Results. In vitro wear rates from the SuperPOD were positively correlated with implantation time (Rho=0.27; p=0.015) and average oxidation (Rho=0.36; p=0.004) at the bearing surface of the retrieved HXLPE liners. All retrieved HXLPE cohorts had lower in vitro wear rates than uncrosslinked positive control (p≤0.03) and higher wear rates than the never-implanted HXLPE cohort (p <0.001). POD wear rates were negatively correlated with small punch ultimate load (p<0.01). However, the in vitro wear rates were not correlated with clinical penetration rates (p=0.71). Discussion. This study investigated the effects of in vivo degradation on 1. st. -generation annealed HXLPE liners. The data in this study suggest that the tribological properties degrade due to in vivo oxidation as the liner is exposed to the in vivo environment. The clinical implications of these findings, however, are not clear as the clinical penetration rates were not correlated with the in vitro POD wear rates. This may be partially due, to decreasing patient activity as they age. These findings will be useful for comparison for evaluating the in vitro wear properties of other HXLPEs, including 2nd generation HXLPE. Acknowledgements. This study was supported by the NIH(NIAMS) R01AR47904

Introduction. Sequentially annealed highly crosslinked polyethylenes (HXLPEs) were introduced in total knee replacement (TKR) starting in 2005 to reduce wear and particle-induced osteolysis. Few studies have reported on the clinical performance of HXLPE knees. In this study, we hypothesized that due to the reduced free radicals, sequentially annealed HXLPE would have lower oxidation levels than gamma inert-sterilized controls. Methods. 145 tibial components were retrieved at consecutive revision surgeries at 7 different surgical centers. 74 components were identified as sequentially annealed HXLPE (X3, Stryker) while the remainder (n = 71) were conventional gamma inert sterilized polyethylene. The sterilization method was confirmed by tracing the lot numbers by the manufacturer. The conventional inserts were implanted for 1.7 years (Range: 0.0–9.3 years), while the X3 components were implanted 1.1 years (Range: 0.0–4.5 years). Surface damage was assessed using the Hood method. Oxidation analysis was performed in accordance with ASTM 2102 following submersion in boiling heptane for 6 hours to remove absorbed lipids. 30 of the conventional and 29 of the HXLPE inserts were available for oxidation analysis. Results. The predominant reasons for revision were loosening, instability, and infection for both material cohorts. None of the highly crosslinked tibial inserts were revised for osteolysis. Pitting, scratching, and burnishing were the predominant damage mechanisms within both material groups. Delamination was not present within the highly crosslinked inserts. Oxidation indices were similar between the two cohorts at the bearing surface, AP face, and the post (p>0.30). Oxidation was lower at the backside surface in the HXLPE group when compared to the gamma inert group (p=0.04). In the HXLPE group, the backside surface had lower oxidation indices than the bearing surface (p = 0.02), post (p < 0.02), and AP Face (p = 0.001). In the HXLPE cohort, only the bearing surface was positively correlated with implantation time (Rho = 0.51; p = 0.01); whereas, the oxidation indices in the gamma inert cohort were not correlated with implantation time. Discussion. This study evaluated the surface damage mechanisms and oxidative stability of 2nd generation HXLPE in total knee replacement. Sequentially annealed HXLPE inserts exhibited comparable surface damage mechanisms and oxidation indices as compared with conventional inserts. Additional, longer-term HXLPE retrievals are necessary to ascertain the long term in vivo stability of these materials in total knee replacement

Different types of highly cross-linked polyethylene (HXLPE) have been introduced widely in acetabular cups in hip prostheses to reduce the incidence of wear debris-induced osteolysis. Also, we reported that HXLPE cups with 28-mm alumina ceramic femoral head exhibited lower wear than conventional PE cups. Recently, the combination of HXLPE cup and larger diameter femoral head is used widely to prevent dislocation. In this study, we examined the wear of HXLPE with 32-mm alumina ceramic femoral head and compared it with the wear of HXLPE with 28-mm alumina ceramic femoral head. The in vivo wear of 60 HXLPE cups (Aeonian; Kyocera Corp., Kyoto, Japan, currently Japan Medical Materials Corp., Osaka, Japan) with 28-mm alumina ceramic femoral head with clinical use for 3.1–9.1 years (mean 7.4 years) and eight HXLPE cups with 32-mm alumina ceramic femoral head used for 2.3–3.2 years (mean 2.8 years) were examined by radiographic analysis. The early wear rate for the first year of HXLPE cups with 28-mm and 32-mm alumina ceramic femoral head were 0.24±0.10 mm/year and 0.29±0.12 mm/year respectively. There was no significant difference in both femoral head groups (p>0.05). The steady wear rate after 1 year were 0.001±0.03 mm/year and −0.03±0.10 mm/year respectively. There was no significant difference either in both femoral head groups (p>0.05). These findings from this radiographic analysis suggest that the early wear rate in the first 1 year probably represents the creep deformation in bedding-in stage; and the steady wear rate after 1 year probably represents mainly the wear than of the creep deformation. By the radiographic analysis, HXLPE cups in both femoral head groups exhibited low steady wear rate. In conclusion, we expect that the combination of HXLPE cup and 32-mm diameter alumina ceramic femoral head has favorable wear properties with possibility of prevention of dislocation in long-term clinical use