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.

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

Summary. Sequentially irradiated and annealed UHMWPE hip and knee retrievals showed subsurface in vivo oxidation in both the articular surface and unloaded surfaces, while three of four never-implanted shelf stored liners had oxidation in the bulk. Introduction. Highly cross-linked polyethylene was developed to improve the wear resistance of UHMWPE bearing surfaces in total hip arthroplasty. First generation irradiated and annealed polyethylene showed high oxidation in vivo, largely attributed to only the partial-quenching of free radicals, along with additional radicals generated during terminal gamma sterilization. A second generation, three-step sequential irradiation and annealing method was advanced with the promise of better oxidative stability and improved mechanical properties. We hypothesised that without the complete elimination of free radicals combined with gas plasma sterilization requiring oxygen-permeable packaging, that this second generation material would be prone to shelf-oxidation in addition to in vivo oxidation. Patients & Methods. Fifty surgically-retrieved sequentially irradiated and annealed, gas plasma-sterilised UHWMPE acetabular liners and tibial bearings (X3™, Stryker, Mahwah, NJ), with in vivo durations of 0.5–73 months, were analyzed at their articular surface and an unloaded surface, along with four never implanted acetabular liners. Infrared microscopy was used to evaluate lipid absorption, oxidation (per ASTM F2102-01ε1) and hydroperoxide levels after nitric oxide staining. Gravimetric swelling analysis assessed cross-link density (per ASTM F2214), and crystallinity measurements were performed using differential scanning calorimetry. Results. There was detectable oxidation (OI > 0.1) in 37 of the 50 components with as little as 2 weeks of in vivo service. Maximum oxidation values averaged OI = 0.30 ± 0.30 (range = 0.03–1.59). Oxidation profiles were predominantly characterised by subsurface oxidation peaks approximately 1–2 mm below the surface, in both the articular surface and rim, along with a pattern of embrittlement induced white banding in four and six year liners. Three short in vivo duration liners (0.1–15.5 month) showed oxidation and degradation of material properties throughout the bulk. Three of four never-implanted liners, with up to five years shelf storage, also showed bulk oxidation (Max OI ≤ 1.5), loss of cross-link density and increased crystallinity. Discussion/Conclusion. High levels of detectable oxidation, subsurface oxidation peaks, and white banding were all identified in sequentially irradiated and annealed UHMWPE retrievals with short in vivo durations. These results raise concerns about the long-term clinical performance of these materials. Oxidation measured in shelf-stored, never implanted liners also raises concerns that liners may already be oxidatively compromised before being implanted into patients. Due to gas plasma sterilization methods, these free-radical containing liners are packaged and stored in air, likely resulting in a pre-implantation oxidation effect similar to that historically reported in gamma-in-air sterilised UHMWPE. Longer-term retrievals are needed to better understand the progress of these in vivo changes and whether or not it will compromise the longevity of the implants

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. 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

One of serious issues in total hip arthroplasty (THA) is the osteolysis which results in aseptic loosening caused by the wear particles from a polyethylene (PE) acetabular cup. In addition, oxidation degradation of PE cup resulting in the fracture or the severe wear caused by the reduction of mechanical properties in vivo is also the issue. The oxidation degradation is considered to be induced by residual free radicals generated by gamma-ray irradiation for cross-linking to reduce wear or for sterilization. In this study, (1) wear property, (2) oxidation degradation of retrieved PE and highly cross-linked PE (CLPE) cups against alumina ceramic femoral heads, and (3) the correlation between those properties were evaluated. The radiographic wear of six conventional PE cups with the mean follow-up of 19.1–23.3 years and 60 CLPE cups with the mean follow-up of 3.1–9.1 years were measured by a non-radiostereometric analysis method (Vectorworks. ®. 10.5 software package). As a retrieval analysis, 26 retrieved acetabular cups were evaluated; 16 cups were ethylene oxide gas-sterilized conventional PE cups with clinical use for 16.0–24.9 years and 10 cups were gamma-ray-sterilized CLPE cups with clinical use for 0.9–6.7 years. The linear and the volumetric wear were measured using a three-dimensional (3D) coordinate measurement machine. The shapes of unworn and worn surfaces with 15- and 30-point intervals, respectively, were measured. Oxidation degradation of the surface, sub-surface and inner for both worn and unworn parts of the retrieved cups was measured using a Fourier-transform infrared (FT-IR) spectroscopy. Oxidation indices were calculated using the peak at 1740 cm. −1. and 1370 cm. −1. according to ASTM F2012. In the radiographic analysis, the linear wear rate of CLPE cups was significantly lower than that of conventional PE cups [Fig. 1]. In the retrieval analysis, the linear wear rate of CLPE cups (mean: 0.07 mm/year) showed a 51% reduction (p = 0.002) compared to conventional PE cups (mean: 0.14 mm/year) [Fig. 2]. The retrieval and the radiographic analysis for both conventional PE and CLPE cups showed similar results (p = 0.7 and 0.1, respectively). Maximum oxidation indices for CLPE cups were similar to those of conventional PE cups regardless of the difference of clinical duration [Fig. 3]. This result is different from in vivo wear, which increases as the clinical duration. For both conventional PE and CLPE cups, the oxidation indices of subsurface were higher than those for surface. The worn parts showed higher oxidation indices than those for unworn parts. From the results, even when the free radicals were so few or absent, the oxidation degradation would be induced in vivo. In conclusion, the wear resistance for CLPE cups was greater than that for conventional PE cups from both radiographic and retrieval analyses. The in vivo oxidation degradation might not be caused by only residual free radicals. It was found that oxidation degradation of PE cups when used with alumina ceramic femoral heads is not correlated to their wear properties

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

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

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. 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

One of important issues of concern in total hip arthroplasty (THA) is osteolysis due to wear debris of ultra-high molecular weight polyethylene (PE), and it often leads to aseptic loosening. Reduction of PE wear debris is essential to prevent osteolysis, and different bearing interfaces as well as improvement of the bearing material itself have been attempted. Alumina ceramics as the bearing material for THA was introduced in Europe and Japan in the 1970s in aim to reduce the PE wear debris. The clinical results have proved the superiority of ceramic on PE couples to metal on PE couples in wear resistance. PE materials cross-liked by irradiation have also demonstrated a significant low wear by in vitro studies. Several types of highly cross-linked polyethylene (CLPE), with the irradiation dose of 50 to 105 kGy, have been developed and extensively used since 1998. In this study, the in vivo wear and oxidation of CLPE acetabular cup combined with ceramic femoral head were evaluated using retrieved cups. Eight retrieved CLPE acetabular cups (Aeonian; Kyocera Corp., Kyoto, Japan, currently Japan Medical Materials Corp., Osaka, Japan) with clinical use for 3–80 months (mean 34 months) were examined. All cups were used against alumina or zirconia ceramic femoral heads. The linear wear of the retrieved CLPE cups was measured using a three-dimensional coordinate measurement machine. The worn surfaces of retrieved CLPE cups were observed by a scanning electron microscope (SEM). Oxidative degradation of the retrieved CLPE cups was expressed in terms of an oxidation index which was calculated from microscopic Fourier transformed infrared spectroscopy analysis, according to ASTM F2102. The linear wear rate of retrieved CLPE cups was in 0.006–0.08 mm/year range, which was similar to the results reported by the previous radiographic study. In the worn surface of the CLPE cup retrieved after clinical use shorter than 39 months, machine marks were observed. In contrast, those retrieved after clinical use of 70 and 80 months were smooth. Oxidation indices of retrieved CLPE cups were: 0.12–0.37 in worn surface and 0.13–0.34 in unworn surface, respectively. There was no difference in the oxidation indices between the worn surface and unworn surface. The retrieved CLPE acetabular cups in this study showed low and stable wear rates. The results showed a notable reduction in wear of the CLPE cups compared to that of conventional PE cups in the previous studies. And also, the oxidation indices of the retrieved CLPE cups were the same level as conventional PE cups. These findings from this retrieval study showed that there is neither progressive wear in the clinical use for 3–80 months, material failures due to wear, delamination nor cracks. The lower wear rate and smooth surface of the CLPE acetabular cup suggest the possibility of reduced wear debris from those cups articulated against the ceramic femoral head. We expect that the CLPE acetabular cup has favorable wear properties in long-term clinical use

Purpose: Several variables related to tourniquet (TQ) inflation contribute to ischemic muscle injury. Among these the duration of ischemia has been identified as a primary factor. The purposes of this study were to investigate the following during and after TQ-induced ischemia during orthopedic trauma surgery:. muscle oxygenation changes measured by near infrared spectroscopy (NIRS);. muscle protein oxidation; and. correlations between muscle oxygenation / hemodynamics and oxidative changes. Method: Consented patients aged 19–69 yrs (n=18) with unilateral ankle fracture requiring surgery at our institution were recruited. A pair of NIRS probes was fixed over the midpoint of the tibialis anterior muscle (TA) on both the injured and healthy legs. A thigh TQ was applied to the injured leg and inflated to 300 mmHg. Using the NIRS apparatus coupled to a laptop with data acquisition software, changes in oxygenated (O2Hb), deoxygenated (HHb), and total hemoglobin (tHb) levels in the TA of both legs were measured before and during TQ inflation, and after release until values returned to baseline. PRE surgical biopsies were collected from the peroneus tertius muscle (PT) immediately after TQ inflation and incision. POST biopsies were collected from the same PT immediately before TQ deflation. Oxidation of PT myosin, actin, and total protein was quantified using Western blot analysis of 4-hydroxynonenal (4-HNE) modified proteins. Data are reported as mean±SD. Results: In PRE biopsies compared to POST biopsies there were large and statistically significant increases in the PT content of 4-NE modified myosin (174.4±128%; P< 1×10-6), actin (223.7±182%; P< 5×10-9), and total protein (567.5±378%; P< 5×10-7). There was a greater increase in PT protein oxidation in male subjects than in female subjects (50.8% difference; P< 0.05). In the TA of the fractured side, there were moderate to strong linear correlations between total protein oxidation and: the relative change in tHb (r=−0.704) and O2Hb (r=−0.415) during the period of TQ inflation and the rate at which the muscle became reoxygenated following TQ release (r=0.502). There was no relationship between muscle protein oxidation and TQ time, nor between muscle protein oxidation and age of patients. Conclusion: TQ-induced muscle ischemia for 21 to 74 min during lower extremity surgery leads to oxidative muscle injury as measured according to myofibrillar contractile protein oxidation. Importantly, we observed that when the TQ was “leaky,” local increases in muscle tHb were associated with a lower magnitude of protein oxidation, however, when local decreases in muscle O2Hb were observed, perhaps due to local blood loss below the TQ, more oxidative changes resulted. Intriguingly, gender appeared to influence the extent of muscle oxidative injury, but age did not. Surprisingly, there was no significant correlation between muscle oxidative injury and the TQ-induced ischemia interval. FUNDING: MSFHR, COF, BCLA

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.

The osseointegration of implants is related to the early interactions between osteoblastic cells and titanium surfaces. The behavior of osteoblast cells was compared on four different titanium surfaces in vitro and in vivo: machined, blasted, plasma spray and micro-arc oxidation.

X-ray diffraction and scanning electron microscope investigations were performed in order to assess the structure and morphology. Biologic and morphologic responses to the osteoblast cell lines (Saos-2) were then examined, using Promega proliferation assay, alkaline phosphatase activity, vβ3 integrin expression and cytoskeleton staining (Rhodamine-Phallodine). The analysis of gene expression for osteocalcin and collagen I was done through RT-PCR. In addition, differential histologic evaluation and interfacial strength at the bone-implant interfaces were then evaluated in the distal femur of four beagle dogs.

In conclusion, micro-arc oxidation of titanium appears to exhibit more favorable osteoblast adhesion and stronger interfacial strength than the compared groups in vitro and in vivo as well.

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.

Since the Oxford knee was first used unicompartmentally in 1982, a small number of bearings have fractured. Of 14 retrieved bearings, we examined ten samples with known durations in situ (four Phase 1, four Phase 2 and two Phase 3). Evidence of impingement and associated abnormally high wear (> 0.05 mm per year) as well as oxidation was observed in all bearings. In four samples the fracture was associated with the posterior radio-opaque wire. Fracture surfaces indicated fatigue failure, and scanning electron microscopy suggested that the crack initiated in the thinnest region. The estimated incidence of fracture was 3.20% for Phase 1, 0.74% for Phase 2, 0.35% for Phase 3, and 0% for Phase 3 without the posterior marker wire. The important aetiological factors for bearing fracture are impingement leading to high wear, oxidation, and the posterior marker wire. With improved surgical technique, impingement and high wear should be prevented and modern polyethylene may reduce the oxidation risk. A posterior marker wire is no longer used in the polyethylene meniscus. Therefore, the rate of fracture, which is now very low, should be reduced to a negligible level.

Introduction

Micro-arc oxidation (MAO) is an electrochemical method used to treat metal surfaces. It provides nanoporous pits, and thick oxide layers, and incorporates calcium and phosphorus into the coating layer of titanium alloy. This modification on the surface of titanium alloy by MAO coating would improve the ability of cementless stems to osseointegrate. In spite of these structural and chemical advantages, clinical study of total hip arthroplasty (THA) using MAO coated stem has not yet been reported. In this study, we evaluated the clinical and radiographic results associated with cementless grit-blasted tapered-wedge stems that were identical in geometry but differed with regard to surface treatment with or without MAO coating.

Introduction:

The solvent extraction step applied in conventional oxidation measurement protocols for UHMWPE retrievals resulted in an elevated oxidation index (OI) in remelted highly cross-linked UHMWPE (RM-HXLPE). The present study seeks to confirm the effect of solvent extraction on OI measurement and to understand the relationships among soak-aging, fluid uptake, and resulting OI from various test protocols.

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.

Biocompatibility of Co-Cr alloy was significantly improved by forming rough TiO2 layer on the surface. The TiO2 layer was formed by coating the Co-Cr alloy with Ti through electron beam deposition followed by micro-arc oxidation (MAO) of the Ti. Biocompatibility of Co-Cr alloy was enhanced by coating with titanium, and it was improved further by micro-arc oxidation treatment. MAO process was dependent on the thickness of coated titanium layer and applied voltage. There were close relationships between the phase, morphology and thickness of TiO2 layer and the applied voltage. Biocompatibility of the specimens coated with Ti and MAO treated after Ti coating were evaluated by in vitro ALP activity tests.