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1.  Low Wear of a Second-generation Highly Crosslinked Polyethylene Liner: A 5-year Radiostereometric Analysis Study 
Background
A sequentially irradiated and annealed, second-generation highly crosslinked polyethylene (XLPE) liner was introduced clinically in 2005 to reduce in vivo oxidation. This liner design has also been shown to reduce wear in vitro when compared with conventional and first-generation crosslinked liners. To date, there is only one study reporting an in vivo wear rate of this liner at 5 years’ followup. However, that study used measurements made from plain radiographs, which have limited sensitivity, particularly when monitoring very low amounts of wear.
Questions/purposes
What is the amount and direction of wear at 5 years using radiostereometric analysis (RSA) in patients who had THAs that included second-generation XLPE?
Methods
We prospectively reviewed 21 patients who underwent primary cementless THA with the same design of XLPE acetabular liner and 32-mm articulation. Tantalum markers were inserted during surgery and all patients had RSA radiographs at 1 week, 6 months, and 1, 2, and 5 years postoperatively. Femoral head penetration within the acetabular component was measured with UmRSA® software. One patient died and two had incomplete radiographs leaving 18 radiographic series for analysis.
Results
The mean amounts of proximal, two-dimensional, and three-dimensional head penetration between 1 week and 5 years were 0.018, 0.071, and 0.149 mm, respectively. The mean proximal, two-dimensional, and three-dimensional wear rates calculated between 1 year and 5 years were all less than 0.001 mm/year with no patient recording a wear rate of more than 0.040 mm/year.
Conclusions
The head penetration of a second-generation XLPE liner remained low at 5 years and the wear rate calculated after the first year was low in all directions. This low level of wear remains encouraging for the future clinical performance of this material.
Level of Evidence
Level IV, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-013-3188-z
PMCID: PMC3792282  PMID: 23893361
2.  Wear of a 5 Megarad Cross-linked Polyethylene Liner: A 6-year RSA Study 
Background
One cross-linked polyethylene (XLPE) liner is manufactured using a lower dose of radiation, 5 Mrad, which may result in less cross-linking. The reported in vivo wear rate of this XLPE liner in patients undergoing THA has varied, and has included some patients in each reported cohort who had greater than 0.1 mm/year of wear, which is an historical threshold for osteolysis. Previous studies have measured wear on plain radiographs, an approach that has limited sensitivity.
Questions/purposes
We therefore measured the amount and direction of wear at 6 years using Radiostereometric analysis (RSA) in patients who had THAs that included a cross-linked polyethylene liner manufactured using 5 Mrad radiation.
Methods
We prospectively reviewed wear in 30 patients who underwent primary THAs with the same design of cross-linked acetabular liner and a 28-mm articulation. Tantalum markers were inserted during surgery and all patients had RSA radiographic examinations at 1 week, 6 months, 1, 2, and 6 years postoperatively.
Results
The mean proximal, two-dimensional (2-D) and three-dimensional (3-D) wear rates calculated between 1 year and 6 years were 0.014, 0.014, and 0.018 mm/per year, respectively. The direction of the head penetration recorded between 1 week and 6 years was in a proximal direction for all patients, proximolateral for 16 of 24 patients, and proximomedial for eight of 24 patients.
Conclusions
The proximal, 2-D and 3-D wear of a XLPE liner produced using 5 Mrad of radiation was low but measurable by RSA after 6 years. No patients had proximal 2-D or 3-D wear rates exceeding 0.1 mm/year. Further followup is needed to evaluate the effect of XLPE wear particles on the development of long-term osteolysis.
doi:10.1007/s11999-013-2789-x
PMCID: PMC3676600  PMID: 23334705
3.  Retrieval Analysis of Sequentially Annealed Highly Crosslinked Polyethylene Used in Total Hip Arthroplasty 
Background
First-generation annealed and second-generation sequentially annealed, highly crosslinked polyethylenes (HXLPEs) have documented reduced clinical wear rates in their first decade of clinical use compared with conventional gamma inert-sterilized polyethylene. However, for both types of annealed HXLPE formulations, little is known about their reasons for revision, their in vivo oxidative stability, and their resistance to mechanical degradation.
Questions/purposes
We asked whether retrieved sequentially annealed HLXPE acetabular liners exhibited: (1) similar reasons for revision; (2) lower oxidation; (3) improved resistance to wear and degradation of mechanical properties; and (4) improved resistance to macroscopic evidence of rim damage when compared with acetabular liners fabricated from single-dose annealed HXLPE.
Methods
One hundred eighty-five revised acetabular liners in two cohorts (annealed and sequentially annealed) were collected in a multicenter retrieval program between 2000 and 2013. We controlled for implantation time between the two cohorts by excluding annealed liners with a greater implantation time than the longest term sequentially annealed retrieval (5 years); the mean implantation time (± SD) for the annealed components was 2.2 ± 1.4 years, and for the sequentially annealed liners, it was 1.2 ± 1.2 years. Reasons for revision were assessed based on medical records, radiographs, and examinations of the retrieved components. Oxidation was measured at the bearing surface, the backside surface, the locking mechanism, and the rim using Fourier transform infrared spectroscopy (ASTM F2102). Penetration was measured directly using a micrometer (accuracy: 0.001 mm). Mechanical behavior (ultimate load) was measured at the superior and inferior bearing surfaces using the small punch test (ASTM F2183). We used nonparametric statistical testing to analyze for differences in oxidation, penetration rates, and ultimate load when adjusting for HXLPE formulation as a function of implantation time.
Results
The acetabular liners in both cohorts were revised most frequently for instability, loosening, and infection. Oxidation indices (OIs) of the sequentially annealed liners were lower than annealed liners at the bearing surface (mean OI difference = 0.3; p < 0.001), the backside surface (mean OI difference = 0.2; p < 0.001), and the rim (mean OI difference = 2.6; p < 0.001). No differences were detected in linear penetration rates between the cohorts (p = 0.10). Ultimate strength at the bearing surface of the HLXPE was not different between sequentially annealed and annealed cohorts (p = 0.72).
Conclusions
We observed evidence of in vivo oxidation in retrieved annealed and, to a lesser extent, retrieved sequentially annealed acetabular liners. However, we observed no association between the levels of oxidation and clinical performance of the liners.
Clinical Relevance
The findings of this study document the oxidative and mechanical behavior of sequentially annealed HXLPE. The reduced oxidation levels in sequentially annealed liners support the hypothesis that annealing in sequential steps eliminates more free radicals. However, as a result of the short-term followup, analysis of longer-term retrievals is warranted.
doi:10.1007/s11999-014-4113-9
PMCID: PMC4317461  PMID: 25537808
4.  Femoral Head Size and Wear of Highly Cross-linked Polyethylene at 5 to 8 Years 
Abstract
Wear of highly cross-linked polyethylene is reportedly independent of head size. To confirm that observation we asked in our population whether head size related to wear with one type of electron beam highly cross-linked polyethylene. Of 146 hips implanted, we evaluated complete clinical and radiographic data for 90 patients (102 hips or 70%). The minimum followup was 5 years (mean, 5.7 years; range, 5–8 years). The head size was selected intraoperatively based on the size of the acetabular component and presumed risk of dislocation. Polyethylene wear measurements were performed in one experienced laboratory using the method of Martell et al. There was no hip with pelvic or femoral osteolysis. The median linear wear rate was 0.028 mm/year (mean, 0.04 mm/year), and the median volumetric wear rate was 25.6 mm3/year (mean, 80.5 mm3/year). Median total volumetric wear was 41.0 mm3 (mean, 98.5 mm3). We found no association between femoral head size and the linear wear rate, but observed an association between larger (36- and 40-mm) head size and volumetric wear rate and total volumetric wear. Although the linear wear rate of polyethylene was not related to femoral head diameter, there was greater volumetric wear (156.6 mm3/year) with the 36- and 40-mm heads. Pending long-term studies of large head sizes, we advise caution in using larger femoral heads in young or active patients and in those with a low risk of dislocation.
Level of Evidence: Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-009-1038-9
PMCID: PMC2772909  PMID: 19690932
5.  Second-generation Modular Acetabular Components Provide Fixation at 10 to 16 Years 
Background
First-generation modular titanium fiber-metal-coated acetabular components had high rates of wear, pelvic osteolysis, and liner dissociation. Second-generation components were designed to reduce the incidence of these problems but it is unclear whether the changes achieved these goals.
Questions/purposes
We asked the following questions: (1) Is the risk of revision surgery for loosening, wear, or liner dissociation low with the second-generation acetabular component? (2) Is the rate of pelvic osteolysis low? (3) Can the liner be exchanged without bone cement?
Methods
We retrospectively reviewed prospectively collected data from 99 patients (118 hips) undergoing THAs with one second-generation modular titanium acetabular component with routine screw fixation and conventional polyethylene. The minimum followup was 10 years (mean, 12 years; range, 10–16 years). We obtained Harris hip scores and examined radiographs for loosening and osteolysis.
Results
At last followup, all acetabular components were well fixed and no titanium shell had been revised or removed. No liner had dissociation. At most recent followup, the mean Harris hip score was 89. We observed pelvic osteolysis in eight hips (7%). There were three reoperations for dislocation (head-liner exchange only) and three loose femoral components revised. Two liners (at 11 and 14 years) were exchanged for wear-pelvic osteolysis.
Conclusions
This second-generation modular titanium fiber-metal-coated acetabular component with screw fixation had no loosening, no liner dissociation, and a low rate of pelvic osteolysis at 10 to 16 years. Liner exchange is practical without use of cement. We continue to use this component with highly crosslinked polyethylene liners.
Level of Evidence
Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-011-1950-7
PMCID: PMC3254771  PMID: 21691908
6.  Second-generation Annealed Highly Cross-linked Polyethylene Exhibits Low Wear 
Background
Compared with conventional polyethylene, first-generation highly cross-linked polyethylenes have low wear, but controversy exists regarding their reduced mechanical strength and/or retained free radicals. Second-generation highly cross-linked polyethylenes have been developed to reduce wear, maintain mechanical strength, and have oxidative resistance, but it is unclear whether they do so.
Questions/purposes
The primary objective of this study therefore was to determine if a second-generation annealed material has low linear wear at 5 years followup. Secondary objectives were to evaluate for overall survivorship, implant fixation, osteolysis, and effect of socket inclination on wear.
Methods
In a multicenter prospective study, we radiographically evaluated 155 patients (167 hips) at 3 years, 124 patients (132 hips) at 4 years, and 46 patients (51 hips) at 5 years. The linear head penetration rate was measured at 6 weeks, 1 year, and yearly through 5 years.
Results
The head penetration per year after the first year of bedding-in was 0.024 mm per year at 3 years, 0.020 mm per year at 4 years, and 0.008 mm per year at 5 years. The average wear rate over 5 years was 0.015 mm per year and represents a 58% improvement over a first-generation annealed highly cross-linked polyethylene. The Kaplan-Meier survivorship (revision for any reason) was 97.8%. We revised no hip for bearing surface failure and observed no osteolysis. Socket inclination did not affect linear wear.
Conclusions
These data suggest the linear wear rate for a second-generation annealed highly cross-linked polyethylene is no greater than that for historic controls of first-generation highly cross-linked polyethylenes, and no untoward complications were encountered with this new material.
Level of Evidence
Level II, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-011-2177-3
PMCID: PMC3348318  PMID: 22161120
7.  Wear Analysis in THA Utilizing Oxidized Zirconium and Crosslinked Polyethylene 
Oxidized zirconium, a material with a ceramic surface on a metal substrate, and highly cross-linked polyethylene are two materials developed to reduce wear. We measured in vivo femoral head penetration in patients with these advanced bearings. We hypothesized the linear wear rates would be lower than those published for cobalt-chrome and standard polyethylene. We retrospectively reviewed a select series of 56 THAs in a relatively young, active patient population utilizing oxidized zirconium femoral heads and highly cross-linked polyethylene acetabular liners. Femoral head penetration was determined using the Martell computerized edge-detection method. All patients were available for 2-year clinical and radiographic followup. True linear wear was 4 μm/year (95% confidence intervals, ± 59 μm/year). The early wear rates in this cohort of relatively young, active patients were low and we believe justify the continued study of these alternative bearing surfaces.
Level of Evidence: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-008-0544-5
PMCID: PMC2600989  PMID: 18946711
8.  Wear of a sequentially annealed polyethylene acetabular liner 
Acta Orthopaedica  2014;85(5):470-473.
Background and purpose
We previously reported on a randomized controlled trial (RCT) that examined the effect of adding tobramycin to bone cement after femoral stem migration. The present study examined femoral head penetration into both conventional and highly crosslinked polyethylene acetabular liners in the same group of RCT patients, with a minimum of 5 years of postoperative follow-up.
Patients and methods
Linear penetration of the femoral head into an X3 (Stryker) crosslinked polyethylene (XLPE) liner was measured in 18 patients (19 hips) using radiostereometric analysis (RSA). Femoral head penetration was also measured in 6 patients (6 hips) with a conventional polyethylene liner (CPE), which served as a control group.
Results
The median proximal femoral head penetration in the XLPE group after 5.5 years was 0.025 mm with a steady-state penetration rate of 0.001 mm/year between year 1 and year 5. The CPE liner showed a median proximal head penetration of 0.274 mm after 7.2 years, at a rate of 0.037 mm/year.
Interpretation
The Trident X3 sequentially annealed XLPE liner shows excellent in vivo wear resistance compared to non-crosslinked CPE liners at medium-term implantation. The rate of linear head penetration in the XLPE liners after > 5 years of follow-up was 0.001 mm/year, which is in close agreement with the results of previous studies.
doi:10.3109/17453674.2014.949044
PMCID: PMC4164863  PMID: 25140986
9.  THA with Highly Cross-linked Polyethylene in Patients 50 Years or Younger 
Highly cross-linked polyethylene has been associated with low in vitro wear, but also has decreased in vitro ultimate yield strength. We therefore asked whether highly cross-linked polyethylene would result in lower outcome scores, wear, or early failure in a young patient population. Seventy THAs in 64 patients were performed using a highly cross-linked (electron beam-irradiated to 9 Mrads) acetabular liner and a cobalt-chrome femoral head. The average age of the patients at surgery was 41 years (range, 19–50 years). The minimum followup was 2.4 years (average, 4 years; range, 2.4–6.5 years). We recorded demographic and clinical data, including Harris hip score. Polyethylene wear measurements were analyzed with a validated, computer-assisted, edge detection method. The average Harris hip score improved from 53 to 92 at last followup. There was no evidence of acetabular or femoral loss of fixation, subsidence, or loosening. Linear wear was undetectable at this followup interval. No patient experienced catastrophic failure or underwent revision surgery. These data show low polyethylene wear rates and no catastrophic failures at early followup in a young patient cohort.
Level of Evidence: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-008-0697-2
PMCID: PMC2706339  PMID: 19142685
10.  More than 50% reduction of wear in polyethylene liners with alumina heads compared to cobalt-chrome heads in hip replacements 
Acta Orthopaedica  2013;84(4):360-364.
Background and purpose
Excessive wear of acetabular liners in hip replacements may lead to osteolysis and cup loosening. Different head materials are currently used. We measured differences in wear between alumina and cobalt-chrome heads with the same polyethylene liner.
Patients and methods
39 patients (43 hips) with osteoarthritis were included in a study with 10-year follow-up. Wear was measured as proximal and 3D penetration of the head in the liner with radiostereometry (RSA). All the patients were followed clinically with Harris hip score (HHS) for up to 10 years. Radiolucent lines and osteolytic lesions were assessed on plain radiographs.
Results
With alumina heads, proximal wear (95% CI) after 10 years was 0.62 (0.44–0.80) mm as compared to 1.40 (1.00–1.80) mm in the cobalt-chrome group. For 3D wear, the results were 0.87 (0.69–1.04) mm for alumina heads and 1.78 (1.35–2.21) mm for cobalt-chrome heads. Median (range) HHS was 98 (77–100) in the alumina group and it was 93 (50–100) in the cobalt-chrome group (p = 0.01). We found no difference in osteolysis between the groups.
Interpretation
We found better wear properties with alumina heads than with cobalt-chrome heads. We recommend the use of alumina heads in patients in whom a high wear rate might be anticipated.
doi:10.3109/17453674.2013.810516
PMCID: PMC3768034  PMID: 23795579
11.  Characteristics of highly cross-linked polyethylene wear debris in vivo 
Despite the widespread implementation of highly cross-linked polyethylene (HXLPE) liners to reduce the clinical incidence of osteolysis, it is not known if the improved wear resistance will outweigh the inflammatory potential of HXLPE wear debris generated in vivo. Thus, we asked: What are the differences in size, shape, number, and biological activity of polyethylene wear particles obtained from primary total hip arthroplasty revision surgery of conventional polyethylene (CPE) versus remelted or annealed HXLPE liners? Pseudocapsular tissue samples were collected from revision surgery of CPE and HXLPE (annealed and remelted) liners, and digested using nitric acid. The isolated polyethylene wear particles were evaluated using scanning electron microscopy. Tissues from both HXLPE cohorts contained an increased percentage of submicron particles compared to the CPE cohort. However, the total number of particles was lower for both HXLPE cohorts, as a result there was no significant difference in the volume fraction distribution and specific biological activity (SBA; the relative biological activity per unit volume) between cohorts. In contrast, based on the decreased size and number of HXLPE wear debris there was a significant decrease in total particle volume (mm3/g of tissue). Accordingly, when the SBA was normalized by total particle volume (mm3/gm tissue) or by component wear volume rate (mm3/year), functional biological activity of the HXLPE wear debris was significantly decreased compared to the CPE cohort. Indications for this study are that the osteolytic potential of wear debris generated by HXLPE liners in vivo is significantly reduced by improvements in polyethylene wear resistance.
doi:10.1002/jbm.b.32902
PMCID: PMC3928672  PMID: 23436587
total hip replacementhighly cross-linked polyethyleneosteolysiswear debrisbiological activity
12.  A Multicenter Approach Evaluating the Impact of Vitamin E-Blended Polyethylene in Cementless Total Hip Replacement 
Orthopedic Reviews  2014;6(2):5285.
Since polyethylene is one of the most frequently used biomaterials as a liner in total hip arthroplasty, strong efforts have been made to improve design and material properties over the last 50 years. Antioxidants seems to be a promising alternative to further increase durability and reduce polyethylene wear in long term. As of yet, only in vitro results are available. While they are promising, there is yet no clinical evidence that the new material shows these advantages in vivo. To answer the question if vitamin-E enhanced ultra-high molecular weight polyethylene (UHMWPE) is able to improve long-term survivorship of cementless total hip arthroplasty we initiated a randomized long-term multicenter trial. Designed as a superiority study, the oxidation index assessed in retrieval analyses of explanted liners was chosen as primary parameter. Radiographic results (wear rate, osteolysis, radiolucency) and functional outcome (Harris Hip Scores, University of California-Los Angeles, Hip Disability and Osteoarthritis Outcome Score, Visual Analogue Scale) will serve as secondary parameters. Patients with the indication for a cementless total hip arthroplasty will be asked to participate in the study and will be randomized to either receive a standard hip replacement with a highly cross-linked UHMWPE-X liner or a highly cross-linked vitamin-E supplemented UHMWPE-XE liner. The follow-up will be 15 years, with evaluation after 5, 10 and 15 years. The controlled randomized study has been designed to determine if Vitamin-E supplemented highly cross-linked polyethylene liners are superior to standard XLPE liners in cementless total hip arthroplasty. While several studies have been started to evaluate the influence of vitamin-E, most of them evaluate wear rates and functional results. The approach used for this multicenter study, to analyze the oxidation status of retrieved implants, should make it possible to directly evaluate the ageing process and development of the implant material itself over a time period of 15 years.
doi:10.4081/or.2014.5285
PMCID: PMC4083306  PMID: 25002933
total hip arthroplasty; antioxidants; PE; UHMWPE; vitamin-E; oxidation; wear; randomized trial
13.  Mid-term results of large diameter heads on cross-linked polyethylene liners in total hip replacement 
Background
Highly cross-linked polyethylene liners in total hip replacement (THR) have allowed the use of larger diameter femoral heads. Larger heads allow for increased range of motion, decreased implant impingement, and protection against dislocation. The purpose of this study is to assess the clinical and radiographic outcomes of patients with large femoral heads THR at 4 years postop.
Materials and methods
Study includes 28 patients who had a primary THR with a 36 mm larger femoral head were retrospectively for minimum 4 years follow-up. All patients received a cementless acetabular shell and a highly cross-linked polyethylene liner with an inner diameter of 36 mm. The median radiographic follow-up was 4 years (range 2.0–6.0), and patients were assessed clinically by Harris hip score.
Results
The mean follow-up is minimum 4 years (range 2–6 years) results in all operated patients showed marked improvement in Harris hip score from preoperative mean 49.1 to 89.9 at 4 years or more follow-up. The complications include superficial infection (n = 2). No dislocation, or no osteolysis was seen in the pelvis or proximal femur, and no components failed due to aseptic loosening. There was no evidence of cup migration, screw breakage, or eccentric wear on the liner.
Conclusion
The mid-term results in this series of patients with LDH using 36 mm femoral head articulating with highly cross linked polyethylene showed excellent clinical, and radiological results, in terms of, joint restoration that replicates the natural anatomy, optimized range of motion without impingement & reduced opportunity for postoperative dislocation.
doi:10.1016/j.jcot.2012.10.003
PMCID: PMC3872809
Large diameter heads; Total hip arthroplasty; Harris hip score
14.  The Incidence of Acetabular Osteolysis in Young Patients With Conventional versus Highly Crosslinked Polyethylene 
Background
Osteolysis is a major mode of hip implant failure. Previous literature has focused on the amount of polyethylene wear comparing highly crosslinked polyethylene (HXPLE) with conventional liners but has not clarified the relative incidence of osteolysis with these two liners.
Questions/purposes
We determined (1) the incidence of osteolysis in HXLPE versus conventional polyethylene (CPE), (2) the ability to detect and evaluate the size of lytic lesions using radiographs compared with CT scans, (3) head penetration in hips without and with lysis, and (4) determined whether acetabular position, head size, and UCLA activity score contributed to lysis.
Methods
We compared head penetration and osteolysis on plain radiographs and presence and volume of osteolysis on CT scans in 48 patients with HXLPE (mean, 46.5 years) and 50 patients with CPE (mean, 43.2 years). The minimum followup was 5 years (average, 7.2 years; range, 5.1–10.9 years),
Results
Osteolysis was apparent on CT in a larger number of patients with CPE liners than HXLPE liners: 12 of 50 (24%) versus one of 48 (2%), respectively. We found no correlation between head penetration and volume of osteolytic lesions. Head penetration was greater in patients with osteolysis. Smaller head sizes were associated with greater wear and those with osteolysis had smaller head sizes; however, there was no difference in acetabular component position or UCLA activity in those with lysis compared with those without.
Conclusions
HXLPE diminished the incidence of osteolysis, but the lack of correlation between penetration and volume of osteolysis suggests other factors other than wear contribute to the development of osteolysis.
Level of Evidence
Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-010-1518-y
PMCID: PMC3018187  PMID: 20824407
15.  History and Systematic Review of Wear and Osteolysis Outcomes for First-generation Highly Crosslinked Polyethylene 
Background
Highly crosslinked polyethylene (HXLPE) was introduced to reduce wear and osteolysis in total joint arthroplasty. While many studies report wear and osteolysis associated with HXLPE, analytical techniques, clinical study design and followup, HXLPE formulation and implant design characteristics, and patient populations differ substantially among investigations, complicating a unified perspective.
Questions/purposes
Literature on first-generation HXLPE was summarized. We systematically reviewed the radiographic wear data and incidence of osteolysis for HXLPE in hip and knee arthroplasty.
Methods
PubMed identified 391 studies; 28 met inclusion criteria for a weighted-averages analysis of two-dimensional femoral head penetration rates. To determine the incidence of osteolysis, we estimated a pooled odds ratio using a random-effects model.
Results
Weighted-averages analyses of femoral head penetration rates in HXLPE liners and conventional UHMWPE liners resulted, respectively, in a mean two-dimensional linear penetration rate of 0.042 mm/year based on 28 studies (n = 1503 hips) and 0.137 mm/year based on 18 studies (n = 695 hips). The pooled odds ratio for the risk of osteolysis in HXLPE versus conventional liners was 0.13 (95% confidence interval, 0.06–0.27) among studies with minimum 5-year followup. We identified two clinical studies of HXLPE in TKA, preventing systematic analysis of outcomes.
Conclusions
HXLPE liner studies consistently report lower femoral head penetration and an 87% lower risk of osteolysis. Reduction in femoral head penetration or osteolysis risk is not established for large-diameter (> 32 mm) metallic femoral heads or ceramic femoral heads of any size. Few studies document the clinical performance of HXLPE in knees.
Electronic supplementary material
The online version of this article (doi:10.1007/s11999-011-1872-4) contains supplementary material, which is available to authorized users.
doi:10.1007/s11999-011-1872-4
PMCID: PMC3126942  PMID: 21431461
16.  Retrieval analysis of Harris-Galante I and II acetabular liners in situ for more than 10 years 
Acta Orthopaedica  2012;83(4):366-373.
Background and purpose
There have been few reports documenting the wear and oxidation performance of the polyethylene bearing surface of HGPI and HGPII THA devices.
We evaluated retrieved HGPI and HGPII acetabular liners that had been in situ for more than 10 years and determined whether there was a relationship between clinical and radiographic factors, surface damage, wear, and oxidation.
Materials and methods
129 HGPI and II acetabular liners with implantation times of > 10 years were retrieved at 4 institutions between 1997 and 2010. The liners were made from a single resin and were gamma radiation-sterilized in air. Surface damage, linear wear, and oxidation index (OI) were assessed. Differences in clinical and radiographic factors, surface damage, linear wear, and OI for the 2 designs were statistically evaluated separately and together.
Results
Articular surface damage and backside damage was similar in the 2 designs. The linear penetration rate was 0.14 (SD 0.07) mm/year for the HGPI liners and 0.12 (SD 0.08) mm/year for the HGPII liners. For both cohorts, the rim had a higher OI than the articular surface. 74% of the liners had subsurface cracking and 24% had a complete fracture through the acetabular rim.
Interpretation
Despite modification of the HGP locking mechanism in the HGPII design, dissociation of the liner from the acetabular shell can still occur if fracture of the rim of the liner develops due to oxidative degradation.
doi:10.3109/17453674.2012.717843
PMCID: PMC3427627  PMID: 22880709
17.  Do First-generation Highly Crosslinked Polyethylenes Oxidize In Vivo? 
Background
Highly crosslinked and thermally treated polyethylenes were clinically introduced to reduce wear and osteolysis. Although the crosslinking process improves the wear performance, it also introduces free radicals into the polymer that can subsequently oxidize. Thermal treatments have been implemented to reduce oxidation; however, the efficacy of these methods with regard to reducing in vivo oxidative degradation remains to be seen. Polyethylene oxidation is a concern because it can compromise the ultimate strength and ductility of the material.
Questions/purposes
We analyzed the oxidation, oxidation potential, and mechanical behavior of thermally treated highly crosslinked polyethylene retrieved acetabular liners.
Methods
Three hundred seven acetabular liners were collected from consecutive revision surgeries at six institutions over a 10-year period. Twenty-four were sterilized using nonionizing methods, 43 were sterilized in an inert environment, 80 were highly crosslinked and annealed, and 160 were highly crosslinked and remelted. Oxidation and oxidation potential were assessed by Fourier transmission infrared spectroscopy. Mechanical behavior was assessed by the small punch test.
Results
Oxidation and hydroperoxide (oxidation potential) indices were elevated in the annealed and gamma inert sterilized groups compared with those of the remelted liners and uncrosslinked gas sterilized controls, particularly at the rim. We also detected an increase in oxidation over time at the bearing surface of the remelted group. Ultimate strength of the polyethylene at the bearing surface was negatively correlated with implantation time for the annealed liners.
Conclusions
Within the first decade of implantation, the clinical outlook for first-generation highly crosslinked polyethylene remains promising. However, ongoing research continues to be warranted for first-generation highly crosslinked polyethylene bearings to monitor the implications of elevated oxidation at the rim of annealed liners as well as to better understand the subtle changes in oxidation at the bearing surface of remelted liners that occur in vivo.
doi:10.1007/s11999-010-1728-3
PMCID: PMC3126962  PMID: 21161740
18.  Continued Improved Wear with an Annealed Highly Cross-linked Polyethylene 
Background
Highly cross-linked polyethylene (HXLPE), created by disrupting the molecular structure of polyethylene, then through the application of heat, encourages creation of new cross-links in the process, resulting in a material with improved wear resistance. The impetuses for this new technology were the unsatisfactory wear properties and subsequent osteolysis of noncross-linked polyethylene. A 72% reduction in wear using highly cross-linked polyethylenes (HXLPE) compared with conventional polyethylene at 5 years was described previously. The longest term followup studies on HXLPE range from 2 to 6 years.
Questions/purposes
We therefore addressed the following questions: (1) Does the improvement in wear observed at the earlier followup continue to 7 to 10 years? (2) What is the incidence of osteolysis in this group of patients and in the control group?
Methods
We retrospectively reviewed 38 prospectively followed patients who had 42 hips with an annealed HXLPE who were followed a minimum of 7 years (average, 8.6 years; SD = 1; range, 7–10.3 years). Wear and osteolysis were compared with those of a control group of 39 patients (40 hips) from a US Investigational Device Exemption (IDE) prospective, randomized study begun in 1996 with conventional polyethylene and followed for a minimum of 6 years (average, 7.5 years; SD = 1.1; range, 6–10.2 years). Linear head penetration was measured from AP radiographs at early, 1-year, 5-year, and most recent followups.
Results
At the average followup, annual linear wear was 0.031 mm (SD = 0.014) for the HXLPE and 0.141 mm (SD = 0.080) for the control group, a 78% reduction. No mechanical failure of the polyethylene was noted in either group. Incidence of osteolysis was 50% in the control group (all lesions confined to proximal Gruen Zones 1 and 7) compared with no cases in the investigational group.
Conclusions
We observed an improvement in wear and no mechanical failures with this annealed material.
Level of Evidence
Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-010-1556-5
PMCID: PMC3032874  PMID: 20844996
19.  The Effect of Poly Sterilization on Wear, Osteolysis and Survivorship of a Press-fit Cup at 10-Year Followup 
Background
During the mid-1990s when our institution was using a press-fit porous-coated cup without supplemental initial fixation for primary THA, the manufacturer transitioned from gamma irradiation to gas plasma for the terminal sterilization of their polyethylene liners.
Questions/purposes
At minimum 10-year followup, we asked whether the fixation achieved by solely relying on a press-fit would be durable and how different liner sterilization methods affected radiographic wear, osteolysis, and survivorship.
Patients and Methods
We retrospectively reviewed 373 patients who underwent 398 primary THAs with a press-fit porous-coated cup between March 1995 and December 1996. Mean age at time of surgery was 61.5 ± 13.3 years and mean followup was 10.4 ± 3.7 years. We determined reasons for revision, survivorship, femoral head penetration, osteolysis, and wear-related complications.
Results
Among 20 revisions involving any component, seven were associated with wear and osteolysis. Kaplan-Meier survivorship, using component revision for any reason as an end point, was 95.7% (95% confidence interval, 93.6%–97.9%) at 10 years. Noncrosslinked liners sterilized with gas plasma demonstrated a mean head penetration rate of 0.20 ± 0.09 mm/year compared with 0.13 ± 0.07 mm/year for liners sterilized with gamma irradiation in air and 0.09 ± 0.04 mm/year for liners sterilized with gamma-irradiation with barrier packaging without oxygen. THAs with increased volumetric wear tended to demonstrate larger osteolytic lesions (r = 0.40) and there tended to be less osteolysis among the liners sterilized with gamma-irradiation with barrier packaging without oxygen. However, there was no difference in survivorship among the sterilization groups and there has been no cup or stem loosening associated with osteolysis.
Conclusions
Durable biologic fixation through 10-year followup can be achieved by solely relying on an initial press-fit. Noncrosslinking gas plasma for terminal sterilization of the polyethylene liners was associated with greater head penetration rate than gamma irradiation.
Level of Evidence
Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-011-2052-2
PMCID: PMC3254762  PMID: 21904891
20.  A comparison of polyethylene wear between cobalt-chrome ball heads and alumina ball heads after total hip arthroplasty: a 10-year follow-up 
Study design
This is a retrospective study comparing polyethylene wear between ceramic ball heads and metal ball heads in total hip arthroplasty.
Background
The ceramic-on-polyethylene bearing option has been introduced as an alternative to metal-on-polyethylene to minimize polyethylene wear debris and reduce subsequent osteolysis and aseptic loosening. However, the reported data were debatable. We designed this retrospective study to compare polyethylene wear between alumina ceramic ball heads and cobalt-chrome ball heads.
Methods
Bilateral simultaneous primary total hip arthroplasty was performed in 22 patients between January 2002 and December 2002, with one side using metal-on-polyethylene bearing surface and the other side using alumina ceramic-on-polyethylene bearing surface. After 10 years of follow-up, the wear rate of polyethylene liner on both sides was measured using the Dorr method and compared.
Results
The annual wear rate of the polyethylene liner was 0.133 mm with a standard deviation of 0.045 in the metal-on-polyethylene group and 0.056 mm with a standard deviation of 0.032 in the ceramic-on-polyethylene group. The wear rate per year was significantly lower in the ceramic-on-polyethylene group (p < 0.001).
Conclusions
Although the implication is still controversial, our study showed that the use of ceramic head lowered the liner wear rate.
Clinical relevance
Ceramic is harder and more resistant to scratching than cobalt-chrome. By increasing polyethylene liner survivorship and decreasing potential osteolytic response and aseptic loosening, ceramic head is a better alternative than cobalt-chrome head.
doi:10.1186/1749-799X-8-20
PMCID: PMC3720196  PMID: 23835248
21.  The Ringloc liner compared with the Hexloc liner in total hip arthroplasty 
Orthopedic Reviews  2009;1(2):e16.
The aim of this study was to compare the 10-year survival rate, pelvic osteolysis frequency and linear head penetration rate of the Hexloc and Ringloc liners used together with a partially threaded porous and hydroxyapatite coated cup and the Bi-Metric uncemented femoral stem. The 15-year results for the cup with the Hexloc liner are also reported. We included 332 consecutive hips (166 Hexloc and 166 Ringloc) on 281 patients in the study. Revisions of prosthesis components were recorded and pelvic osteolytic lesions were assessed using radiographs and computed tomography. The linear head penetration rate was measured using the Martell method. The 10-year survival rate of the liner with revision due to liner wear and/or osteolysis as endpoint was 88% for the Hexloc liner and 98% for the Ringloc liner. The 15-year survival rate of the Hexloc liner was 67%. Pelvic osteolysis was found in 27% of the Hexloc and 19% of the Ringloc hips. After 15 years, 53% of the Hexloc hips had developed an osteolytic lesion. The linear head penetration rate was 0.16 mm/year for the Hexloc liner and 0.12 mm/year for the Ringloc liner. This paper is the first to describe the rapidly deteriorating survival up to 15 years with the old generation gamma-in-air sterilized polyethylene used in Hexloc liners. The newer Ringloc liner with the ArCom™ polyethylene has superior clinical results but a linear wear rate and frequency of osteolytic lesions that is higher than expected.
doi:10.4081/or.2009.e16
PMCID: PMC3143985  PMID: 21808678
primary; total hip arthroplasty; osteolysis; cup; wear.
22.  Cross-linked Compared with Historical Polyethylene in THA: An 8-year Clinical Study 
Wear particle-induced osteolysis is a major cause of aseptic loosening in THA. Increasing wear resistance of polyethylene (PE) occurs by increasing the cross-link density and early reports document low wear rates with such implants. To confirm longer-term reductions in wear we compared cross-linked polyethylene (irradiation in nitrogen, annealing) with historical polyethylene (irradiation in air) in a prospective, randomized clinical study involving 48 patients who underwent THAs with a minimum followup of 7 years (mean, 8 years; range, 7–9 years). The insert material was the only variable. The Harris hip score, radiographic signs of osteolysis, and polyethylene wear were recorded annually. Twenty-three historical and 17 moderately cross-linked polyethylene inserts were analyzed (five patients died, three were lost to followup). At 8 years, the wear rate was lower for cross-linked polyethylene (0.088 ± 0.03 mm/year) than for the historical polyethylene (0.142 ± 0.07 mm/year). This reduction (38%) did not diminish with time (33% at 5 years). Acetabular cyst formation was less frequent (39% versus 12%), affected fewer DeLee and Charnley zones (17% versus 4%), and was less severe for the cross-linked polyethylene. The only revision was for an aseptically loose cup in the historical polyethylene group. Moderately cross-linked polyethylene maintained its wear advantage with time and produced less osteolysis, showing no signs of aging at mid-term followup.
Level of Evidence: Level I, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-008-0628-2
PMCID: PMC2650055  PMID: 19030941
23.  Clinical Comparison of Polyethylene Wear with Zirconia or Cobalt-Chromium Femoral Heads 
Ceramic femoral heads were developed to reduce the wear of conventional ultrahigh-molecular-weight polyethylene (UHMWPE) bearing surfaces in THA. We compared the wear rates of PE acetabular components bearing against femoral heads of zirconia (Zr) or cobalt-chromium (CoCr) in young patients. One surgeon inserted CoCr femoral heads in all 33 patients (33 hips) having THA for primary osteoarthritis from 1996 to 1997 and then Zr femoral heads in all 34 patients (36 hips) from 1998 to 1999. The mean age of the entire cohort was 52.5 years (range, 29–64 years). The shells were solid and hydroxyapatite (HA) -coated, liners were argon-sterilized UHMWPE, and head size was 28 mm. The minimum clinical followup was 56 months (mean, 65 months; range, 56–77 months); minimum 5-year radiographs were available for 62 of the 68 patients. Wear analysis of digitized anteroposterior (AP) radiographs was performed with a computerized method. Demographic data were comparable in the two groups. Mean femoral head penetration rate was similar in the two types of heads (CoCr: 0.25 mm/year; range, 0.21–0.33 mm/year; Zr: 0.23 mm/year; range, 0.20–0.29 mm/year), as was mean linear wear (CoCr: 1.22 mm; range, 0.28–3.78 mm; Zr: 1.11 mm; range, 0.15–2.05 mm). There were no revisions. These data support skepticism regarding the clinical wear advantage of Zr compared with CoCr femoral heads. The explanation for the clinical similarity of wear, despite the theoretical advantages of ceramic heads, needs further investigation.
Level of Evidence: Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-009-0799-5
PMCID: PMC2745450  PMID: 19326182
24.  Retrieved Highly Crosslinked UHMWPE Acetabular Liners Have Similar Wear Damage as Conventional UHMWPE 
Background
Highly crosslinked UHMWPE is associated with increased wear resistance in hip simulator and clinical studies. Laboratory and case studies, however, have described rim fracture in crosslinked acetabular liners. Controversy exists, therefore, on the relative merits of crosslinked liners over conventional liners in terms of wear performance versus resistance to fatigue cracking.
Questions/purposes
We asked whether crosslinked liners would show less surface damage than conventional liners but would be more susceptible to fatigue damage.
Methods
We examined 36 conventional UHMWPE and 39 crosslinked UHMWPE retrieved implants with similar patient demographics and identical design for evidence of wear damage, including articular surface damage, impingement, screw-hole creep, and rim cracks.
Results
We observed no difference in wear damage scores for the two liners. Conventional liners more frequently impinged but were more often elevated with smaller head sizes. We observed creep in approximately 70% of both types of liners. Incipient rim cracks were found in five crosslinked liners, and one liner had a rim fracture. Only one conventional liner had an incipient rim crack.
Conclusions
Contrary to our expectation, damage was similar between crosslinked and conventional UHMWPE liners. Moreover, the 15% occurrence (six of 39) of incipient or complete fractures in crosslinked liners as compared with a 3% occurrence (one of 36) in conventional liners may have implications for the long-term performance of crosslinked liners. Longer-term studies will be necessary to establish the fate of rim cracks and thus the overall clinical fatigue performance of crosslinked liners.
doi:10.1007/s11999-010-1552-9
PMCID: PMC3018192  PMID: 20844998
25.  Clinical and radiographic results and wear performance in different generations of a cementless porous-coated acetabular cup 
International Orthopaedics  2007;32(2):181-187.
We compared clinical results and wear performance in two different generations of a cementless porous-coated cup, analysing the long-term results of 83 uncemented Harris-Galante I cups (32-mm femoral head) and 93 uncemented Harris-Galante II cups (28-mm femoral head). All polyethylene liners were gamma irradiated in air. Polyethylene linear wear was estimated using a software package. The minimum follow-up was 10 years. Nine Harris-Galante I cups and two Harris-Galante II cups were revised due to aseptic loosening or polyethylene problems. The mean femoral head penetration at 6 weeks after surgery was 0.15 ± 0.05 mm for the Harris-Galante I cups and 0.12 ± 0.03 for the Harris-Galante II cups (p < 0.001);but mean wear was 0.13 ± 0.23 mm per year for the Harris-Galante I cups and 0.11 ± 0.10 for the Harris-Galante II cups (p = 0.740). Most of the metallic shells in both groups showed stable fixation. The so-called second-generation cups had lower initial polyethylene wear that resulted in less polyethylene wear at the latest the follow-up, but the overall wear rate was similar in both groups despite the different femoral head sizes and the improved locking mechanism.
doi:10.1007/s00264-006-0305-6
PMCID: PMC2269018  PMID: 17265157

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