Wear of high-dose gamma-irradiated polyethylene in total hip replacements

The 'Japanese paradox' of total hip arthroplasty: where are we going?

INTRODUCTION

There is a worldwide trend toward 'revisiting' cemented total hip arthroplasty (THA). In Japan, however, cemented THAs accounts for 11%, and the percentage of cemented hemiarthroplasty is estimated to be less than 10%. This review was designed to reconsider the option of cemented THA and to encourage policy changes in Japan to support the best possible care for patients.

AREA COVERED

In this article, we reviewed the history of THA and the current situations of the world, based on past reports and nationwide registries. Merits and demerits of cemented THA were evaluated from various perspectives.

EXPERT OPINION

Cemented THA had great advantages, including establishment of the acetabular cup, diversity of the femoral stem, antibiotic-loaded acrylic cement, revision, low incidence of periprosthetic fracture, and hemiarthroplasty. In patients older than 75 years of age, cemented THA resulted in the lowest risk of revision. Guidelines for femoral neck fracture recommended the use of cemented hemiarthroplasty in many countries because of low incidence of periprosthetic fracture. Numerous contradictions regarding implant price and cost of operations have also been noted in Japan. For the patients, we need to rethink what is truth and what is fiction.

Stable polyethylene inlay fixation and low polyethylene wear rate in fixed-bearing total knee arthroplasty at five to six years' follow-up

Aims

Micromotion of the polyethylene (PE) inlay may contribute to backside PE wear in addition to articulate wear of total knee arthroplasty (TKA). Using radiostereometric analysis (RSA) with tantalum beads in the PE inlay, we evaluated PE micromotion and its relationship to PE wear.

Methods

A total of 23 patients with a mean age of 83 years (77 to 91), were available from a RSA study on cemented TKA with Maxim tibial components (Zimmer Biomet). PE inlay migration, PE wear, tibial component migration, and the anatomical knee axis were evaluated on weightbearing stereoradiographs. PE inlay wear was measured as the deepest penetration of the femoral component into the PE inlay.

Results

At mean six years' follow-up, the PE wear rate was 0.08 mm/year (95% confidence interval 0.06 to 0.09 mm/year). PE inlay external rotation was below the precision limit and did not influence PE wear. Varus knee alignment did not influence PE wear (p = 0.874), but increased tibial component total translation (p = 0.041).

Conclusion

The PE inlay was well fixed and there was no relationship between PE stability and PE wear. The PE wear rate was low and similar in the medial and lateral compartments. Varus knee alignment did not influence PE wear.

Effect of gamma irradiation on carbon dot decorated polyethylene-gold@ hydroxyapatite biocomposite on titanium implanted repair for shoulder joint arthroplasty

High disappointment rate of the ligament to hard tissue mending after the medical procedure has dependably been a testing issue in rotator cuff repair. Considering the elasticity of carbon dot decorated polyethylene (f-CDs-PE) and osteogenic movement of gold substituted hydroxyapatite (Au@HA) bioceramic, f-CDs-PE-Au@HA biocomposite coatings were created by an electrophoretic deposition method (EPD), the in vivo and in vitro bioactivity and cytocompatibility were researched. The physico-chemical properties of f-CDs-PE-Au@HA biocomposite coatings were characterized using fourier transform infra-red (FTIR) and X-Ray diffractometery (XRD). The morphology of the fabricated biocomposites was analyses via scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods. With a gamma-irradiation of f-CDs-PE-Au@HA biocomposite coating (BC₂), the bond and multiplication of cells on biocomposite coating were improved. The specimen with a f-CDs-PE-Au@HA biocomposite (BC₂) demonstrated a most noteworthy alkaline phosphatase activity articulation. The animal model consequences additionally show that the f-CDs-PE-Au@HA biocomposite (BC₂) had great bioactive and cytocompatibility, which could develop the association of collagen and the arrangement of ligament and hard tissue. Expansion of the gamma-ray irradiation with f-CDs-PE-Au@HA biocomposite coating (BC₂) at the tendon- hard tissue crossing point was exhibited to reinforce the mending entheses, increment hard tissue and tendon development and progress collagen association contrasted and control. The above outcomes have recommended that the progressive, implantable and solid stringy platforms built utilizing EPD extraordinary potential for enlargement of rotator cuff tears-recuperating.

Differences in Femoral Head Penetration Between Highly Cross-Linked Polyethylene Cemented Sockets and Uncemented Liners

BACKGROUND

This study aimed at investigating differences in femoral head penetration between highly cross-linked polyethylene (HXLPE) cemented sockets and uncemented liners during 5 years postoperatively.

METHODS

Ninety-six patients (106 hips) with a mean age of 64.4 (range, 35-83) years underwent total hip arthroplasty using a HXLPE cemented socket or liner and were respectively divided into cemented (35 patients [37 hips]) and uncemented (61 patients [69 hips]) groups. Femoral head penetrations were evaluated on both anteroposterior (AP)-view and Lauenstein-view radiographs, and mean polyethylene (PE) wear rates were calculated based on femoral head penetration from 2 to 5 years. Multivariate analyses were performed to assess risk factors for PE wear.

RESULTS

At 5 years postoperatively, the cemented and uncemented groups exhibited proximal direction femoral head penetrations of 0.103 mm and 0.124 mm (P = .226) and anterior direction penetrations of 0.090 mm and 0.151 mm (P = .002), respectively. The corresponding mean PE wear rates were 0.004 mm/y and 0.009 mm/y in the AP-view (P = .286) and 0.005 mm/y and 0.012 mm/y in the Lauenstein-view (P = .168), respectively. Left-side operation and high activity were independent risk factors for PE wear on AP-view.

CONCLUSION

When HXLPE was used, all mean PE wear rates were very low and those of cemented sockets and uncemented liners were very similar. PE particle theory suggests that the occurrence of osteolysis and related aseptic loosening might consequently decrease.

Effect of e-beam sterilization on the in vivo performance of conventional UHMWPE tibial plates for total knee arthroplasty

Although the introduction of highly cross-linked polyethylene is effective in reducing the amount of wear, there are still major concerns regarding the use of this material in total knee arthroplasty (TKA), essentially due to the reduction of fatigue resistance and toughness. Monitoring the in vivo performance of different types of UHMWPE is a much needed task to tackle the lack of information on which should be the most reliable choice for TKA. The present study was aimed at investigating the mid-term degradation of electron beam sterilized conventional UHMWPE tibial plates. Visual inspection enabled to grade the surface damage of 12 retrievals according to the Hood's score: the total wear damage correlates to the in vivo time (Spearman's ρ=0.681, p<0.05) and BMI (ρ=0.834, p<0.001). Surface degradation was less severe than that quantified in similar studies on γ-sterilized UHMWPE. Raman and infra-red spectroscopies were utilized to unfold the microstructural modifications. In the load zone, polyethylene whitened damage regions were noticed in the inserts implanted longer than 1year, in which oxidation index (OI) is clearly higher than 1 (max 8). The maximum OI (ρ=0.802, p<0.005) and α_c (ρ=0.816, p<0.005) correlate to the implantation time in the load zone. The crystallinity increased along with the extent of oxidation. Concentration of absorbed species from synovial fluid is higher in the contact zone and correlates to maximum OI (Spearman's ρ=0.699, p=0.011). Absorption was promoted in the contact area by the mechanical action of the femoral counterpart and it exacerbated the oxidative degradation in retrievals with high concentration of absorbed species. In the non-load zone, mild but detectable oxidation was observed, probably due to free radicals trapped after sterilization.

STATEMENT OF SIGNIFICANCE

Although several clinical studies on retrieved tibial bearings have been published so far, monitoring and comparing the in vivo performance of different types of UHMWPE is still a much needed task. The present study reports for the first time results on the effect of sterilization by electron beam on the mid-term in vivo performance of conventional UHMWPE tibial plates. In the present investigation, visual inspection of wear damage based on the Hood's scoring method, Raman micro-spectroscopy and Fourier-transformed infrared spectroscopy were utilized to unveil the damage, the microstructural modifications and the oxidation occurred during implantation. The findings of this investigation have been discussed and compared to previous clinical studies on γ-air sterilized, γ-inert sterilized tibial bearings.

Fifteen-Year Comparison of Wear and Osteolysis Analysis for Cross-Linked or Conventional Polyethylene in Cementless Total Hip Arthroplasty for Hip Dysplasia-A Retrospective Cohort Study

BACKGROUND

Cross-linked polyethylene (XLPE) acetabular liners used in cementless total hip arthroplasty (THA) have demonstrated better wear resistance at 10 years compared with conventional polyethylene (CPE) liners. No clinical studies have compared XPLE to CPE liners beyond 10 years.

METHODS

We performed a 15-year retrospective cohort study on cementless THA performed in patients with developmental hip dysplasia to measure the differences in polyethylene wear rates and the presence of osteolysis. Twenty-four THAs with XLPE and 17 THAs with CPE were evaluated. The mean age of patients was 55.9 years (41-68) in the XLPE group and 54.4 years (40-67) in the CPE group. The mean follow-up period was 15.1 years (13.9-16.1) in the XLPE group and 15.2 years (14.5-16.0) in the CPE group.

RESULTS

The XLPE group had a significantly lower wear rate at 5 and 10 years compared with the CPE group; however, no significant difference was found at 15 years (XLPE group, 0.040 mm/y; CPE group, 0.034 mm/y). In addition, the incidence of osteolysis did not differ significantly between the groups. However, the incidence of excessive wear between 10 and 15 years after surgery in the XLPE group was significantly higher than that in the CPE group.

CONCLUSION

XLPE demonstrated no advantage in the wear rate or the incidence of osteolysis at 15 years, despite having superior wear resistance up to 10 years. It is concerning that the incidence of excessive wear was higher in the XLPE group between 10 and 15 years, and this finding should alert the arthroplasty community to this possible problem with the more highly cross-linked polyethylene.

Effect of Argon Plasma Treatment on Tribological Properties of UHMWPE/MWCNT Nanocomposites

Ultra-high molecular weight polyethylene (UHMWPE) is widely used in artificial joints in the replacement of knee, hip and shoulder that has been impaired as a result of arthritis or other degenerative joint diseases. The UHMWPE made plastic cup is placed in the joint socket in contact with a metal or ceramic ball affixed to a metal stem. Effective reinforcement of multi-walled carbon nanotubes (MWCNTs) in UHMWPE results in improved mechanical and tribological properties. The hydrophobic nature of the nanocomposites surface results in lesser contact with biological fluids during the physiological interaction. In this project, we investigate the UHMWPE/MWCNTs nanocomposites reinforced with MWCNTs at different concentrations. The samples were treated with cold argon plasma at different exposure times. The water contact angles for 60 min plasma-treated nanocomposites with 0.0, 0.5, 1.0, 1.5, and 2.0 wt % MWCNTs were found to be 55.65°, 52.51°, 48.01°, 43.72°, and 37.18° respectively. Increasing the treatment time of nanocomposites has shown transformation from a hydrophobic to a hydrophilic nature due to carboxyl groups being bonded on the surface for treated nanocomposites. Wear analysis was performed under dry, and also under biological lubrication, conditions of all treated samples. The wear factor of untreated pure UHMWPE sample was reduced by 68% and 80%, under dry and lubricated conditions, respectively, as compared to 2 wt % 60 min-treated sample. The kinetic friction co-efficient was also noted under both conditions. The hardness of nanocomposites increased with both MWCNTs loading and plasma treatment time. Similarly, the surface roughness of the nanocomposites was reduced.

Ceramic on ceramic hip prostheses: a review of past and modern materials

Ceramic on ceramic hip prostheses are an increasingly popular choice for hip replacement. Modern manufacturing techniques and developments have increased the strength and reliability of ceramic materials. The alternative bearing couples such as metal-on-polyethylene and metal-on-metal are more inclined to wear and produce particulate debris. Despite reports of fractures and stripe wear, harder, more inert and more wear resistant, modern ceramic-ceramic hip replacements provide a strong alternative to traditional bearings.

Development of a BiotriboPOD testing methodology for the wear evaluation of orthopaedic biomaterials

A Biotribo-POD apparatus has been developed, which provides an efficient and reliable methodology for the wear evaluation of orthopaedic biomaterials.

Wear of '100 Mrad' cross-linked polyethylene: effects of packaging after 30 years real-time shelf-aging

Studies have shown that gamma-irradiation of polyethylene (PE) generally results in degradation by surface oxidation. However, from 1970 to 1978 Oonishi et al. used ultra-high-molecular-weight polyethylene (UHMWPE) cross-linked and sterilized by 100 Mrad of gamma-irradiation in air (100 Mrad PE) for total hip prostheses, and obtained excellent clinical results extending for 30 years. In the present study, we used a hip joint simulator to investigate the wear characteristics of 100 Mrad PE cups which had been shelf-aged for an extremely long period (30 years). The PE cups, aged in an air-containing triple polyethylene package for 30 years (packaged 100 Mrad PE), showed low wear with 3.4 mg of weight loss, even after 5 x 10(6) cycles. In contrast, non-packaged 100 Mrad PE showed considerable wear: 47.0 mg at run-in ((0-0.25) x 10(6) cycles) and 114.1 mg at the end of 5 x 10(6) cycles. The substantially, lower wear even in the presence of an oxidized surface layer for the packaged 100 Mrad PE, was comparable to the low wear seen on retrieved 100 Mrad PE after 30 years of clinical use. The long-term shelf-storage conditions, which affect the surface oxidative degradation of PE, are assumed to be the key factor in the wear-resistance of gamma-irradiated UHMWPE.

Comparison of steady state femoral head penetration rates between two highly cross-linked polyethylenes in total hip arthroplasty

Given that the manufacture of highly cross-linked polyethylene (HXLPE) is not standardized, the behavior of these materials may vary. Our study compares minimum 5-year steady state femoral head penetration rates using the Martell method, in 2 HXPLEs produced by different manufacturers. Patients received a primary hip arthroplasty using an uncemented acetabular component with an HXLPE liner and a 28-mm femoral head. Forty-seven patients in group A received an HXLPE liner (Reflection XLPE, Smith and Nephew Inc, Memphis, Tenn), and 36 patients in group B received a different HXLPE liner (Longevity, Zimmer Inc, Warsaw, Ind). Average follow-up was 6.42 years in group A and 7.64 years in group B. The steady state head penetration rates were not significantly (P > .05) different between the HXPLE groups over the midterm with 0.026 mm/y and 0.025 mm/y in groups A and B, respectively.

Results of total hip arthroplasties in the young patient; further evidence for a barrier against articular wear debris by hydroxyapatite coatings

We examined the hypothesis that the circumferential osseous apposition around HA-coated implants forms a protective barrier against articular wear debris. Sixty-five hydroxyapatite-coated total hip arthroplasties in 57 patients (age <50years) with polyethylene-metal articulation were evaluated regarding PE-wear, osteolysis, and clinical outcome at a minimum of 10 years follow-up. There was no correlation between PE-wear and osteolysis of the femoral zones or cup zones I and III. A strong Pearson correlation was found between polyethylene wear and osteolysis around cup zone II, where the cup only consisted of polyethylene (p<0,01). The aseptic failure rate was 1.5% for the femoral component and 4.5% for the cup after 10 years of follow-up. The average Harris Hip Score was 90 and the average Engh score for fixation was 23 after 10 years . Around HA-coated parts of the prosthesis bone formation remained stable, regardless of the degree of polyethylene wear. The average linear polyethylene wear was 0,16 mm/year. The circumferential osseous apposition of the HA-coated implants possibly formed a protective barrier against articular wear debris. The use of cups with a backside gap resulted in PE-wear associated osteolysis in cup zone II and may be considered to be best avoided.

Evaluation of sequentially crosslinked ultra-high molecular weight polyethylene

This study was undertaken to investigate the effect of crosslinking ultra-high molecular weight polyethylene (UHMWPE) in a sequential manner to the final desired dose and to compare the results to single-dose crosslinking. To verify these results, an explanted, commercially available, sequentially crosslinked component was characterized. Finally, additional tensile testing was conducted to determine if tensile-sample thickness has a significant effect on the mechanical properties of UHMWPE. Based upon this well-controlled study with the same starting material, there is no apparent benefit of sequential crosslinking over crosslinking by single dose in any of the mechanical, thermophysical, physical, or oxidative properties evaluated in this study. In contrast, the soak temperature of the postirradiation heat treatment was more influential and exhibited statistically significant effects on the stability, structure, and properties of the resultant material. Compared to virgin material, crosslinking always resulted in decreases in tensile strength, elongation, and impact strength. These results were confirmed by characterization of a retrieved, sequentially crosslinked (X3) cup. All of the metrics derived for the retrieved cup were virtually identical to the sequential- and single-dose-crosslinked materials produced in this study. Examination of the effect of tensile-sample thickness demonstrated that there are significant effects on the resultant properties. In particular, the ultimate tensile strength of UHMWPE can be elevated by conducting tensile tests with thin specimens.

UHMWPE for arthroplasty: past or future?

Wear debris related osteolysis is recognised as being the main cause of failure in joint replacements based on UHMWPE inserts. However, many solutions and "new" polyethylenes have been suggested in order to address this issue. This review discusses "historical" issues associated with UHMWPE, such as oxidation, sterilization method and storage, as well as "new" topics, such as crosslinking and stabilization. The final aim is to aid orthopaedic surgeons in their selection of polyethylene inserts and in the information given to the patients. The main problem for the polymer is degradative oxidation, which is caused by the combination of the irradiation used for sterilization and oxygen, and which leads to a decrease in wear resistance and mechanical properties. Irradiation and packaging in the absence of oxygen can only reduce the oxidation, while sterilization with gas (EtO or gas plasma) is the only method that effectively eliminates it. Manufacturing processes are of great relevance to the clinical duration and must be considered by surgeons. Crosslinked polyethylene has been developed for joint inserts due to its superior wear resistance compared to conventional UHMWPE; to prevent the oxidation, crosslinked polyethylene requires post-irradiation thermal treatment, which reduces its mechanical properties and which depends on the producer. Several good clinical results from the use of crosslinked acetabular cups have reported at mid-term, while early results for knee replacements are also encouraging. Recently, the use of the antioxidant vitamin E (alpha-tocopherol) has been introduced for joint prostheses in order to prevent the oxidation of both crosslinked and noncrosslinked UHMWPE.

The creep and wear of highly cross-linked polyethylene: a three-year randomised, controlled trial using radiostereometric analysis

The creep and wear behaviour of highly cross-linked polyethylene and standard polyethylene liners were examined in a prospective, double-blind randomised, controlled trial using radiostereometric analysis. We randomised 54 patients to receive hip replacements with either highly cross-linked polyethylene or standard liners and determined the three-dimensional penetration of the liners over three years. After three years the mean total penetration was 0.35 mm (SD 0.14) for the highly cross-linked polyethylene group and 0.45 mm (SD 0.19) for the standard group. The difference was statistically significant (p = 0.0184). From the pattern of penetration it was possible to discriminate creep from wear. Most (95%) of the creep occurred within six months of implantation and nearly all within the first year. There was no difference in the mean degree of creep between the two types of polyethylene (highly cross-linked polyethylene 0.26 mm, SD 0.17; standard 0.27 mm, SD 0.2; p = 0.83). There was, however, a significant difference (p = 0.012) in the mean wear rate (highly cross-linked polyethylene 0.03 mm/yr, SD 0.06; standard 0.07 mm/yr, SD 0.05). Creep and wear occurred in significantly different directions (p = 0.01); creep was predominantly proximal whereas wear was anterior, proximal and medial. We conclude that penetration in the first six months is creep-dominated, but after one year virtually all penetration is due to wear. Highly cross-linked polyethylene has a 60% lower rate of wear than standard polyethylene and therefore will probably perform better in the long term.

Reduction of osteolysis with use of Marathon cross-linked polyethylene. A concise follow-up, at a minimum of five years, of a previous report

We previously reported wear data at a minimum of two years following thirty-four total hip replacements with a Marathon cross-linked polyethylene liner and twenty-four replacements with a conventional (gamma-sterilized-in-air) Enduron polyethylene liner. In this current study, with sequential five-year radiographs, wear rates were determined with use of linear regression analysis. The Marathon polyethylene had average wear rates of 15.4 mm(3)/yr and 8.0 mm(3)/million cycles. The Enduron polyethylene had average wear rates of 55.5 mm(3)/yr and 29.9 mm(3)/million cycles. The adjusted volumetric wear rate of the Marathon polyethylene was 73% lower than that of the Enduron polyethylene (p = 0.001). Osteolysis developed in eight of the twenty-four hips with an Enduron liner but was not apparent in any hip with a Marathon liner.

Wear in molded tibial inserts: knee simulator study of H1900 and GUR1050 polyethylenes

Hi-fax 1900 tibial inserts were used in the IB-1 total knee replacement (TKR) beginning 1978, soon followed by the AGC design. Such direct compression molded (DCM) inserts was relatively immune to oxidation. Unfortunately the Hi-fax 1900 resin (H1900) was taken off the market in year 2004. As an alternate, GUR1050 was introduced in the Vanguard TKR. However there appeared to be little or no wear comparisons of molded inserts. Therefore the study aim was to compare wear performance of GUR1050 to the historical H1900. The hypothesis was that Hi-fax and GUR1050 would show comparable wear performance. The Vanguar was a posterior-cruciate sacrificing design (Biomet Inc.). All tibial inserts were sterilized by gamma-radiation (3.2 Mrad) under argon. A 6-channel, displacement-controlled knee simulator was used with serum lubricant (protein concentration 20 mg/mL). Wear assessments were by gravimetric methods and linear regression techniques. The gross weight-loss trends over 2.5 Mc duration demonstrated excellent linear behavior with good agreement between TKR sets (<+/-10%). Fluid sorption artifacts in control represented less than 5% of gross wear magnitudes. Thus suitable corrections could be made in determining net wear. The H1900 and GUR1050inserts demonstrated net wear-rates of 3.6 and 3.4 mm(3)/Mc, respectively. This difference was not found to be statistically significant. This wear study demonstrated that GUR1050 inserts were indistinguishable from the Hi-fax 1900 in terms of laboratory wear performance, proving our hypothesis. Given the excellent clinical history of DCM Hi-fax 1900, the GUR1050 should be an ideal candidate for TKR.

Oxidation and wear of 100-Mrad cross-linked polyethylene shelf-aged for 30 years

Some previous studies suggest that aging influences wear and oxidatively degraded nonsterilized ultra-high-molecular-weight polyethylene (UHMWPE) exhibits decreased wear resistance. We therefore asked whether shelf-aging storage conditions influenced degradation and wear resistance of gamma-irradiated UHMWPE. We examined oxidation and wear of 100-Mrad gamma-irradiated UHMWPE (100-Mrad polyethylene) cups shelf-aged for 30 years without (n=2) or with (n=2) packages. The oxidation index of the unpackaged 100-Mrad polyethylene surface (4) was higher than that of the packaged one (2.7). The packaged 100-Mrad polyethylene cup exhibited a high wear resistance with a steady wear rate of 0.5 mg/10(6) cycles. In contrast, the unpackaged 100-Mrad polyethylene exhibited an extremely high initial wear rate of 187.9 mg/10(6) cycles over the first 0.25 x 10(6) cycles with a subsequently reduced wear rate of 5 mg/10(6) cycles after 5 x 10(6) cycles. Packaging over long periods inhibits surface oxidation and maintains the wear resistance of gamma-irradiated UHMWPE cups.

Dose effects of cross-linking polyethylene for total knee arthroplasty on wear performance and mechanical properties

Wear performance and mechanical properties of cross-linking polyethylene (XLPE) tibial inserts were investigated using a knee simulator, scanning electron microscopy (SEM), and a small punch test (SPT). Ultrahigh molecular weight PE made from GUR1050 resin was irradiated at doses ranging from 0 to 200 kGy and then machined into tibial inserts followed by annealing. The knee simulator was run for up to four million cycles. As the radiation dose increased from 0 to 100 kGy, the wear rate decreased dramatically, yielding 95% wear reduction at 100 kGy. The microwear features observed by SEM supported the dose-dependent wear reduction. The SPT for XLPE after the simulation test showed that, as the radiation dose increased from 0 to 200 kGy, the ultimate displacement decreased dose-dependently, while the ultimate load increased from 0 to 75 kGy and decreased from 75 to 200 kGy. The resulting toughness of the PE increased to its maximum at a dose of 50 kGy and then decreased with higher doses up to 200 kGy. PE cross-linked with radiation doses from 25 to 75 kGy had greater toughness than virgin, nonirradiated PE. However, PE irradiated with 100 kGy or more had lower toughness than virgin PE. These data suggest that a certain amount of irradiation enhances both wear performance and toughness of PE tibial inserts. Although a certain amount of cross-linking would be effective for clinical application of PE tibial inserts, an optimal radiation dose should be much smaller than that used in current XLPE in total hip arthroplasty.

Analysis of retrieved acetabular components of three polyethylene types

The polyethylene used in total hip arthroplasty has gone through many changes over the past several decades, including consolidation processes, resin types, method of sterilization, packaging, and the extent of crosslinking. To isolate the in vivo performance of material changes from implant system design changes, we assessed the postretrieval surface wear and damage of components made from three different polyethylene types used in a single implant system. The polyethylene types investigated are representative of the sequentially available bearing materials that have dominated use in total hip arthroplasty over the last several decades. Forty-six components with implantation durations of 12 to 96 months were assessed for surface wear and damage and for socket wear and creep volume change. Acetabular components made from highly crosslinked polyethylene had a 50% lower total damage score than components made from polyethylene that was either gamma-sterilized in air or in nitrogen. The wear and creep socket volume change was 80% and 90% lower for the highly crosslinked components compared with the gamma-sterilized in air and nitrogen groups, respectively. These data of direct component measurement are consistent with earlier predictions that recent changes in polyethylene material processing can lead to clinically improved bearing performance.

An integrated solution to acetabular revision surgery

The three salient reasons for failure of acetabular revision surgery have been failure of fixation, wear and lysis, and dislocation. This review focuses on the major progress made in addressing these three items, leading to an overall approach integrating three contemporary techniques with a strong likelihood of improving acetabular revision surgery. These three techniques are the use of hemispheric cementless acetabular components, alternate bearings, and big heads.

Wear of highly cross-linked polyethylene acetabular cup in Japan

The wear characteristics of ultra-high-molecular-weight polyethylene acetabular cups irradiated with 6.0 to 7.5 Gy of gamma-irradiation were studied in a hip simulator and in vivo in 70 hips for 6 to 39 months. The linear wear was 2.5% to 4.5% of the wear seen in conventional polyethylene cups. A biphasic wear pattern was observed over time with a relatively large wear in the first year and a subsequent leveling of the wear rate curve. The linear wear rate in the second phase (steady state) was 0.006 mm/y. The extent of decrease in clinical wear of 6.0-Mrad polyethylene (Aeonian, Kyocera Corp, Kyoto, Japan) cups is comparable with the decrease of the in vitro wear measured by the hip simulation test.

Wear and toughness of crosslinked polyethylene for total knee replacements: a study using a simulator and small-punch testing

Severe loading and complex kinematics in total knee replacement make wear performance and toughness of the polyethylene in tibial inserts important. We investigated wear of crosslinked polyethylene using a knee simulator and measured toughness using small-punch testing. GUR1050 rods were gamma-irradiated in air at doses from 0 to 200 kGy, annealed in nitrogen, and machined into tibial inserts. The simulator was run to 4 million cycles, and wear rates determined from weight loss. Wear rate decreased by 54, 78, and 95% as radiation dose increased from 50 to 75 to 100 kGy, respectively. At every dose, toughness was significantly less after simulator testing, but the difference between control and wear-tested polyethylene, considered to be due to fatigue damage accumulation, was smallest at 50 kGy. The simulator-tested polyethylene that received 35 to 75 kGy had slightly higher toughness than equivalent material that received no irradiation. However, the toughness of simulator-tested polyethylene that received 150 and 200 kGy was lower than that of the simulator-tested polyethylene that received no irradiation. Our results suggest that an optimal irradiation dose may exist for crosslinked polyethylene for use in TKR and that the optimum dose would be less than the 100 kGy or more that are used in some current crosslinked polyethylene for hip replacement.

Arthroplasty options for the young patient: Oxinium on cross-linked polyethylene

Our purpose was to determine whether metal femoral heads scratch with in vivo use, to characterize the scratching that occurs, and to determine whether this scratching affected polyethylene wear. Assessment of 133 consecutive retrieved femoral heads showed that metal femoral heads do scratch with in vivo use, that cobalt-chromium femoral heads are more scratch resistant than titanium alloy heads, and that scratching seems to be time dependent. Profilmetry studies showed that all roughness parameters (average roughness, maximum peak to lowest valley distance, mean peak height above the mean surface line, estimate of small peaks above the main plateau of the surface, and estimate of the depth of the valleys below the mean plateau of the surface with the exception of the symmetry of the profile about its mean line) showed increased roughness with time of use. Cobalt-chromium and Oxinium femoral heads were damaged in a dislocation model. Assessment of these femoral heads in a wear simulator revealed that against conventional polyethylene, a damaged Oxinium femoral head had no more wear than a new cobalt-chromium articulation on the same polyethylene (36.5/million cycles versus 38.4 mm/million). Against cross-linked polyethylene, a damaged Oxinium femoral head had minimal wear (1.5 mm cubed per Mc).

The effect of geometry and abduction angle on the stresses in cemented UHMWPE acetabular cups--finite element simulations and experimental tests

BACKGROUND

Contact pressure of UHMWPE acetabular cup has been shown to correlate with wear in total hip replacement (THR). The aim of the present study was to test the hypotheses that the cup geometry, abduction angle, thickness and clearance can modify the stresses in cemented polyethylene cups.

METHODS

Acetabular cups with different geometries (Link: IP and Lubinus eccentric) were tested cyclically in a simulator at 45 degrees and 60 degrees abduction angles. Finite element (FE) meshes were generated and two additional designs were reconstructed to test the effects of the cup clearance and thickness. Contact pressures at cup-head and cup-cement interfaces were calculated as a function of loading force at 45 degrees, 60 degrees and 80 degrees abduction angles.

RESULTS

At the cup-head interface, IP experienced lower contact pressures than the Lubinus eccentric at low loading forces. However, at higher loading forces, much higher contact pressures were produced on the surface of IP cup. An increase in the abduction angle increased contact pressure in the IP model, but this did not occur to any major extent with the Lubinus eccentric model. At the cup-cement interface, IP experienced lower contact pressures. Increased clearance between cup and head increased contact pressure both at cup-head and cup-cement interfaces, whereas a decreased thickness of polyethylene layer increased contact pressure only at the cup-cement interface. FE results were consistent with experimental tests and acetabular cup deformations.

CONCLUSION

FE analyses showed that geometrical design, thickness and abduction angle of the acetabular cup, as well as the clearance between the cup and head do change significantly the mechanical stresses experienced by a cemented UHMWPE acetabular cup. These factors should be taken into account in future development of THR prostheses. FE technique is a useful tool with which to address these issues.

The role of macrophages in osteolysis of total joint replacement

The osteolysis associated with conventional polyethylene on metal total joint replacements is associated with the formation of an inflamed periprosthetic membrane rich in macrophages, cytokines and implant-derived wear particles. There is a wealth of evidence to indicate that the presence and activation of macrophages in the periprosthetic tissues around joint replacements is stimulated by UHMWPE particles. Particles within the size range 0.1-1.0 microm have been shown to be the most reactive. Animal studies have provided increasing evidence that, of the milieu of cytokines produced by particle-stimulated macrophages, TNF-alpha is a key cytokine involved in osteolysis. Recent advances in the understanding of the mechanisms of osteoclastogenesis and osteoclast activation at the cellular and molecular level have indicated that bone marrow-derived macrophages may play a dual role in osteolysis associated with total joint replacement. Firstly, as the major cell in host defence responding to UHMWPE particles via the production of cytokines and secondly as precursors for the osteoclasts responsible for the ensuing bone resorption.

Bioactive cement or ceramic/porous coating vs. conventional cement to obtain early stability of the acetabular cup. Randomised study of 96 hips followed with radiostereometry

Ninety patients (96 hips) scheduled for THA were stratified to fixation of the acetabular component in three main groups of about equal size. Fluoride cement, porous coated press-fit cup with ceramic coating or Palacos cum Gentamicin cement were used. All patients received Spectron EF stem. The migration of the cups and the femoral head penetration into the socket were measured with radiostereometric analysis. At 2 years the choice of fixation did not influence the migration or rotation of the cup. Patients with compromised bone quality showed increased three-dimensional (3D or total) migration. Proximal and 3D penetration rates were increased in cemented compared with the uncemented cups (p<0.001), which probably not could be related to the choice of fixation. Appearance of radiolucent lines was almost equal in the two cemented groups. Uncemented cups had less radiolucent lines at 2 years. Fluoride containing cement or uncemented fixation did not improve the early postoperative stability of the socket.

Radial head prosthesis with a mobile head

Radial head replacement is a useful method in the treatment of comminuted radial head fractures. Because such injuries are a common clinical problem and many complications have been reported after radial head replacements, a new radial head prosthesis is proposed. This new design, based on the shape-dimensional identification of the radial head, consists of two parts. The head, made of ultra-high molecular weight polyethylene, is articulated with a Vitallium stem. A series of functional quality and strength tests were conducted on this new prosthetic design. The implant was also examined via the finite element method. General preclinical investigations of clinical cases show that this prosthesis is a very promising design.

Highly cross-linked polyethylene in cemented THA: randomized study of 61 hips

Highly cross-linked polyethylene (PE) has been introduced as an alternative bearing material in total hip arthroplasty (THA) because of high wear resistance in laboratory tests but the clinical experience of this material is limited. We evaluated a highly cross-linked PE (warm irradiated adiabatic melting, absorbed dose, 95 kGy) in a randomized study of cemented THAs. Cups of the same design but made of conventionally gamma irradiated PE (absorbed dose, 25-40 kGy) constituted the control group. Sixty-one hips (30 women, 30 men) with a median age of 55 years (range, 35-70 years) were included. All patients received a Spectron stem with 28-mm CoCr head. Radiostereometric examinations with the patient supine or standing were done at regular intervals. Wear was measured with the patient in the supine position from the first postoperative week, whereas examinations done with the patient standing were initiated 3 months after the operation. Dual x-ray absorptiometry and conventional radiography were used to evaluate the bone mineral density and the radiolucencies around the acetabular component. Fifty-two patients (53 hips; 25 highly cross-linked, 28 control) have been followed up for 2 years. At the 2-year followup, the highly cross-linked cups showed 50% reduction of proximal wear compared with the control group, when the patients were studied standing. When evaluated supine, the difference in proximal wear did not reach significance. The migration of the socket, the relative changes of periprosthetic bone mineral density, and the progression of radiolucencies between the immediately postoperative followup and 2-year followup did not differ. Highly cross-linked PE showed increase resistance to wear. Different mechanical properties of the two types of PE studied did not alter the performance of the cup in terms of fixation, periprosthetic bone loss, and radiographic appearance. However, the followup is short and these results are preliminary.

Early head penetration into cemented Hylamer Ogee socket

The authors reviewed 18 consecutive cemented total hip arthroplasties with the Hylamer Ogee socket. The average follow-up period was 47 months. All Hylamer Ogee sockets were sterilized by gamma irradiation in air, and the average period from production to surgery was 12 months. Two-dimensional penetration of the femoral head into the Hylamer Ogee socket was determined from anteroposterior radiographs of the pelvis using a digitizer. The average head penetration rate of the present series was 0.36 mm/y. Osteolysis around both components was found in 6 cases (30%). Of 4 cases defined as aseptic loosening, 2 were revised during the follow-up period. To detect component loosening because of catastrophic high wear of the cemented Hylamer Ogee socket as early as possible, precise radiographic follow-up is essential.

Study of retrieved acetabular sockets made from high-dose, cross-linked polyethylene

Although ultra-high molecular weight polyethylene (UHMWPE) has stable chemical properties, chemical degradation, such as oxidation reaction, progresses with long-term clinical use. The purpose of this study was to investigate the change in properties of polyethylene (PE) in vivo by examining retrieved UHMWPE sockets and high-dose, cross-linked PE (100 Mrad PE) sockets. Twenty retrieved sockets (including 2 100 Mrad PE sockets), which were implanted from 1970 to 1996, were used for analysis. The oxidation index of 100 Mrad PE sockets was approximately the same as that of the normal UHMWPE sockets in worn areas. These long-term clinical results indicate that 100 Mrad PE is sufficiently stable for clinical use and that free radicals would not affect progression of oxidation significantly.

Gamma-irradiated cross-linked polyethylene in total hip replacements--analysis of retrieved sockets after long-term implantation

The purpose of this study was to evaluate the mechanical and chemical characteristics of gamma-irradiated, cross-linked polyethylene after long-term service in vivo. Two gamma-irradiated ultra high molecular weight polyethylene (RCH 1000, molecular weight: 10(6)) total hip replacement sockets were retrieved at 15 and 16 years after implantation. Mechanical and chemical characteristics of the sockets were evaluated in comparison with nonirradiated sockets. Significant surface oxidation occurred in the nonirradiated sockets; up to 75% of that seen in the irradiated ones. The mechanical properties of the irradiated sockets were not subject to increased deterioration in the presence of high free radical content. The cross-link was stable and was retained for a long period both in vivo and in ambient air. These data indicate that gamma-irradiated polyethylene was not subject to increased oxidative degradation during long-term service in vivo and confirmed the usefulness of this material as an articulating surface in total hip replacement.