Cross-linked Polyethylene Acetabular Liners Research Articles

Clinical Performance of Highly Cross-Linked Polyethylenes in Total Hip Arthroplasty

Aseptic loosening secondary to wear-debris-induced osteolysis has been identified as the leading cause of late failure of total hip arthroplasty. Highly cross-linked polyethylene acetabular liners were developed as one approach to reducing this wear. Preclinical laboratory wear testing showed a number of cross-linked polyethylenes to have dramatically less wear than the polyethylene that had been in use for several decades. After the initial bedding-in phase (one to two years), the percent reductions in the wear rate, as indicated by the amount of penetration of the head into the socket evident on serial radiographs, have been comparable with what was predicted from preclinical hip-simulator testing of the highly cross-linked polyethylenes. To our knowledge, there have been no reports of clinically relevant osteolysis that was clearly attributable to wear of a highly cross-linked polyethylene acetabular liner. However, the clinical performance of these materials should be closely monitored with long-term follow-up.

Aspherical Femoral Head with Highly Cross-Linked Ultra-High Molecular Weight Polyethylene Surface Cracking

Hip simulator and early clinical studies of highly cross-linked ultra-high molecular weight polyethylene have demonstrated less wear and less femoral head penetration when compared with conventional ultra-high molecular weight polyethylene1-6. However, cross-linking also alters some of the mechanical properties of ultra-high molecular weight polyethylene, including its ultimate tensile strength, strain to failure, fracture toughness, and fatigue crack propagation resistance7-9. Analyses of early retrieved highly cross-linked components have shown initiation of surface cracking, which is possibly related to the decrease in ductility caused by cross-linking10. A reduction in ductility, fracture, and fatigue properties is the hallmark of material embrittlement. Accordingly, newer so-called second-generation highly cross-linked polyethylenes have been developed in an effort to better retain the desirable mechanical properties of conventional ultra-high molecular weight polyethylene as well as the benefits of cross-linking11. Wear behavior of conventional and highly cross-linked ultra-high molecular weight polyethylene acetabular liners can be affected by the geometry of the femoral head. Geometrical factors include not only roughness associated with asperities and machining marks but also asphericity of the implant. Roughening of cobalt-chromium femoral heads occurs in vivo and may increase wear of the liner12-14. Root-mean-square roughness values of clinically retrieved cobalt chromium components heads have been reported to be between 0.15 and 0.20 μm13,14. Asphericity, or out-of-roundness, of the femoral head influences the bearing wear of the implant. It is possible to have an extremely smooth, polished femoral head surface that has relatively large-size scale deviations from the optimal implant shape. Asphericity can manifest as a region of relative flatness or as a protrusion15. Substantial asphericity of the head has been associated with increased acetabular wear16. This case report focuses on a retrieved …

Rim Cracking of the Cross-Linked Longevity Polyethylene Acetabular Liner After Total Hip Arthroplasty

Studies have suggested that cross-linked polyethylene bearings reduce wear rates from 40% to 100% compared with conventional polyethylene. However, the reduced mechanical properties of highly cross-linked polyethylene have the potential to be a limiting factor in device performance. We reviewed a series of retrieved acetabular liners with a fracture of the superior rim to assess the factors that played a role in their failure. Four Longevity acetabular bearings, which had been retrieved from two patients after seven to twenty-seven months in vivo, were visually examined for clinical damage, were assessed with use of Fourier transform infrared spectroscopy to determine the level of oxidation, and were analyzed for mechanical properties and fracture surface characterization. Control data were obtained from never-implanted devices and from global reference ultrahigh molecular weight polyethylene bar stock as an industry calibration material. All four retrieved liners demonstrated articular surface wear modes, which in most cases were rated as moderate, and none were rated as severe. All showed cracking or rim failure of the liner at the superior aspect along the groove in the polyethylene that engages the locking ring of the shell. The retrieved liners had no measurable oxidation, and the mechanical properties were comparable with those of never-implanted material. There was no notable in vivo degradation of the retrieved liners. Important factors related to failure appear to be thin polyethylene at the cup rim, relatively vertical cup alignment, and the material properties of the highly cross-linked polyethylene that are decreased relative to conventional polyethylene. The critical dimension with respect to rim failure in modular liners appears to be the minimum thickness at the equatorial region.

Rim Cracking of the Cross-Linked Longevity Polyethylene Acetabular Liner After Total Hip Arthroplasty

Rim Cracking of the Cross-Linked Longevity Polyethylene Acetabular Liner After Total Hip Arthroplasty

Retrieval analyses of highly cross-linked polyethylene acetabular liners four and five years after implantation

Two Durasul highly crosslinked polyethylene liners were exchanged during revision surgery four and five years after implantation, respectively. The retrieved liners were evaluated macroscopically and surface analysis was performed using optical and electron microscopy. A sample of each liner was used to determine the oxidation of the material by Fourier transform infrared spectroscopy. Samples of the capsule were examined histologically. The annual wear rate was found to be 0.010 and 0.015 mm/year, respectively. Surface analysis showed very little loss of material caused by wear. Histological evaluation revealed a continuous neosynovial lining with single multinucleated foreign-body giant cells. Our findings showed no unexpected patterns of wear on the articulating surfaces up to five years after implantation and no obvious failure of material.

Dislocation of Primary Total Hip Arthroplasty with 36 and 40-mm Femoral Heads

Some authors suggest the use of larger (36 and 40 mm) femoral heads against highly cross-linked polyethylene acetabular liners will reduce the prevalence of early dislocation after primary total hip arthroplasty (THA). We prospectively followed 61 consecutive patients at high risk for dislocation to determine the prevalence of early dislocation after primary THA with 36 and 40 mm femoral heads. We established specific indications for the use of these larger heads in primary arthroplasty. There were 65 hips in 61 patients with a minimum followup of 1 year (mean 2 years, range 1-4 years). There were 55 36 mm heads and 10 40 mm heads. All arthroplasties were performed by the posterior approach with capsular repair. The prevalence of early dislocation was 4.6% (3 of 65). There was one patient with an anterior dislocation and two with posterior dislocation. No patient underwent reoperation for dislocation. There was no dislocation in the 10 hips that had a 40 mm head. We identified no complications related to the larger femoral heads. The use of larger femoral heads did not notably reduce the prevalence of early dislocation after primary THA in high risk patients compared to historical controls.

Clinical Performance of a Durasul Highly Cross-linked Polyethylene Acetabular Liner for Total Hip Arthroplasty at Five Years

Clinical Performance of a Durasul Highly Cross-linked Polyethylene Acetabular Liner for Total Hip Arthroplasty at Five Years

Ex Vivo Wear of Conventional and Cross-linked Polyethylene Acetabular Liners

Explanted highly cross-linked polyethylene acetabular liners show third-body scratching. It was suggested that this surface damage could increase the wear rate of highly cross-linked polyethylene. We investigated the wear behavior of surgically explanted highly cross-linked and conventional acetabular liners using a hip simulator. Highly cross-linked explants showed no weight loss. The scratches and original machine marks of the highly cross-linked liners present at explantation remained during testing; the wear rates of these liners were 1.1 +/- 2.3 mg/million cycles, representing weight gain. In contrast, conventional liners showed wear rates of -12.9 +/- 1.4 mg/million cycles, representing weight loss. Wear was associated with rapid surface polishing and scratch elimination. After testing, the liners were melted to trigger shape memory and recover plastic deformation-induced surface changes. Highly cross-linked liners showed substantial recovery of original machining marks after melting, indicating that the scratches were a result of plastic deformation and not wear. None of the conventional polyethylenes showed any recovery after melting. The wear resistance of the highly cross-linked polyethylene studied was not compromised by surface changes that occurred during the first year of in vivo service.

Clinical Performance of a Durasul Highly Cross-Linked Polyethylene Acetabular Liner for Total Hip Arthroplasty at Five Years

Highly cross-linked polyethylene is currently the most common articulation surface used for total hip arthroplasty. The hypothesis of the present study was that the Durasul highly cross-linked polyethylene acetabular liner would have less wear at five years than would a conventional polyethylene liner used in association with the same total hip replacement system. Forty-three consecutive patients (fifty hips) underwent total hip replacement with an uncemented titanium porous-coated metal cup and a Durasul liner that was mated with a 28-mm cobalt-chromium femoral head. Thirty-one patients (thirty-seven hips) were followed for at least five years. Thirty-five other patients (thirty-seven hips) underwent total hip arthroplasty with the same system but with a conventional polyethylene liner, and these patients also were followed for five years. Clinical assessment was performed with use of the Harris hip score and a patient self-assessment examination. Radiographic analysis included measurements of acetabular component position, fixation, and osteolysis. Femoral head penetration of the Durasul liners was compared with that of the conventional liners. The clinical results as determined on the basis of Harris hip scores and patient self-assessment examinations did not differ between the Durasul group and the control group. The mean bedding-in penetration was 0.054 +/- 0.07 mm for the Durasul group and 0.059 +/- 0.154 mm for the control group. The subsequent penetration, with elimination of the bedding-in wear, resulted in a linear wear rate of 0.029 +/- 0.02 mm per year for the Durasul group, compared with 0.065 +/- 0.03 mm per year for the control group (p < 0.005). The annual penetration at one and five years was 0.074 mm and 0.011 mm, respectively, for the Durasul group, compared with 0.151 mm and 0.04 mm, respectively, for the control group. While the qualitative wear pattern of the highly cross-linked polyethylene liner was the same as that of the conventional polyethylene liner, the annual linear wear rate was 45% of that seen with the conventional polyethylene liner. Therefore, we believe that these early data support the continued use of this highly cross-linked polyethylene liner for total hip arthroplasty.

Wear and surface cracking in early retrieved highly cross-linked polyethylene acetabular liners.

A higher degree of cross-linking has been shown to improve the tribological properties of ultra-high molecular weight polyethylene in laboratory studies; however, its effect on in vivo behavior has not been well established. We investigated in vivo wear mechanisms in retrieved highly cross-linked polyethylene acetabular liners in order to determine if early in vivo wear behavior is accurately predicted by hip-simulator studies. A total of twenty-four liners (twenty-one explanted and one unimplanted highly cross-linked liners and two explanted ethylene-oxide-sterilized non-cross-linked liners) were examined for this study. The average age of the patients was 59.9 years, and the average time in vivo was 10.1 months. Articular surface damage on the front and back sides of the liners was assessed with an optical scoring system. Surface quadrants were assigned a grade from 0 to 3 according to the observed wear mechanisms and the percentage of surface affected. The micromechanisms of liner damage were evaluated with use of scanning electron microscopy. The average front and back-side explant damage scores were 11 (range, 2 to 26.5) and 6.7 (range, 3.7 to 13.3), respectively. There was consistent evidence of early surface deformation and cracking. All explants exhibited some form of surface change, including surface cracking, abrasion, pitting, or scratching. The original machining marks on the liner surface were observed to be either unaltered, drastically distorted, or absent. Highly cross-linked ultra-high molecular weight polyethylene acetabular liners that were retrieved at an average of ten months after implantation exhibited signs of surface damage that had not been predicted by in vitro hip-simulator studies. These devices had not failed clinically as a result of wear. The discrepancy between in vitro and in vivo wear surfaces may be due to variability in terms of in vivo lubrication and cyclic loading or may represent early surface damage mechanisms that are not well demonstrated by long-term simulator studies.

A prospective, randomized clinical study comparing marathon and enduron polyethylene acetabular liners: 3 year results

In 1999, the authors began a prospective, randomized study to compare the clinical performance of DePuy’s highly crosslinked polyethylene acetabular liner (Marathon) to that of conventional Enduron polyethylene sterilized by gas plasma. Over the course of two years, 236 hips were enrolled in the IRB approved study. At the writing of this abstract, 126 patients had a minimum follow-up of 3 years. For these patients, we used a computer-assisted radiographic technique to measure polyethylene wear rates. At 3.2 years, the mean true wear rate for the Marathon liners was significantly less than that of the non-irradiated Enduron liners (0.12 vs. 0.22 mm/yr).Moreover, a significantly greater percentage of Marathon liners had true wear rates less than 0.1 mm/year than did Enduron liners (62% vs. 22%). These initial clinical data confirm laboratory tests demonstrating a reduction in wear with Marathon polyethylene as compared to non-irradiated Enduron polyethylene. The reduction in mean wear rate was coupled with a significantly greater proportion of low-wearing liners in the Marathon group. Of note, however, at this short follow-up both groups continue to have outliners with large head penetration rates, which tend to inflate the mean wear rate of each population.

Surface analysis of early retrieved acetabular polyethylene liners: a comparison of conventional and highly crosslinked polyethylenes

In vivo wear behavior of 16 highly cross-linked and 19 conventional polyethylene acetabular explants, at an average in vivo duration of 6 months were studied. Highly cross-linked groups showed machining marks from the original manufacturing process in some areas and extensive scratching and some polishing of the articulating surfaces. The conventional group showed greater loss of machining marks, scratching, and polishing. Representative samples were melted to allow recovery of plastic deformation and to show true removal of material caused by wear. Melt-recovery experiments consistently showed the disappearance of surface scratches and the restoration of the original machining marks in the highly cross-linked explants. In the conventional group, few of the scratches were eliminated and only limited restoration of the machining marks was apparent. These observations support the hypothesis that the early in vivo scratching of highly cross-linked polyethylene acetabular liners is primarily caused by plastic deformation.