Polyethylene Acetabular Component Research Articles

Three-dimensional analysis of multiple wear vectors in retrieved acetabular cups.

The wear of polyethylene acetabular components is an important issue in total hip arthroplasty. The amount of wear has been measured in many studies, but few have addressed other mechanical aspects of wear in vivo. We used the shadowgraph method to measure the wear vectors in 104 retrieved acetabular cups that had been made by a single manufacturer, and we identified more than one wear vector in thirty-one cups (30 per cent). We hypothesized that the most likely explanation of multiple wear vectors was loosening of the acetabular implant with a change in the orientation of the implant in the pelvis. To test this hypothesis, we estimated the extent of motion of the cup in situ on the basis of differences in angles measured from serial radiographs of sixteen hips. We then used linear transformation of the three-dimensional vectors to compare the wear directions measured in the retrieved implants with the wear directions predicted from the radiographs. The change in wear direction predicted on the basis of in vivo motion of the cup never corresponded to the actual difference between wear vectors in the retrieved implants. Our results suggest that multiple wear vectors may be commonly found in retrieved implants, but loosening of the acetabular cup does not account for the multiple vectors. Additional observations suggest that impingement between the edge of the acetabular cup and the femoral component may be associated with multiple wear vectors. These results have implications for the investigation of the general mechanisms of wear in vivo and suggest that clinical or wear-testing scenarios that assume a single direction of wear may underestimate the over-all amount of volumetric wear.

Wear of Polyethylene Acetabular Components in Total Hip Arthroplasty. An Analysis of One Hundred and Twenty-eight Components Retrieved at Autopsy or Revision Operations*

We evaluated the rates of volumetric wear and the patterns of wear of 128 acetabular components retrieved during an autopsy or a revision operation between one and twenty-one years after total hip arthroplasty. Twenty-two all-polyethylene components were retrieved at autopsy from hips that had been functioning well at the time of death (Group A). The remaining 106 components--eighty-four all-polyethylene components (Group B) and twenty-two metal-backed components (Group C)--were retrieved during revision operations. All 128 components had been inserted with cement. The mean rate of volumetric wear, determined directly with a fluid-displacement method, was thirty-five cubic millimeters per year (range, eight to 116 cubic millimeters per year) for Group A, sixty-two cubic millimeters per year (range, eight to 256 cubic millimeters per year) for Group B, and ninety-four cubic millimeters per year (range, twelve to 284 cubic millimeters per year) for Group C. Multivariate regression analysis showed a significant relationship (p < 0.05) between the size of the femoral head and the calculated mean annual rate of volumetric wear. The rate of volumetric wear was highest in association with thirty-two-millimeter femoral heads and lowest in association with twenty-two-millimeter heads; according to linear regression analysis, this represented a 7.5 per cent increase (Group A) or a 10 per cent increase (Group B) in the rate of wear for every one-millimeter increase in the size of the head. Linear regression analysis also showed a significant relationship between the duration that the implant had been in situ and the rate of wear (p < 0.05), with the rate being highest initially after the operation and decreasing with an increasing duration in situ. With the numbers available, the patient's age and gender and the side of the arthroplasty did not have a significant relationship to the annual rate of volumetric wear. Increased thickness of the polyethylene was related to a decreased rate of wear (p < 0.05) in the group of metal-backed components, which had a 25 per cent increase in the rate of wear for every one-millimeter decrease in thickness, but not in the other groups. The estimated median annual rates of wear, after adjustment of confounding variables to a hypothetical constant set of median values for the parameters (duration in situ, 132 months; diameter of the femoral head, twenty-six millimeters; and thickness of the polyethylene, eight millimeters), were significantly different among the three groups of components (p < 0.05). Histological evaluation of the worn surfaces showed the predominant mechanisms of wear to be abrasion and adhesion rather than fatigue-cracking or delamination. The highly worn areas were polished to a glassy finish on gross examination, but scanning electron microscopy showed numerous multidirectional scratches along with fine, drawn-out fibrils with a diameter of one micrometer or less oriented parallel to each other. These fibrils are the most likely source of submicrometer wear particles. Thus, wear appeared to occur mostly at the surface of the components and to be due to large-strain plastic deformation and orientation of the surface layers into fibrils that subsequently ruptured during multidirectional motion.

Survivorship analysis of cemented total hip arthroplasty acetabular components implanted with second-generation techniques

The clinical and radiographic results of primary cemented total hip arthroplasty performed by a single surgeon, with particular emphasis on the performance of acetabular components implanted with so-called second-generation cement techniques, were studied. Seventy hips with 48 metal-backed and 22 polyethylene acetabular components were followed for a mean of 9 years (range, 5–11.5 years). The clinical results were evaluated using a recognized hip score. The fixation status of the cemented acetabular component was evaluated using two methods of measuring radiolucent lines at 5 years and at the last evaluation. Acetabular component loosening was defined as a circumferential radiolucent line, component migration, or revision for loosening. This study was unable to confirm the findings of others that demonstrated higher failure rates with cemented metal-backed components when compared with all-polyethylene components. The survival of cemented acetabular components with 28-mm head femoral prostheses was worse than the survival of cemented acetabular components with 22-mm femoral heads in other published reports, despite advances in cement techniques. Because of the high rate of loosening of cemented 28-mm-inner-diameter acetabular components at 5 and 10 years, the authors no longer use these cemented components for acetabular reconstruction.

Cobalt chromium molybdenum metal combination for modular hip prostheses.

The development of a metal combination for modular hip systems was motivated by the following observations: (1) wear particles from polyethylene acetabular components can lead to a foreign body reaction and late aseptic loosening and (2) well designed all metal hip prostheses had very low wear rates, usually causing no osteolytic problems. The following challenges had to be met: (1) metal alloy with the maximum wear resistance; (2) the optimal clearance (difference in diameter) between 28-mm ball head and acetabular component; and (3) equipping modern, modular hip systems with metal combinations while maintaining compatibility with existing components. The realization of a metal combination consisted of the stable anchoring of a standard metal lining in a polyethylene insert that, combined, is intended to provide adequate load transfer and fit to either the bone cement bed or the titanium shell. The metal lining is manufactured from a carbide containing cobalt chromium molybdenum wrought alloy (Protasul-21WF). From 1988 to 1995, approximately 40,000 metal combinations (Metasul) were implanted. From these, 44 single components, with a maximum time in situ of 5.5 years, were retrieved and examined. The total linear wear rate averaged 2 to 5 micrometers per year per component after the initial conditioning phase. Under these conditions, particle induced late aseptic loosening is not to be expected.

Paper #18 Variables affecting the wear of polyethylene acetabular components

Paper #18 Variables affecting the wear of polyethylene acetabular components

The Otto Aufranc Award

Despite studies to determine their causes, significant variations in polyethylene acetabular component wear rates, radial cracking of component rims, and occasional delamination cannot be explained. A subsurface white band frequently occurs in such damaged components. These damaged components often are gamma sterilized. To date, the origin of the band and its effect on polyethylene chemical and mechanical properties, and hence, clinical performance, have not been confirmed, and correlations between radiation sterilization and clinical wear have not been made. By developing techniques for polyethylene retrieval testing and rating, chemical analysis, and mechanical analysis, this research has determined that gamma sterilization in air alters the chemical and mechanical properties of polyethylene over time, resulting in high subsurface oxidation, reduced ductility, and reduced strength. Gamma sterilization-induced oxidation is found to be most severe in the subsurface region of components, and coincides with zones of significantly reduced strength and ductility. This chemical and mechanical property degradation is time dependent and is not typically visible until after 3 years' postirradiation. The presence of the subsurface white band significantly correlates with clinical cracking and delamination observed in retrieved components. Wear of the retrieved components often is observed to have progressed into this heavily oxidized, weakened, and embrittled zone. A method for accelerated aging shows that irradiating in air causes oxidation damage in polyethylene components that is not seen with other sterilization methods. Modifications of gamma sterilization techniques to minimize this damage are discussed.

Failure of uncemented polyethylene acetabular components

The authors describe the mode of failure of the Ring UPM (Downs Brothers, Surrey, United Kingdom) uncemented metal-on-plastic total hip arthroplasty. Erosion of the external surface of the uncemented acetabular cup led to early loosening in eight cases. The subsequent production of large quantities of polylethylene debris caused massive granulomata, resulting in osteolysis of the acetabulum and femur. Revision surgery was difficult because of the loss of bone stock. The serious consequences of failure of this design lead to the conclusion that uncemented, nonmetalbacked polyethylene acetabular components should not be used.

Bone reaction to uncemented threaded polyethylene acetabular components.

One hundred and eighty-one cementless total hip arthroplasties with threaded polyethylene acetabular components, carried out between 1980 and 1981, have been reviewed retrospectively. Discrepancy between the complaints of the patients with loose components and destruction of acetabular bone led to the development of a four stage radiological grading system which would enable loosening to be anticipated in routine cases. There was a high percentage of loosening (33%) in our series and direct bone-polyethylene contact gave rise to severe granulomatous reactions around the implants. Strict radiological follow up and early revision surgery is indicated in this type of arthroplasty.

Production of cytokines around loosened cemented acetabular components. Analysis with immunohistochemical techniques and in situ hybridization.

The chronic inflammatory response to wear particles from orthopaedic joint implants is believed to cause osteolysis and to contribute to prosthetic loosening. Previous in vitro experiments have demonstrated that particulate debris from joint implants causes cells in culture to release products that have been implicated in this pathological bone resorption. The purpose of the current study was to investigate the in vivo features of this complex process in patients who had had a total hip replacement. Membraneous tissue was obtained from the cement-bone interface of ten polyethylene acetabular components that had been revised for aseptic loosening in ten patients. The immunoperoxidase technique, which involves the use of specific antibodies for each cell type, showed that macrophages were the predominant cellular constituents but also that fibroblasts, many of which were not identified on plain histological study, were present and were actively producing collagen. T lymphocytes were present variably, but they generally composed less than 10 percent of the cells. Particulate debris (polyethylene, methylmethacrylate, and metal) was present in all membrane specimens but was intracellular only in macrophages and multinucleated giant cells. 35S-labeled nucleic-acid probes, complementary to human interleukin-1-beta and to platelet-derived growth-factor-2 messenger RNA (mRNA), were hybridized with serial tissue sections. Hybridization demonstrated interleukin-1-beta mRNA predominantly in macrophages, and not in fibroblasts or in T lymphocytes to any major extent. In contrast, immunolocalization demonstrated interleukin-1-beta protein on both macrophages and fibroblasts, suggesting that macrophages release interleukin-1-beta, which then binds to both fibroblasts and macrophages. Platelet-derived growth-factor transcripts were found in both macrophages and fibroblasts.

Polyethylene wear in total hip arthroplasty in patient-matched groups: A comparison of stainless steel, cobalt chrome, and titanium-bearing surfaces

Osteolysis and component loosening secondary to polyethylene (PE) debris are of paramount concern to today's joint replacement surgeon. This retrospective clinical study measures linear wear in 568 implanted total hip prostheses in which three different metals were used as bearing surfaces (307 stainless steel T-28 [Zimmer, Warsaw, IN], 162 cobalt chrome Tr-28 [Zimmer], and 99 nonion implanted titanium Miami Orthopedic Surgical Consultants [Biomet, Warsaw, IN] prostheses) implanted by a single surgeon over an 8-year period. The acetabular component in all cases was nonmetal-backed compression-molded PE, and all components were cemented. Linear wear was measured using the radiographic technique described by Livermore et al. (The effect of femoral head size on wear of the polyethylene acetabular component. J Bone Joint Surg 72A: 518, 1990) in which change in acetabular component thickness is determined from serial radiographs. A separate evaluation of this technique confirmed accuracy to within 0.18 mm. Radiographs were also evaluated for femoral and acetabular radiolucencies, femoral subsidence, and osteolysis. Patients were matched for sex, age, weight, and length of follow-up period to eliminate these retrospective variables for comparison of wear. The patient-matched groups consisted of 77 patients from each group (43 women, 34 men) with the following demographics: age, 66 years; weight, 158.9 lbs.; follow-up period, 7.9 years. Results revealed linear wear rates of 0.06 stainless steel, 0.05 cobalt chrome, and 0.08 titanium in the patientmatched groups. These differences were not significant based on analysis of variance ( P>.05). Radiolucencies, osteolysis, and component subsidence did not correlate with rates of PE wear. This study is the first to evaluate PE wear with different bearing surfaces in a clinical series. Cobalt chrome produces the lowest amount of PE debris when used as a bearing surface. However, this was not significantly less than nonion implanted titanium.

In vivo wear of polyethylene acetabular components.

Polyethylene acetabular cups retrieved at revision surgery were measured by a shadowgraph technique to determine linear wear, and the values were compared with those obtained from radiographs. There was a close correlation between them, although the radiographic measurements slightly underestimated the true wear. Average linear wear rates for surface-replacement components were much greater than those for conventional prostheses with femoral heads up to 32 mm in diameter. Volumetric wear, calculated using a new formula, was found to be less than previously reported in vivo, and similar in magnitude to the results of experimental wear tests in vitro. The volumetric wear rates were greatest for the surface-replacement components and, for conventional components, were found to increase in a linear manner with component diameter.

Efficacy of Alumina Ceramic Heads for Cemented Total Hip Arthroplasty

Fifty-seven cemented total hip arthroplasties (THAs) were reviewed in cases of osteoarthrosis secondary to congenital dysplasia or dislocation. The bearing surface of the prosthesis used in this series consists of a polyethylene acetabular component on an alumina ceramic head. All acetabular components were positioned at the same level as the original acetabulum, and an autologous femoral head graft was performed for 18 hips. The follow-up period ranged from five to eight years, averaging six years two months. The latest survey showed excellent and good results for 53 hips (92.9%). Four acetabular components (7%) and two femoral components (3.5%) showed roentgenographic evidence of loosening. Only one hip (1.8%) had to be treated with revision surgery for femoral component loosening. None of the cases suffered a broken ceramic head. The use of a total hip prosthesis with an alumina ceramic head in THA is likely to lead to excellent results for patients with osteoarthrosis of the hip.

Cementless uncoated polyethylene acetabular components in total hip replacement. Review of five- to 10-year results

We reviewed the results of 545 consecutive total hip replacements using a cementless non-coated high-density polyethylene acetabular component combined with a cemented Müller stem at five to 10 years. In all, 421 patients (445 hips) were available for review, 118 by questionnaire and 303 by examination and radiography. Of these, 86% had a good or excellent result. We found a high rate of radiological loosening of the cup after the sixth year, and a high rate of clinical loosening after the eighth year. Loosening was commoner in women, in younger patients and where a smaller size of acetabulum had been used. Calcar resorption was significantly related to loosening of the acetabulum. Loosening appeared to be mainly due to polyethylene debris produced by micro-movement of the acetabulum against the bone, which had resulted in a giant cell foreign body reaction and subsequent bone erosion. We have abandoned the use of this prosthesis and suggest that direct contact between bone and polyethylene should be prevented by a coating of metal or some other material.

Effect of femoral head size on wear of the polyethylene acetabular component.

A technique was developed to determine the wear of the acetabular component of a total hip replacement by examination of standardized initial and follow-up radiographs. Three hundred and eighty-five hips were followed for at least 9.5 years after replacement. The least amount and rate of linear wear were associated with use of a femoral head that had a diameter of twenty-eight millimeters (p less than 0.001). The greatest amount and mean rate of linear wear occurred with twenty-two-millimeter components, but these differences were not statistically significant. The greatest volumetric wear and mean rate rate of volumetric wear were seen with thirty-two-millimeter components (p less than 0.001). A wider radiolucent line in acetabular Zone 1 was associated with use of the thirty-two-millimeter head. The amounts of resorption of the proximal part of the femoral neck and of lysis of the proximal part of the femur both correlated positively with the extent of linear and volumetric wear; this suggests an association between the amount of debris from wear and these changes in the femoral neck and proximal part of the femur.

Comparison between straight- and curved-stem M�ller femoral prostheses

Between 1977 and 1982, 545 cemented femoral prostheses were implanted, in combination with a noncoated cementless polyethylene acetabular component (RM cup). Three hundred and eighty-one straight-stem and 76 curved-stem Müller femoral components were implanted, as well as 88 collared components with a 130-mm stem and a 130 degrees neck-shaft angle, derived from a long-stem steel prosthesis. Survivorship analysis of revisions for aseptic loosening at 10 years revealed 97% straight-stem survival, 91.6% curved-stem survival, and 88.3% 130 degrees stem survival. "Survival" curves were also constructed for radiological loosening, and the survival rates (patients without radiological evidence of loosening) were 69.8%, 78.8%, and 63.1% respectively at 10 years. The 130 degrees collared stem was associated with significantly less acetabular loosening than the other prostheses. This resulted in less calcar resorption, but there was a higher rate of stem loosening. Acetabular loosening and associated wear products appear to be responsible for calcar resorption, and stress shielding of the calcar appears to be of minor importance in the pathogenesis of aseptic stem loosening. Better cementing techniques have improved survivorship of the curved-stem prosthesis, and early fears of high rates of radiological loosening with the straight stem have not been substantiated.

Dissociation of a metal-backed polyethylene acetabular component: A case report

A case of early failure of a total hip arthroplasty presenting as a dislocation is discussed. After failed attempts at closed reduction, an open procedure revealed that the polyethylene insert of the acetabulum had sparated from its metal backing. The increasing use of metal-backed acetabular components in total hip arthroplasty produces another mechanical interface that may fail: the metal-polyethylene interface. Surgeons should consider this possibility in dislocations of total hip prostheses that cannot be reduced by closed means.

Fracture of a metal-backed acetabular cup: A case report

In this case of fracture of a metal-backed polyethylene acetabular component after a total hip arthroplasty, there was no history of difficulties prior to the component fracture and no history of trauma.

Soft-tissue response to total hip surface replacement.

Tissue reaction to prosthesis wear debris and its relationship to prosthetic loosening was investigated. Eighteen dogs underwent hip surface replacement; 6 animals accounted for 6 control and 6 carbon hips, and 13 experimental animals accounted for 13 implanted carbon and 13 cobalt-chromium-molybdenum (CoCrMo) prostheses. Both kinds of prostheses articulated against a high-density polyethylene acetabular component. One year after implantation, tissue response to the prostheses was evaluated according to a semiquantitative method, and a total tissue score indicating the degree of tissue response was obtained. The total tissue score was then compared with the normalized final vertical ground reaction force (GRF) for each hip in the animals with bilateral hip replacements. Compared with the controls, significantly greater tissue response was seen in both kinds of prosthetic hips (p = .001). No statistically significant difference in the tissue response of the two types of hip prostheses was noted, although the tissue response score of the CoCrMo demonstrated a trend toward more severe reaction than the carbon. No statistical difference in tissue reaction was noted for loosened components as compared with tightly fixed components. Amount of wear debris was the best predictor of component loosening. Gait analysis demonstrated a statistically significant negative correlation between GRF and total tissue score (p = .036), and between GRF and wear debris score (p = .034). The results of this study suggest that GRF may predict the amount of wear debris in the tissues surrounding a total hip surface arthroplasty, and that severity of pain is related to the degree of tissue response.

Mechanical loosening of total hip prostheses. A radiographic and roentgen stereophotogrammetric study.

Twenty patients were examined by standard radiography and roentgen stereophotogrammetric analysis (RSA) during a two-year period after total hip arthroplasty. Eleven of the acetabular components migrated cranially and three femoral components migrated distally. This migration was most rapid during the first four months after operation. Our findings support the possibility that mechanical loosening is initiated by thermal injury during polymerisation of the cement; the less frequent migration of the metallic femoral component compared with the polyethylene acetabular component may be because the metal acts as a heat sink. Standard radiographs were inadequate for assessment of early mechanical loosening, whereas RSA could reveal migration within four months of the arthroplasty.

In vivo construction of a metal-backed, high-molecular-weight polyethylene cup during McKee-farrar revision total joint arthroplasty: A case report

The need for revision total hip arthroplasty after metal-to-metal articulating prostheses is well known. An alternative to conventional acetabular revision in the clinical circumstance of isolated femoral component loosening is in vivo construction of a metal-backed, high-molecular-weight polyethylene (HMWPE) acetabular component. This surgical approach reduces the likelihood of intraoperative acetabular bone loss, should minimize subsequent loosening, and virtually eliminates the source of metallic wear debris. Follow-up evaluation after 3 years revealed maintenance of the acetabular component position and a satisfactory clinical result. In vivo construction of a metal-backed HMWPE acetabular component is an effective alternative in the management of this potentially difficult orthopedic problem.