Clinical comparison of polyethylene wear with zirconia or cobalt-chromium femoral heads

Head, acetabular liner composition, and rate of revision and wear in total hip arthroplasty: a Bayesian network meta-analysis

Total hip arthroplasty (THA) is a common procedure for patients suffering from hip pain e.g. from osteoarthritis, osteonecrosis, or hip fractures. The satisfaction of patients undergoing THA is influenced by the choice of implant type and material, with one key factor being the selection of the appropriate material combination for the bearing surface. In this Bayesian network meta-analysis, we investigated the impact of material combinations for the bearing surface on the longevity of hip implants. The wear penetration rate per year and the total wear penetration in the liner resulting from different material combinations, as well as the survival rate at last follow-up, were examined. We analyzed a total of 663,038 THAs, with 55% of patients being women. Mean patient age was 59.0 ± 8.1 years and mean BMI 27.6 ± 2.6 kg/m2. The combination of an aluminium oxide (Al2O3) head and an Al2O3 liner demonstrated the lowest wear penetration at last follow-up and the lowest rate of wear penetration per year. Additionally, the combination of a crosslinked polyethylene (XLPE) liner and a zircon oxide (ZrO2) head demonstrated the lowest rate of revision at last follow-up. These findings underscore the importance of careful material selection for hip implant bearing surfaces to optimize their longevity and patient satisfaction after THA.

Risk factors for liner wear and head migration in total hip arthroplasty: a systematic review

Total hip arthroplasty (THA) is a successful orthopaedic surgical procedure, and its longevity depends on bearing components and implant fixation. Optimizing polyethylene and ceramics has led to improved wear parameters and contributed to improved long-term outcomes. The present systematic review investigated whether time span from implantation, patient characteristics and performance status exert an influence on liner wear and head migration in THA. This study was conducted in conformity to the 2020 PRISMA guidelines. All the clinical investigations which reported quantitative data on the amount of liner wear and head migration in THA were considered. Only studies which reported quantitative data at least on one of the following patient characteristics were suitable: mean age, mean BMI (kg/m2), sex, side, time span between the index THA and the last follow-up (months) were eligible. A multiple linear model regression analysis was employed to verify the association between patient characteristics and the amount of liner wear and/or head migration. The Pearson Product-Moment Correlation Coefficient was used to assess the association between variables. Data from 12,629 patients were considered. The mean length of the follow-up was 90.5 ± 50.9 months. The mean age of patients at surgery was 58.4 ± 9.4 years, and the mean BMI was 27.2 ± 2.5 kg/m2. 57% (7199 of 12,629 patients) were women, and in 44% (5557 of 12,629 patients) THAs were performed on the left. The mean pre-operative Harris hip score was 46.5 ± 6.0 points. There was evidence of a moderate positive association between the amount of liner wear and the time elapsed between the index surgery to the follow-up (P = 0.02). There was evidence of a moderate positive association between the amount of head migration and the time elapsed between the index surgery to the follow-up (P = 0.01). No further statistically significant association was found. The time elapsed between the index surgery to the follow-up was the most important factor which influence the head migration and liner wear in THA. Patients' characteristics and preoperative physical activity did not influence the amount of head migration and liner wear.

Five-year polyethylene cup migration and PE wear of the Anatomic Dual Mobility acetabular construct

INTRODUCTION

Dual mobility implants have been successful in reducing postoperative hip dislocation but mid-term results of cup migration and polyethylene wear are missing in the literature. Therefore, we measured migration and wear at 5-year follow-up using radiostereometric analysis (RSA).

MATERIALS AND METHODS

A cohort of 44 patients (mean age 73, 36 female) with heterogeneous indications for hip arthroplasty but all with a high risk of hip dislocation received total hip replacement (THA) with The Anatomic Dual Mobility X3 monoblock acetabular construct and a highly crosslinked polyethylene liner. RSA images and Oxford Hip Scores were obtained perioperatively and 1, 2, and 5 years postoperatively. Cup migration and polyethylene wear were calculated using RSA.

RESULTS

Mean 2-year proximal cup translation was 0.26 mm (95% CI 0.17; 0.36). Proximal cup translation was stable from 1- to 5-year follow-up. Mean 2-year cup inclination (z-rotation) was 0.23° (95% CI - 0.22; 0.68) and was greater in patients with osteoporosis compared to patients without osteoporosis (p = 0.04). Using 1-year follow-up as baseline, the 3D polyethylene wear rate was 0.07 mm/year (0.05; 0.10). Oxford hip scores improved 19 (95% CI 14; 24) points from mean 21 (range 4; 39) at baseline, to 40 (9; 48) 2 years postoperatively. There were no progressive radiolucent lines > 1 mm. There was 1 revision for offset correction.

CONCLUSIONS

Anatomic Dual Mobility monoblock cups were well-fixed, the polyethylene wear rate was low, and the clinical outcomes were good until 5-year follow-up suggesting good implant survival in patients of different age groups and with heterogeneous indications for THA.

COMPETITIVE LIFE TIME ASSESSMENT OF SrO-ZTA/SrO-ZTA AND CoCrMo/UHMWPE HIP PROSTHESIS BEARINGS

The hip joint envisages the prime load bearing structure among other joints in the human body. Hip joint failure leads to the replacement of the hip joint prosthesis. This research work focuses on the proper selection of bearing couple materials for the hip joint to improve the performance and life. Herein, the stress and deformation of different bearing couple materials are analysed in the perspective of transient dynamic analysis under jogging load cycle. Selective hip joint bearing (femoral head-liner) couples are SS316L on UHMWPE (MoP), CoCrMo on UHMWPE (MoP), Ti6Al4V on SrO-ZTA (MoC), SrO-ZTA on UHMWPE (CoP) and SrO-ZTA on SrO-ZTA (CoC) encountered, respectively. The SrO-ZTA on SrO-ZTA (CoC) bearing couple generates the less Von Mises stress of 180.88 MPa. Load bearing pressure and Archard law predict the wear depth of CoCrMo on UHMWPE (MoP) and SrO-ZTA on SrO-ZTA (CoC) bearing couples are 0.141 mm/year and 0.031 mm/year, respectively. In simultaneous, the theoretical wear volume for CoCrMo on UHMWPE (MoP) and SrO-ZTA on SrO-ZTA (CoC) bearing couples are found as 35.46[Formula: see text]mm3/year and 2.62[Formula: see text]mm3/year, respectively. The wear depth and wear volume are supporting the available clinical retrievals and exist in well acceptable range. Competitive wear analysis data ensures 15 years safe life of SrO-ZTA on SrO-ZTA (CoC) hip prosthesis bearing.

Long-term outcomes of total hip arthroplasty in patients younger than 55 years: a systematic review of the contemporary literature

Background

Total hip arthroplasty (THA) is increasingly performed in younger patients despite the lack of comprehensive assessment of long-term outcomes. We systematically reviewed the contemporary literature to assess the 1) indications, 2) implant selection and long-term survivorship, 3) complication and reoperation rates and 4) radiographic and functional outcomes of primary THA in patients younger than 55 years.

Methods

We searched the Embase and MEDLINE databases for English-language articles published between 2000 and 2018 that reported outcomes of primary THA in patients younger than 55 years with a minimum follow-up duration of 10 years.

Results

Thirty-two studies reporting on 3219 THA procedures performed in 2434 patients met our inclusion criteria. The most common preoperative diagnoses were avascular necrosis (1044 [32.4%]), osteoarthritis (870 [27.0%]) and developmental dysplasia of the hip (627 [19.5%]). Modular implants (3001 [93.2%]), cementless fixation (2214 [68.8%]) and metal-on-polyethylene bearings (1792 [55.7%]) were frequently used. The mean 5- and 10-year survival rates were 98.7% and 94.6%, respectively. Data on survival beyond 10 years were heterogeneous, with values of 27%–99.5% at 10–14 years, 59%–84% at 15–19 years, 70%–77% at 20–24 years and 60% at 25–30 years. Rates of dislocation, deep infection and reoperation for any reason were 2.4%, 1.2% and 16.3%, respectively. The mean Harris Hip Score improved from 43.6/100 to 91.0/100.

Conclusion

Total hip arthroplasty in patients younger than 55 years provides reliable outcomes at up to 10 years. Future studies should evaluate the outcomes of THA in this population at 15–20 years’ follow-up.

Finite element analysis of polyethylene wear in total hip replacement: A literature review

Evaluation and prediction of wear play a key role in product design and material selection of total hip replacements, because wear debris is one of the main causes of loosening and failure. Multifactorial clinical or laboratory studies are high cost and require unfeasible timeframes for implant development. Simulation using finite element methods is an efficient and inexpensive alternative to predict wear and pre-screen various parameters. This article presents a comprehensive literature review of the state-of-the-art finite element modelling techniques that have been applied to evaluate wear in polyethylene hip replacement components. A number of knowledge gaps are identified including the need to develop appropriate wear coefficients and the analysis of daily living activities.

No Difference in Conventional Polyethylene Wear Between Yttria-stabilized Zirconia and Cobalt-chromium-molybdenum Femoral Heads at 10 Years

BACKGROUND

Concerns have arisen regarding deterioration of wear properties of yttria-stabilized zirconia (YSZ) femoral head on conventional polyethylene (PE) bearings due to YSZ phase transformation.

QUESTIONS/PURPOSES

The purpose of this study was to determine if there is a difference in long-term PE wear properties between YSZ and cobalt-chromium-molybdenum (Co-Cr-Mo) femoral heads.

METHODS

Ten-year radiographic wear assessment was performed on a cohort of patients enrolled in a prospective randomized clinical trial comparing total hip arthroplasty with YSZ or Co-Cr-Mo femoral heads on conventional, non-cross-linked PE.

RESULTS

PE linear wear, annualized wear, and steady-state wear rates remained low and similar between groups. No cases of osteolysis were observed.

CONCLUSIONS

Measured conventional PE wear was similar between YSZ and Co-Cr-Mo femoral heads with the steady-state wear rates for both remaining below the generally accepted threshold at which osteolysis typically occurs. Whether clinically relevant phase transformation with YSZ femoral heads occurs is uncertain; however, the use of YSZ femoral heads in this study was not associated with increased PE wear, osteolysis, or deterioration of wear properties.

Retrieved Magnesia-Stabilized Zirconia Femoral Heads Exhibit Minimal Roughening and Abrasive Potential

BACKGROUND

The degradation of ceramic femoral heads made of yttria-stabilized zirconia (Y-TZP) because of tetragonal-to-monoclinic phase transformation in vivo is well-described, whereas magnesia-stabilized zirconia (Mg-PSZ) ceramics resist phase transformation in a warm aqueous environment. The purpose of this study was to evaluate phase transformation, changes in surface topography, and roughness parameters, including changes in surface polarity and abrasiveness, among retrieved zirconia femoral heads.

METHODS

A total of 69 Y-TZP and 86 Mg-PSZ-retrieved femoral heads were examined, with 5 never-implanted heads of each type as controls. Selected heads were scanned by x-ray diffraction, to measure % monoclinic phase. All heads were scanned by optical profilometry to find visual evidence of degradation and to measure surface roughness, surface polarity, and the functional roughness parameters. Monoclinic phase % and roughness data were plotted vs time in vivo.

RESULTS

Visual evidence of phase transformation was observed among Y-TZP femoral heads, and some exhibited pitting. Y-TZP femoral heads roughened and become more abrasive in vivo, although those made by CeramTec exhibited less degradation than those by Morgan and Saint Gobain. In contrast, Mg-PSZ heads did not exhibit pitting, undergo phase transformation, or roughen in vivo, and retained a negative surface polarity.

CONCLUSION

All Y-TZP femoral heads exhibited increased phase transformation with time in vivo, although not all Y-TZP heads exhibited catastrophic roughening. No phase transformation was observed on Mg-PSZ femoral heads after up to 19.2 years in vivo. The lack of degradation among Mg-PSZ retrievals suggests a lower wear potential in joint replacement.

The study of wear behaviors on abducted hip joint prostheses by an alternate finite element approach

An acetabular cup with larger abduction angles is able to affect the normal function of the cup seriously that may cause early failure of the total hip replacement (THR). Complexity of the finite element (FE) simulation in the wear analysis of the THR is usually concerned with the contact status, the computational effort, and the possible divergence of results, which become more difficult on THRs with larger cup abduction angles. In the study, we propose a FE approach with contact transformation that offers less computational effort. Related procedures, such as Lagrangian Multiplier, partitioned matrix inversion, detection of contact forces, continuity of contact surface, nodal area estimation, etc. are explained in this report. Through the transformed methodology, the computer round-off error is tremendously reduced and the embedded repetitive procedure can be processed precisely and quickly. Here, wear behaviors of THR with various abduction angles are investigated. The most commonly used combination, i.e., metal-on-polyethylene, is adopted in the current study where a cobalt-chromium femoral head is paired with an Ultra High Molecular Weight Polyethylene (UHMWPE) cup. In all illustrations, wear coefficients are estimated by self-averaging strategy with available experimental datum reported elsewhere. The results reveal that the THR with larger abduction angles may produce deeper depth of wear but the volume of wear presents an opposite tendency; these results are comparable with clinical and experimental reports. The current approach can be widely applied easily to fields such as the study of the wear behaviors on ante-version, impingement, and time-dependent behaviors of prostheses etc.

PREDICTING THE WEAR OF SOFT-ON-HARD BEARING COUPLES FOR HUMAN HIP PROSTHESIS USING FINITE ELEMENT CONCEPTS

Wear of bearing couples is one of the major concerns in artificial hip implantation. To minimize the wear of hip bearing surfaces, several new materials have been introduced and tested including metal-on-metal, ceramic-on-ceramic and hard-on-hard combinations. The present study involves prediction of wear on ultra-high molecular weight polyethylene (UHMWPE) cup against Co–Cr, alumina and zirconia femoral head by applying the three-dimensional (3D) physiological loads as well as angular motions on these bearing couples to calculate the contact pressure using finite element concepts. The linear and volumetric wear of bearing surfaces increase with increase in gait cycles. Overall, the Zirconia–UHMWPE combination showed least wear, when compared with Alumina–UHMWPE and Co–Cr–UHMWPE combinations. The present study also revealed that the Zirconia–UHMWPE combinations showed less volumetric wear than the Alumina–Alumina bearing which is at present used in artificial hip resurfacements.

The case for ceramic-on-polyethylene as the preferred bearing for a young adult hip replacement

The optimum choice of bearing surfaces in total hip arthroplasty, particularly in the younger and more active patient, remains controversial. Despite several studies demonstrating good long-term results for the metal-on-polyethylene articulation, there has been a recent vogue towards the utilisation of hard-on-hard bearings for younger patients due, in part, to concerns regarding polyethylene induced osteolysis. However, well-documented complications concerning metal-on-metal bearings and the risk of fracture in ceramic-on-ceramic bearings have raised concerns regarding the principle of the hard-on-hard bearing in the active patient. With recent technological advancements in the manufacture of both polyethylene and alumina ceramics, the in vitro properties of each material with regards to strength and toughness have been significantly improved. In addition, ceramic femoral heads have consistently been shown to produce less in vivo polyethylene wear than similar sized metal heads. This paper aims to critically review the biomechanical, in vivo and clinical studies related to the use of the ceramic on polyethylene bearing, and highlights its potential use as the preferred bearing for a young adult hip replacement.

Higher wear-rate of third-generation metal-backed Reflection cups with eto-sterilised UHMWPE at a mean 13 years follow-up

Polyethylene (PE) wear and osteolysis is a recognised problem with non-cross linked PE liners and first generation modular cup designs. Wear particles induce osteolysis leading to aseptic loosening. We retrospectively compared the linear PE wear and implant survival and revision rates of the Reflection Cup and the Duraloc 300. After a mean clinical follow-up of 13 years (range 11-15 years), the 2D linear PE wear-rate of the Reflection liner (n = 68) was 0.23 mm/year, with a mean total wear of 3.14 mm (1.04-7.36), SD 1.45. The wear-rate of the Duraloc 300 cups (n = 32) was 0.14 mm/year, with a mean total wear of 1.84 mm (0.55-4.63), SD 1.07. The difference in PE wear-rate as well as mean total wear was highly significant (p = 0.0001). There was a positive correlation between wear-rate and both Oxford Hip Score and Harris Hip Score (p = 0.02). Large acetabular cup size (>54 mm), HA coating on the stem and age <50 years did not influence PE wear. The higher wear-rate in the Reflection liners could be related to the EtO sterilisation. Intermediate and long-term follow-up is advisable.

Large ceramic femoral heads: what problems do they solve?

Large ceramic femoral heads offer several advantages that are potentially advantageous to patients undergoing both primary and revision total hip replacement. Many high-quality studies have demonstrated the benefit of large femoral heads in reducing post-operative instability. Ceramic femoral heads may also offer an advantage in reducing polyethylene wear that has been reported in vitro and is starting to become clinically apparent in mid-term clinical outcome studies. Additionally, the risk of taper corrosion at a ceramic femoral head-neck junction is clearly lower than when using a metal femoral head. With improvements in the material properties of both modern ceramic femoral heads and polyethylene acetabular liners that have reduced the risk of mechanical complications, large ceramic heads have gained popularity in recent years.

Wear comparison between conventional and highly cross-linked polyethylene against a zirconia head: a concise follow-up, at an average 10 years, of a previous report

We previously reported the results of wear comparison at a minimum of 5 years between highly cross-linked polyethylene (HXLPE) and conventional polyethylene (PE) against a zirconia femoral head. We now report the mean wear at 10 years for 52 patients (56 hips) of the original cohort of 61 patients (65 hips) who had undergone primary total hip arthroplasty at our hospital between November 1999 and August 2000. The mean steady-state linear wear rate of HXLPE was 0.045 mm/y, compared with 0.080 mm/y for conventional PE (P=.0003). The incidence of osteolysis was 25% in the conventional PE group compared with 0% in the HXLPE group. Our study demonstrated that the steady-state wear rate for HXLPE remains significantly lower than that for conventional PE against a zirconia femoral head at a mean of 10 years after implantation.

Long-term outcomes of a new model of anatomical hydroxyapatite-coated hip prosthesis

This prospective study was designed to evaluate 196 Anatomique Benoist Giraud (ABG II) total hip arthroplasties which were implanted between September 1999 and December 2000. A minimum 11 years follow up was completed in 183 cases. The bearing surfaces were polyethylene-zirconia in 84 cases, polyethylene-metal in 42 and ceramic-ceramic in 57. Changes in the femoral stem design, in relation to the previous ABG I model, have led to a significant improvement in stress-shielding. Polyethylene wear rate was lower by more than 50% compared with non-crosslinked polyethylene. Excellent and good results were obtained in 90.32% of cases, and implant survival was 98.39% at the end of follow-up.

In vivo wear performance of highly cross-linked polyethylene vs. yttria stabilized zirconia and alumina stabilized zirconia at a mean seven-year follow-up

Background

Zirconia was introduced as an alternative to alumina for use in the femoral head. The yttria stabilized zirconia material was improved by adding alumina. We evaluated highly cross-linked polyethylene wear performance of zirconia in total hip arthroplasty. The hypothesis was that alumina stabilized zirconia could decrease highly cross-linked polyethylene wear.

Methods

Highly cross-linked polyethylene wear was measured with a computerized method (PolyWare) in 91 hips. The steady-state wear rates were measured based on the radiographs from the first year postoperatively to the final follow-up and were compared between hips with yttria stabilized zirconia and alumina stabilized zirconia.

Results

The steady-state wear rate of highly cross-linked polyethylene against zirconia was 0.02 mm/year at a mean follow-up of 7 years. No significant difference was observed between groups with yttria stabilized zirconia and alumina stabilized zirconia.

Conclusions

Addition of alumina to the zirconia material failed to show further reduction of highly cross-linked polyethylene wear and our hypothesis was not verified.

Wear resistant performance of highly cross-linked and annealed ultra-high molecular weight polyethylene against ceramic heads in total hip arthroplasty

The purpose of this study was to examine the effects of ceramic femoral head material, size, and implantation periods on the wear of annealed, cross-linked ultra-high molecular weight polyethylene (UHMWPE) (XLPE) in total hip arthroplasty compared to non-cross-linked conventional UHMWPE (CPE). XLPE was fabricated by cross-linking with 60 kGy irradiation and annealing. Femoral heads made from zirconia and alumina ceramics and cobalt-chrome (CoCr) of 22 or 26 mm diameter were used. In this retrospective cohort study, the femoral head penetration into the cup was measured digitally on radiographs of 367 hips with XLPE and 64 hips with CPE. The average follow-up periods were 6.3 and 11.9 years, respectively. Both XLPE creep and wear rates were significantly lower than those of CPE (0.19 mm vs. 0.44 mm, 0.0001 mm/year vs. 0.09 mm/year, respectively). Zirconia displayed increased wear rates compared to alumina in CPE; however, there was no difference among head materials in XLPE (0.0008, 0.00007, and -0.009 mm/year for zirconia, alumina, and CoCr, respectively). Neither head size or implantation period impacted XLPE wear. In contrast to CPE, XLPE displayed low wear rates surpassing the effects of varying femoral head material, size, implantation period, and patient demographics. Further follow-up is required to determine the long-term clinical performance of the annealed XLPE.

Head material influences survival of a cemented total hip prosthesis in the Norwegian Arthroplasty Register

BACKGROUND

High prosthesis survival is reported for total hip prostheses with metal and alumina heads, but direct comparisons of a single prosthesis design with one of two different head materials has seldom been studied. Prostheses with zirconia heads are less commonly used than metal and alumina heads, and the few reports suggest variable results with zirconia heads.

QUESTIONS/PURPOSES

We therefore asked: (1) Would metal heads provide better survival of a cemented total hip arthroplasty (THA) than alumina heads? (2) Would metal heads provide better survival of a cemented THA than zirconia heads?

METHODS

We searched in the Norwegian Arthroplasty Register for cemented primary THA cup/stem combinations that simultaneously had been used with different head materials. The only THA that fulfilled these inclusion criteria was the cemented Reflection All-Poly/Spectron EF (cup/stem) that had during 2001 to 2006 been used both with alumina (n = 448) and cobalt-chromium (n = 5229) heads; that implant had also been used with zirconia (n = 275) and cobalt-chromium heads (n = 3195) during 1997 to 2003, and we included patients with this THA from these two time intervals in the study. All cups were conventional polyethylene. We estimated prosthesis survival and relative revision risks adjusting for age, sex, and diagnosis. The followup in the two study materials was until December 2010.

RESULTS

The survival at 8 years of the Spectron EF/Reflection THAs, inserted with alumina and cobalt-chromium heads during 2001 to 2006, was 92.3% and 94.0%, respectively. The Reflection/Spectron EF THA had inferior survival with zirconia heads compared with cobalt-chromium heads (relative risk, 1.7). At 12 years, the survival rate was 88.1% with cobalt-chromium heads and 74.8% with zirconia heads.

CONCLUSIONS

Alumina femoral heads provided no advantage over cobalt-chromium heads on midterm prosthesis survival. THAs with zirconia heads had inferior survival.

LEVEL OF EVIDENCE

Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Superior accuracy of model-based radiostereometric analysis for measurement of polyethylene wear: A phantom study

Objectives

The accuracy and precision of two new methods of model-based radiostereometric analysis (RSA) were hypothesised to be superior to a plain radiograph method in the assessment of polyethylene (PE) wear.

Methods

A phantom device was constructed to simulate three-dimensional (3D) PE wear. Images were obtained consecutively for each simulated wear position for each modality. Three commercially available packages were evaluated: model-based RSA using laser-scanned cup models (MB-RSA), model-based RSA using computer-generated elementary geometrical shape models (EGS-RSA), and PolyWare. Precision (95% repeatability limits) and accuracy (Root Mean Square Errors) for two-dimensional (2D) and 3D wear measurements were assessed.

Results

The precision for 2D wear measures was 0.078 mm, 0.102 mm, and 0.076 mm for EGS-RSA, MB-RSA, and PolyWare, respectively. For the 3D wear measures the precision was 0.185 mm, 0.189 mm, and 0.244 mm for EGS-RSA, MB-RSA, and PolyWare respectively. Repeatability was similar for all methods within the same dimension, when compared between 2D and 3D (all p > 0.28). For the 2D RSA methods, accuracy was below 0.055 mm and at least 0.335 mm for PolyWare. For 3D measurements, accuracy was 0.1 mm, 0.2 mm, and 0.3 mm for EGS-RSA, MB-RSA and PolyWare respectively. PolyWare was less accurate compared with RSA methods (p = 0.036). No difference was observed between the RSA methods (p = 0.10).

Conclusions

For all methods, precision and accuracy were better in 2D, with RSA methods being superior in accuracy. Although less accurate and precise, 3D RSA defines the clinically relevant wear pattern (multidirectional). PolyWare is a good and low-cost alternative to RSA, despite being less accurate and requiring a larger sample size.

Reduced wear of cross-linked UHMWPE using magnesia-stabilized zirconia femoral heads in a hip simulator

BACKGROUND

To reduce wear, the ideal bearing surface in joint arthroplasty should be smooth and hydrophilic. Ceramics generally offer better wettability than metals and can be polished to a smoother finish. However, clinical studies have found no reduction in liner wear when using yttria-stabilized zirconia (Y-TZP) instead of cobalt chromium alloy (CoCr) femoral heads.

QUESTION/PURPOSES

We (1) determined whether a hard, diamond-like carbon (DLC) coating would enhance the wettability of CoCr and magnesia-stabilized zirconia (Mg-PSZ) femoral heads without increasing roughness, and (2) compared their wear performance.

METHODS

In an observational study limited to CoCr and Mg-PSZ heads, we measured roughness and contact angle on as-received and DLC-coated heads. Eight heads then were subjected to 11 million cycles of wear in a hip simulator against cross-linked ultrahigh molecular weight polyethylene (XLPE) liners.

RESULTS

Mg-PSZ femoral heads were smoother and more hydrophilic than CoCr heads. Although DLC coatings did not reduce roughness, they reduced the contact angle of CoCr and Mg-PSZ substrates, which may provide enhanced lubrication in vivo. In hip simulator tests, liners bearing against CoCr heads wore at a greater rate compared with Mg-PSZ heads. The DLC coating on Mg-PSZ heads did not reduce wear further.

CONCLUSIONS

The wear rate of XLPE versus Mg-PSZ was seven times less than CoCr heads, probably owing to lower roughness and greater wettability of Mg-PSZ heads.

CLINICAL RELEVANCE

The use of Mg-PSZ femoral heads should lead to reduced wear in vivo compared with CoCr heads, but the clinical benefit of DLC-coated Mg-PSZ is unclear.

Wear and surface analysis of 38 mm ceramic-on-metal total hip replacements under standard and severe wear testing conditions

The purpose of this study was to compare the wear of zirconia-toughened alumina (ZTA) and alumina femoral heads tested against as-cast CoCrMo alloy acetabular cups under both standard and severe wear conditions. A new severe test, which included medio-lateral displacement of the head and rim impact upon relocation, was developed. This resulted in an area of metal transfer and an area of increased wear on the superior-anterior segment of the head that were thought to be due to dislocation and rim impact respectively. While the wear of all ceramic heads was immeasurable using the gravimetric method, the wear rates for the metallic cups from each test were readily calculated. An average steady state wear rate of 0.023 ± 0.005 mm3/106 cycles was found for the cups articulating against ZTA under standard wear conditions. A similar result had previously been obtained for the wear of cups articulated against alumina heads of the same size (within the same laboratory). Under severe wear conditions an increase in the metallic cup steady state wear rate was found with the ZTA and alumina tests giving 0.623 ± 0.252 and 1.35 ± 0.154 mm3/106 cycles respectively. Wear of the ceramic heads was detected using atomic force microscopy which showed, under severe wear conditions, a decrease in polishing marks and occasional grain removal. The surfaces of the ZTA heads tested under standard conditions were virtually unchanged from the unworn samples. Friction tests showed low friction factors for all components, pre and post wear.

Effects of metal-on-metal wear on the host immune system and infection in hip arthroplasty

BACKGROUND AND PURPOSE

Joint replacement with metal-on-metal (MOM) bearings have gained popularity in the last decades in young and active patients. However, the possible effects of MOM wear debris and its corrosion products are still the subject of debate. Alongside the potential disadvantages such as toxicity, the influences of metal particles and metal ions on infection risk are unclear.

METHODS

We reviewed the available literature on the influence of degradation products of MOM bearings in total hip arthroplasties on infection risk.

RESULTS

Wear products were found to influence the risk of infection by hampering the immune system, by inhibiting or accelerating bacterial growth, and by a possible antibiotic resistance and heavy metal co-selection mechanism.

INTERPRETATION

Whether or not the combined effects of MOM wear products make MOM bearings less or more prone to infection requires investigation in the near future.

The final follow-up plain radiograph is sufficient for clinical evaluation of polyethylene wear in total hip arthroplasty. A study of validity and reliability

BACKGROUND AND PURPOSE

Radiostereometric analysis (RSA) is a highly accurate tool for assessment of polyethylene (PE) wear in total hip arthroplasty (THA); however, PE wear measurements in clinical studies are often limited to plain radiographs. We evaluated the agreement between PE wear measured with PolyWare software, which uses plain radiographs, and by model-based RSA, which uses stereo radiographs.

METHODS

Measurements of PE wear postoperatively and at final follow-up (after mean 6 years) on plain radiographs of 12 patients after cementless THA were evaluated with PolyWare software and the results were compared with those from RSA as the gold standard (Model-based RSA using elementary geometrical shape models; EGS-RSA). With PolyWare, we either used the final radiographic follow-up (PW1) only or both the postoperative follow-up and the final follow-up (PW2).

RESULTS

The 2D mean wear measured (in mm) was 0.80, 1.07, and 0.60 for the PW2, PW1, and RSA method. 2D intra-method repeatability was similar for PW1 and RSA with limits of agreement (LOAs, in mm) of ± 0.22, and ± 0.23, respectively. 2D inter-method concurrent validity was best between PW1 and EGS-RSA with LOAs of ± 0.55. For 2D linear wear measurements, the PW1 method had a clinical repeatability similar to that of RSA.

INTERPRETATION

PW1 is sufficient for retrospective determination of 2D wear from medium-term wear measurements above 0.5 mm, It alleviates the need for baseline plain radiographs, has a clinical precision similar to that of RSA, and is easy and inexpensive to use.