Zirconia femoral head fractures: a clinical and retrieval analysis

Zirconia ageing is related to total hip arthroplasty aseptic loosening. A study of 45 retrieved zirconia heads

BACKGROUND

Y-TZP zirconia heads were recalled by the Food and Drug Administration (FDA) in 2001 and zirconia alone was no longer used in orthopedics. Tunnel furnace sintering was suspected of producing defects responsible for early material failure. As Zirconia Toughened Alumina (ZTA) matrices are widely used as bearing material and contain zirconia grains, there remains a need to better understand the in vivo ageing process of zirconia and its clinical implications when the material is produced by batch furnace sintering, the validated sintering process.

QUESTIONS/OBJECTIVES

Is there an association between the ageing of batch furnace produced zirconia and THA revision?

METHODS

45 retrieved femoral heads, batch furnace sintered only, were analyzed. Roughness was measured by 3D profilometry, phase transfer by μRaman spectroscopy. Clinical data were compared with material characteristics.

RESULTS

Irrespective of the cause of revision, all heads showed a crystallographic phase transition from tetragonal to monoclinic over 19.5%. A correlation was found between the phase change, roughness increase and aseptic loosening, with a threshold set at 24.5% of monoclinic phase.

CONCLUSIONS

The ageing process of zirconia may lead to aseptic loosening, which, in the absence of contrary evidence, prohibits its use as the sole component of orthopedic materials. ZTA matrices should be clinically monitored, especially in young patients, and better in vitro modelling needs to be performed.

LEVEL OF EVIDENCE

IV; Case series.

Material-Intrinsic NIR-Fluorescence Enables Image-Guided Surgery for Ceramic Fracture Removal

Hip arthroplasty effectively treats advanced osteoarthritis and is therefore entitled as "operation of the 20th century." With demographic shifts, the USA alone is projected to perform up to 850 000 arthroplasties annually by 2030. Many implants now feature a ceramic head, valued for strength and wear resistance. Nonetheless, a fraction, up to 0.03% may fracture during their lifespan, demanding complex removal procedures. To address this, a radiation-free, fluorescence-based image-guided surgical technique is presented. The method uses the inherent fluorescence of ceramic implant materials, demonstrated through chemical and optical analysis of prevalent implant types. Specifically, Biolox delta implants exhibited strong fluorescence around 700 nm with a 74% photoluminescence quantum yield. Emission tails are identified extending into the near-infrared (NIR-I) biological transparency range, forming a vital prerequisite for the label-free visualization of fragments. This ruby-like fluorescence could be attributed to Cr within the zirconia-toughened alumina matrix, enabling the detection of even deep-seated millimeter-sized fragments via camera-assisted techniques. Additionally, fluorescence microscopy allowed detection of µm-sized ceramic particles, enabling debris visualization in synovial fluid as well as histological samples. This label-free optical imaging approach employs readily accessible equipment and can seamlessly transition to clinical settings without significant regulatory barriers, thereby enhancing the safety, efficiency, and minimally invasive nature of fractured ceramic implant removal procedures.

Comprehensive Review on Biomaterials and Their Inherent Behaviors for Hip Repair Applications

Developing biomaterials for hip prostheses is challenging and requires dedicated attention from researchers. Hip replacement is an inevitable and remarkable orthopedic therapy for enhancing the quality of patient life for those who have arthritis as well as trauma. Generally, five types of hip replacement procedures are successfully performed in the current medical market: total hip replacements, hip resurfacing, hemiarthroplasty, bipolar, and dual mobility systems. The average life span of artificial hip joints is about 15 years, and several studies have been conducted over the last 60 years to improve the performance and thereby increase the lifespan of artificial hip joints. Present-day prosthetic hip joints are linked to the wide availability of biomaterials. Metals, ceramics, and polymers are some of the most promising types of biomaterials; nevertheless, each biomaterial has advantages and disadvantages. Metals and ceramics fail in most applications owing to stress shielding and the emission of wear debris; ongoing research is being carried out to find a remedy to these unfavorable responses. Recent research found that polymers and composites based on polymers are significant alternative materials for artificial joints. With growing research and several biomaterials, recent reviews lag in effectively addressing hip implant materials' individual mechanical, tribological, and physiological behaviors. This Review comprehensively investigates the historical evolution of artificial hip replacement procedures and related biomaterials' mechanical, tribological, and biological characteristics. In addition, the most recent advances are also discussed to stimulate and guide future researchers as they seek more effective methods and synthesis of innovative biomaterials for hip arthroplasty application.

The effect of GelMA/alginate interpenetrating polymeric network hydrogel on the performance of porous zirconia matrix for bone regeneration applications

Bone tissue is a natural composite, exhibiting complicated structures and unique mechanical/biological properties. With an attempt of mimicking the bone tissue, a novel inorganic-organic composite scaffolds (ZrO2-GM/SA) was designed and prepared via the vacuum infiltration method and the single/double cross-linking strategy by blending GelMA/alginate (GelMA/SA) interpenetrating polymeric network (IPN) into the porous zirconia (ZrO2) scaffold. The structure, morphology, compressive strength, surface/interface properties, and biocompatibility of the ZrO2-GM/SA composite scaffolds were characterized to evaluate the performance of the composite scaffolds. Results showed that compared to ZrO2 bare scaffolds with well-defined open pores, the composite scaffolds prepared by double cross-linking of GelMA hydrogel and sodium alginate (SA) presented a continuous, tunable and honeycomb-like microstructure. Meanwhile, GelMA/SA showed favorable and controllable water-uptake capacity, swelling property and degradability. After the introduction of IPN components, the mechanical strength of composite scaffolds was further improved. The compressive modulus of composite scaffolds was significantly higher than the bare ZrO2 scaffolds. In addition, ZrO2-GM/SA composite scaffolds had highly biocompatibility and displayed a potent proliferation and osteogenesis of MC3T3-E1 pre-osteoblasts compared to bare ZrO2 scaffolds and ZrO2-GelMA composite scaffolds. At the same time, ZrO2-10GM/1SA composite scaffold regenerated significantly greater bone than other groups in vivo. This study demonstrated that the proposed ZrO2-GM/SA composite scaffolds had great research and application potential in bone tissue engineering.

Evaluation of Mechanical and Electrical Performance of Aging Resistance ZTA Composites Reinforced with Graphene Oxide Consolidated by SPS

This paper presents a study of Al₂O₃–ZrO₂ (ZTA) nanocomposites with different contents of reduced graphene oxide (rGO). The influence of the rGO content on the physico-mechanical properties of the oxide composite was revealed. Graphene oxide was obtained using a modified Hummers method. Well-dispersed ZTA-GO nanopowders were produced using the colloidal processing method. Using spark plasma sintering technology (SPS), theoretically dense composites were obtained, which also reduced GO during SPS. The microstructure, phase composition, and physico-mechanical properties of the sintered composites were studied. The sintered ZTA composite with an in situ reduced graphene content of 0.28 wt.% after the characterization showed improved mechanical properties: bending strength was 876 ± 43 MPa, fracture toughness—6.8 ± 0.3 MPa·m^1/2 and hardness—17.6 ± 0.3 GPa. Microstructure studies showed a uniform zirconia distribution in the ZTA ceramics. The study of the electrical conductivity of reduced graphene oxide-containing composites showed electrical conductivity above the percolation threshold with a small content of graphene oxide (0.28 wt.%). This electrical conductivity makes it possible to produce sintered ceramics by electrical discharge machining (EDM), which significantly reduces the cost of manufacturing complex-shaped products. Besides improved mechanical properties and EDM machinability, 0.28 wt.% rGO composites demonstrated high resistance to hydrothermal degradation.

Updates in biomaterials of bearing surfaces in total hip arthroplasty

Total hip arthroplasty (THA) is one of the most successful surgical procedures. It entails replacement of the damaged or diseased joint surface with artificial materials. Various materials had been developed and used to achieve optimal outcomes, including longer survivorship and minimal complications. The primary materials used in the manufacture of THA implants are polymers, metal alloys, and ceramics. The failures of THA mainly result from aseptic loosening due to the production of wear particles and the development of periprosthetic joint injection. A lot of advancement and introduction of new biomaterials in THA implants’ armamentarium are designed to avoid the common failure mechanisms and improve the longevity of the implants. In this review, we discussed various aspects of commonly used biomaterials in THA implants, to provide some updated information.

Does artificial aging correctly predict the long-term in-vivo degradation behavior in zirconia hip prostheses?

BACKGROUND

Accelerated hydrothermal aging has long been one of the most widely accepted quality control tests for simulating low-temperature degradation (LTD) in zirconia-containing implants used in total hip arthroplasty (THA). However, it is still unclear how much consistency there is between the experimental prediction from the internationally-standardized tests and the actual measurements from surgically-removed implants after a long period of implantation. This question is fundamentally related to a lack of understanding of mechanical/tribological contribution to the in-vivo LTD kinetics.

OBJECTIVE

The main purpose of this study is to validate the clinical relevance of standardized accelerated aging by comparing artificially-aged and in-vivo used prostheses, and to clarify the long-term effects of in-vivo mechanics/tribology on the LTD progression upon service in the body environment.

METHODS

Surface magnitudes of phase transformation and residual stress in zirconia femoral head retrievals (13.1-18.4 yrs) were evaluated by using confocal Raman microspectroscopy.

RESULTS

The long-term aging behavior in unworn head surface was in agreement with the experimental prediction estimated as 1 h aging at 134 °C = 4 years in-vivo. However, the current aging protocols based on ASTM and ISO criteria were not accurately predictive for the worn surfaces, and the tribologically-induced phase transformation and tensile stress were up to 6.5-times and 3.3-times higher than the environmentally-induced ones.

CONCLUSION

Our study suggests that wear/scratching, frictional heating, tribochemical reactions, and metal transfer may become far more intense triggers to phase transformation than the mere exposure to body fluid.

The Influence of Surface Preparation, Chewing Simulation, and Thermal Cycling on the Phase Composition of Dental Zirconia

The effect of dental technical tools on the phase composition and roughness of 3/4/5 yttria-stabilized tetragonal zirconia polycrystalline (3y-/4y-/5y-TZP) for application in prosthetic dentistry was investigated. Additionally, the X-ray diffraction methods of Garvie-Nicholson and Rietveld were compared in a dental restoration context. Seven plates from two manufacturers, each fabricated from commercially available zirconia (3/4/5 mol%) for application as dental restorative material, were stressed by different dental technical tools used for grinding and polishing, as well as by chewing simulation and thermocycling. All specimens were examined via laser microscopy (surface roughness) and X-ray diffraction (DIN EN ISO 13356 and the Rietveld method). As a result, the monoclinic phase fraction was halved by grinding for the 3y-TZP and transformed entirely into one of the tetragonal phases by polishing/chewing for all specimens. The tetragonal phase t is preferred for an yttria content of 3 mol% and phase t″ for 5 mol%. Mechanical stress, such as polishing or grinding, does not trigger low-temperature degradation (LTD), but it fosters a phase transformation from monoclinic to tetragonal under certain conditions. This may increase the translucency and deteriorate the mechanical properties to some extent.

In vivo aging of zirconia dental ceramics - Part I: Biomedical grade 3Y-TZP

OBJECTIVE

In vivo aging of biomedical grade 3Y-TZP ceramics in the oral environment was assessed and compared to artificially accelerated in vitro hydrothermal aging extrapolations at 37°C.

METHODS

88 discs were pressed and sintered (1450-1500°C) from two commercial 3Y-TZP compositions containing 0.25% Al₂O₃ to generate finer- and coarser-grained specimens. As-sintered (AS) and airborne-particle abraded (APA; 50μm Al₂O₃) surfaces were investigated. In vivo aging was performed by incorporating specimens in lingual flanges of complete dentures of 12 edentulous volunteers who wore them continuously for up to 24 months. For comparison, in vitro hydrothermal aging at 134°C was also performed and analysed by XRD and (FIB)-SEM. Data was statistically analysed with linear regression models.

RESULTS

Finer and coarser-grained specimens exhibited statistically insignificant differences in aging in vivo. The monoclinic fraction (X_m) on AS surfaces abruptly increased to ∼8% after 6 months. The aging process then proceeded with slower linear kinetics (∼0.24%/month). After 24 months, X_m reached ∼12%. The calculated maximum transformed layer was 0.385μm representing one layer of transformed grains. APA surfaces were highly aging resistant. The initial X_m of ∼4.0% linearly increased by 0.03%/month in vivo. In vitro aging exhibited an initial induction period, followed by linear aging kinetics. Coarser-grained AS surfaces aged significantly faster than fine-grained (2.41%/h compared to 2.16%/h). APA discs aged at a rate of 0.3%/h in vitro. Microcracking within a single grain and pull-out of grain clusters were observed on aged AS surfaces.

SIGNIFICANCE

Biomedical grade 3Y-TZP was susceptible to in vivo aging. After 2 years in vivo, the aging kinetics were almost 3-times faster than the generally accepted in vitro-in vivo extrapolation.

Early Short-Term Postoperative Mechanical Failures of Current Ceramic-on-Ceramic Bearing Total Hip Arthroplasties

Although ceramic-on-ceramic (CoC) bearings have been shown to produce the smallest amount of wear volume in vitro as well as in vivo studies when used for total hip arthroplasties (THA), concerns about the failure of these bearing surfaces persist due to early failures observed after short postoperative time. In this study, an exhaustive analysis of the early failure occurred on the new generation of ceramic bearings, consisting of a composite alumina matrix-based material reinforced with yttria-stabilized tetragonal zirconia (Y-TZP) particles, chromium dioxide, and strontium crystals, was performed. For this study, 118 CoC bearings from 117 patients were revised. This article describes a group of mechanical failure CoC-bearing BIOLOX THA hip prosthesis patients without trauma history. The retrieved samples were observed under scanning electron microscopy (SEM), composition was analyzed with energy dispersive X-ray spectroscopy (EDX), and damaged surfaces were analyzed by grazing-incidence X-ray diffraction (GI-XRD) and white light interferometry. In the short term, CoC articulations provided similar mechanical behavior and functional outcome to those in XLPE cases. However, 5% more early mechanical failures cases were observed for the ceramic components. Although the fracture rate of third generation CoC couples is low, the present study shows the need to further improve the third generation of CoC-bearing couples for THA. Despite the improved wear compared to other materials, stress concentrators are sources of initial crack propagation, such as those found in the bore-trunnion areas. Moreover, in view of the evidence observed in this study, the chipping observed was due to the presence of monoclinic phase of the Y-TZP instead of tetragonal, which presents better mechanical properties. The results showed that total safety after receiving a THA is still a goal to be pursued.

Chemical durability of high translucent dental zirconia

This review describes low temperature degradation (LTD), discoloration, and erosion of high translucent dental zirconia and discusses its chemical durability in comparison with other CAD/CAM materials. The LTD of zirconia strongly depended on the firing temperature, yttria content, surface treatment, and heat treatment. Glass ceramics for CAD/CAM were remarkably etched in a lactic acid at 60°C, KOH solution at 60°C, and saline solution at 90°C, whereas zirconia showed no changes in these solutions. Glass ceramics and hybrid resins for CAD/CAM showed significant discoloration in a red wine and rhodamine B solution at 37°C, whereas zirconia showed no discolorations in either solution. It was concluded that high translucent dental zirconia has the highest chemical durability among dental CAD/CAM materials.

Phase Transformation and Roughening in Artificially Aged and Retrieved Zirconia-Toughened Alumina Femoral Heads

BACKGROUND

Zirconia-toughened alumina (ZTA) used in hip arthroplasty contains yttria-stabilized zirconia (Y-TZP) as a toughening agent. However, Y-TZP is well known to degrade in vivo from tetragonal to monoclinic phase transformation. The stability of never-implanted ZTA femoral heads was evaluated in a severe artificial aging test, with retrieved ZTA heads also evaluated for clinical relevance. We hypothesized that ZTA would degrade due to tetragonal-to-monoclinic phase transformation, with changes in surface topography and progressive roughening. Y-TZP specimens served as a positive comparison group, while magnesia-stabilized zirconia (Mg-PSZ), which does not undergo phase transformation, served as a stable comparison group.

METHODS

Monoclinic phase concentration, surface topography, and roughness of never-implanted ZTA, Y-TZP, and Mg-PSZ heads were measured by X-ray diffraction and optical profilometry, before and after 2 rounds of 24 hours of hydrothermal aging. Explanted ZTA heads were characterized by the same methods.

RESULTS

After 48 hours in an autoclave, the surface of ZTA heads exhibited irregularly spaced protrusions about 20-30 nm high by 100-150 μm in diameter, with significant increases in monoclinic phase concentration (from 12.2% to 21.3%) and surface roughness. Similar features were observed on the surface of explanted ZTA heads, with 33% monoclinic phase after 2.7 years in vivo.

CONCLUSION

Based on data collected from ZTA retrievals, this artificial aging test underestimated the amount of phase transformation in vivo. Phase transformation and surface roughening of ZTA heads steadily increased without reaching a plateau, which may lead to stress concentrations and weakening of the ceramic material, and could result in late fracture and wear.

Recent updates for biomaterials used in total hip arthroplasty

Background

Total hip arthroplasty (THA) is probably one of the most successful surgical interventions performed in medicine. Through the revolution of hip arthroplasty by principles of low friction arthroplasty was introduced by Sir John Charnley in 1960s. Thereafter, new bearing materials, fixation methods, and new designs has been improved. The main concern regarding failure of THA has been the biological response to particulate polyethylene debris generated by conventional metal on polyethylene bearing surfaces leading to osteolysis and aseptic loosening of the prosthesis. To resolve these problems, the materials of the modern THA were developed since then.

Methods

A literature search strategy was conducted using various search terms in PUBMED. The highest quality articles that met the inclusion criteria and best answered the topics of focus of this review were selected. Key search terms included ‘total hip arthroplasty’, ‘biomaterials’, ‘stainless steel’, ‘cobalt-chromium’, ‘titanium’, ‘polyethylene’, and ‘ceramic’.

Results

The initial search retrieved 6921 articles. Thirty-two articles were selected and used in the review.

Conclusion

This article introduces biomaterials used in THA and discusses various bearing materials in currentclinical use in THA as well as the newer biomaterials which may even further decrease wear and improve THA survivorship.

Mechanisms induced by transition metal contaminants and their effect on the hydrothermal stability of zirconia-containing bioceramics: an XPS study

Zirconia containing bioceramics suffer from low temperature degradation in biological and hydrothermal environments, and the presence of transition metal contamination has been shown to greatly affect the zirconia stability in different materials. In this paper, X-ray photoelectron spectroscopy was used to investigate the compositional and structural variations of different zirconia containing hip-joint bioceramics with and without transition metal stains in hydrothermal environments. Non-stained and stainless-steel-stained femoral head samples of 3 mol% Y2O3 doped tetragonal zirconia polycrystals (3Y-TZP) and zirconia-toughened alumina (ZTA) subjected to isothermal treatments in water vapor were investigated with quantifying their respective compositional XP lines. The outputs of these spectroscopic experiments revealed a significant difference in the off-stoichiometric reactions taking place at the surface of zirconia-containing ceramics in the presence and absence of transition metal contamination. The complex off-stoichiometric chemistry that occurred in the presence of metal contaminants could be interpreted in terms of defect-related chemical reactions among metal, water vapor, and oxide lattice, with a crucial contribution of the alumina phase in the transformation kinetics of ZTA.

A Survey of the Prevalence of and Techniques to Prevent Trunnionosis

Trunnionosis of total hip arthroplasty (THA) components has been an increasingly reported complication. Consensus is lacking regarding preventive practices and the overall incidence of trunnionosis. In this study, fellowship-trained adult reconstruction orthopedic surgeons were surveyed to identify expert opinions. A 25-question, web-based survey regarding trunnionosis incidence, prevention, and biomaterials was sent to 345 fellowship-trained adult reconstruction orthopedic surgeons in North America. The survey yielded 151 (43.8%) responses from surgeons with a mean of 11.97±9.49 years of experience. These surgeons believe that the material composite of the head-neck junction is the most important contributor to trunnionosis. They often choose a ceramic head with a metal alloy stem to reduce trunnionosis. They more commonly impact the femoral head 3 times than once. Fifty-one percent believe that trunnionosis leads to THA failure for between 0% and 2% of all THA revisions, whereas 48.3% believe that the failure rate is greater than 2%. More than half (53.6%) of these surgeons recommend a revision THA if a patient's serum cobalt level is greater than 10 µg/L, regardless of symptom presence. The incidence of trunnionosis appears to be increasing due to changes in implants and/or an increased awareness of the problem, with 48.3% of these surgeons believing that trunnionosis is the primary cause of THA failure for more than 1 in 50 patients. Some suggested preventive measures include cleaning and drying the trunnion, using ceramic femoral heads, matching THA components, and adding titanium sleeves on well-fixed stems that are retained during revision surgery. [Orthopedics. 2018; 41(4):e557-e562.].

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.

Long Term Survivorship of a Severely Notched Femoral Stem after Replacing the Fractured Ceramic head with a Cobalt-Chromium Head

Background:

Although ceramic head fracture occurs infrequently today, in the event of a fracture, the resulting revision surgery can prove very challenging, since the ceramic particles lodge into the surrounding soft tissue and can cause rapid implant failure

Case Presentation:

A case of long term survivorship of a severed notched femoral stem after replacing the fractured femoral head with a cobalt-chromium one is reported in a 40-year old woman with hip dysplasia who underwent an uncomplicated total hip arthroplasty. The incident of ceramic femoral head fracture occurred 14 months postoperatively without reporting any significant trauma. Intraoperative findings at revision were a multifragmented femoral head and a damaged polyethylene insert along with diffuse metallosis and excessive wear of the cone of the stem. Both the stem and the acetabular component were stable. After removal of ceramic fragments, metallotic tissue excision and careful lavage of the joint, the inlay was replaced by a similar one and a cobalt-chromium femoral head was placed to the existing notched taper of the firmly incorporated stem. At the 13^th year follow up examination, the patient had no pain, used no walking aids, and had normal activity with no signs of wearing or loosening in the plain x-rays.

Conclusion:

Despite current recommendations of using ceramic femoral heads in cases of fracture or to revise the severely damaged stems we were able to provide a long term survivorship up to 13 years postoperatively of a cobalt-chromium femoral head applied to a severe damaged stem.

Surface and Mechanical Characterization of Dental Yttria-Stabilized Tetragonal Zirconia Polycrystals (3Y-TZP) After Different Aging Processes

Yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) is a ceramic material used in indirect dental restorations. However, phase transformation at body temperature may compromise the material's mechanical properties, affecting the clinical performance of the restoration. The effect of mastication on 3Y-TZP aging has not been investigated. 3Y-TZP specimens (IPS E-max ZirCAD and Z5) were aged in three different modes (n=13): no aging (control), hydrothermal aging (HA), or chewing simulation (CS). Mechanical properties and surface topography were analyzed. Analysis of variance showed that neither aging protocol (p=0.692) nor material (p=0.283) or the interaction between them (p=0.216) had a significant effect on flexural strength, values ranged from 928.8 MPa (IPSHA) to 1,080.6 MPa (Z5HA). Nanoindentation analysis showed that material, aging protocol, and the interaction between them had a significant effect (p<0.001) on surface hardness and reduced Young's modulus. The compositional analysis revealed similar yttrium content for all the experimental conditions (aging: p=0.997; material: p=0.248; interaction material×aging: p=0.720). Atomic force microscopy showed an effect of aging protocols on phase transformation, with samples submitted to CS exhibiting features compatible with maximized phase transformation, such as increased volume of the material microstructure at the surface leading to an increase in surface roughness.

Primary total hip arthroplasty using 3rd generation ceramic-on-ceramic articulation

PURPOSE

Ceramic-on-ceramic (CoC) is currently a popular bearing combination in young patients in primary total hip arthroplasty (THA). The purpose of this study was to evaluate clinical and radiographic results and complications of cementless THA with 3rd generation CoC articulation.

MATERIALS AND METHODS

From April 2001 to January 2008, 310 primary THAs were performed in 300 patients using 3rd generation CoC articulation. The mean follow-up period was 8.9 years and the mean age at index surgery was 54.6 years. Patient clinical outcome was evaluated with the Harris Hip Score. Radiographic evaluations was performed to analyse osteolysis, implant fixation and loosening.

RESULTS

Mean Harris Hip Score at last follow-up was 95.4 (76-100). Radiographic analysis demonstrated no evidence of stem or cup loosening and there were no cases of osteolysis. Ceramic wear was not detectable on the plain radiograph. Complications requiring revision occurred in 12 cases; 2 ceramic head fractures, 4 dislocations, 2 deep infections and 4 cases of periprosthetic fracture. The cohort had an overall revision rate of 3.9%.

CONCLUSIONS

Clinical outcomes using cementless THA with 3rd generation CoC articulation were satisfactory. Although the mechanical properties of ceramic materials have improved, there are still problems such as ceramic fracture and squeaking. More clinical study and investigation for alternative bearing are necessary to reduce complications. 4th generation CoC or ceramic on cross linked polyethylene may address some of these issues.

Effect of accelerated aging on dental zirconia-based materials

OBJECTIVE

To investigate the effect of aging on phase transformation and mechanical properties of yttria-tetragonal zirconia polycrystal (Y-TZP).

MATERIALS AND METHODS

Fully-sintered Y-TZP slabs, IPS E-max ZirCAD (ZC - Ivoclar) and Z-5 ceramic (Z5 - C5 Medical Werks), were artificially aged in autoclave for: 0, 30, 60 or 90min. Flexural strength (FS), crystalline changes (X-ray diffraction analysis - XRD) and surface topography were analyzed. 0 and 90min-aged samples were evaluated by nanoindentation to measure hardness and modulus, and results were compared using Wilcoxan Mann Whitney rank sum test (p≤0.05). FS results were compared using two-way ANOVA and Tukey HSD (α=0.05).

RESULTS

Material factor had significant effect (p=0.001) on flexural strength (Z5=966.95MPa; ZC=847.82MPa), but aging did not. Nanoindentation showed incidence of typical load/depth curves combined with some exhibiting features compatible with cracking. When typical curves were considered, aging had no effect on the modulus and hardness, but hardness was dependent on material type. A steady increase in the m phase related to aging time was observed for ZC samples. The maximum incidence of m phase was 6.56% for Z5/60min.

SIGNIFICANCE

Flexural strength is not affected by surface transformation in dental Y-TZP. Hydrothermal aging has an effect on m content and surface topography of different zirconia brands, but mechanical tests that can precisely characterize surface changes in aged Y-TZP are still missing.

The evolution of the trunnion

Implant modularity has recently come under increasing scrutiny due to concerns regarding wear, corrosion and potential adverse reactions to metal debris. This review outlines the evolution and development of the femoral stem trunnion and relates this to contemporary issues now encountered.Despite different manufacturers producing what appear to be similar trunnion designs, there is still a lack of standardisation, with small but significant design variations. Wear and corrosion is certainly not a new phenomenon, but recent changes in design and the use of larger metal head sizes has potentially made the problem more prevalent. These issues along with steps to avoid these problems are discussed.

Effect of neck length on third-generation ceramic head failure; finite element and retrieval analysis

BACKGROUND

Optimized design using finite element analysis (FEA) has considerably increased the longevity of ceramic implants in total hip arthroplasty. Unlike previous FEA studies, a 28-mm head with a short neck was found to be prone to failure, even with third-generation ceramic. We conducted a finite element analysis of the third-generation ceramic head failure according to neck lengths and a retrieval analysis of the four fractured ceramic heads.

METHODS

Models of real specimens were created for short-, medium-, and long-neck heads made of alumina, based on data given by the manufacturer and reverse engineering design. Static loading was simulated in a series of five steps to 46 kN, and fatigue loading consisting of 10(7) cycles was simulated in walking (4.3 kN) and high-impact (10 kN) conditions to determine the safety factor.

RESULTS

Although the maximum principal stress of the long-neck design was the greatest, consistent with a previous FEA study, the safety factor was the lowest at the inner corner between the roof and tapered bore of the ceramic head with the short-neck design in both fatigue-loading conditions. Furthermore, surface analysis of one head revealed that the fracture was propagated from the inner corner between the roof and tapered bore into the base of the ceramic head.

CONCLUSION

Our results suggest that the short-neck design with a 28-mm ceramic head has a greater potential risk of ceramic failure than other designs.

Primary Total Hip Arthroplasty Using Third Generation Ceramic-Ceramic Articulation: Results after a Minimum of Three-years of Follow-up

Purpose

This study assessed the short term clinicoradiological results of primary total hip arthroplasty using third generation ceramic-ceramic articulation Accolade TMZF femoral stems.

Materials and Methods

Two hundred and seventy two patients (294 hips) with primary total hip arthroplasty using third generation ceramic-ceramic articulation Accolade TMZF femoral stems who had been followed-up for a minimum of 3 years were included. Clinicoradiological results were analyzed and postoperative complications were observed.

Results

At final follow-up, mean Harris hip score was increased from 52 to 94 points. On radiogical evaluation, the average acetabular inclination was 42 degrees and the average acetabular anteversion was 15 degrees. Neither osteolysis nor loosening were observed around the acetabulum or proximal femur. Among 294 acetabular cups, 293 cups (99.66%) achieved stable fixation. Regarding the 294 femoral stems, 286 (97.28%) had bony fixation, 7 (2.38%) had fibrous fixation, and none were found to have unstable stem fixation. Proximal bone resorption was observed in 17 hips (5.78%; only Grade 1) and radiolucent lines were observed in 88 hips (29.93%), however, all were around the distal smooth portion of the stems. Postoperative complications included dislocation in 6 hips (2.04%), heterotopic ossification in 3 hips (1.02%), ceramic fractures in 4 hips (1.36%), superficial infection in 1 hip (0.34%), and squeaking in 8 hips (2.72%).

Conclusion

The short term clinicoradiological results of primary total hip arthroplasty using third generation ceramic-ceramic articulation and Accolade TMZF femoral stems together with Secur-Fit acetabular cups were satisfactory. However, problems such as ceramic fractures and squeaking after arthroplasty were observed. Additional studies are necessary in order to develop methods that may reduce or eliminate these complications.

Synthesis of calcium phosphate-zirconia scaffold and human endometrial adult stem cells for bone tissue engineering

To address the hypothesis that using a zirconia (ZrO2)/ β-tricalcium phosphate (β-TCP) composite might improve both the mechanical properties and cellular compatibility of the porous material, we fabricated ZrO2/β-TCP composite scaffolds with different ZrO2/β-TCP ratios, and evaluated their physical and mechanical characteristics, also the effect of three-dimensional (3D) culture (ZrO2/β-TCP scaffold) on the behavior of human endometrial stem cells. Results showed the porosity of a ZrO2/β-TCP scaffold can be adjusted from 65% to 84%, and the compressive strength of the scaffold increased from 4.95 to 6.25 MPa when the ZrO2 content increased from 30 to 50 wt%. The cell adhesion and proliferation in the ZrO2/β-TCP scaffold was greatly improved when ZrO2 decreased. Moreover, in vitro study showed that an osteoblasts-loaded ZrO2/β-TCP scaffold provided a suitable 3D environment for osteoblast survival and enhanced bone regeneration. We thus showed that a porous ZrO2/β-TCP composite scaffold has excellent mechanical properties, and cellular/tissue compatibility, and would be a promising substrate to achieve both bone reconstruction and regeneration needed during in vivo study for treatment of large bone defects.

Comparison of the osteogenic potential of titanium- and modified zirconia-based bioceramics

Zirconia is now favored over titanium for use in dental implant materials because of its superior aesthetic qualities. However, zirconia is susceptible to degradation at lower temperatures. In order to address this issue, we have developed modified zirconia implants that contain tantalum oxide or niobium oxide. Cells attached as efficiently to the zirconia implants as to titanium-based materials, irrespective of surface roughness. Cell proliferation on the polished surface was higher than that on the rough surfaces, but the converse was true for the osteogenic response. Cells on yttrium oxide (Y₂O₃)/tantalum oxide (Ta₂O₅)- and yttrium oxide (Y₂O₃)/niobium oxide (Nb₂O₅)-containing tetragonal zirconia polycrystals (TZP) discs ((Y, Ta)-TZP and (Y, Nb)-TZP, respectively) had a similar proliferative potential as those grown on anodized titanium. The osteogenic potential of MC3T3-E1 pre-osteoblast cells on (Y, Ta)-TZP and (Y, Nb)-TZP was similar to that of cells grown on rough-surface titanium. These data demonstrate that improved zirconia implants, which are resistant to temperature-induced degradation, retain the desirable clinical properties of structural stability and support of an osteogenic response.

Advances in zirconia toughened alumina biomaterials for total joint replacement

The objective of this article is to provide an up-to-date overview of zirconia-toughened alumina (ZTA) components used in total hip arthroplasties. The structure, mechanical properties, and available data regarding the clinical performance of ZTA are summarized. The advancements that have been made in understanding the in vivo performance of ZTA are investigated. This article concludes with a discussion of gaps in the literature related to ceramic biomaterials and avenues for future research.

Fracture of ceramic bearing surfaces following total hip replacement: a systematic review

Ceramic bearing surfaces are increasingly used for total hip replacement, notwithstanding that concern is still related to ceramic brittleness and its possible mechanical failure. The aim of this systematic review is to answer three questions: (1) Are there risk factors for ceramic component fracture following total hip replacement? (2) Is it possible to perform an early diagnosis of ceramic component failure before catastrophic fracture occurs? (3) Is it possible to draw guidelines for revision surgery after ceramic components failure? A PubMed and Google Scholar search was performed and reference citations from publications identified in the literature search were reviewed. The use of 28 mm short-neck femoral head carries an increased risk of fracture. Acetabular component malposition might increase the risk of ceramic liner fractures. Synovial fluid microanalysis and CT scan are promising in early diagnosis of ceramic head and liner failure. Early revision is suggested in case of component failure; no consensus exists about the better coupling for revision surgery. Ceramic brittleness remains a major concern. Due to the increased number of ceramic on ceramic implants, more revision surgeries and reports on ceramic components failure are expected in the future. An algorithm of diagnosis and treatment for ceramic hip failure is proposed.

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.

Deceleration of hydrothermal degradation of 3Y-TZP by alumina and lanthana co-doping

Zirconia has been used as an orthopaedic material since 1985 and is increasingly used in dental applications. One major concern with the use of zirconia is the significant loss in mechanical properties through hydrothermal degradation, with the uncontrolled transformation of tetragonal to monoclinic (t→m) zirconia. We report on the addition of alumina and lanthana as dopants to an yttria-stabilized tetragonal zirconia polycrystal ceramic as an effective strategy to significantly decelerate the hydrothermal degradation kinetics, without any loss of mechanical properties, in particular, fracture toughness. Hydrothermal degradation was studied on the exposed surface as well as in the sub-surface region using Raman microspectroscopy, atomic force microscopy and cross-sectional transmission electron microscopy, providing a comprehensive insight into the mechanism of propagation of the t→m transformation. The addition of dopants resulted in the reduction of monoclinic zirconia nucleation rate at the surface and a substantial deceleration of the overall transformation kinetics, in particular a greatly reduced propagation of the transformation into the bulk and decreased grain boundary microcracking. High-resolution transmission electron microscopy analysis showed that the co-dopant cations segregate to the grain boundaries where they play a key role in the stabilization of the zirconia tetragonal phase.

Abrasive wear and metallosis associated with cross-linked polyethylene in total hip arthroplasty

A 34-year-old female patient received a cobalt-chromium (CoCr) alloy femoral head on cross-linked polyethylene total hip replacement for the revision of her fractured ceramic-on-ceramic total hip replacement. The CoCr alloy femoral head became severely worn due to third-body abrasive wear by ceramic particles that could not be removed by synovectomy or irrigation at revision surgery. Ceramic particles were found embedded in the cross-linked polyethylene liner. The CoCr alloy femoral head exhibited a total mass loss of 14.2 g and the generated wear particles triggered metallosis in the patient. The present case study suggests not revising a fractured ceramic-on-ceramic total hip replacement with a CoCr alloy femoral head and a cross-linked polyethylene liner to avoid metallosis due to third-body abrasive wear.

Porous zirconia/hydroxyapatite scaffolds for bone reconstruction

OBJECTIVE

Highly porous apatite-based bioceramic scaffolds have been widely investigated as three-dimensional (3D) templates for cell adhesion, proliferation, and differentiation promoting the bone regeneration. Their fragility, however, limits their clinical application especially for a large bone defect.

METHODS

To address the hypothesis that using a ZrO(2)/hydroxyapatite (HAp) composite might improve both the mechanical properties and cellular compatibility of the porous material, we fabricated ZrO(2)/HAp composite scaffolds with different ZrO(2)/HAp ratios, and evaluated their characteristics. In addition, porous ZrO(2)/HAp scaffolds containing bone marrow derived stromal cells (BMSCs) were implanted into critical-size bone defects for 6 weeks in order to evaluate the bone tissue reconstruction with this material.

RESULTS

The porosity of a ZrO(2)/HAp scaffold can be adjusted from 72% to 91%, and the compressive strength of the scaffold increased from 2.5 to 13.8MPa when the ZrO(2) content increased from 50 to 100wt%. The cell adhesion and proliferation in the ZrO(2)/HAp scaffold was greatly improved when compared to the scaffold made with ZrO(2) alone. Moreover, in vivo study showed that a BMSCs-loaded ZrO(2)/HAp scaffold provided a suitable 3D environment for BMSC survival and enhanced bone regeneration around the implanted material.

SIGNIFICANCE

We thus showed that a porous ZrO(2)/HAp composite scaffold has excellent mechanical properties, and cellular/tissue compatibility, and would be a promising substrate to achieve both bone reconstruction and regeneration needed in the treatment of large bone defects.

Orthopedic applications of silicon nitride ceramics

Silicon nitride (Si(3)N(4)) is a ceramic material developed for industrial applications that demand high strength and fracture resistance under extreme operating conditions. Recently, Si(3)N(4) has been used as an orthopedic biomaterial, to promote bone fusion in spinal surgery and to develop bearings that can improve the wear and longevity of prosthetic hip and knee joints. Si(3)N(4) has been implanted in human patients for over 3 years now, and clinical trials with Si(3)N(4) femoral heads in prosthetic hip replacement are contemplated. This review will provide background information and data relating to Si(3)N(4) ceramics that will be of interest to engineering and medical professionals.

Kinetics and the role of off-stoichiometry in the environmentally driven phase transformation of commercially available zirconia femoral heads

The low-temperature polymorphic transformation behavior of two types of commercially available femoral head, both made of 3 mol.% Y(2)O(3)-stabilized tetragonal ZrO(2) polycrystals (3Y-TZP), was examined by in vitro experiments. Both materials contained a small amount (0.25 wt.%) of Al(2)O(3), but they differed slightly in their SiO(2) impurity content, in the morphology and crystallinity of the dispersed Al(2)O(3) phase, and in grain size. In vitro experiments were conducted in a water-vapor environment at temperatures in the range 90-134°C and for periods of time up to 500 h. Despite the materials having the same nominal composition, quite different behaviors were found in the hydrothermal environment for the two types of femoral head investigated. A phenomenological description of the kinetics of monoclinic nuclei formation/growth led to the experimental determination of activation energy values for the environmentally driven polymorphic transformation. From the material physics viewpoint, cathodoluminescence spectroscopy enabled us to rationalize the role of surface stoichiometry on the mechanisms leading to polymorphic transformation. Spectroscopic experiments unveiled some new relevant aspects of surface off-stoichiometry, which lie behind the different phase transformation kinetics experienced by the investigated femoral heads.

State of the art in hard-on-hard bearings: how did we get here and what have we achieved?

Total hip arthroplasty has shown excellent results in decreasing pain and improving function in patients with degenerative disease of the hip. Improvements in prosthetic materials, designs and implant fixation have now resulted in wear of the bearing surface being the limitation of this technology, and a number of hard-on-hard couples have been introduced to address this concern. The purpose of this article is to review the origins, development, survival rates and potential advantages and disadvantages of the following hard-on-hard bearings for total hip arthroplasty: metal-on-metal standard total hip arthroplasty; metal-on-metal hip resurfacing arthroplasty, ceramic-on-ceramic total hip arthroplasty; and ceramic-on-metal bearings. Improvements in the manufacturing of metal-on-metal bearings over the past 50 years have resulted in implants that provide low wear rates and allow for the use of large femoral heads. However, concerns remain regarding elevated serum metal ion levels, potential teratogenic effects and potentially devastating adverse local tissue reactions, whose incidence and pathogenesis remains unclear. Modern total hip resurfacing has shown excellent outcomes over 10 years in the hands of experienced surgeons. Current ceramic-on-ceramic bearings have demonstrated excellent survival with exceptionally low wear rates and virtually no local adverse effects. Concerns remain for insertional chipping, in vivo fracture and the variable incidence of squeaking. Contemporary ceramic-on-metal interfaces are in the early stages of clinical use, with little data reported to date. Hard-on-hard bearings for total hip arthroplasty have improved dramatically over the past 50 years. As bearing designs continue to improve with new and modified materials and improved manufacturing techniques, it is likely that the use of hard-on-hard bearings will continue to increase, especially in young and active patients.

Zirconia-hydroxyapatite composite material with micro porous structure

OBJECTIVES

Titanium plates and apatite blocks are commonly used for restoring large osseous defects in dental and orthopedic surgery. However, several cases of allergies against titanium have been recently reported. Also, sintered apatite block does not possess sufficient mechanical strength. In this study, we attempted to fabricate a composite material that has mechanical properties similar to biocortical bone and high bioaffinity by compounding hydroxyapatite (HAp) with the base material zirconia (ZrO(2)), which possesses high mechanical properties and low toxicity toward living organisms.

METHODS

After mixing the raw material powders at several different ZrO(2)/HAp mixing ratios, the material was compressed in a metal mold (8 mm in diameter) at 5 MPa. Subsequently, it was sintered for 5 h at 1500°C to obtain the ZrO(2)/HAp composite. The mechanical property and biocompatibility of materials were investigated. Furthermore, osteoconductivity of materials was investigated by animal studies.

RESULTS

A composite material with a minute porous structure was successfully created using ZrO(2)/HAp powders, having different particle sizes, as the starting material. The material also showed high protein adsorption and a favorable cellular affinity. When the mixing ratio was ZrO(2)/HAp=70/30, the strength was equal to cortical bone. Furthermore, in vivo experiments confirmed its high osteoconductivity.

SIGNIFICANCE

The composite material had strength similar to biocortical bones with high cell and tissue affinities by compounding ZrO(2) and HAp. The ZrO(2)/HAp composite material having micro porous structure would be a promising bone restorative material.

Effect of heat treatment after accelerated aging on phase transformation in 3Y-TZP

Our purpose was to investigate the effect of heat treatment on the reversibility of the tetragonal to monoclinic transformation in 3Y-TZP, and associated surface roughness. The goals were to determine the onset temperature of the reverse transformation, and characterize surface roughness after accelerated aging, and after aging followed by heat treatment. 3Y-TZP disc-shaped specimens were sintered at temperatures from 1300 to 1550 degrees C. The reversibility of the transformation was investigated by X-ray diffraction (XRD) after accelerated aging, followed by heat treatment at temperatures from 350 degrees C up to 850 degrees C. The surface roughness (R(rms)) was measured by atomic force microscopy after polishing, after accelerated aging for 1 or 10 h, and after aging followed by heat treatment. XRD showed that the fraction of m-phase increased linearly with grain size after aging for 10 h (1.0-29.8%). The transformation was reversed for all groups after heat treatment at 850 degrees C/min., with only trace amounts of m-phase remaining for the group sintered at 1550 degrees C. A significant increase in mean surface roughness was observed after accelerated aging (1.59-7.45 nm), compared to polished groups (0.83-1.0 nm). However, the mean surface roughness after accelerated aging for either 1 or 10 h, followed by heat treatment at 850 degrees C/min. (1.18-2.1 nm), was not significantly different from that of the polished groups. This was attributed to the reverse transformation. XRD revealed that the monoclinic to tetragonal transformation, was complete after heat treatment at 500 degrees C for 1 min, for specimens sintered at 1550 degrees C and aged 10 h.

Prospective randomized trial comparing alumina ceramic-on-ceramic with ceramic-on-conventional polyethylene bearings in total hip arthroplasty

This prospective randomized study aims to compare the outcome between an alumina ceramic-on-ceramic (CC) articulation with a ceramic on ultra-high-molecular-weight polyethylene articulation (CP). Fifty-six hips in 55 patients with mean age 42.2 (range, 19-56) each received uncemented components, a 28-mm alumina head with randomization of acetabular liner. Mean St Michael's outcome score for each group with up to 10 years follow-up (median, 8 years; range, 1-10) was 22.8 and 22.9, respectively (P = .819). Wear was identified in all but 1 CP replacement, but only 12 of the 23 CC. Mean wear in the CP group was 0.11 mm/y and 0.02 mm/yr in the CC group (P < .001). Other than significantly greater wear in the polyethylene group, there was no significant difference in midterm outcome between the 2 groups.

Mechanical properties of hydroxyapatite-zirconia compacts sintered by two different sintering methods

Microwave sintering is traditionally employed to reduce the sintering temperature required to densify powder compacts. The effect of microwave heating on hydroxyapatite (HA)-zirconia (ZrO2) green bodies has been investigated in order to understand how microwave energy may affect the physical and mechanical properties of the resultant densified composites. Laboratory synthesised nano-sized HA and a commercial nano-sized ZrO2 powder have been ball milled to create mixtures containing 0-5 wt% ZrO2 loadings. Compacts were microwave sintered at either 700, 1000 or 1200 degrees C with a 1 h hold time. Comparative firings were also performed in a resistive element furnace using the same heating profile in order to assess the differences between conventional and microwave heating on the physical, mechanical and microstructural properties of the composites. Samples sintered at 700 degrees C show little sign of densification with open porosities of approximately 50%. Composites conventionally sintered at 1000 degrees C were between 65 and 75% dense, whereas the samples microwave sintered at this temperature were between 55 and 65% dense. Samples sintered at 1200 degreesbC showed the greatest degree of densification (>80%) with a corresponding reduction in open porosities. TCP generation occurred as a consequence of sintering at 1200 degrees C, even with 0 wt% ZrO2, and increased degradation of the HA phase to form significant amounts of TCP occurred with increasing additions of ZrO2, along with increasing open porosity. Nanosized ZrO2 prevents the densification of the HA matrix by effectively pinning grain boundaries and this effect is more pronounced in the MS materials. Similar strengths are achieved between the microwave and conventionally sintered samples. Greater amount of open porosity and pore interconnectivity are seen in the MS samples, which are considered to be useful for biomedical applications as they can promote osteo-integration.

Delta ceramic-on-alumina ceramic articulation in primary THA: prospective, randomized FDA-IDE study and retrieval analysis

Wear and osteolysis continue to be major reasons for revision surgery in THA. Ceramic-on-ceramic bearings eliminate polyethylene wear debris. The newest generation of these bearings incorporate nanosized, yttria-stabilized tetragonal zirconia particles producing an alumina matrix composite. We asked whether this new material would perform as well as a conventional bearing in terms of functional hip scores, radiographic migration and osteolysis, complications and survival. As part of a US FDA investigational device exemption study (G000075), we conducted an initial prospective safety study of 21 alumina matrix composite femoral heads articulating on alumina liners followed by a prospective, randomized study with 44 more of these articulations and 45 zirconia femoral heads on polyethylene liners. The minimum followup for all patients was 26 months (mean, 73 months; range, 26-108 months). Harris hip scores and radiographic findings were similar in the two groups as was survivorship (trial 95% versus control 93%). There were three reoperations in the trial group and three in the control group. A fractured head retrieval showed a 33% monoclinic transformation with an increase in surface roughness from 3 to 5 nm at the main wear zone. While our numbers were insufficient to compare device-related complications, the trial device performed as well as the control device in terms of reoperation, and clinical and radiographic outcome. The alumina matrix composite femoral head on an alumina liner provided high survivorship.

LEVEL OF EVIDENCE

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

Differences in highly cross-linked polyethylene wear between zirconia and cobalt-chromium femoral heads in Japanese patients: a prospective, randomized study

The purpose of this study was to compare highly cross-linked polyethylene wear between the zirconia head and the cobalt-chromium head in Japanese patients. A prospective, randomized study was performed to evaluate the outcomes in 32 hips that had zirconia heads and in 30 hips that had cobalt-chromium heads. The mean follow-up periods of both groups were same (5 years). There were no significant differences between the zirconia head and the cobalt-chromium head in the mean polyethylene linear wear per year and the mean volumetric polyethylene wear per year in the steady phase. This study indicates that zirconia head offers no benefits over metal head in terms of wear reduction at 5 years in Japanese patients who have lightweight and thin polyethylene liners.

Modular ulnar head decoupling strength: a biomechanical study

PURPOSE

Knowing the assembly and disassembly forces of modular ulnar head implants will be invaluable to the surgeon faced with the challenge of either revising or extracting the implant. Our goal in this study was to evaluate the decoupling strength of the modular ulnar head implant as a function of assembly impaction force for the 3 most commonly used combinations of modular ulnar head implants.

METHODS

Assembly forces and axial decoupling strength for 3 combinations of modular ulnar head implants were measured on an Instron 4206 instrument. Correlations between Morse taper decoupling strength and assembly forces were investigated.

RESULTS

The cobalt chrome head-cobalt chrome stem Morse taper couple showed the most predictable correlation with impaction assembly force, followed by cobalt chrome head-titanium stem couple and ceramic head-titanium couple, respectively.

CONCLUSIONS

Peak assembly impaction blow at the time of implantation determines the ultimate decoupling strength of the modular ulnar head Morse taper for all 3 material combinations studied. Prosthesis-specific regression curves will permit the surgeon to estimate decoupling force as a function of impact force.

Evaluation of phase stability in zirconia femoral heads from different manufacturers after in vitro testing or in vivo retrieval

Yttria-stabilized zirconia femoral heads from 3 different manufacturers were tested in vitro with respect to their phase stability and compared with retrieved zirconia heads. The monoclinic content on the surface of unused heads was analyzed by confocal Raman spectroscopy after exposure for increasing times to moist atmosphere. The increase in monoclinic content was then plotted as a function of geometric location on the head surface of the head and compared with that measured at similar locations after in vivo exposure. Profiles of residual stress associated to polymorphic transformation were also measured from the collected Raman spectra. A striking finding was that, in some samples, polymorphic transformation occurred since the very early stage of the environmental exposure even if those samples belonged to new-generation products.