No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Silicon nitride bearings: an alternative to oxide ceramics in total hip arthroplasty
... With their superior performance, ceramic ball bearings occupy a position that cannot be ignored in many key technical fields. As a key component of the ceramic ball, its shape contour accuracy greatly affects the performance of bearings [1][2][3]. As an important basis for evaluating the rotation accuracy and interchangeability of bearings, higher spherical error and surface waviness deviation will lead to greatly reduced rotation accuracy and life of bearings. ...
This paper aims to obtain the best shape accuracy evaluation algorithm for silicon nitride ceramic balls after lapping, and to extract the initial signal of the ball surface to improve the accuracy and reliability of the algorithm. The research methods of this paper are as follows: Firstly, an analysis of the uniform envelope of the lapping trajectory of ceramic balls is carried out to verify whether the lapping trajectory after processing can achieve a consistent envelope on the balls’ surface. On this basis, it is found through experiments that the standard deviation SD between the roundness deviations of different contour sections is small. The value is maintained at approximately 0.03 μm, and the roundness deviation can approximately replace the spherical deviation. Then the different contour sections of the sphere are sampled by the Taylor roundness instrument. Considering the uncertainty, the sampling points of different contour sections are averaged and used as the original signal of the sphere surface. Then the EMD method is used to process the signal to be detected on the sphere surface. The initial signal of the sphere surface is extracted by judging whether the number of ripples Kc obtained by decomposition is greater than the critical value. Then the initial signal is used as the input value of the approximation algorithm. Through the roundness deviation approximation algorithm based on the least square method, the given minimum approximation domain range is finely processed. The divided fine points are used as the center of the circle to intersect with the initial signal. The maximum, minimum, and range of each circle are calculated to obtain the roundness error based on the minimum circumscribed circle, the maximum inscribed circle, and the minimum region method. Finally, the calculated values are compared with those obtained by the traditional algorithm. The experimental results of this paper show that the algorithm is consistent with the roundness error measured by the instrument, compared with the mainstream evaluation criteria. In summary, the conclusions can be drawn as follows: Through a large number of experimental cases and comparative experiments, the algorithm has high accuracy and reliability. The research results of this paper have essential reference significance for accurately evaluating the shape accuracy of ceramic balls in actual production.
... There are several simulator studies have been accomplished [13][14][15]. Recently, Affatato et al. accomplished the first in vitro wear behavior comparison between silicon nitride and ZTA head, the results are very promising [16]. ...
Background
With regard to the ceramic hip joint implant, given the concerns in ceramic about the alumina brittleness and zirconia instability, is there any alternative material solution for the orthopedic implant? Beyond the metastable oxide ceramics, along the echelon of advanced technical ceramics, looking at the non-oxide ceramic, the silicon nitride could be an excellent candidate for the joint implant’s application. The purpose of this study is to investigate the safety, effectiveness and to demonstrate the potential of this silicon nitride hip implant.
Methods
According to the related ISO (International Organization for Standardization) standards, a series of in vitro (nine) & in vivo (five) tests, which had been accomplished for the aforementioned aim. Especially, the total hip replacement in pigs had been achieved, as per the authors’ knowledge, this is the first time to apply the THA (Total Hip Arthroplasty) in the big animal.
Results
Refer to the ISO 6474-2, in comparison with the current monopolized German product, this silicon nitride ceramic hip implant has high strength, high hardness, excellent fracture toughness, lower density, better wear resistance, good biocompatibility, inherent stability, corrosion resistance and bioactivity, bone integration capability.
Conclusions
This silicon nitride ceramic will be an admirable alternative solution with superior comprehensive property that can withstand the toughest conditions in the most demanding applications like in orthopedic and beyond.
... Although the silicon nitride is well known as a self-lubricated material, its wear resistance as the hip joint prosthesis still needs to be demonstrated according to ISO 14242 which is also the regulatory prerequisite. There are several simulator studies have been accomplished [ 13,14,15] . Recently, S. Affatato et al. accomplished the rst in-vitro wear behavior comparison between silicon nitride and ZTA head, the results are very promising [ 16] . ...
Background: With regard to the ceramic hip joint implant, given the concerns in ceramic about the alumina brittleness and zirconia instability, is there any alternative material solution for the orthopaedic implant? Beyond the metastable oxide ceramics, along the echelon of advanced technical ceramics, looking at the non-oxide ceramic, the silicon nitride could be an excellent candidate for the joint implant’s application. The purpose of this study is to investigate the safety, effectiveness and to demonstrate the potential of this silicon nitride hip implant.
Methods: According to the related ISO (International Organization for Standardization) standards, a series of in-vitro (nine) & in-vivo (five) tests, which had been accomplished for the aforementioned aim. Especially, the total hip replacement in pigs had been achieved, as per the authors’ knowledge, this is the first time to apply the THA (Total Hip Arthroplasty) in the big animal.
Results: Refer to the ISO 6474-2, in comparison with the current monopolized German product, this silicon nitride ceramic hip implant has high strength, high hardness, excellent fracture toughness, lower density, better wear resistance, good biocompatibility, inherent stability, corrosion resistance and bioactivity, bone integration capability.
Conclusions: This silicon nitride ceramic will be an admirable alternative solution with superior comprehensive property that can withstand the toughest conditions in the most demanding applications like in orthopedic and beyond.
... Their presence masks the true wear rate of the bearing. Wear rates for hard-onhard bearings are lower than XLPE, with AMC and ZTA ceramics providing the best wear performance; however, protein precipitation during in vitro wear tests may also play a role in the variability of these wear measurements [502]. Table 1b shows that PVD ceramic coatings or OxZr also provide improved wear resistance because of their high hardness, but only in articulation against polyethylene. ...
Advanced bioceramics have played integral roles in treatment modalities for damaged or diseased human joints and osseous defects. This paper reviews the uses and properties of ceramics and ceramic coatings variously employed as articulation devices in hip, knee, shoulder, and other joints, either as self-mated surfaces, or against polyethylene (both conventional and highly cross-linked versions), or for osseous- fixation as arthrodesis devices, bone scaffolds, and substitutes in the spine or extremities. The modern uses of oxide and non-oxide materials in these applications will be discussed, followed by an assessment and comparison of their mechanical and physicochemical properties. Recent developments in new bioceramic materials and composites along with advanced processing and testing methods are presented. Advanced bioceramics and coatings are expected to have increasing use in orthopaedics because of their unique combination and range of properties including strength and toughness, hardness and wear resistance, biocompatibility, bacteriostasis, and osseointegration.
Several studies have shown that the coefficient of friction of self-mated silicon nitride in water decreases from an initially high value to about 0.002 after a certain run-in period. Since the worn surfaces become extremely smooth, the low friction is attributed to the initiation of hydrodynamic lubrication by a thin water film at the interface. The possibility of mixed lubrica-tion, i.e., hydrodynamic lubrication by water and boundary lubrication due to the presence of colloidal silica on the wearing surfaces, has also been proposed. The purpose of our study is to investigate the influence of load, speed, and surface roughness on the duration of the run-in period. The results confirmed that a low coefficient of friction is obtained following a run-in per-iod when a wear scar of sufficient size is developed to reduce the contact stress. The run-in period, during which the coefficient of friction is fairly high, was shorter for smoother surfaces and at higher loads and speeds. The low friction behavior was found to be unstable and occasional high friction spikes were observed. The surfaces of the wear tracks and wear scars contained a series of striations parallel to the sliding direction and exhibiting plastic deformation, delamination and fracture. The striations that appeared to be associated with the high friction spikes, could form as a result surface film breakdown. Although these results are consistent with the proposed mechanisms of hydrodynamic lubrication or mixed lubrication, it is proposed that the low friction behavior may be also related to fundamental interactions between two hard and elastically deforming surfaces cov-ered with hydrogen-terminated oxide films.
ZTA (alumina toughened by 20 wt.% zirconia), hot-pressed silicon nitride (with totally 10 wt.% Y2O3 and Al2O3 as additives) and TZP (pressureless-sintered yttria stabilized zirconia) ceramics were implanted by various doses (5 × 1016 ions/cm 2 ∼ 1 × 1018 ions/cm2) of Ti, Zr, and Cr ions with a MEVVA (metal vapor vacuum arc) source implanter. The bending strength of these ceramics was investigated. It was discovered that, for different ceramics, different behaviors were presented with the same doses of implantation ions. For alumina and zirconia ceramics, the bending strength increased with increasing implantation doses of Ti and Zr ions, but decreased with high dose of Cr ions. For silicon nitride ceramics, however, the bending strength originally increased with smaller doses of metals implanted, and decreased with higher doses of metals of Ti, Zr, and Cr ions. The different behaviors are correlated to the different variations in compositions and microstructures of ceramics after ion implantation.
In the 1st generation (January 1982 to February 1985), a tibial UHMWPE plate was fixed on an alumina tray and an alumina stem was positioned at the center of the tray. The prostheses can be used as both a cementless and cement fixation. In the 2nd generation (Jun. 1990 to Apr. 1996), an alumina tray was changed to metal tray. The prostheses were fixed with cement. In the 3rd generation (since Mar. 1993), a femoral component was coated with alumina beads for rigid fixation of bone cement on alumina. In the 2nd and 3rd generation, Interface Bioactive Bone Cement (IBBC) technique was used. In the 1st generation, TKP was performed on 137 patients (103 RA and 34 OA). Follow-up term was 15-18 years. Generally, cementless fixation was performed. Follow-up rate was 80%. The probability of revision and loosening was very high in cementless fixation and very low in cement fixation. In the 2nd and the 3rd generation, TKA was performed on 112 patients (RA 74 and OA 38) and 111 patients (RA 69 and OA 42), respectively, and follow-up terms were 4 to 10 years and 2 to 7 years, respectively. The radiolucent line appeared only on the small areas of few cases. In wear of TKP, alumina is superior to metal. IBBC has advantages of both HA coating cementless fixation and cement fixation.
For some years ceramic bearing balls based on silicon nitride have been routinely used in technical practice. An important property of bearing balls is their strength, but appropriate testing methods are still missing. In this paper four different methods for strength testing are applied to commercial bearing balls. Each of the tests needs a different type of specimen, their preparation needs a very different effort, and the stress state applied to the specimens is also very different. This causes pros and cons, which are discussed in detail. The conventional 4-point bending test characterises the material in the interior of the balls. The applied stress state is uniaxial. The machining of the bending bars out of the balls is time intensive and costly. The ball on three balls test also characterises interior of the balls. The stress state is biaxial. The machining of the disc shaped specimens out of the balls is less expensive than the production of bending bars, but the finish of the tensile loaded surface needs special care. The data of both types of tests can be converted into each other using Weibull theory. The specimens in the triple ball crush test are as-received bearing balls, which are squeezed together. This causes some kind of contact loading, as will also occur in service. Failure is caused by the creation and growth of contact cracks, followed by a collapse of the compressed and cracked material. A detailed analysis of test results is complicated. It can be speculated that the component's behaviour is mainly influenced by the toughness of the material and that the flaws in the material or at the component's surface are of less significance. In the newly developed notched ball test the highest stressed region is a part of the original surface of the balls. Machining of the notch is straightforward. The stress state is almost uniaxial. The strength depends on size of flaws in the surface region. Therefore the notched ball test is a relevant measure to characterize the quality of the bearing balls.
is the crack resistance at ”infinite” crack length. It is convincingly shown that this so-called R-curve equation correctly
predicts K∞, which is comparable to the conventionally measured Mode I plain-strain fracture toughness, KIc, of the same material. The fundamental constants in the fracture-mechanics-based equations are discussed, emphasizing the
aspects pertinent to the small specimens used in the MDBT. Results are presented on 8 materials: ZnS, glass-ceramic, Si3N4, Ti5Si3, SiC, Ni3Ge, NiAl and Ti-46.5A1-2.1Cr-3.0Nb-0.2W. All are brittle except for the latter two, which undergo slight plastic deformation
before fracturing. The resulting values of K∞ are in excellent agreement with published values derived from conventional measurements, providing considerable confidence
in the method.
where Q is a constant and K∞ is the crack resistance at ”infinite” crack length. It is convincingly shown that this so-called R-curve equation correctly
predicts K∞, which is comparable to the conventionally measured Mode I plain-strain fracture toughness, KIc, of the same material. The fundamental constants in the fracture-mechanics-based equations are discussed, emphasizing the
aspects pertinent to the small specimens used in the MDBT. Results are presented on 8 materials: ZnS, glass-ceramic, Si3N4, Ti5Si3, SiC, Ni3Ge, NiAl and Ti-46.5A1-2.1Cr-3.0Nb-0.2W. All are brittle except for the latter two, which undergo slight plastic deformation
before fracturing. The resulting values of K∞ are in excellent agreement with published values derived from conventional measurements, providing considerable confidence
in the method.
BackgroundHighly cross-linked polyethylene (HXLPE), created by disrupting the molecular structure of polyethylene, then through the
application of heat, encourages creation of new cross-links in the process, resulting in a material with improved wear resistance.
The impetuses for this new technology were the unsatisfactory wear properties and subsequent osteolysis of noncross-linked
polyethylene. A 72% reduction in wear using highly cross-linked polyethylenes (HXLPE) compared with conventional polyethylene
at 5years was described previously. The longest term followup studies on HXLPE range from 2 to 6years.
Questions/purposesWe therefore addressed the following questions: (1) Does the improvement in wear observed at the earlier followup continue
to 7 to 10years? (2) What is the incidence of osteolysis in this group of patients and in the control group?
MethodsWe retrospectively reviewed 38 prospectively followed patients who had 42 hips with an annealed HXLPE who were followed a
minimum of 7years (average, 8.6years; SD=1; range, 7–10.3years). Wear and osteolysis were compared with those of a control
group of 39 patients (40 hips) from a US Investigational Device Exemption (IDE) prospective, randomized study begun in 1996
with conventional polyethylene and followed for a minimum of 6years (average, 7.5years; SD=1.1; range, 6–10.2years).
Linear head penetration was measured from AP radiographs at early, 1-year, 5-year, and most recent followups.
ResultsAt the average followup, annual linear wear was 0.031mm (SD=0.014) for the HXLPE and 0.141mm (SD=0.080) for the control
group, a 78% reduction. No mechanical failure of the polyethylene was noted in either group. Incidence of osteolysis was 50%
in the control group (all lesions confined to proximal Gruen Zones 1 and 7) compared with no cases in the investigational
group.
ConclusionsWe observed an improvement in wear and no mechanical failures with this annealed material.
Level of EvidenceLevel III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
The friction and wear behaviour of ceramics, Al2O3, ZrO2(PSZ), SiC and Si3N4, were studied with three kinds of pin-on-disk machines under the following four conditions: in vacuum at pressures ranging from 10−6 Pa to 105 Pa in either nitrogen or oxygen, in nitrogen with organic compound vapours of C2H5OH, CH3COOH, (CH3)2CO, C6H14 and C6H6, in humiditycontrolled air, and in deionized water.
We retrospectively analysed concentrations of chromium and cobalt ions in samples of synovial fluid and whole blood taken from a group of 92 patients with failed current-generation metal-on-metal hip replacements. We applied acid oxidative digestion to our trace metal analysis protocol, which found significantly higher levels of metal ion concentrations in blood and synovial fluid than a non-digestive method. Patients were subcategorised by mode of failure as either ‘unexplained pain’ or ‘defined causes’. Using this classification, chromium and cobalt ion levels were present over a wider range in synovial fluid and not as strongly correlated with blood ion levels as previously reported. There was no significant difference between metal ion concentrations and manufacturer of the implant, nor femoral head size below or above 50 mm. There was a moderately positive correlation between metal ion levels and acetabular component inclination angle as measured on three-dimensional CT imaging.
Our results suggest that acid digestion of samples of synovial fluid samples is necessary to determine metal ion concentrations accurately so that meaningful comparisons can be made between studies.
Adverse reactions to metal debris have been reported to be a cause of pain in metal-on-metal hip arthroplasty. We assessed the incidence of both symptomatic and asymptomatic adverse reactions in a consecutive series of patients with a modern large-head metal-on-metal hip arthroplasty.
We studied the early clinical results and results of routine metal artifact-reduction MRI screening in a series of 79 large-head metal-on-metal hip arthroplasties (ASR; DePuy, Leeds, UK) in 68 patients. 75 hips were MRI scanned at mean 31 (12-52) months after surgery.
27 of 75 hips had MRI-detected metal debris-related abnormalities, of which 5 were mild, 18 moderate, and 4 severe. 8 of these hips have been revised, 6 of which were revised for an adverse reaction to metal debris, diagnosed preoperatively with MRI and confirmed histologically. The mean Oxford hip score (OHS) for the whole cohort was 21. It was mean 23 for patients with no MRI-based evidence of adverse reactions and 19 for those with adverse reactions detected by MRI. 6 of 12 patients with a best possible OHS of 12 had MRI-based evidence of an adverse reaction.
We have found a high early revision rate with a modern, large-head metal-on-metal hip arthroplasty. MRI-detected adverse rections to metal debris was common and often clinically "silent". We recommend that patients with this implant should be closely followed up and undergo routine metal artifact-reduction MRI screening.
We conducted a longitudinal study including patients with the same type of primary hybrid total hip replacement and evaluated patient activity and femoral osteolysis at either five or ten years post-operatively. Activity was measured using the University of California, Los Angeles scale. The primary outcome was the radiological assessment of femoral osteolysis. Secondary outcomes were revision of the femoral component for aseptic loosening and the patients’ quality of life. Of 503 hip replacements in 433 patients with a mean age of 67.7 years (30 to 91), 241 (48%) were seen at five and 262 (52%) at ten years post-operatively. Osteolytic lesions were identified in nine of 166 total hip replacements (5.4%) in patients with low activity, 21 of 279 (7.5%) with moderate activity, and 14 of 58 (24.1%) patients with high activity. The risk of osteolysis increased with participation in a greater number of sporting activities. In multivariate logistic regression adjusting for age, gender, body mass index and the inclination angle of the acetabular component, the adjusted odds ratio for osteolysis comparing high vs moderate activity was 3.6 (95% confidence interval 1.6 to 8.3). Stratification for the cementing technique revealed that lower quality cementing increased the effect of high activity on osteolysis. Revision for aseptic loosening was most frequent with high activity. Patients with the highest activity had the best outcome and highest satisfaction.
In conclusion, of patients engaged in high activity, 24% had developed femoral osteolysis five to ten years post-operatively.
Alumina-on-alumina bearings in total hip arthroplasty have been developed in an attempt to minimise debris and the occurrence of osteolytic lesions. The outstanding tribological properties of this bearing system are explained by low surface roughness, high hardness for major scratch resistance, and high wettability. Since the 1970s, technological improvements in the manufacturing process of alumina components together with a better understanding of Morse taper technology have provided a surgical grade material with high density, high purity and small grains. Published studies on the outcome of total hip arthroplasty performed with this new generation of implants showed high survivorship especially in young and active patients, with survival rates free of revision of 90.8% to 97.4% at ten years. However, concern remains over ceramic liner fracture and squeaking, which has been noted recently with increasing prevalence. This review will discuss the current knowledge on the use of alumina-on-alumina bearings.
The findings of a fifteen year clinical study of patients who underwent anterior interbody fusion of lower spine using reaction bonded silicon nitride intervertebral spacers were presented. No slippage, subsidence or reaction was found in case of the ten-year review of 16-patients. The overall patient satisfaction decreased in case of ten-year review in comparison with the five-year review. The progressive degeneration, which is expected to be the result of stress shielding due to elastic modulus mismatch, is also observed in nine of thirteen cases assessed.
Silicon nitride has been researched intensively, largely in response to the challenge to develop internal combustion engines with hot-zone components made entirely from ceramics. The ceramic engine programs have had only partial success, but this research effort has succeeded in generating a degree of understanding of silicon nitride and of its processing and properties, which in many respects is more advanced than of more widely used technical ceramics. This review examines from the historical standpoint the development of silicon nitride and of its processing into a range of high-grade ceramic materials. The development of understanding of microstructure-property relationships in the silicon nitride materials is also surveyed. Because silicon nitride has close relationships with the SiAlON group of materials, it is impossible to discuss the one without some reference to the other, and a brief mention of the development of the SiAlONs is included for completeness.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Silicon nitride material has been traditionally used as bearing material due to its superior performance against bearing steel. Its successful application as a bearing element has led to the development of rolling contact applications in turbomachinery and automotive industries. In the case of latter, this is especially true for the engine manufacturing industry where its excellent rolling contact performance can make significant savings on warranty cost for engine manufactures. In spite of these advantages, the remaining limitation for their broader application is the high component machining cost. Further understanding of rolling contact performance of silicon nitride in relation to its surface integrity will enable engine manufacturers to produce components that meet the design requirements while at the same time reduce the machining cost. In the present study, the relationship between the C-sphere strength of a silicon nitride and its rolling contact fatigue life is investigated. The C-sphere test is used here to compare the strengths of three batches of sintered reaction-bonded silicon nitride (SRBSN) specimens with different subsurface quality induced by variation of machining parameters. In parallel, the rolling contact fatigue (RCF) performance of those machining conditions is studied on a modified four-ball tester. The results show that the most aggressively machined specimens have the weakest C-sphere strength and the shortest RCF life. This positive relationship can give component manufacturers a valuable reference when they make selections of candidate material and finishing standards.
The wear properties of two kinds of Si3N4 exposed to high and low humidity are examined experimentally at various sliding speeds. Bearing steel is used as the disk material under pin-on-disk-type sliding conditions. The wear rates of the pressureless sintered plus hot isostatically pressed Si3N4 are slightly lower than those of pressureless sintered Si3N4. It is observed that adsorbed moisture and the sliding speed markedly affect the wear properties of Si3N4. The highest wear rate is obtained with a high humidity and low sliding speed. As the sliding speed increases, the wear rates are decreased and the effect of the humidity on the wear rates of the Si3N4 is reduced. Three suggestions are made to explain the high wear rate of the Si3N4 pin specimen at a high humidity. One suggestion is the effect of the material property change caused by the absorbed water molecules. Another is the plowing action of the hard particles of Fe2O3 formed as a result of the oxidation of the bearing steel disk. The other suggestion is the corrosion effect at the Si3N4 surface. An increase in the sliding speed is supposed to reduce the effect of the humidity on the wear rate of Si3N4 by raising the temperature of both the bearing steel disk and the Si3N4 pin specimen. Measurement of the temperature of the disk surface shows a significant change with sliding speed.
Friction and wear properties of silicon nitride were investigated using ball-on-disk tribometer under various relative humidity levels (RHL). Friction tests were conducted against various metals (copper, nickel, titanium, aluminium). The results show that the influence of humidity depends on the material of the couples. Tribological behaviour of silicon nitride sliding on very reactive metals such as titanium and aluminium is not influenced by RHL. In contrast, the friction coefficient and wear mechanism of nickel and copper are strongly affected by adsorbed films of water vapour. Tribological properties of Si3N4/Si3N4 couple were also studied and the effect of humidity was analyzed.
It is thought that all-ceramics artificial hip joints should have good geometric conformity between sockets and femoral heads to avoid stress concentration. So using end-face apparatus, we investigated the steady state friction and wear between flat surfaces of three ceramics (alumina, silicon carbide and silicon nitride) lubricated with bovine serum solution. According to the results, the coefficient of friction and the specific wear rate of silicon nitride are much higher than those of alumina and silicon carbide. The coefficient of friction of silicon carbide is the lowest and that of alumina is close to silicon carbide. The specific wear rate of alumina is very low and that of silicon carbide is also low. In atomic force microscopy, we observed smooth surfaces covered with tribofilm for all of the ceramics. Visually, we observed distinct grooves on silicon nitride surface, while the alumina and the silicon carbide surfaces were scarcely changed. In conclusion, alumina and silicon carbide could be candidates for all-ceramic hip joint.
The manufacturing of the Si3N4 reinforced biomorphic microcellular SiC composites for potential medical implants for bone substitutions with good biocompatibility and physicochemical properties was performed in a two step process. First, wood-derived porous Si/SiC ceramics with various porosities were produced by liquid silicon infiltration (LSI) at 1550 °C with static nitrogen atmosphere protection (0.1 MPa), followed by subsequent partial removing of the Si in vacuo at 1700 °C for different periods of time. Secondly, the final porous Si3N4 fiber/SiC composite was obtained by further chemical reaction of nitrogen with the infiltrated residual silicon at 1400 °C for 4 h under high concentration flowing nitrogen atmospheres (0.5 MPa). The bending strengths of the porous Si3N4 fiber/SiC composite at axial and radial direction were measured as 180.03 MPa and 90 MPa respectively. The improvement in bending strength was primarily attributed to grain pull-out and bridging enhanced by the elongated β-Si3N4 grains cross-linked in the depth of the pore channels. The TG analysis showed an obvious improvement in oxidation resistance of the nitride specimens.
Structural ceramics are used in diverse tribological applications due to their unique properties that include resistance to abrasion and erosion, resistance to corrosive wear, wear resistance at elevated temperatures, low density and unique electrical, thermal and magnetic properties. Applications include precision instrument bearings, cutting tool inserts, prosthetic articulating joints and engine components. Following a brief overview of the processing methods applied to alumina, silicon nitride and silicon carbide, the wear behaviour of these ceramics is reviewed. The wear behaviour changes as the load or the coefficient of friction is increased. This change is associated with a drastic increase in wear at a critical load that depends on the material and test conditions. This transition from mild to severe wear occurs through a microfracture process at the sliding contact. Contact mechanics is used to develop a simple model to determine whether contact failure occurs by a classical brittle process (i.e. cone cracking) or a quasi-plastic behaviour (i.e. small microcracks distributed below the contact surface). The model provides estimates of the transition load within a factor of two of the experimentally obtained values and indicates that the brittle behaviour dominates the observed transition from mild to severe wear in the three ceramics evaluated in this study. The limitations of the model and its use in design of tribological components are discussed. The role of lubrication and tribochemical reactions between ceramic surfaces and atmospheric moisture on the wear behaviour is discussed.
DLC coatings are of enormous interest for biotribological applications due to their biocompatibility, auto-lubricious, and non-stick properties. The most demanding implant is the hip joint. Alternative materials to metal alloys are being increasingly investigated aiming low wear debris volume, in any case innocuous wear particles. Silicon nitride (Si3N4) ceramics are light, tough, mechanical resistant, inert materials, turning them suitable for high-load medical applications. In this study, Si3N4 polished substrates were coated with adherent DLC coatings grown by DC magnetron sputtering to reduce of the friction forces against any antagonist material. Surface characterization results showed that the developed material is quite hydrophobic, with a total surface tension of 45.7 mN/m (polar component: 9.1 mN/m; dispersive component: 36.6 mN/m), and a zeta potential of −35.0±1.3 mV. In vitro testing using an acellular simulated body fluid (SBF) showed no apatite layer formation ability, as confirmed by SEM observation and analysis of the solution ions concentration with immersion time. MG63 osteoblast-like cells showed poor adhesion on the DLC films but the adherent cells displayed a normal morphology and, as compared to standard polystyrene tissue culture plates, exhibited a higher cell growth rate, suggesting no indication of cytotoxicity. Results suggested that the novel DLC-coated Si3N4 biomaterial should be adequate to be used for articular prostheses medical application.
Silicon nitride ceramics are used under conditions were high strength, hardness and wear resistant is necessary. The increasing use of Si3N4-ceramics as ceramic ball bearings and valves in chemical apparatus demand an understanding of the relations between microstructure and corrosion behaviour of silicon nitride ceramics in different environments. The stability of the ceramics against corrosion in acids and bases is mostly controlled by the stability of the grain boundary. Therefore, the influence of different rare earth ions and the influence of the crystallisation of the grain boundary on the stability in sulphuric acid were investigated. The results showed that the nature of the rare earth has a minor influence on the corrosion behaviour. The stability against corrosion of the ceramics with amorphous grain boundaries is mostly controlled by the amount of the SiO2 in the grain boundary. The crystallisation of the grain boundary can improve or not change the corrosion behaviour depending on the amount of crystalline grain boundary phases and the composition (stability) of the residual amorphous grain boundary phase. The results are discussed in the context with previous investigation and some systematisation of the corrosion behaviour of Si3N4 in acids and bases is given.
Bearing surfaces made of ceramic materials are an alternative to metal-on-polyethylene (PE) articulations in total hip arthroplasty and total knee arthroplasty. The advantage of ceramic surfaces in total joints is the reduction in wear rates compared with metal-on-PE. Lower wear rates result in a decreased volume of wear particles produced by the articulating surfaces. In theory, this should reduce the risk of periprosthetic osteolysis and premature implant loosening, thereby contributing to the longevity of prosthetic joints. In addition to ceramics, other alternative bearings, such as highly cross-linked PE and metal-on-metal, also offer decreased wear rates when compared with metal-on-PE articulations in total joint arthroplasty. Alumina and zirconia ceramics are familiar to orthopedic surgeons because both materials have a long history of use in total joint bearings. Alumina-on-alumina ceramic total hip articulations are now available in the United States from several implant manufacturers. Composite materials made by combining alumina and zirconia, metal-on-ceramic articulations, and new ceramic materials will offer even more choices as the search for the ideal bearing combination in total joint arthroplasty continues. The purpose of this article is to review the material properties, clinical applications, evolution, and limitations of the ceramic materials used in total joint bearings.
The effect of adsorbed water on the characteristics of friction of both silicon nitride and silicon carbide was studied experimentally using a pin-on-flat-type friction apparatus at a slow sliding speed of 10 mm min−1. Silicon nitride and silicon carbide powder were hot pressed under the sintering conditions of pressure, 30 MPa, and temperatures 1800 °C and 2100 °C respectively.A continuous increase in friction during reciprocal sliding was observed for the sliding of silicon nitride in laboratory air with a relative humidity of 50% ± 5%. It was attributed to a decrease in the protective surface layer during reciprocal sliding. The effects of time intervals in reciprocal sliding, environmental humidity and temperature on the formation of the surface layer were examined. Experimental results showed that shorter time intervals, lower humidity and higher surface temperature increased the sliding friction of ceramics. These influences were also attributed to the decrease in the effect of adsorbed water on sliding friction, because the above sliding conditions prevented the formation of a protective surface layer.
The surface quality of tribochemically polished silicon nitride was explored. Since a previous study has shown that chromic(VI) acid produces the best combination of polishing rate and surface quality, silicon nitride surfaces polished in 3 wt % chromic acid have been examined in detail. These surfaces are ultrasmooth and defect‐free. No worn particles are observed on the surface nor in the liquid. The surface roughness measured by atomic force microscopy is 0.5 nm at 50 μm cutoff length and 2 nm at 150 μm. On a large scale, the surface roughness is 6 nm at 8 mm cutoff; the latter corresponds to a slight macroscopic curvature with a radius of 94 m. Secondary ion and photoelectron emission measurements showed that the polished surfaces are free of chromium. When stored in air, they are covered with the same oxide layer as a fracture surface. Surface residual stress measurements by X‐ray diffraction indicate the presence of a very small compressive stress of 50 MPa. No degradation of the fracture strength is found. The average fracture strength measured by the biaxial stress method is about 770 MPa. © 1999 The Electrochemical Society. All rights reserved.
Purpose – Testing of silicon nitride (Si3N4) or silicon carbide (SiC), sliding on itself in water, revealed that hydrodynamic lubrication can be obtained at low-sliding velocity. The purpose of this paper is to study the performance of Si3N4-metals pairs, sliding in water. Design/methodology/approach – Ball on disc unidirectional sliding tests are run with Si3N4 against tool steel, stainless steel and cast iron in water. The friction force is recorded continuously and the wear is evaluated at the end of the run by geometric technique. In addition, SiC sliding on itself in oxidant solution (3 per cent solution of CrO3 in water) is tested. Findings – The measured friction and wear of water-lubricated Si3N4 against metals are higher compared to Si3N4 sliding on itself. At the end of the run-in SiC, lubricated by the oxidant solution, obtains hydrodynamic lubrication and friction and wear are lower than in water-lubricated SiC. Research limitations/implications – The experimental results obtained are valid within the range of load and sliding velocity applied – 1-10?N, 0.04-0.33?m/s, respectively. The Si3N4 sliding against metals in water over sliding distance of 3,000?m has not shown tendency towards hydrodynamic lubrication. Originality/value – The paper presents test data on friction and wear properties of Si3N4 sliding against metals in water. The low friction and ball wear rate of the SiC, lubricated by the oxidant solution, shows the potential of the 3 per cent distilled water solution of CrO3 to surpass water as a lubricant for SiC sliding bearings.
Nanometer scale single asperity tribochemical wear of silicon nitride was examined by measuring the wear of atomic force microscope tips translated against a variety of substrates in aqueous solutions. We show that the chemical nature of the substrate plays an important role: significant wear was observed only when the substrate surface is populated with appropriate metal-hydroxide bonds. Mica and calcite substrates, whose water-exposed cleavage surfaces lack these bonds, produced little if any tip wear. As a function of contact force FN and scan duration t, the length of the tips in this work decreases approximately as (FNt)0.5. We propose that pressure-induced intermediate states involving hydroxyl groups form on both the tip and the substrate; chemical reactions subsequently form transient bridging chemical bonds that are responsible for tip wear. © 2002 American Institute of Physics.
We report here the study on tribological behavior of -Sialon in aqueous medium. The results derived from a wide range of test conditions are briefly discussed. A reduction in friction coefficient from 0.7 to 0.03 and a decrease in wear rate by two orders of magnitude were achieved under low load (9.8 N) and high speed (>0.54 m/s) conditions. The tribological behavior of -Sialon/Si3N4 ceramics was then compared with Si3N4/Si3N4 tribopairs.
A 25 nm thick α-alumina layer was deposited on a turbine-grade silicon nitride by sol-gel dip coating and subsequent heat treatment in air at 1200°C. This layer had a nanometer grain structure. Silicon nitride protected by this thin layer showed a significant improvement in oxidation resistance over its uncoated counterpart after 200 cyclic exposures in air at 1250°C. The oxide layer grown on the coated silicon nitride also exhibited superior surface morphology, compared with the uncoated silicon nitride.
A ceramic hip-joint femoral head, made of a zirconia-toughened alumina-matrix material with the addition of small amounts of mixed oxides, has been evaluated with respect to environmental surface degradation in a moist environment. Microscopic insight into environmental surface degradation could be obtained according to Raman and fluorescence microprobe spectroscopies. By adopting an optimized confocal configuration for the optical probe, spectroscopic assessments could be performed in very shallow volumes, thus minimizing the effect on the spectra of sub-surface portions of the material. Two main phenomena have been envisaged: (i) transformation of zirconia dispersoids from tetragonal to monoclinic polymorph, induced by aging periods at 121°C (0.1 MPa) in a vapor environment (in addition to a fraction of a monoclinic polymorph ≅20 vol% present in the as-received femoral head); (ii) evolution of the (equilibrium) residual stress field stored within the joint surface from a tensile field in the as-received material to a slightly compressive stress field after several hours of aging in a moist atmosphere. Exposures in vapor >50 h brought the joint surface into an increasingly tensile stress state. This residual stress field on the material surface may hinder the long-term wear resistance of the load-bearing femoral head, especially in the presence of microscopic impingements by microseparation contact and third-body wear.
Atomic force microscopy (AFM) has been systematically used to image the surface of a femoral head made of alumina/zirconia composite (henceforth referred to as zirconia-toughened alumina, ZTA), in comparison with two types of commercially available femoral heads made of monolithic zirconia. AFM experiments were conducted before and after in vitro exposure in water moist environment. All materials contained zirconia partly stabilized with yttria. AFM observations were performed on wide areas of several heads of each type (i.e., in the order of several tens of μm2), in order to ensure statistical reliability in the topologic measurements. Tetragonal-to-monoclinic phase transformation, which was quantitatively characterized by confocal Raman spectroscopy, showed significant difference among the investigated samples. Such differences were similarly found with respect to both roughness and time needed for topologic changes to occur. Variation of topologic statistic parameters, such as skewness and kurtosis of surface height histograms, confirmed the main impact of zirconia grain size on the environmental stability of the head surface, the finer the grain size the higher the stability.
In the preceding paper, it was shown that aluminum ion implantation significantly improves the oxidation resistance of Si3N4 ceramics under the influence of sodium. Not only is the oxidation rate reduced by up to an order of magnitude, the phase and morphological characteristics of the oxides grown on aluminum-implanted samples are improved as well. The role of aluminum in negating the detrimental effect of sodium on the oxidation resistance of Si3N4 ceramics can be interpreted on the basis of network modification of the oxide layers by sodium and aluminum cations. The degree of improvement in the oxidation resistance does not, however, necessarily increase with the aluminum concentration. A simple quantitative analysis is presented which correlates the optimum aluminum implant concentration and the sodium content in the gas phase for the optimization of the oxidation resistance of Si3N4 ceramics.
Friction coefficients and wear rates of hot-pressed Si3N4 have been measured in a ball-on-flat linear-sliding geometry at temperatures ranging from room temperature to 1273 K in Ar and air containing up to 63% H2O. In inert environments, the friction coefficients (ranging between 0.6 and 0.7) are independent of temperature, and wear rates increase with temperature. In oxidizing environments, the friction and wear are reduced by the presence of tribochemical reaction products. Friction coefficients and wear rates are lowered when the wear debris spontaneously forms into rolls, oriented perpendicular to the direction of relative motion, at high H2O levels in the temperature range of 873 to 1073 K.
The fracture behavior of a zirconia-toughened alumina-matrix composite (added with small amounts of mixed oxides) for ceramic hip joint prostheses has been evaluated with emphasis placed on the effect of environmental surface degradation in moist environment. Accelerated aging tests were performed up to 300 h in an autoclave operating at 121°C (under 0.1 MPa pressure) in vapor environment, which represents a quite severe environmental testing condition. Besides conventional fracture mechanics characterizations, including different types of fracture toughness test, microscopic insight into the effect of environmental surface degradation on toughness could be obtained according to Raman and fluorescence microprobe spectroscopy. The main outcomes of this study were as follows: (i) after 10-h autoclaving (according to ISO standard recommendation) no significant change of monoclinic volume fraction and fracture toughness could be detected; (ii) after very long exposure time (300 h) the monoclinic phase content increased and the surface fracture toughness decreased by approximately 30%, although it was still above the toughness level of pure alumina; and (iii) the bulk toughness was unaffected by autoclave exposure, independent of exposure time elongation.
Hot-isostatically-pressed, additive-free Si3N4 ceramics were implanted with aluminum at multi-energies and multidoses to achieve uniform implant concentrations at 1, 5, and 10 at.% to a depth of about 200 nm. The oxidation behavior of unimplanted and aluminum-implanted Si3N4 samples was investigated in 1 atm flowing oxygen entrained with 100 and 220 ppm NaNO3 vapor at 900–1100°C. Unimplanted Si3N4 exhibits a rapid, linear oxidation rate with an apparent activation energy of about 70 kJ/mol, independent of the sodium content in the gas phase. Oxides formed on the unimplanted samples are rough and are populated with cracks and pores. In contrast, aluminum-implanted Si3N4 shows a significantly reduced, parabolic oxidation rate with apparent activation energies in the range of 90–140 kJ/mol, depending on the sodium content as well as the implant concentration. The oxides formed on the implanted samples are glassy and mostly free from surface flaws. The alteration of the oxidation kinetics and mechanism of Si3N4 in a sodium-containing environment by aluminum implantation is a consequence of the effective modification of the properties of the sodium silicates through aluminum incorporation.
The formation of a tribochemical layer on silicon nitride sliding in water is studied. The wear mode changes from mechanically dominated wear to tribochemically dominated wear as sliding distance increases. The silica tribochemical layer is formed on the friction surface and reduces the friction. Introducing an additive that accelerates the formation of colloidal silica makes the running-in distance shorter. The activation energy for tribochemical reaction is estimated to be as small as 1/6–1/8 of that for static reaction.
The most commonly used bearing couple in prosthetic hip or knee joint replacements consists of a cobalt–chrome (CoCr) metal alloy articulating against ultrahigh-molecular-weight polyethylene. Ceramics have been used as an alternative to metal-on-polyethylene in joint replacement surgery of arthritic hips and knees since the 1970s. In prosthetic hip and knee bearings, ceramic surfaces offer a major benefit of drastically reduced wear rates and excellent long-term biocompatibility, which can increase the longevity of prosthetic hip and knee joints. This benefit is important clinically because hip and knee replacement has become a very common surgical procedure, particularly in the United States, and because these procedures are being increasingly performed in younger patients who place greater demands on the prosthetic bearings. However, ceramics are brittle and the risk of catastrophic bearing failure in vivo, while rare, is a major concern. Improvements in material quality, manufacturing methods, and implant design have resulted in a drastic reduction of the incidence of such failures, so that modern ceramic bearings are safe and reliable if used with components of proven design and durability. Future material improvements are actively being investigated to reduce the risk of ceramic-bearing failures even further. The purpose of this article is to review the structure, properties, applications, and limitations of the ceramics that have been used in orthopedic bearings, and to describe the new ceramic composite materials and surface treatments that will be available for joint replacement surgery in the near future.
The use of self-reinforcement by larger elongated grains in silicon nitride ceramics requires judicious control of the microstructure to achieve high steady-state toughness and high fracture strength. With a distinct bimodal distribution of grain diameters, such as that achieved by the addition of 2% rodlike seeds, the fracture resistance rapidly rises with crack extension to steady-state values of up to 10 MPam1/2 and is accompanied by fracture strengths in excess of 1 GPa. When the generation of elongated reinforcing grains is not regulated, a broad grain diameter distribution is typically generated. While some toughening is achieved, both the plateau (steady-state) toughness and the R-curve response suffer, and the fracture strength undergoes a substantial reduction. Unreinforced equiaxed silicon nitride exhibits the least R-curve response with a steady-state toughness of only 3.5 MPam1/2 coupled with a reduced fracture strength.
Friction and wear of silicon nitride sliding against the same material is investigated in aqueous solutions: distilled water, 1% H2O2 and 3% NaCl. The friction coefficient (μ) of silicon nitride in water decreases from 0.8 to 0.01 during sliding. In a 1% H2O2 solution, the friction coefficient decreases at an earlier stage of sliding than in pure water. But in 3% NaCl solution, the friction coefficient keeps a high value (μ = 0.8) during sliding over 1000 m. Analysis of the wear debris of silicon nitride in 3% NaCl solution shows that the composition of the debris corresponds to Na:Si:O = 1:2–3:4–5, which supposedly suppresses the lubricating surface friction force on the sliding solid surfaces. The analytical results support the theory that the silicon nitride surface sliding with a low friction coefficient is composed of a reactive site substitutable by a Na+ ion. The results indicate that the lubricant film which supports the high contact pressure between silicon nitride surfaces includes the hydroxide of silicon. A structural model of the sliding surface is proposed.
The paper reviews some of the extensive research in the field of ceramic rolling element bearings that has been carried out over the past decade or so. As a result of this work hot isostatically pressed silicon nitride (HIPed Si3N4), has emerged as an extremely promising material for fabricating high performance all-ceramic or hybrid steel/ceramic rolling contact bearings. Compared with conventional steel bearings silicon nitride bearings have been shown to offer significant benefits in terms of rolling contact fatigue life, and the lower density of the material greatly reduces the dynamic loading at ball/raceway contacts in very high speed applications such as machine tool spindles and gas turbine engines. Investigations have shown the particular benefits of using silicon nitride bearings in severe lubrication and wear conditions such as extreme temperature, large temperature differential, high speed, ultra-high vacuum and in safety-critical applications where, for example, they can respond to the requirements of short periods of oil-off operation in an aircraft engine. Other benefits which have been demonstrated are corrosion resistance and tolerance of contaminated lubricants. As a result of their sustained development and testing it is expected that silicon nitride bearings will continue to achieve wide acceptance in all types of applications.
Silicon nitride-based ceramics are potential candidates as materials for orthopedic implants due to their chemical stability associated with suitable fracture toughness and propitious tribologic characteristics. Therefore, in this work, dense silicon nitride components are investigated considering their suitability as biomaterials. Initially, two different compositions of silicon nitride were considered, using ytterbium, yttrium and aluminum oxides as sintering aids. The materials were sintered in a carbon resistance furnace under nitrogen atmosphere and were analyzed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) in order to characterize the microstructure. Indentation method was applied in order to obtain hardness and fracture toughness measurements, and in vitro test of cytotoxicity was performed for a preliminary biological evaluation. A microstructure composed of grains of beta-silicon nitride distributed in a secondary phase was observed. The samples achieved fracture toughness values of 5 MPa m1/2 and Vickers hardness values of 13 GPa. Since a nontoxic behavior has been observed during the cytotoxicity tests with the samples, this finding suggests that silicon nitride-based ceramic can be used as a material for clinical applications.
Silicon nitride has demonstrated to be a potential candidate for clinical applications because it is a non-cytotoxic material and has satisfactory fracture toughness, high wear resistance and low friction coefficient. In this paper, samples of silicon nitride, which were kept into rabbits' tibias for 8 weeks, and the adjacent bone tissue were analysed by scanning electron microscopy in order to verify the bone growth around the implants and the interaction between the implant and the bone. Bone growth occurred mainly in the cortical areas, although it has been observed that the newly bone tends to grow toward the marrow cavity. Differences were observed between the implants installed into distal and proximal regions. In the first region, where the distance between the implant and the cortical bone is greater than in the proximal region, the osteoconduction process was evidenced by the presence of a bridge bone formation toward the implant surface. The results showed that silicon nitride can be used as biomaterial since the newly bone grew around the implants.
Friction and wear of Si3N4 sliding on itself were measured at room temperature in different gaseous and liquid environments. At low sliding speed the friction coefficient ƒ is 0.85 in dry argon and nitrogen and 0.8 in laboratory air and oxygen. In dry gases, wear occurs by two fracture mechanisms: within 1 μm of the surface, asperity contact produces very large local stresses and cracking on a very fine scale; 3–5 μm deeper the fracture follows weaknesses of the material and is intergranular fracture with some transgranular cleavage. No evidence of plastic deformation was obtained. In water- and humidity-saturated gases wear is predominantly by a tribochemical reaction which produces an amorphous protective layer in humid gas and dissolution in liquid water. In intermediate humidity, wear is a combination of fracture and tribochemistry; the latter increases adhesion between wear particles to form a layer of compacted wear particles on the wear track. The fact that humidity decreases wear in Si3N4 and increases it in A12O3 is explained by the differences in chemical reactivity and susceptibility to stress corrosion cracking between the two materials.
As the loosening of a hip joint is caused by the tissue response to polyethylene wear particles, ceramic-ceramic joints are needed for long-term or permanent replacements. We have compared the start up and steady state friction of four ceramic materials against themselves lubricated with 1 wt.% water solution of carboxymethyl cellulose sodium salt (CMC-Na 1 wt.% water solution). The experimental results indicate that the coefficients of start up and steady state friction of silicon nitride-on-silicon nitride are the highest of the four ceramic materials, and the coefficients of start up and steady state friction of silicon carbide-on-silicon carbide are the lowest of the four ceramic materials (except at the low load of 40 N under the test conditions).
We examined a new-generation yttria-stabilized zirconia head manufactured by NGK 1 year after total hip arthroplasty. Monoclinic content of the retrieved head was twice that of the unused head at the pole and equator. A fourfold increase in monoclinic content was observed at 5 mm below the equator. Transformation from the tetragonal phase to the monoclinic phase occurred in the new generation zirconia with alumina doping within a relatively short period in vivo.
The use of highly cross-linked polyethylene is now commonplace in total hip arthroplasty. Hip simulator studies and short-term in vivo measurements have suggested that the wear rate of highly cross-linked polyethylene is significantly less than that of conventional ultra-high molecular weight polyethylene. However, long-term data to support its use are limited. The aim of this study was to compare the intermediate-term steady-state wear of highly cross-linked polyethylene compared with that of conventional ultra-high molecular weight polyethylene acetabular liners in a prospective, double-blind, randomized controlled trial with use of radiostereometric analysis.
Fifty-four patients were randomized to receive hip replacements with either conventional ultra-high molecular weight polyethylene acetabular liners (Zimmer) or highly cross-linked polyethylene liners (Longevity; Zimmer). All patients received a cemented, collarless, polished, tapered femoral component (CPT; Zimmer) and an uncemented acetabular component (Trilogy; Zimmer). Clinical outcomes were assessed and the three-dimensional penetration of the head into the socket was determined for a minimum of seven years. Linear regression was used to calculate the steady-state wear rate following the creep-dominated penetration seen during the first year.
At a minimum of seven years postoperatively, the mean total femoral head penetration was significantly lower in the highly cross-linked polyethylene group (0.33 mm; 95% confidence interval [CI], ±0.10 mm) than it was in the ultra-high molecular weight polyethylene group (0.55 mm; 95% CI, ±0.10 mm) (p = 0.005). The mean steady-state wear rate of highly cross-linked polyethylene was 0.005 mm/yr (95% CI, ±0.015 mm/yr), compared with 0.037 mm/yr (95% CI, ±0.019 mm/yr) for conventional ultra-high molecular weight polyethylene (p = 0.007). No patient in the highly cross-linked polyethylene group had a wear rate above the osteolysis threshold of 0.1 mm/yr, compared with 9% of patients in the ultra-high molecular weight polyethylene group.
This study demonstrates that highly cross-linked polyethylene has a significantly lower steady-state wear rate compared with that of conventional ultra-high molecular weight polyethylene. Longer-term follow-up is required to determine if this will translate into improved clinical performance and longevity of these implants.
In vitro analysis has shown that oxidized zirconium on ultra-high molecular weight polyethylene has better wear properties than cobalt-chromium on ultra-high molecular weight polyethylene. The purpose of this study was to determine if oxidized zirconium femoral components performed better than cobalt-chromium in vivo and if the use of oxidized zirconium components had clinical adverse effects.
Forty consecutive patients (eighty knees) underwent simultaneous bilateral cruciate-retaining total knee arthroplasty for primary osteoarthritis from January 2002 to December 2003. For each patient, the knees were randomized to receive the oxidized zirconium femoral component, with the contralateral knee receiving the cobalt-chromium component. Outcome measures included the Western Ontario and McMaster Universities Osteoarthritis Index, Knee Injury and Osteoarthritis Outcome Score, Knee Society score, and British Orthopaedic Association patient satisfaction scale. Radiographic outcomes include the Knee Society total knee arthroplasty roentgenographic evaluation and scoring system and measurement of radiographic wear. Patients and assessors were blinded to the treatment groups and results.
There were no significant differences in clinical, subjective, and radiographic outcomes between the two implants at five days, six weeks, and one, two, or five years postoperatively. At five years following surgery, 38% of the patients preferred the cobalt-chromium knee compared with 18% who preferred the oxidized zirconium knee (p = 0.02) and 44% had no preference.
Five-year outcomes after total knee arthroplasty with oxidized zirconium and cobalt-chromium femoral components showed no significant differences in clinical, subjective, and radiographic outcomes. Patients had no preference or preferred the cobalt-chromium prosthesis to the oxidized zirconium prosthesis at the time of the five-year follow-up. There were no adverse effects associated with the use of oxidized zirconium femoral implants.
Polyethylene wear, with resultant particle-induced osteolysis, is a cause of late failure of total knee arthroplasty. The causes of both wear and osteolysis are multifactorial; still, improvements in the polyethylene liner have been investigated. Available highly cross-linked polyethylene tibial liners and patellar prostheses differ greatly in the amount and method of irradiation, thermal treatments, and sterilization techniques they undergo. Several varieties of highly cross-linked polyethylene reduce the gravimetric and volumetric wear of tibial liners in knee simulator studies. However, reduced fracture toughness and the generation of smaller and possibly more reactive particles also have been reported with some varieties of polyethylene. Clinical studies of the use of highly cross-linked polyethylene in total knee arthroplasty are limited. Two nonrandomized trials of highly cross-linked polyethylene in total knee arthroplasty have reported a nonsignificant decrease in radiolucent lines at 2 and 5 years, respectively. The risks of using highly cross-linked polyethylene include fracture of the liner or of a posterior-stabilized tibial post, liner dislodgement or locking mechanism disruption, and possibly more osteolysis. Highly cross-linked polyethylene tibial liners may be considered for younger, more active patients. However, until additional clinical results are available, a cautious approach is warranted to the widespread use of highly cross-linked polyethylene in total knee arthroplasty.