Ceramic Ball Heads Research Articles

Update about ceramics in orthopaedics

Pure alumina ceramic has been, in clinical, used in orthopaedics since 1971 and currently up to five million components have been implanted. Alumina offers advantages like stability, biocompatibility and low wear, however it has limited strength. Applications are limited by design considerations. Engineers in biomaterials have worked on improving the performances of the material by optimising the manufacturing process. To fulfil surgeons and patients increasingly exacting requirements, ceramists have also developed a new ceramic composite, the alumina matrix composite (AMC). This material combines the great principles of reinforcement of ceramics with its tribological qualities and presents a better mechanical resistance than alumina. The examination of the tribological situation of AMC, especially under challenging condition of hydrothermal ageing, shows the aptitude of this material in wear applications. The US Food and Drug Administration has approved the ceramic ball heads articulating against polyethylene inserts. Since its introduction, more than 65,000 ball heads and 40,000 inserts of the Alumina Matrix Composite have been implanted. With a six-year clinical experience, no complication has been reported to the manufacturer. Improved toughness and the excellent wear, makes it a potentially more flexible alternative to the more traditional alumina for hip prostheses.

Emergence of the alumina matrix composite in total hip arthroplasty

Pure alumina ceramic has been in clinical use in orthopaedics since 1971 and, currently, up to 5 million components have been implanted. Alumina offers advantages like stability, biocompatibility and low wear; however, it has limited strength. Applications are limited by design considerations. Engineers in biomaterials have worked on improving the performance of the material by optimising the manufacturing process. To fulfil surgeons' and patients' increasingly exacting requirements, ceramists have also developed a new ceramic composite, the alumina matrix composite (AMC). This material combines the great principles of the reinforcement of ceramics with its tribological qualities and presents a better mechanical resistance than alumina. The examination of the tribological situation of AMC, especially under the challenging conditions of hydrothermal ageing, shows the aptitude of this material in wear applications. The US Food and Drug Administration (FDA) has approved ceramic ball heads articulating against polyethylene inserts. Since its introduction, more than 65,000 ball heads and 40,000 inserts of AMC have been implanted. With a 6-year follow up, no complication has been reported to the manufacturer. Improved toughness and the excellent wear of AMC makes it a potentially more flexible alternative to the more traditional alumina for hip prostheses.

Long-term results of cementless primary total hip arthroplasty with a threaded cup and a tapered, rectangular titanium stem in rheumatoid arthritis and osteoarthritis

The aim of this study was to assess the outcome of primary cementless total hip arthroplasty in rheumatoid arthritis patients and to compare the results with osteoarthritis patients. Sixty-four patients (77 hips) with rheumatoid arthritis and 120 patients (135 hips) with osteoarthritis had a conical-shaped Zweymueller threaded cup and a tapered, rectangular Zweymueller stem implanted and were assessed after an average of 12.5 years. The endpoints for survival analysis were failure of one or both components due to radiographic loosening or revision. Revision was defined as exchange of cup, stem or both. When the PE-insert or the ceramic ball head were exchanged leaving cup and stem in place, e.g. for PE-wear or dislocation, this was not considered a revision but a re-intervention. No differences were found in survival rates; however, in the rheumatoid arthritis group there was an increased rate of malposition of the cup, avulsions of the greater trochanter, and increased bone resorption in the trochanteric region. This study shows that despite altered biomechanical properties of rheumatoid bone, mechanical stability and osseous integration of cementless prosthesis are not compromised and, although a higher complication rate did occur, long-term survival is excellent.

Finite Element Analysis on Proof Testing of Ceramic Ball Heads for Total Hip Replacements: Trauma Loading Considerations

Trauma related loading of hip prostheses has been reported as a cause of failure of implanted ceramic materials, ball and/or cup. In this study a computer simulated model is made to evaluate contact pressures and stresses in the stem/ball contact pair, as well as stress concentration regions in the ceramic cup. A 3D Non-Linear Finite Element Analysis was performed in a “proof test” scenario. A high peak trauma-like loading of 15 KN was used. 28mm ball heads (in diameter) were modeled and two sizes for taper lock were simulated to report their influence on the contact pressure over the critical areas of the ballhead. It was found that the ball head cone’s depth has a major incidence in the stress and contact pressure surrounding the stem when an impact load is applied. The best stress and pressure configurations were found for the case of the stem lying completely inside the ballhead.

The Ceramic Option in Ball Head Revision Surgery

A ceramic ball head design with metal sleeves was developed to be used in revision surgery if the stem is well fixed in the bone.

Safety of Ceramic Components

A statistical analysis of ceramic implant failure is presented. It is shown that the majority of failures occure within the first 12 months after implantation. From this characteristic distribution the prediction of the total failure rate is possible even for the latest years of production. There have been considerable improvements of the reliability in the past 5 years. Furthermore, there is evidence that the failure rate strongly depends on ball head diameter. For the largest ceramic ball head of 36mm diameter up to now no failure has been reported. From these results it is concluded that ceramic implant failure is in general released by individual circumstances. In particular, the probability of failure may be strongly increased in the case of limited mobility and an increased risk of impingement. In the case of a well developed specific surgeon training and right choice of the ceramic implant system the ceramic components provide an extremely reliable and safe solution for the patient.

On the fracture of a zirconia ball head

Y-TZP ball heads were introduced into the market in 1985. Since then these components have had wide diffusion in hip replacements, due to their good mechanical performance and reliability. Namely, only a few papers were published up to year 2000 reporting failures of Y-TZP ball heads. The worldwide recall in August 2001 of some Y-TZP batches changed this situation. This paper analyse the material of a ceramic ball head that fractured in vivo 34 months after surgery. The retrieved fragments were submitted for visual inspection, fractographic analysis by optical microscopy, X-ray diffractometry, and FEG-SEM ceramography analysis. The results obtained show that the hydrothermal stability of the material had only a secondary role in the fracture. The literature reporting on failures of THR making use of Y-TZP ball heads is discussed.

Stress Concentration Regions in Ceramic Ball Heads for Total Hip Replacement Considering Trauma-Like Loading

A high stress condition in the hip system may cause fracture of the ball head. This failure may appear after a heavy accident such as sudden fall. The aim of this investigation is to make a computer simulated model of the hip system to evaluate the regions of stress concentration as well as the pressure in the stem-ball junction. 3D Non-Linear Finite Element Analyses were performed taking into consideration a high peak load to simulate trauma conditions. Ball heads from 22 to 36 mm in diameter were modeled, and also two sizes for taper lock were simulated to report their influence on the stresses over the critical areas of the ball head. Two different materials of common ball head ceramics (Alumina and Zirconia) were considered to evaluate its relation to the stresses produced. It was found that the ball head cone’s depth has major incidence in the stress concentration surrounding the stem when an impact load is applied, and that a deeper cone may offer a more relieved loading configuration when considering stress related parameters such as Von Mises stress, contact pressure and friction stress.

Improvement of the reliability of ceramic hip joint implants

The aim of this article is to present the optimization of a proof test procedure of ceramic hip joint ball heads. The proof test rejects defective samples in the production line before being implanted into human body. Thereby on every ceramic ball head a static load is applied, which is somewhat higher than the maximum physiological load. The magnitude of the applied load should not damage the samples which are free of flaws in the high stress area. The configuration of the proof test influences the stress distribution in the ball head, which should be similar to the physiological case. To determine the stress distribution, a non-linear finite element (FE) analysis was performed and the results were validated by measurements. With an iterative approach based on FE calculations the proof test configuration was optimized in such a way that the stress distribution in the ball head is similar to the stress distribution in vivo. In this study all ball heads showed very high fatigue resistance after being proof tested and fulfilled the requirements of the FDA ( Food and Drug Administration, USA) described in the Guidance Document for the Preparation of Premarket Notifications for Ceramic Ball Hip System. The probability of a fracture of an implanted ceramic ball head can be decreased by the presented optimized proof test procedure. Latter can thus improve the reliability of ceramic hip joint ball heads. The study was supported by the KTI ( Commission for Technology and Innovation, Switzerland).

Mixed oxides prosthetic ceramic ball heads. Part 3: effect of the ZrO 2 fraction on the wear of ceramic on ceramic hip joint prostheses. A long-term in vitro wear study

Using ceramic materials it is possible to obtain a number of beneficial mechanical properties such as considerable hardness, good chemical resistance, high tensile strength, and a good fracture toughness. The use of ceramic-on-ceramic as bearing surfaces for hip joint prostheses has been reported to produce a lower wear rate than other combinations (i.e. metal-on-polyethylene and ceramic-on-polyethylene) in total hip artroplasty. These advantages may increase the life expectancy of hip implants and improve the life of patients. Two new types of mixed-oxide ceramics (alumina and yttria-stabilised zirconia) femoral heads and acetabular cups containing different ratios of alumina and zirconia were compared with pure commercial alumina in terms of wear behaviour in a hip joint simulator. Hip joint wear simulator studies were carried out with a full-peak load of 2030 N and a frequency of 1 Hz in bovine calf serum. After 10 million cycles the measured weight loss of all specimens was very low. However, the experimental results did not show any significant difference between the new experimental mixed-oxide ceramics prototype and the commercial ceramic material couplings.

Alumina ceramic bearings for hip endoprostheses: the Austrian experiences.

The current authors review clinical and retrieval experiences with hemispheric monolithic alumina ceramic sockets (Group 1), implanted between 1976 and 1979, and similar modular titanium sockets with alumina ceramic inlays (Group 2), implanted between 1990 and 1995. Both cementless sockets articulated with alumina ceramic femoral ball heads for total hip joint replacements. Clinical followup of patients with hemispheric monolithic alumina ceramic sockets (Group 1, 138 sockets) resulted in a total failure rate of 19.6% after 5 to 20 years. Radiologic analysis of eight stable sockets showed migration of 0.2 mm to 2.89 mm, but in four sockets at risk for late aseptic failure after an average followup of 12.5 years as much as 13.4 mm of migration was seen. Histologic evaluation revealed pseudosynovial membranes as thick as 1 mm with fine birefringent wear particles within mononuclear macrophages around two stable retrieved sockets. The membranes around four loose sockets were 6 to 10 mm thick and also heavily loaded with larger alumina wear particles. After 7 years followup clinical analysis of patients with modular titanium sockets with alumina ceramic inlays (Group 2, 30 sockets) resulted in four revisions, compared with one revision of 50 identical sockets (control group) with polyethylene instead of alumina ceramic inlays. Wear particle analyses in scanning electron microscopy showed significantly more particles (x 10(9) +/- standard deviation/g dry tissue) from the control group (4.26+/-6.38), compared with alumina ceramic bearings of Group 1 (0.70+/-0.79), and of Group 2 (1.62+/-2.13). The alumina particle sizes ranged between 0.13 and 78.38 microm. The mean annual linear wear of 38.8 microm was calculated for the bearings in Group 1, and of 26.94 microm for bearings in Group 2. These results support the good tribologic and biologic performance of alumina ceramic bearings for total hip arthroplasty.

Mixed-oxides prosthetic ceramic ball heads. Part 2: effect of the ZrO2 fraction on the wear of ceramic on ceramic joints.

Three different types of mixed-oxides ceramic ball heads have been investigated for their wear behaviour against acetabular cups of the same materials in a hip joint simulator. Mixed-oxides ceramics have been indicated in literature as a promising compromise between strength and wear but no reports are available on the influence of a percentage of zirconia in a ceramic femoral head when sliding against itself. Mixed-oxides ceramic acetabular cups and femoral heads were tested on a simulator apparatus with a sinusoidal load in presence of bovine calf serum. The experimental results did not show any significant difference between the experimental and commercial ceramic material couplings. These results were found to be in accord with those developed in Part 1.

Mixed oxides prosthetic ceramic ball heads. Part 1: effect of the ZrO 2 fraction on the wear of ceramic on polyethylene joints

Although mixed oxides ceramics have been indicated in the literature as a promising compromise between strength and wear, to the authors’ knowledge no reports are available on the influence of the percentage of zirconia in ceramic femoral heads when sliding against polyethylene cups. Two types of mixed oxides ceramic ball heads (alumina plus, respectively, 60 and 80% of zirconia) were compared to pure zirconia and pure alumina heads in terms of wear behaviour against UHMWPE in a hip joint simulator. Polyethylene cups and ceramic femoral heads were fixed on a simulator apparatus with a sinusoidal movement and load in presence of bovine calf serum. The experimental results did not show significant difference between the two experimental ceramic materials or in comparison with pure materials. Considering that all specimens, regardless of the material, had the same level of surface roughness, this roughness factor seems to have a more relevant role than the mix of oxides used to manufacture the ceramic head. Wear tests are conducted on materials used in prosthetic hip implants in order to obtain quality control and to acquire further knowledge of the tribological processes that involve joint prostheses, therefore reducing the risk of implant failure of innovative prostheses.

Reliability of ceramic components for total hip endoprostheses

AbstractThe material and component requirements for ceramic femoral ball heads in total hip replacement systems are described and briefly discussed. Reliability is correlated to the homogeneity of the material in terms of microstructure and Weibull modulus, and to the design of the components. Stress distribution can be analysed by finite element analysis. Based on controlled and specialised processing and the stress analysis data the design can be optimised. Proof testing, as part of final inspection, is an efficient method for eliminating components having strengths at the low end of the strength distribution spectrum.

Friction in hip-joint prostheses and its influence on the fixation of the artificial head.

The head of an implanted hip joint endoprosthesis is exposed to torques, which are transferred during gait due to the friction between the head and the cup prosthesis. In prostheses with ceramic ball heads, which are widely used now, and in which the head is fixed onto the stem by conical clamping, these torques could possibly affect the connection. In this study, torques transferred from the cup to the head are compared to the torques which are required to loosen the head from the metallic spigot. The results show that for the investigated head and taper types and sizes, under normal conditions the connection is safe with respect to undesired rotation. However, it is shown that for polluted sliding surfaces the fixation strength could possibly be exceeded.

Clinical wear behaviour of ultra-high molecular weight polyethylene cups paired with metal and ceramic ball heads in comparison to metal-on-metal pairings of hip joint replacements.

In the course of 30 years of hip endoprosthetics, a number of material combinations for the cups and balls of total hip prostheses have proven successful under clinical conditions. Favourably priced hip prostheses with polyethylene cups and metal balls are available for older patients with a moderate range of activity. Polyethylene wear of 100-300 microns/year is to be expected with these models. Ceramic balls (aluminium oxide for diameters 32 and 28 mm and zirconium oxide for 22 mm) paired with polyethylene cups are recommended for patients with a life expectancy of 10 to 20 years, because the expected polyethylene wear rate with this material combination is only 50-150 microns/year. In other words, the life cycle of the polyethylene cup is doubled, when it is paired with a ceramic ball. A similar polyethylene wear rate is also to be expected with oxygen-deep-hardened TiAlNb metal balls, which are currently the subject of a clinical field study. Last but not least, CoCrMoC metal-metal and Al2O3 ceramic ceramic pairings, which have the lowest wear rate of 2-20 microns/year, are available for highly active patients with a life expectancy of more than 20 years. As far as the cup-ball pairing is concerned and under the current pressure of costs, the surgeon should be able to select the optimum hip prosthesis model for every patient from these three categories.

The colour of medical-grade zirconia (Y-TZP)

Optical spectroscopy, ESR spectroscopy, and standard and wavelength- and-temperature-resolved thermoluminenscence spectroscopy of as-sintered and γ-irradiated medical-grade yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) material showed that the pronounced colour change, after irradiation, from off-white to a purplish-grey shade can be related to two electronic transitions at local defects in the crystal lattice. The first transition could be associated with an electron-hole state characterized by an oxygen ion trapped in the vicinity of a yttrium ion (Y'ZrO*) and can be correlated with an optical absorption band at 2.6 eV (480 nm). The second transition is presumably an extrinsic defect correlated with an optical absorption band at 3.2 eV (395 nm). From the experimental results it can be concluded that those local electronic defects responsible for the colour change on γ-irradiation do not influence safety-related mechanical or chemical properties of the ceramic femoral ball heads of hip endoprostheses produced from Y-TZP.

Development in medical-grade alumina during the past two decades

Medical-grade alumina (Al 2O 3) ceramic has been used in various clinical applications for the past two decades. The primary applications have been in orthopedic and dental implants. The most successful application is the femoral ball head for hip endoprostheses. Up to May 1993 more than 2 million heads have been used worldwide. The following topics will be discussed: Properties and design of ceramic femoral ball heads for total hip replacement (THR), safety factors, standards and government regulations, and future development.

Implant materials for hip endoprostheses: old proofs and new trends.

To judge the significance of a hip joint replacement, the clinical results over 10-20 years must be evaluated. Today, still over half of all hip endoprostheses involves cement fixation. The rest is uncemented, in direct contact with bone. Total hip prostheses with polyethylene cups are equipped either with cobalt-, iron-, surface-hardened titanium-based metal or Al2O3 ceramic ball heads. The pairing Al2O3/Al2O3 and CoCrMoC metal/metal for cups and balls are extremely wear resistant. Most of the cementless cups have spherical or conical cobalt- or titanium-based metal shells with inserts made of polyethylene or CoCrMoC metal. For the fixation stems, high-strength iron-, cobalt- or titanium-based wrought metals are preferred. A taper spigot connection between metallic or ceramic ball heads and stems allows a modular design of hip joint replacements. We have learnt much from the mistakes of the last 40 years in hip endoprosthetics, and there is no excuse to repeat them again.

Increasing the safety of ceramic femoral heads for hip prostheses

Since 1974 Biolox ceramic femoral ball heads have been used successfully for artificial modular hip joints. The revision rate due to ball head fracture is lower than 0.02%. This is an extremely low value. In this article it is shown how the safety of a ceramic ball head can be improved using the procedures of HIPing, engraving by laser technique, and 100% proof testing. By applying these means the materials properties density, grain size, grain size distribution, and the strength of the ball head, i.e. the fracture load can be improved significantly.