Ceramic Ball Heads Research Articles

Microstructure and Defect-Based Fatigue Mechanism Evaluation of Brazed Coaxial Ti/Al2O3 Joints for Enhanced Endoprosthesis Design.

Alumina-based ceramic hip endoprosthesis heads have excellent tribological properties, such as low wear rates. However, stress peaks can occur at the point of contact with the prosthesis stem, increasing the probability of fracture. This risk should be minimized, especially for younger and active patients. Metal elevations at the stem taper after revision surgery without removal of a well-fixed stem are also known to increase the risk of fracture. A solution that also eliminates the need for an adapter sleeve could be a fixed titanium insert in the ceramic ball head, which would be suitable as a damping element to reduce the occurrence of stress peaks. A viable method for producing such a permanent titanium–ceramic joint is brazing. Therefore, a brazing method was developed for coaxial samples, and two modifications were made to the ceramic surface to braze a joint that could withstand high cyclic loading. This cyclic loading was applied in multiple amplitude tests in a self-developed test setup, followed by fractographic studies. Computed tomography and microstructural analyses—such as energy dispersive X-ray spectroscopy—were also used to characterize the process–structure–property relationships. It was found that the cyclic loading capacity can be significantly increased by modification of the surface structure of the ceramic.

Alumina, Zirconia and Their Composite Ceramics with Properties Tailored for Medical Applications

Although in 1977 the first ceramic composite material had been introduced into the market, it was a long time before composite materials were qualified for medical applications. For a long period high purity alumina ceramics have been used as ball-heads and cups. Because of their brittleness, in 1986 yttria stabilized zirconia has been introduced into this application, because of higher strength and fracture toughness. However, due to its hydrothermal instability this material disappeared in orthopaedic applications in 2000. Meanwhile a composite materials based on an alumina matrix with dispersed metastable tetragonal zirconia particles and in-situ formed hexagonal platelets became the standard material for ceramic ball-heads, because of their excellent mechanical strength, hardness and improved fracture toughness. Especially fracture toughness can be improved further by special material formulations and tailored microstructure. It has been shown that a mixed stabilisation of zirconia by yttria and ceria with dispersed alumina and hexagonal platelets overcomes the hydrothermal instability and excellent materials properties can be achieved. Such materials do have big potential to be used in dental applications. Furthermore, these materials also can be seen as a new generation for ball-heads, because of their enhanced fracture toughness. All materials are described within these articles. In order to achieve the required properties of the materials, special raw materials are required. Therefore, it is quite important to understand and know the raw material manufacturing procedures.

THE CERAMIC MODULAR HEAD IMPROVEMENT IN THE DESIGN OF A TOTAL HIP REPLACEMENT

For the first time, a design of a modular ceramic ball head of a total hip joint replacement (THR) friction pair has been developed, which has the properties of a metal in conjunction with the stem neck and the properties of a ceramics on bearing surface of the pair. This is achieved by creating a low-cost, low-toxic, durable fixed connection of the head made of alumina or zirconia ceramics and the titanium-based alloy sleeve to obtain a brazed joint that is efficient in human synovial fluid. With the help of finite element analysis, a quantitative assessment of the strength and rigidity of the proposed head design was performed and its use in modern hip arthroplasty was indicated. The approbation of the proposed design solutions for creating a THR ceramic head with a titanium-based alloy sleeve brazed was carried out.

Influence of Different Damage Patterns of the Stem Taper on Fixation and Fracture Strength of Ceramic Ball Heads for Total Hip Replacement.

Background Modularity finds frequent application in total hip replacement, allowing a preferable individual configuration and a simplified revision by retaining the femoral stem and replacing the prosthetic head. However, micromotions within the interface between the head and the stem taper can arise, resulting in the release of wear debris and corrosion products. The aim of our experimental study was to evaluate the influence of different taper damages on the fixation and fracture stability of ceramic femoral heads, after static and dynamic implant loading. Methods Ceramic ball heads (36 mm diameter) and 12/14 stem tapers made of titanium with various mild damage patterns (intact, scratched, and truncated) were tested. The heads were assembled on the taper with a quasistatic load of 2 kN and separated into a static and a dynamic group afterwards. The dynamic group (n = 18) was loaded over 1.5 million gait cycles in a hip wear simulator (ISO 14242-1). In contrast, the static group (n = 18) was not mechanically loaded after assembly. To determine the taper stability, all heads of the dynamic and static groups were either pulled off (ASTM 2009) or turned off (ISO 7206-16). A head fracture test (ISO 7206-10) was also performed. Subsequent to the fixation stability tests, the taper surface was visually evaluated in terms of any signs of wear or corrosion after the dynamic loading. Results In 10 of the 18 cases, discoloration of the taper was determined after the dynamic loading and subsequent cleaning, indicating the first signs of corrosion. Pull-off forces as well as turn-off moments were increased between 23% and 54% after the dynamic loading compared to the unloaded tapers. No significant influence of taper damage was determined in terms of taper fixation strength. However, the taper damage led to a decrease in fracture strength by approximately 20% (scratched) and 40% (truncated), respectively. Conclusion The results suggest that careful handling and accurate manufacturing of the stem taper are crucial for the ceramic head fracture strength, even though a mild damage showed no significant influence on taper stability. Moreover, our data indicate that a further seating of the prosthetic head may occur during daily activities, when the resulting hip force increases the assembly load.

Incidence of Modern Alumina Ceramic and Alumina Matrix Composite Femoral Head Failures in Nearly 6 Million Hip Implants

BackgroundBecause of improvements in ceramic materials and manufacturing, the incidence of ceramic failures has decreased over time. Recent concerns with corrosion have contributed to an increase in ceramic ball head utilization. The purpose of this study is to report the incidence of modern alumina bearing failures from a single major ceramic manufacturer in nearly 6 million hip implants and to identify trends in the modes of failure of these implants. MethodsBeginning in the year 2000, CeramTec AG (Plochingen, Germany) began a comprehensive program for reporting and gathering failure data on its products. From January 1, 2000, to December 31, 2013, over 3.2 million pure alumina (PA) and 2.78 million alumina matrix composite (AMC) ceramic ball heads were implanted worldwide. During this period, there were 672 PA and 28 AMC femoral head fractures. The fractures were analyzed with respect to time to failure, head size, and implant factors. ResultsThe incidence of clinical fractures of modern PA femoral heads and AMC femoral heads was 1 in 5000 (0.0201%) and 1 in 100,000 (0.0010%), respectively (P < .0001). The majority of implant failures (80%) occurred within 48 months following surgery (P < .01). Fractures were usually associated with specific events such as trauma, mismatched components, and dislocations. Large-diameter PA heads were associated with a lower rate of fracture compared to smaller-diameter femoral heads (0.0316% for 28-mm heads vs 0.0080% for heads 32 mm or greater [P < .01]). Similar trends were observed with AMC heads. The neck lengths of the femoral ball heads were also a factor: a short-taper 28-mm ball head was more likely to fracture compared to other neck lengths (P < .01). ConclusionModern PA ceramic heads are reliable with extremely low risk of fracture. The reliability is even better with AMC heads.

Are asymmetric metal markings on the cone surface of ceramic femoral heads an indication of entrapped debris?

BackgroundThe probability of in vivo failure of ceramic hip joint implants is very low (0.004-0.05%). In addition to material flaws and overloading, improper handling during implantation can induce fractures of the ceramic ball head in the long term. Identifying the causes of an in vivo fracture contributes to improved understanding and potentially to further reduction of the fracture probability for patients. Asymmetric metal markings on the cone surface of in vivo ball head fractures have been reported. The question, therefore, is whether asymmetric loading is the sole cause or whether additional factors, specifically contamination entrapped in the taper fit, also contribute or are even the main cause.MethodsThe influence of the asymmetric physiological load configuration on resulting metal markings in the cone surface of an alumina femoral ball head with and without biological contaminants was investigated. Static and cyclic tests on ball heads were carried out in a load configuration of 0° (axisymmetric) and 40° in a physiological environment. The analysis of the metal marking was carried out to gain a better understanding of the processes that contribute to the generation of metal marking. Fractography was carried out to determine the fracture initiation of failed ball heads.ResultsDifferent types and sizes of residuals entrapped in the conical surface are shown to yield strongly asymmetric metal marking patterns. All heads tested without contaminants exhibited an almost homogenous distribution of residual metal markings around the circumference of the ceramic cone surface at the proximal end of the bore hole. The failure of ball heads that contained entrapped contaminants revealed a common fracture pattern. The site of fracture initiation on two of the failed heads was in the entrance region of the bore hole on the superior half of the head.ConclusionAsymmetric metal markings observed on the ball heads tested in this investigation are most probably caused by the presence of contaminants entrapped in the taper fit. Homogenous metal mark distributions around the circumference indicate proper assembly of the ball head without entrapped contaminants. It should, however, be noted that different taper designs may possibly result in different marking patterns.

Low aseptic loosening and revision rate in Zweymüller-Plus total hip arthroplasty with ceramic-on-ceramic bearings

A recent comparative study reported lower revision rate and higher survival in ceramic-on-ceramic (CoC) than in metal-on-metal (MoM) coupling in Zweymüller-Plus THA. We retrospectively studied 87 consecutive patients (94 hips), who primarily received Zweymüller-Plus THA (SL-Plus stem, ceramic 28-mm ball head, Bicon cup) with third-generation CoC bearing surfaces for osteoarthritis. Survival, revision and osteolysis rate were studied and compared to those observed in historical series from this institution with the same THA and MoM articulation. The mean ± SD follow-up was 7.4 ± 1.7 years (range 6-10 years). Four hips (4%) in four patients were revised 1-6 years following primary implantation: one (1%) for aseptic loosening of SL-Plus stem and Bicon 5 years after index surgery; one (1%) for malpositioning of the Bicon and recurrent dislocations 1 year following implantation; and two (2%) for septic loosening 1 and 6 years postoperatively. Intraoperatively on inspection, there were neither findings for impingement in the revised hips, nor fracture of the Bicon ceramic inlay and ball head. Expansile osteolysis was shown around SL-Plus stem and Bicon in the revised for aseptic loosening hip. With revision of any component for aseptic loosening as the endpoint, the survival was 99% (95% CI 91-100%), while for revision for any reason, it was 95% (95% CI 87-98%) at 10 years. Zweymüller-Plus THA with CoC bearings showed, at mid-term follow-up, high survival and low revision rate for aseptic loosening. These rates were better than the historical series of the same THA with MoM articulation performed by the same surgeon. Level IV.

A comparison of polyethylene wear between cobalt-chrome ball heads and alumina ball heads after total hip arthroplasty: a 10-year follow-up

Study designThis is a retrospective study comparing polyethylene wear between ceramic ball heads and metal ball heads in total hip arthroplasty.BackgroundThe ceramic-on-polyethylene bearing option has been introduced as an alternative to metal-on-polyethylene to minimize polyethylene wear debris and reduce subsequent osteolysis and aseptic loosening. However, the reported data were debatable. We designed this retrospective study to compare polyethylene wear between alumina ceramic ball heads and cobalt-chrome ball heads.MethodsBilateral simultaneous primary total hip arthroplasty was performed in 22 patients between January 2002 and December 2002, with one side using metal-on-polyethylene bearing surface and the other side using alumina ceramic-on-polyethylene bearing surface. After 10 years of follow-up, the wear rate of polyethylene liner on both sides was measured using the Dorr method and compared.ResultsThe annual wear rate of the polyethylene liner was 0.133 mm with a standard deviation of 0.045 in the metal-on-polyethylene group and 0.056 mm with a standard deviation of 0.032 in the ceramic-on-polyethylene group. The wear rate per year was significantly lower in the ceramic-on-polyethylene group (p < 0.001).ConclusionsAlthough the implication is still controversial, our study showed that the use of ceramic head lowered the liner wear rate.Clinical relevanceCeramic is harder and more resistant to scratching than cobalt-chrome. By increasing polyethylene liner survivorship and decreasing potential osteolytic response and aseptic loosening, ceramic head is a better alternative than cobalt-chrome head.

What an Orthopedic Surgeon Should Know: Selection of a Bearing Couple in Case of Revision After a Fractured Ceramic Component

Revision surgery for fractured ceramic components in total hip arthroplasty (THA) potentially leaves small ceramic fragments in the joint capsule, and the fragments might become embedded in polyethylene (PE) acetabular liners. The purpose of this study was to determine the wear behavior of metal femoral ball heads and ceramic femoral ball heads tested with highly cross-linked and conventional polyethylene liners in the presence of ceramic debris. A worst-case scenario, assuming embedding of ceramic fragments in the PE liner, contamination of the test environment with third-body ceramic debris and continuous subluxation, was simulated in vitro. High wear rates were found for metal femoral ball heads, being 1,010 times higher when compared to ceramic femoral ball heads tested with XPE liners and 560 times higher when compared to ceramic femoral ball heads tested with PE liners. The test results indicate the use of ceramic femoral ball heads for revision surgery in the presence of ceramic fragments.

Bearing Surface Choice: A European Experience

The choice of bearing surfaces in Europe is subject to several factors such as marketing system and support, expenditure on health and reimbursement, age and activity level, different medical education and tradition. Our study shows an inhomogenous situation concerning the distribution of bearing surfaces in Europe. Our evaluation revealed that in Scandinavian countries, modular crosslinked PE inserts in combination with modular metal ball heads are dominant. In Central Europe, modular crosslinked and ceramic inserts combined with modular ceramic ball heads are favored. Countries like UK, Ireland, Spain, Portugal, Czech. Rep. and Poland mainly use modular standard and crosslinked PE inserts paired with modular metal ball heads. In our view we see a rising trend for advanced bearings, which means that more ceramic or crosslinked inserts paired with ceramic ball heads would be used in total hip replacement in Europe.

Fretting Corrosion and Trunnion Wear—Is it Also a Problem for Sleeved Ceramic Heads?

Some modular bearing systems with large diameter metal-on-metal articulation have exhibited higher than usual revisions due to corrosion and metal debris originating from modular metal connections. Large diameter ceramic-on-ceramic bearings exist, which use a titanium alloy adapter sleeve for fixing the ceramic ball head to the stem taper. This study addresses the issue of taper fretting and corrosion for large ceramic bearings with standard and a newly designed experimental setup. While large metal diameter heads have been shown to be a cause for failure of THA, our results demonstrate that large ceramic heads even with a metal adapter sleeve have no effect on corrosion of modular taper connections.

Early Results of Revision Hip Arthroplasty Using a Ceramic Revision Ball Head

In the case of a ceramic fracture or cup revision with exchange of the ceramic ball head on a used stem, there is always the danger of another ceramic fracture when using a standard ceramic ball head owing to a possibly damaged stem taper. The purpose of this study was to analyze the results of revision hip arthroplasty using a new ceramic revision ball head. Ninety-one patients, who underwent revision hip arthroplasty using a ceramic revision ball head, were analyzed clinically. The Harris hip score and visual analog scale score increased significantly. There were no further ceramic fractures or noises. Especially, in cases with a damaged taper or ceramic fracture, surgeons should consider using a ceramic revision ball head in combination with a ceramic or a polyethylene insert.

Ceramic Versus Metal Femoral Heads in Combination With Polyethylene Cups: Long-Term Wear Analysis at 20 Years

Bearing surfaces are an important implant-related factor in the process of wear and resulting osteolysis. Especially, polyethylene (PE) wear is known to be a major reason for aseptic loosening of the acetabular and femoral components in total hip replacement (THR). In the past, several studies showed the advantages of ceramic femoral ball heads compared with metal ball heads with respect to the resulting PE wear. In this framework, we posed the question whether ceramic and metal ball heads still resulted in similar clinical outcome regarding PE wear after 20-year follow-up. Additionally, we investigated whether wear and osteolysis were correlated within these groups and compared our findings with results from appropriate publications. In this prospective study, 93 nonselected, consecutive uncemented hip arthroplasties were performed in 80 patients with use of the titanium-coated Robert Mathys (RM) cup and the cementless Spotorno stem. Eighty ceramic and 13 metal femoral heads with a diameter of 32 mm were used. The mean age of the patients was 52 years. The average follow-up was 19.3 years. No patient was lost for follow-up. The metal group showed a mean wear rate of 0.190 mm/year, whereas the ceramic group had 0.107 mm/year ( P = 0.025). The rate of revision cases was clearly higher within the CoCrMo group showing 6 revisions in 13 cases (46.2%) compared with 11 in 80 cases (13.8%) within the ceramic group. Wear rates were positively correlated to femoral head material ( P = 0.025), stem osteolysis ( P = 0.003), cup osteolysis ( P = 0.011), cup revision ( P = 0.041), and cup inclination ( P = 0.012). This long-term study shows that during a period of 20 years, ceramic ball heads generate less linear PE wear compared with metal ball heads, thus causing significantly less osteolysis and revisions of either component.

Influence of various types of damage on the fracture strength of ceramic femoral heads

Ceramic-on-ceramic articulations are a frequently used bearing for total hip replacements. This success mainly is due to their excellent tribological properties. Ceramics can withstand high pressure loads due to its brittleness but only low bending stresses. A ceramic ball head fracture is the result of subcritical crack growth. This kind of fracture in vivo can abet by damage or contamination of the stem cone. The main goal of this work is to provide a risk assessment of different possible damage mechanisms and contaminations that may result in lower fracture strength of a ceramic ball head. To simulate potential causes, different types and dimensions of metal wire, foils, hair, and lubricants were inserted between the ceramic ball head and the metal cone of the stem. The test results clearly show that fracture strength is negatively influenced by most of the inhomogeneities between the cone and the head because they increase the peak stresses acting on a part of the ceramic ball head. The results of this article clearly confirm the demand for an undamaged taper fit "free of contamination" between the ceramic head and the metal cone during implantation.

S-37 In-Vivo like Testing of Ceramic Ball Heads

Alumina (Al2O3) bearings in total hip arthroplasty lead to low wear rates, but catastrophic failure of Al2O3 femoral heads, while rare, remains a concern. In the present work, a composite of Al2O3 and niobium (Nb) was tested in vitro for potential use as an alternative femoral head material in vivo. Dense composite laminates of Al2O3 and Nb were fabricated by hot pressing, and their microstructure and mechanical properties were evaluated. The flexural strength of Al2O3–Nb laminates in four-point loading was 720 ± 40 MPa, compared with a value of 460 ± 110 MPa for Al2O3. Scanning electron microscopy and X-ray diffraction showed a well-bonded interface between the Al2O3 and Nb without measurable formation of an interfacial reaction phase. The interfacial shear strength between Al2O3 and Nb, measured by a double-notched specimen test, was 290 ± 15 MPa. The feasibility of fabricating prototype femoral heads (32 mm in diameter), consisting of an Al2O3 surface layer (2–3 mm thick) and a Nb core, by hot pressing was shown. The composite femoral head combined the low wear of an Al2O3 articulating surface with the safety of a ductile metal femoral head.

Proof testing of ceramic femoral heads for hip joint implants

A proof test procedure for the rejection of defective ceramic hip ball heads in the production line is presented. The procedure consists of applying a load to each ceramic ball head. This load, being somewhat higher than the maximum physiological load, should not cause any damage in cases where the highly stressed areas are free of flaws. In this procedure, a polymer ring is positioned inside the ball head bore between a socket and the head of a tie bolt. Once the tie bolt is pulled downwards, the ring creates a radial pressure on the inner bore surface of the ball head. With an iterative approach based on finite element analysis, the proof test design was optimized in order to obtain a stress distribution in the ball head similar to that resulting in in vivo conditions. The calculated results were validated by strain gauge measurements performed on an assembled proof test apparatus. Several polymers were considered for the ring. Ultrahigh-molecular-weight polyethylene (UHMWPE grade RCH 1000) showed the best durability properties and lowest wear rates. The requirement to perform 1000 reruns without significant reduction of stress in the ball head was fulfilled. Although other proof test procedures for ceramic femoral heads already exist, the procedure presented in this article shows advantages concerning maintenance and operating costs.

Optimization of the stress distribution in ceramic femoral heads by means of finite element methods

Ceramic ball heads for total hip replacement are highly loaded in vivo and must meet the sternest requirements concerning strength and safety. High stresses inside the ball head originate from the press fit between the conical stem (made of titanium alloy or steel) and the borehole of the ball. The aim of this study was the development of an optimized contour at the fillet inside the ball head by means of numerical methods, in order to reduce local stress concentrations. The computer-aided optimization method was applied on the customary engineering fillet radius to reduce local stress peaks. The local notch stress of the examined ball head design was reduced by up to 27 per cent for the relevant load cases. Verification by rupture testing of prototypes turned out to be difficult for axisymmetric load cases, since the static fracture load is governed by the hoop stresses in the contact area of the taper (global maximum), thus making it difficult to prove a local improvement. The sensitivity of the design to asymmetric loading was clearly shown (varying the load angle and bearing type). Stress relocation in the ball-stem interface at higher burst loads indicated the necessity of optimizing each ceramic femoral head design individually (i.e. for different borehole depths).

Failure analysis of in vivo fractured ceramic femoral heads

Ceramics are more and more used for hip joint implants due to their excellent biocompatibility, longevity, corrosion and wear resistance. Despite these excellent material properties, their fracture toughness is low compared to metals. Various studies reported the probability of in vivo fracture occurring on an implanted ceramic femoral head is in the range of 0.004–0.05%. Besides material flaws and overloading, improper handling during implantation may induce fractures of the ceramic ball head on the long term. Even though the exact cause of failure could not be clarified in most of the cases, there is strong suspicion that the presence of biological contaminants may constitute the primary cause of failure. Asymmetric wear traces observed on fragments of in vivo fractured alumina femoral head endorse the assumption that a non-uniform load was introduced in the ball head. This study focuses on the influence of blood and bone chips located in the stem–ball interface and of scratches on the metal tapers on the strength of alumina ball heads. Mechanical tests on 26 samples according to ISO 7206-10 were performed to identify the effect of contaminants and altered taper on the static fracture load. The experimental study showed that relatively small contaminants induce considerable decreases of the static fracture load. A blood drop of 30 mg reduced the fracture load by more than 60% while a bone chip as small as 4 mg reduced it to less than half the reference fracture load. In a third experimental series, the change of fracture load with a 5–10 mm scratch on the stem was found to be in the range of the standard deviation and thus no clear influence could be observed. Since any alteration of the interface between metal taper and ceramic ball head through contaminants yields a non-uniform load introduction leading to a reduction of the static fracture load, an absolute clean interface is of primary importance.

Influence of contaminants in the stem—ball interface on the static fracture load of ceramic hip joint ball heads

The probability of in-vivo failure of ceramic hip joint implants is very low (0.05-0.004 per cent). Besides material flaws and overloading, improper handling during implantation may induce fractures of the ceramic ball head in the long term. This study focuses on the influence of contaminants located in the stem-ball interface and on the use of damaged metal tapers on the strength of ceramic ball heads. Mechanical tests on alumina ball heads according to the standard ISO 7206-10 were performed to identify their effect on the static fracture load. A decrease of up to 90 per cent with respect to the reference static fracture load was found when contaminants such as bone chips, soft tissue, or blood were present. Reductions of 57 per cent and 27 per cent were observed for deformed stem cross-sections (from circular to elliptical) and for flattened stems respectively, making deformed stems another influential parameter. Since any alteration of the interface between the metal taper and the ceramic ball head yields a nonuniform load introduction and hence results in stress concentrations, its presence has to be avoided.

Interchangeability of the ceramic ball heads of various endoprosthesis systems. Technical report

Today, the type of hip joint prosthesis implanted is usually chosen on the basis of the patient's age and anatomic conditions, and in particular depending on whether it is a first or second hip replacement. Not infrequently, it is desirable or necessary to combine different prosthesis systems, especially when changing prostheses. In many cases this is possible. The ceramic ball heads of different systems are also interchangeable, provided certain criteria (e.g., manufacturer) are satisfied.