Alumina ceramic femoral heads

Owing to an extraordinary amount of research performed, today there exist a large variety of clinical options to combine femoral heads and acetabular cups. In Europe these medical products are being marketed under the brand names BIOLOX and BIOLOX forte by CeramTec AG (Plochingen, Germany) (Clarke and Willmann, 1994 Willmann, 2002) and BIONIT by Mathys European Orthopaedics (Bettlach, Switzerland). In 2000, the market volume of ceramic femoral heads amounted to about 30 Mio DM corresponding to 90 000 pieces, 90% of which were made from alumina (see Chapter 2). 

The reliability of ceramic femoral heads is closely related to their mechanical properties. Previously, measurement of the load to fracture of 107 explanted alumina (Biolox ) femoral ball heads did not reveal any fatigue of the material (Willmann, 1998). This can be related to the very favorable relationship between... 

Femoral ball heads of hip endoprostheses made from bioinert ceramics such as alumina or zirconia have to sustain high mechanical stresses, resorp-tion/corrosion by aggressive body fluid and abrasive wear over the lifetime of the implant in the human body of 15-20years. Some important properties of ceramic femoral ball heads are listed in Table 2.3 (Willmann, 1995). Mechanical properties of alumina and zirconia are discussed in Chapter 4.1. 

For about 40 years, chemically very pure, extremely fine-grained polycrystalline alumina ceramics have been used to fashion femoral heads of hip endoprostheses (Boutin, 1972,1981). 

Table 4.1 further shows essential mechanical properties of several products of CeramTec s BIOLOX family of alumina-based materials for femoral heads of hip endoprostheses as well as those of BIONIT manufactured by Mathys Orthopadie GmbH (Bettlach, Switzerland). It is evident that decreasing the grain size of the ceramic precursor powders increases both the flexural strength and the fracture toughness of the material dramatically. 

The mechanical performance of femoral heads and acetabular cups made from alumina have been the subject of intense research and development effort as it is crucial for the longevity of the endoprosthetic hip implant. Hence, the failure probability of these ceramic construction parts has been investigated and expressed by the Weibull probability density function. As safe design of... 

The application of ceramic materials in hip arthroplasty has its origins in Europe and Japan. Pierre Boutin, in collaboration with Ceraver, Inc., from France, first reported on the clinical results of COC hip arthroplasty in 1971 and 1972. In 1977, Shikata in Japan introduced the concept of using alumina femoral heads with UHMWPE acetabular components. 

The 2001 recall has not, however, dampened the general enthusiasm for ceramic materials in orthopedics. Alumina is currently the ceramic material of choice for orthopedic applications, either for articulations with UHMWPE or for use in COC alternate bearings. Starting at the end of 2002, a new alumina composite material (BIOLOX Forte CeramTec, Plochingen, Germany) has been available as a femoral head material (Merkert 2003). This ceramic composite, consisting of 75% alumina matrix, is reinforced by 25% zirconia. The improved strength of this new ceramic composite, in comparison with alumina and zirconia, is summarized in Table 6.2. Clinical studies are still needed to determine the effectiveness and reliability of this new biomaterial. 

Arising from the chemical stability and high surface finish and accurate dimensions, there is a very low friction torque between the alumina femoral heads and the acetabular cup, leading to a low wear rate. Combinations of ceramic head/UHMWPE cup and ceramic head/ceramic cup were tested and compared to the metal head/UHMWPE cup. The wear resistance of the ceramic head/UHMWPE cup combination over metal/UHMWPE has improved from 1.3 to 34 times in the laboratory and from three to four times clinically (27,28). No alumina wear particles from retrieved ceramic/UHMWPE were found, whereas UHMWPE wear particles from microns to millimetres in size were found in the retrieved... 

Starting in lune 2000, a new alumina matrix nanocomposite material (BIOLOX Delta, CeramTec, Plochingen, Germany) has been available as a femoral head material [101]. This ceramic biomaterial is now broadly used across the orthopedic industry in both femoral heads and acetabular liners. According to the manufacturer, more than 320,000 femoral heads and 160,000 acetabular inserts have been implanted on a worldwide basis as of 2008 [106]. The primary advantage of this alumina matrix composite is its increased strength, fracture toughness, and wear resistance relative to alumina (Table 6.2) [112]. 

FIGURE 6.19 Comparison of a ceramic revision femoral head fabricated from zirconia-toughened alumina (ZTA) with primary ceramic heads. The revision head has a metal sleeve to regenerate die trunnion of a femoral stem, which may become damaged in vivo. 

Zirconia initially enjoyed a low overall failure rate, similar to alumina, until the events of 2001 forced St. Gobain Desmarquest to suspend its international sales of orthopedic ceramic products. For example, in one of the groups of recalled zirconia femoral heads, a total of 227 in vivo fractures were reported for a series of 683 manufactured heads, corresponding to a fracture rate of 33%, according to the data made pubhcly available by St. Gobain [151],... 

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