ABSTRACT
Proof testing is an overload test used for high demand materials that must have 100% of the components tested to sort out those components with possible internal flaws. The relationship of high proof loads applied short-term, low service load, and service time of proof tested components is shown. Proof testing is now technically and clinically validated. Ceramic femoral heads that have been proof tested have been used clinically for 4 years and a significant reduction of the failure rate from 0.015% to 0.004% has resulted. However, component service life is critical and has to be protected in unison with the prosthesis manufacturer and the hospital. Because ceramics are rigid, joining of ceramic components with metals requires special attention. Specifications of the tapers and/or connection surfaces have to be appropriate to the needs of the ceramic and the manufacturer of ceramic components and the prosthesis manufacturer must adhere to strict specifications and inspection techniques. In the surgical area, training in the proper use of ceramics is a key factor to the successful performance of ceramic components.
Subject(s)
Ceramics , Hip Prosthesis , Materials Testing , Humans , Stress, MechanicalABSTRACT
We studied the wear of state-of-the-art alumina/alumina total hip joints with the uniaxial five-station, and the three-axis single-station hip joint simulators of Helsinki University of Technology. The diameters of the joints were 26, 28 and 32 mm. Visual examination and weighing of the components showed no wear. Scanning electron microscopy showed that (a) the wear marks were slight, consisting of removal of grains, multidirectional grooving and mild abrasion, (b) the wear mechanisms were similar to those seen in components removed from patients, and (c) there was no marked difference in the specimens worn in the uniaxial vs. three-axis simulator. The coefficient of friction was measured throughout the 5 million cycle wear test with the three-axis simulator. The average value was 0.007. We conclude that alumina/alumina joints had low wear and friction under the present test conditions. The results are promising, since minimal wear is one of the prerequisites for long-term success in prosthetic joints.
Subject(s)
Aluminum Oxide/standards , Hip Prosthesis/standards , Biomechanical Phenomena , Equipment Failure Analysis , Friction , Humans , Materials Testing , Microscopy, Electron, Scanning , Prosthesis DesignABSTRACT
Femoral ball heads of aluminium oxide or zirconium oxide ceramics are used for total hip replacement. This application is based on their attractive tribological properties. Standard and state-of-the-art are femoral ball heads made of alumina (Al2O3) articulating against acetabular cups of polyethylene (PE-UHMW) and zirconia (Y-TZP) heads articulating against polyethylene cups. A very attractive wear couple is ceramic-on-ceramic. Some of the various ceramic combinations have been tested using the ring-on-disc method according to ISO 6474. The combination alumina/alumina was found to produce extremely low wear; catastrophic wear was found for the combinations alumina/Y-TZP and Y-TZP/Y-TZP.
Subject(s)
Ceramics , Hip Prosthesis , Aluminum Oxide , Humans , In Vitro Techniques , Materials Testing , Microscopy, Electron, Scanning , Prosthesis Failure , Surface Properties , ZirconiumABSTRACT
Femoral ball heads made of aluminium or zirconium oxide ceramics are used for total hip replacement. This application is based on their attractive tribological properties. Standard and state-of-the-art with good wear properties are femoral ball heads made of alumina (Al2O3) articulating against polyethylene (PE-UHMW) acetabular cups (since 1974) and zirconia (Y-TZP) heads articulating against polyethylene cups (since 1986). The best tribological combinations are alumina heads articulating against alumina cups. Zirconia has better mechanical properties (for example, bending strength or fracture toughness) than alumina. Therefore R&D is going on to design zirconia acetabular cups. The wear characteristics of zirconia (Y-TZP) articulating against itself were investigated using a ring-on-disc testing device according to ISO 6474. The high wear rate emphasized that medical-grade zirconia (Y-TZP according to ISO/ DIS 13356) should not be used for acetabular cups.
Subject(s)
Hip Prosthesis , Zirconium , Aluminum , Biocompatible Materials , Femur , Humans , Microscopy, Electron, ScanningABSTRACT
In the field of hip arthroplasty, there is a clearly recognizable towards the use of modular acetabular cups involving metal-backed sockets into which cup inserts made of either polyethylene or alumina ceramic (Biolox forte) can be fitted. The design aspects for this concept have already been discussed in [17]. In the present paper, we discuss the question of component reliability and the criteria for testing acetabular cups with ceramic inserts. To date, neither standards nor government regulations for ceramic cups are available. In the absence of such regulations, those laid down bei the American Food and Drug Administration (FDA), together with our own longterm experience with femoral ceramic heads are used as a guide for the testing of ceramic cup inserts.
Subject(s)
Acetabulum , Ceramics , Hip Prosthesis , Biomechanical Phenomena , Equipment Safety , Humans , Prosthesis Design , Prosthesis Failure , Weight-Bearing/physiologyABSTRACT
The articulating components of a total hip prosthesis are the spherical femoral head and the acetabular cup. Particularly high rates of wear are seen with cups made of polyethylene, and the abrasion particles cause osteolysis, which often makes surgical revision necessary. Despite considerable progress in the development of total hip replacement systems over the last 20 years, there is still a need to eliminate or further minimize the problem of osteolysis, which is also referred to as polyethylene disease. Clinical experience over the last 20 years has shown that by using Biolox (medical grade alumina) femoral heads and acetabular cups it is possible to achieve very low wear rates, which histological studies have shown to be readily tolerated. The secondary conditions needed to develop modern modular ceramic acetabular cup inserts are discussed. For the fixation of cup inserts, the well known taper fixation concept has proved to be of value. A concept taking into account the needs of the surgeon and the manufacturing constraints applying to ceramic materials is proposed.
Subject(s)
Acetabulum , Ceramics , Hip Prosthesis , Polyethylenes , Humans , Prosthesis Design , Prosthesis FailureABSTRACT
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.
