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Biomedical subjects

G Willmann

Publications and source records attributed to G Willmann.

At least 37 records · Page 2Linked to original sources
PubMed1997

[Ceramic cups for hip endoprostheses. 3: On the problem of osseointegration of monolithic cups].

The combination of ceramic with ceramic offers the option of minimising wear and the need for revision in total hip replacement. At first, uncemented monolithic ceramic sockets were implanted. Some of these did not prove successful. The prerequisites for fixation of an implant by bony integration are discussed i.e. the structural and surface compatibility of an implant. The reasons for the high revision rate associated with monolithic ceramic sockets are discussed. Using monolithic ceramic sockets only contact osteogenesis can in principle be achieved, which does not suffice for good long-term fixation. In many cases, soft tissue can be found at the ceramic socket/bone interface, and the ceramic sockets may as a result migrate and penetrate, creating conditions that elevate the rate of wear to unacceptable levels.

Biomechanical Phenomena↗
PubMed1996

Wear characteristics of sliding pairs of zirconia (Y-TZP) for hip endoprostheses.

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.

Aluminum↗
PubMed1996

[Ceramic acetabulum cup inserts for hip endoprostheses].

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.

Acetabulum↗
PubMed1996

[Design considerations for improving the acetabular cup of the ESKA hip endoprosthesis by using the ceramic/ceramic wear couple].

Since 1987, cementless THR acetabular components with coarsely reticulate surfaces (S&G, ESKA) have been implanted in the Department of Orthopaedic Surgery of the Alfried Krupp Hospital in Essen. By 31st December 1995, 590 of these components had been implanted. Follow-up of the first 51 of these completely cement free THRs revealed loosening in an only single case (2%). Despite these good medium-term results, however, it must be expected that over a ten-year period, the life of the THR will decrease, the probable reason being increasing debris caused by polyethylene (PE) wear leading to aseptic loosening. An alternative to the PE/ceramic system of opposing materials would be ceramic/ceramic. Experience to date has shown that the biological inertness of ceramic does not allow ingrowth and bony integration to take place. Against this background an acetabular component employing a metal backing with the 3-dimensional reticulate surface mentioned above and a Biolox ceramic cup insert articulating with a Biolox ceramic femoral head was designed. The result is a cement free modular THR with optimal bony integration properties and articulating surfaces. To investigate the superiority of this new concept, a comparative study involving two groups of 50 patients each, one group receiving the PE/ceramic system, the other the new ceramic/ceramic system, has been initiated.

Acetabulum↗
PubMed1996

[Ceramic acetabulum components for hip endoprostheses. 2: Evaluating design and safety].

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.

Acetabulum↗
PubMed1995

[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.

Ceramics↗
PubMed1995

[Materials for hip endoprostheses--alternatives to standard materials].

A review of current clinically applied biomaterials for the femoral heads and acetabular cups of total hip prostheses (UHMWPE, CoCrMo alloys, alumina and zirkonium) in terms of their resistance to wear is presented. Further developments in metallic and ceramic materials over the last few years have now left UHMWPE as the weakest link in the prosthesis material chain. Alternative materials aimed at improving the tribological properties of the femoral head/acetabular head system are presented. New surface hardening and coating techniques for titanium alloys, polymer coatings, optimized UHMWPE, as well as various carbon-fibre-reinforced synthetic materials are described. The advantages, disadvantages and prospects of these materials are compared with those of standard materials and documented in experimental and clinical studies.

Biocompatible Materials↗
PubMed1995

[A new port catheter system of aluminum oxide ceramics].

Implantable port catheter systems are becoming increasingly important, as they often permit out-patient treatment for many indications that would otherwise require hospitalization. Moreover, they also increase the safety/reliability of infusion therapy in critical inpatients. For a variety of reasons, the materials used so far, i.e. steel, titanium and various plastics have not been completely satisfactory. The main disadvantage of metallic systems is the formation of artefacts in tomographic images, while the shortcomings of plastics are mechanical, e.g. chip formation and early membrane failure. Against this background, a port catheter system made of alumina ceramic, which is largely free of the disadvantages of the other materials, was developed. The expected advantages in terms of complication rate and radiological artefacts, were fully confirmed by the evaluation of 160 monitored patients.

Aluminum Oxide↗
PubMed1995

[Osseointegration of titanium test bodies of different surface properties in metaphyseal bone sites of the dog--a biomechanical and histological analysis].

The alternative to the anchoring of an endoprosthesis by means of cement is the biological fixation by an ingrowth of bone into the implant surface (osseointegration). We examined the implant fixation properties of titanium experimental devices with 3 different surface structures after press-fit implantation into the bony bed of 12 dogs. One third of the 48 implants had a micro-structured surface roughened by grit-blasting, one third a roughened surface with an additional macro-groove structure (combination surface), and the remaining third a porous hydroxyapatite (HA) coating. Twelve weeks after implantation the bony ingrowth was evaluated biomechanically by measuring the force required to pull out the implant from the surrounding bone and histologically by morphometric assessment of microradiographs. In the pull-out-experiment the shearing forces were significantly lower (p < 0.01) in the devices with a roughened surface in comparison to the devices with a micro- and macro-structured surface and the HA surface. Thus, there was no significant difference between the forces required to pull out the devices with the porous HA surface and those with the combination surface. The histomorphometric assessment of bone density in the immediate vicinity of the implant and the extent of the direct contact surface of the bone implant resulted in no significant difference in all 3 groups. We did not find an interposing layer of fibrous tissue at the interface. We can demonstrate that roughening of the surface in combination with a groove structure creates a better bond between implant and bone than a roughening alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

[20 years aluminum oxide ceramics for medical applications].

For the past 20 years, femoral heads have been successfully employed for modular total hip prostheses. To date, some 2 million ceramic femoral heads have been implanted, mainly in Europe, but also in North America and Japan. The majority of these are BIOLOX heads having a diameter of 28 mm and with the so-called European taper 12/14. The most important properties and the arguments in favour of using alumina ceramic for total hip prostheses are outlined, and safety aspects discussed. Some secondary requirements for these systems with ceramic cups or cup inserts, which are now meeting with increased interest, are considered.

Aluminum Oxide↗
PubMed1993

[Fretting in modular design implant systems].

Fretting is a problem of load-bearing implants (hip, knee) especially when modular in design and employing different materials. In contrast, fretting has not yet been observed in dental implants. In the case of ceramic femoral heads and cups (e.g. BIOLOX) no problems with fretting have so far been reported. The state-of-the-art is discussed and assessed.

Biomechanical Phenomena↗
PubMed1991

[Fracture load of ceramic ball heads of hip joint prostheses].

To ensure the stability of ceramic ball heads of hip joint prostheses over the long term, both standards for the material and FDA-regulations for the components have been established. In this paper the philosophy underlying design and reliability is discussed. On the basis of fracture loads determined for Biolox ball heads the high level of stability and reliability that has been achieved and can now be guaranteed, is demonstrated.

Aluminum Oxide↗
PubMed1990

[The color of implants of aluminum oxide ceramics].

Ceramic implants are manufactured from aluminium oxide ceramics (Al2O3) doped with magnesium oxide (MgO). The yellow or brown discoloration following gamma-sterilization does not constitute a material defect, but rather a property of the material. This chromic effect is explained in the following article.

Aluminum Oxide↗