[Polyethylene as an implant material]. / Polyethylen als Implantatwerkstoff.

Since the early 1960s, ultrahigh-molecular weight polyethylene (UHMWPE) has been one of the most frequently and successfully used materials in total joint replacement. However, in the course of clinical usage, various weaknesses of the material became apparent including wear and aging properties. As a result of research on this polymer, several improvements in the quality of the raw material, the processing, and the sterilization have been introduced. These changes paired with an improved knowledge of the viscoelastic behavior of UHMWPE have led to an improved design of the components to meet the requirements of the given material characteristics and in turn to better clinical results. In the 1990s, investigations focused on the influence of radiation on the molecular structures of polyethylene. Gamma radiation treatment in air leads to an important decrease in the molecular weight with reduced tribological behavior and accelerated aging. In contrast, a nitrogen atmosphere during irradiation and storage can improve the linkage of the polyethylene and promote the positive effects of radiation treatment. This effect can be further intensified by increased radiation levels. Such highly cross-linked polyethylenes demonstrate extremely low wear rates in vitro;however, other material properties are also changed. First reports on fissures in highly cross-linked polyethylene explants demonstrate that only long-term clinical trials can allow a final verdict on the clinical potential of highly cross-linked polyethylenes.

Metal-on-metal articulation for artificial hip joints: laboratory study and clinical results.

As wear is inevitable with artificial joint replacement, it has to be minimized to avoid possible aseptic loosening following osteolysis due to particle-initiated foreign body reaction. Co-Cr-Mo-C alloys have a long history with only minimum wear when articulating with themselves. This investigation shows that the choice of the alloy has an effect on the wear rate of this articulation couple. Tribological studies in a screening device, a pendulum apparatus and a hip joint simulator showed a marked influence of the environment as well as the diameter of the implants with metal-on-metal articulation. A wear-resistant combination with low friction characteristics has been developed by using a wrought Co-Cr-Mo-C alloy and reducing the implant diameter to 28 mm. Clinical wear rates are comparable with laboratory data and demonstrate the potential of the metal-on-metal articulation to solve the problem of wear-induced osteolysis of hip joint endoprostheses.

[UHMW-polyethylene as the substance for articulating components of joint prostheses]. / UHMW-Polyethylen als Werkstoff für artikulierende Komponenten von Gelenkendoprothesen.

In recent years there has been an increase in the incidence of problems with UHMWPE used in implants. In particular the risk of osteolysis and loosening resulting from the body's reactions to polyethylene wear particles must be eliminated. A variety of investigations with UHMWPE provided hints on how to improve the quality of the original material, machining and reduction of contaminants, which have since been implemented. The knowledge gained of the visco-elastic behaviour of this polymer makes it possible to optimize the design of implant components. The need to sterilize the component parts with ionizing radiation results in changes in the structure of UHMWPE. Via oxidation and acceleration of the ageing process of the material, irradiation in air reduces the molecular weight, which is important for the tribological properties. The use of a nitrogen atmosphere during irradiation and for storage makes it possible to take advantage of the positive effects of this method of sterilization via cross-linking of the polyethylene. Positive ductile properties are thus maintained and the resistance to wear is increased. An investigation of 134 components explanted during re-operation revealed a wide scatter in the results of wear. One of the reasons for increased polyethylene wear is the additional abrasive effect of particles of bone cement that get into the space between the articulating components; this can be minimized by a meticulous cementing technique.

Total hip joint replacement using a CoCrMo metal-metal sliding pairing.

Late loosening in total hip replacement is explained by a foreign body reaction of the connective tissue along the bone-implant interface due to polyethylene debris. In contrast, metal-metal prostheses of the McKee type implanted in the sixties, may still work perfectly today without any signs of osteolysis along the bone-cement interface, proving that metal-metal pairing is superior to prostheses with polyethylene cups and proving also that cement anchorage may be adequate for fixation. A new metal-metal total hip joint is presented, that has been implanted 90 times between 1988 and 1991.

[Exposure of surgical/orthopedic operating room personnel to monomer vapors during the use of bone cements--review of the literature and report of experiences]. / Exposition des chirurgischen/orthopädischen OP-Personals durch Monomer-Dämpfe bei der Anwendung von Knochenzementen--Literaturstudie und Erfahrungsbericht.

PMMA bone cements are used for the fixation of artificial joint replacements. During their application in the operating theater, a small amount of the monomer evaporates. Operating room staff and surgeons are often not adequately informed about the negative properties and the effects on health of these vapours. Basic information about monomers and their toxicity, and safety regulations have been compiled. On the basis of present knowledge, the authors do not regard the repeated use of bone cement throughout the course of a day to represent a hazard to health.

Joint replacement components made of hot-forged and surface-treated Ti-6Al-7Nb alloy.

We have developed a titanium-aluminium alloy with the inert alloying element niobium. The optimal composition was found to be Ti-6Al-7Nb (Protasul-100). This custom-made alloy designed for implants shows the same alpha/beta structure as Ti-6Al-4V and exhibits equally good mechanical properties. The corrosion resistance of Ti-6Al-7Nb in sodium chloride solution is equivalent to that of pure titanium and Ti-6Al-4V. This is due to a very dense and stable passive layer. Highly stressed anchorage stems of different hip prosthesis designs have been made from hot-forged Ti-6Al-7Nb. The polished surfaces of hip, knee and wrist joints made of Ti-6Al-7Nb and articulating against polyethylene are surface-treated by means of a very hard and 3-5 microns thick titanium nitride coating (Tribosul-TiN) or by oxygen diffusion hardening (Tribosul-ODH) to a depth of 30 microns.

Total Hip Joint Replacement Using a CoCrMo Metal-Metal-Sliding Pairing.

Late loosening in total-hip replacement is explained by a foreign body reaction of the connective tissue along the bone-implant interface due to polyethylene debris. In contrast, metal-metal prostheses of the McKee type implanted in the sixties, may still work perfectly today without any signs of osteolysis along the bone-cement interface, providing that metal-metal pairing is superior to prostheses with polyethylene cups and providing also that cement anchorage may be adequate for fixation. A new metal-metal total hip joint is presented, that has been implanted 62 times between 1988 and 1990. Key words: total hip replacement, metal-metal pairing.

[Joint prostheses components of warm-forged and surface treated Ti-6Al-7Nb alloy]. / Gelenkprothesen-Komponenten aus warmgeschmiedeter und oberflächenbehandelter Ti-6Al-7Nb-Legierung.

In 1978 development of a TiAl alloy with the inert alloying element niobium was initiated. In 1984, the optimal composition was found to be Ti-6Al-7Nb (Protasul-100). This custom-made alloy for implants has the same alpha/beta micro-structure and equally good mechanical properties as Ti-6Al-4V. The corrosion resistance of Ti-6Al-7Nb is better than that of pure titanium and Ti-6Al-4V, due to the very dense and stable passive layer. Since 1985, highly stressed anchoring stems of various hip prosthesis designs have been manufactured from hot-forged Ti-6Al-7Nb/Protasul-100. Polished surfaces of hip, knee or wrist joints made of Ti-6Al-7Nb intended to articulate with polyethylene are surface-treated by the application of a very hard, 3-5 microns thick titanium nitride coating (Tribosul-TiN), or by oxygen diffusion hardening (Tribosul-ODH) to a depth of 30 microns.

New surface modification for Ti-6Al-7Nb alloy: oxygen diffusion hardening (ODH).

PVD-TiN coating and N+ implantation of Ti-6Al-7Nb alloy resulted in surface hardening to a depth of less 3 microns. The new oxygen diffusion hardening (ODH) treatment increased the hardness gradually to 50 microns. PUD-TiN showed an improvement in the tribological properties, while N+ implantation increased the PE wear rate. The wear rate of the ultrahigh-molecular-weight as well as the friction coefficient were reduced to one-half of the values achieved with the combination of CoCrMo-alloy when paired against the ODH-treated surface. In pairing with ZrO2-containing bone cement the ODH-treated surface showed only a minimal reaction.

[The wear behavior of capsules and heads of CoCrMo casts in long-term implanted all-metal hip prostheses]. / Verschleissverhalten von Pfannen und Kugeln aus CoCrMo-Gusslegierung bei langzeitig implantierten Ganzmetall-Hüftprothesen.

We conducted an investigation on total hip prostheses with cups and balls made of cast CoCrMo alloy that were implanted 10-20 years ago; our results showed that this metal/metal alloy showed very low wear and tear. In comparison, the polyethylen/metal alloy showed a 40 times higher wear in the polyethylene part. Based on these promising long-term clinical results, the metal/metal alloy is again of great interest for total hip prostheses.