Among the many complications that lead to revision surgery of a Total Hip Replacement, aseptic loosening is still the most frequent one. Taking into account the role of wear debris in the event cascade leading to aseptic loosening, many different technical approaches have been developed thus far to minimize the volume of wear debris from THR bearings. Taking into account the role of material hardness in the wear of the system, a considerable effort has been devoted e.g. to improve by irradiation the polymeric chains crosslinking in UHMWPE, to optimise the distribution of carbides in Cobalt-Chromium alloys, to increase the hardness of different metallic alloys by the formation of hard ceramic layers by chemical or physic treatments.

Nevertheless, it is noted that the wear behaviour of ceramic bearings made out pure alpha-alumina remained unsurpassed thus far, and that it is a reference for THR bearing wear since 38 years of clinical use.

Today, hip replacement has become a rather frequent treatment that has been extended to many young and active patient. This has made more challenging the design of implants and of bearings because of the extension of the lifespan of the replacements and of the higher activity level they have to face. Moreover, the appropriate selection of the bearing couple is becoming more and more relevant, as it is noted that a relevant number of implant are operating in off-normal conditions. These are including verticalized sockets, presence of third bodies in the bearing gap, microseparation of the bearing components during the gait cycle, joint sub-luxations and impingemets due to patient activity either to ligament laxity. In these of-normal conditions not all the bearings perform in the same way, giving rise to conditions that may give rise to acute or chronic complications, in some cases of still unknown consequences e.g. surface layer spallation or delamination – leading to UHMWPE catastrophic wear, or sustained increase of Cr, Co, Ni ions in the body.

In Ceramic-on-Ceramic bearings a typical complication is stripe wear, that has been documented in pure alpha-alumina in case of verticalized sockets either following the repeated shocks due to joint microseparation. Other complication specific to ceramic are the fractures of the components due to severe traumas (like e.g. in road accidents) either inlay chipping that may take place intraoperatively.

To overcome these limits, the favourable properties of zirconia have been exploited to improve strength and toughness of alumina in a composite material, reinforced further by platelets nucleated in-situ during sintering. The mechanical properties of the new Alumina Matrix Composite (AMC) are superior to the ones of both alumina and of yttria-stabilized zirconia, without the handicap of Low Temperature Degradation (LTD) due to hydrothermal reactions with the biologic environment. Nevertheless, this do not mean that the material has unlimited performances, and care is demanded in its use especially in devices more challenging in design.

Design and materials selection and optimisation are the-factors affecting the performance of the modern TKR. In this study new surface treatments were performed and investigated on CoCrMo with the goal to minimize the wear in a new total knee prosthesis design.

Three surface finishing treatments were considered and applied to cast CoCrMo alloy specimens. A surface polishing treatment performed by mass finishing technique was applied on machined CoCrMo. ACoCrMo coating, obtained by Magnetron Sputtering Physical Vapour Deposition (PVD) technique, was applied on mass finished CoCrMo specimens. Conventional hand polishing performed by silicon carbide papers followed by a final diamond past polishing was considered as reference material. For this study not cross-linked not sterilized UHMWPE was used. Surface morphology obtained by the surface treatments was investigated by SEM, Atomic Force Microscopy, and non contact laser profilometry. The microstructure and micro-hardness of CoCrMo alloy was investigated as well. Wear tests were performed in bovine serum using two screening wear test machines. A final wear test was performed on the new knee pros-thesis design using a knee wear simulator, up to five millions cycles.

CoCrMo PVD coating performed on CoCrMo substrate was capable to eliminate and to fill all the surface defects originated by the casting process of the CoCrMo alloy. Such surface defects could not be eliminated by hand polishing or mass finishing process alone. Vickers micro-hardness was improved by the mass finishing treatment. Although the roughness measured on the mass finished specimens was not the lowest, screening wear test produced for them the best results. Wear simulator test performed on the mass finished knee femoral prostheses sliding against UHMWPE, confirmed very low UHMWPE wear generation.

The mass finishing surface treatment applied to cast CoCrMo alloy specimens and femoral components is capable to polish the surface to the level required by standards. The PVD coating investigated was capable to improve the surface morphology of the alloy and to eliminate all the surface micro defects. Nevertheless, the screening wear tests indicated that the mass finishing treatment generate the lowest wear. The results were confirmed by wear simulator test. This study indicated that the mass finishing surface treatment can be effectively applied for the polishing of the femoral components of knee prosthesis.

The choice to use alumina in the manufacture of a low-wear THR bearing made by Boutin and its co-workers has proven its effectiveness in almost 35 years of clinical use. A continuous development process aimed to improve mechanical properties led to today’s materials that exhibit extreme high reliability.

The recent introduction in clinical use of alumina matrix composites represents the latest evolution of alumina that thanks to high hardness, toughness, and bending strength allow to manufacture new design of ceramic components. Composites obtained introducing zirconia in the alumina matrix, known as Zirconia Toughened Alumina (ZTA) are candidate for use in THA bearings from a long time. A real breakthrough was represented by alumina ceramics toughened both by zirconia both by platelets nucleated in-situ during sintering (Zirconia-Platelet Toughened Alumina - ZPTA).

The chemical composition and the microstructure of ZPTA were optimised to achieve a ceramic material joining strength of more than 1200MPa, Vickers hardness 1975, fracture toughness of 6,5 MPa m-1/2, andextremely low wear also in the most severe simulator tests performed in microseparation mode The paper reviews the improvements introduced in the technology of ceramic for arthoplasty, and their effects on the microstructural properties and on the performances of the past and actual generation of ceramic for THR bearings, and summarise the results obtained in the development of alumina matrix composites.

The extension of THR to younger and more demanding patients implies the need of bearings enhancing the implants survival, raising the interest on hard-on-hard bearings (metal-on-metal and ceramic-on-ceramic). The standard bearing diameters in THR range from 7/8in (22,225 mm) to 32 mm. Larger diameter bearings were used by McKee-Farrar and Ring THR a solution that was abandoned after the success of Charnley Low Friction Arthroplasty that offered the advantage of much lower torques at the implant-bone interface, due also to the state-of-the-art of the cementation in the early 1960s. Increasing the diameter of THR bearings offers several advantages in terms of increased stability of the joint, as a larger displacement is necessary to produce the joint subluxation, and for a given neck diameter the risk of impingement is reduced while the prosthesis range of motion is increased. The reduced wear of metal-on-metal and ceramic-on-ceramic bearings has led recently to revitalise the design concept of the early THR designs, and large diameter joints today are available in sizes ranging from 36 to 52 mm. Large metal-on-metal bearings are used mostly in resurfacing prostheses. This surgery, which requires a specific surgical training, is indicated for patients performing physical activity, as those patients are relatively young, and have a long life expectation. This raises-some concerns, as increased cobalt and chromium concentrations were measured in the blood and urine of patients having Metal on Metal bearings and the effect of such high metal concentration in the long time is still unknown, as it is controversial if the metal ions are originated by wear debris of by the corrosion of the implant. Recently 36 mm ceramic on ceramic bearings were introduced in THR as a solutions to overcome many of the problems of metal-on-metal joints. Ceramic-on-ceramic bearings have a 35-year clinical history in THR. The extremely low wear of these joints is well assessed , as well as the extreme biocompatibil-ity of the material and the absence of local and systemic negative reaction to ceramic debris. Besides the enhanced safety of the design of the 36 mm heads, the development of thin ceramic inserts allowed to limit the overall diameter of the cup. It is expected that the use of the new alumina matrix composites will allow to further enhance the performances of large diameter ceramic THR bearings.

Aim. Ceramic-ceramic coupling is currently used in Orthopaedics in younger patients with longer life expectance, for the high biocompatibility of these materials. More recently new ceramic materials have been developed with better mechanical properties in comparison to Alumina, as the Alumina Matrix Composites by Transformation Toughened and in situ Plateled Reinforcement (ZPTA). The aim of the study was to analyze the biological properties of this material in comparison to Alumina and Zirconia. Materials and methods. Cylinders of different ceramic materials were inserted into surgical created defect of proximal metaepiphysis of New Zealand White adult rabbits to analyze the bone response to ceramics. Percentage of bone ceramic contact was measured. Massive inflammatory response was analyzed by intraarticullar injection of powders of different materials; while chronic low grade response as the one observed in long term well functioning implants was tested by implantation of low cohesive ceramic pellets under patellar tendons of rabbits: thank to leg movements few particles were released in time. Systemic host response was tested analyzing peripheral organs of animals. Results. Connective tissue was present at bone ceramic interface whatever materials used: no statically differences were observed in term of bone ceramic contact among Alumina, Zirconia and ZPTA. Inflammatory response with new vessels was observed around powders, especially with small diameter; while low cohesive pellets did not elicited inflammatory response neither systemic toxicity. Discussion and conclusion. Our results confirm that Alumina Matrix Composites by Transformation Toughened and in situ Plateled Reinforcement, as well as Alumina and Zirconia ceramics, induces a low inflammatory reaction in periprosthetic tissues without any systemic toxicity, due to massive or chronic release. So thank to its higher mechanical properties than Alumina and Zirconia, it should be indicated for ceramic to ceramic coupling in Orthopaedic Surgery.

Aims: Yttria-stabilised Zirconia (Y-TZP) ball heads were introduced into the market in 1985. Since then these components have had wide diffusion in hip replacements, due to their good mechanical performance and reliability. Namely, only a few papers were published up to now reporting failures of Y-TZP ball heads. The worldwide recall in August 2001 of some Y-TZP batches changed this situation. The recall was due to an high number of fractures, that were somehow linked to the spontaneous phase transition in Y-TZP. The revision surgery of a zirconia head belonging to the batches in above that fractured 34 months after implant gave us the opportunity to retrieve the fragments for analysis, and to draw some conclusions about the cascade of events that led to the ball head fracture.

Methods: The retrieved specimens were submitted to visual inspection by optical microscopy to analyze the fracture pattern, then selected samples were cut and analysed by FEG-SEM equipped with backscattered CEN-TAURUSA8 detector. Specimen were analysed without any coating. Grain size were measured by SEM-coupled computerized image analysis on thermally etched samples. Phase composition was investigated by XRD. Density was determined by the Archimedes’ method. Periprosthetic tissue membrane collected at revision surgery was observed by light and Scanning Electron Microscopy coupled with EDAX.

Results: XRD showed that maximum of about 60% monoclinic phase was present in the inner cone near the chamfer, while in the outer polished surface only 3% monoclinic phase was present. SEM demonstrated that the zone near to the surface of the taper, in the core of the ball head, consisted of an inhomogeneous structure formed by dense agglomerates of Y-TZP grains, about 10 mm in diameter, within a matrix of lower density. A crack network originated from the above mentioned inhomogeneous zone, and extended through the outer part of the sample which consists of well densified material. Histologic sections showed the presence of many metal particles in a poor in vessels stroma; ceramic appeared as polygonal shape granules of different dimension, ranging from 2 to 10 B5m.

Conclusions: The Authors demonstrated that the likely initiator of the failure is to be sought in subcritical crack growth of the defects due the uncontrolled densification during sintering, enhanced by the wet environment and by cyclic loading. The hydrothermal stability of the material had only a secondary role in the fracture.

Aims: PMMA is currently used as grouting agent of arthroprostheses and for filling of bone cavities after bone curettage. It is moreover used as a carrier of antibiotics in the local treatment of bone infections and it has been proposed as a carrier of antiblastic drugs in the local treatment of bone metastases. The aim of this study is to analyse the biological properties and compressive strenght of PMMA-Methotrexate mixture to be used for the local treatment of bone metastases.

Methods: Cylinders of PMMA containing Methotrexate in different concentrations were manufactured according to ASTM F-451. Cylinders of PMMA were used as control. The porosity of the cylinders was characterised by SEM. Drug elution rate in saline solution was measured by HPLC. The biological activity of Methotrexate was analysed on human breast cancer cells using MTT test at different time (from 5 minutes to 30 days). Compressive tests was performed in conformity to ASTM F-451 on PMMA- Methotrexate samples and control as-made and after 30 days of aging in saline

Results: SEM analysis showed the presence of granules of Methotrexate on the surface of as-made cylinders that can be readily released from PMMA cylinders. The release occurred in large amount within 24 hours after immersion. We observed a relative release rate is more sustained in samples containing the drug in lower concentration. Also the biological activity was time dependent: cell death decreased progressively from 60% at 24 hours to 10% at 30 days.

Compressive tests showed no statistical differences between PMMA cylinders containing Methotrexate and controls before and after aging in saline.

Conclusions: The results show that PMMA-Metho-trexate may be considered an interesting option in the treatment of bone metastases because cement allows mechanical resistance after bone curettage or resection and Methotrexate improves locally anticancer activity.

Zirconia has considered a good material for manufacturing of ball heads in total hip replacement due to high mechanical properties of this ceramic material. However in the literature the problem of heads biocompatibility is still debated. The Authors reported their experience in ten years of research on the biological properties of this material. In vitro tests were performed onto materials in form of powders, analyzing the inhibitory effects on human lymphocyte mitogenesis, and in form of plates measuring adhesion and spreading of 3T3 fibroblasts. A mutagenic test was also performed. In vivo tests were performed by injection of powders in mice and evaluating the survival of animals according to ASTM F – 750. We also inserted ceramic in form of cylinders into proximal tibial metaphysis of NZW rabbits and analysed local and systemic reaction due to material diffusion. We also developed a system of production of Zirconia particles by inserting ceramics under patellar tendon of NZW rabbits.

In vitro tests showed that Zirconia powders and plates induced a similar effect of Alumina ones; no mutagenic effect were observed using our samples, demonstrating that Zirconia has no carginogenic effects. In any case the diffusion of particles didn’t show modifications into internal organs (lung, kidney, liver, spleen) of mice and rabbits. In time (one year after operation) the connective tissue present at bone ceramic interface is transformed into lamellar bone.

Our experience demonstrates that Zirconia may be considered a good material for prosthetic implants.