Use of ceramic bearings in hip arthroplasty: correct implantation and review of clinical and radiographic results.

Ceramic materials are widely used in hip prosthetic surgery. Faced with important developments in the design and characteristics of the materials, ceramic-on-ceramic (CoC) are today the bearings in Total Hip Replacement (THR) showing the minimal wear rate. Moreover, ceramic wear debris demonstrated the absence of local and systemic toxicity. This makes ceramic bearing particularly suitable for active patients, whatever their age. The results show excellent survival rates of THRs with ceramic components and excellent clinical and radiographic scores with follow-up close to 20 years. However, the excellent outcomes of THRs with ceramic bearings are depending on appropriate and correctly performed surgical technique.

Ceramic Total Knee Arthroplasty: Ready to Go?

Total knee arthroplasty (TKA) is a well-established surgical procedure in the late stages of knee osteoarthritis. Nevertheless, this procedure is associated with a percentage of unsatisfactory results and biomechanical failures, with aseptic loosening being the most common cause of revision. Beside these problems, cutaneous and systemic hypersensitivity reactions to metals have arisen as an increasing concern after joint arthroplasties, even if allergies against implant materials are still a quite rare and not well-known problem. Ceramic composites have been recently used in prosthetic components, showing minimum wear and excellent long-term results in total hip replacement, due to their high resistance to scratching and their better wettability with respect to cobalt-chromium alloy. Furthermore, the biologic response to debris generated from these bearings is less aggressive. Knee joint simulator tests and clinical results demonstrate promising results of TKAs with ceramic components that should led to benefit for the patients.

Fabrication, characterization and cell cultures on a novel composite chitosan-nano-hydroxyapatite scaffold.

This paper deals with the characterizations made during the development of a nano-HAp loaded chitosan scaffold, obtained by the freeze-drying technique combined with a novel in situ crystal growth method. The nano-composites were characterized by a highly porous and interconnected structure. The XRD patterns and calculated domain sizes of the HAp nano-crystals nucleated on the chitosan scaffolds are very similar to the ones recorded for deproteinated bone apatite. Both osteoblasts (MG63) and mesenchimal cells (hMSC) were showing good proliferation and adhesion onto the scaffolds. The presence of extensive filopodia and excellent spreading in and around the interconnected porous structure, indicated a strong cellular adhesion and growth. Moreover a good hMSC osteogenic differentiation has been verified. The observations related to well-developed structure morphology, physicochemical properties and high cytocompatibility suggest that the obtained chitosan-nHA porous scaffolds are potential candidate materials for bone regeneration.

An original method for the evaluation of in vivo controlled release of the ceramic materials.

In recent years, the use of ceramic materials in orthopaedics and dentistry is becoming increasingly popular. However, it is important to know their biological and mechanical properties to optimize their use. The aim of this study is to describe a specific method to assess in vivo the effects of chronic release of ceramic materials implanted, in relation also to the type of material, pellets or powders. This was achieved by implanting ceramic powders and pellets, formed by low cohesion grains, in the patellar tendon of 48 New Zealand adult rabbits (24 with powders and 24 with pellets). The motion of the joint allowed easily and progressively the release of grains, detached from surface of the pellets and released to the joint space. Animals were sacrificed at different intervals (1, 3, 6, 12 months). Retrieved knee joints underwent X-Ray, histological and ultrastructural analysis.

FEM analysis of RF breast ablation: multiprobe versus cool-tip electrode.

BACKGROUND: Radio-frequency ablation (RFA) has recently received much attention as an effective minimally invasive strategy for the local treatment of tumors. The purpose of this study was to evaluate the efficacy of single-needle cool-tip RF breast ablation in terms of temperature distribution and duration of the procedure as compared to multiprobe RF breast ablation. MATERIALS AND METHODS: Two different commercially available radiofrequency ablation needle electrodes were compared. Finite-element method (FEM) models were developed to simulate the thermoablation procedures. A series of ex vivo radiofrequency thermal lesions were induced to check the response of the FEM calculations. RESULTS: Data obtained from FEM models and from ex vivo procedures showed that cool-tip RF breast ablation assures better performances than multiprobe RF breast ablation in terms of temperature distribution and duration of the procedure. Histopathological analysis of the cool-tip RF thermoablated specimens showed successful induction of coagulation necrosis in the thermoablated specimens. CONCLUSION: Data obtained from FEM models and from ex vivo procedures suggest that the proposed cool-tip RF breast ablation may kill more tumor cells in vivo with a single application than the multiprobe RF breast ablation.

Methotrexate-added acrylic cement: biological and physical properties.

BACKGROUND: Previous reports have demonstrated the suitability of adding different chemotherapeutic drugs to acrylic cement for the treatment of bone metastases. The best results so far have been obtained with methotrexate (MTX) for which diffusion from the implanted cement has been demonstrated both in vitro and in vivo. In this study the suitability of adding MTX to acrylic cement as local adjuvant chemotherapy was investigated. METHODS: Using an in vitro model of human breast cancer cells we demonstrated that the drug is eluted in an active form able to exert a cytotoxic effect over a long period of time. The use of different concentrations of drug on the kinetic of elution and on the mechanical properties of cement was also evaluated. RESULTS: The results obtained suggest that the release of MTX is higher at the beginning and progressively decreases over time being affected by the concentration of drug used. Our results also demonstrated that the addition and the subsequent elution of MTX does not alter the compressive properties of the cement. CONCLUSION: These findings confirm the suitability of MTX-supplemented cement and support its use as an effective aid for the management of bone metastases requiring surgical curettage and acrylic cement implantation for structural support.

Zirconia heads in perspective: a survey of zirconia outcomes in total hip replacement.

Zirconia ball heads have been implanted successfully from the late 1980s, but reports of wear and fractures have raised concerns about this ceramic biomaterial. This paper reviews the literature on clinical wear of zirconia-polyethylene bearings, zirconia head degradation and fractures, analysing the different factors that have led to clinical failure, such as material source, manufacturing process and type of polyethylene. The results underline the need for more homogeneous clinical series. Careful follow-up of patients with zirconia-polyethylene bearings is recommended.

On the fracture of a zirconia ball head.

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 year 2000 reporting failures of Y-TZP ball heads. The worldwide recall in August 2001 of some Y-TZP batches changed this situation. This paper analyse the material of a ceramic ball head that fractured in vivo 34 months after surgery. The retrieved fragments were submitted for visual inspection, fractographic analysis by optical microscopy, X-ray diffractometry, and FEG-SEM ceramography analysis. The results obtained show that the hydrothermal stability of the material had only a secondary role in the fracture. The literature reporting on failures of THR making use of Y-TZP ball heads is discussed.

Fracture of a Y-TZP ceramic femoral head. Analysis of a fault.

We studied factors contributing to the initiation of fracture and failure of a zirconia ceramic femoral head. The materials retrieved during a revision total hip replacement were submitted to either visual, stereomicroscopic and scanning electron microscopy (SEM) or SEM and energy-dispersive X-ray analysis. X-ray diffraction was performed in order to investigate the extent of tetragonal to monoclinic phase transition. Histological examination was performed on the periprosthetic tissues. The results showed that failure was due to the propagation during clinical use of defects which may have been introduced into the material during the processing of the ceramic, rather than those intrinsic to zirconia. The literature relating to previous failures of zirconia components is reviewed.

Alumina and zirconia ceramics in joint replacements.

Ceramic biomaterials have gained widespread use in arthroprostheses joints. Ceramic oxides including alumina as á -corundum Al2 O3 and zirconia, as yttria-stabilised zirconia polycrystals, were used in large number of patients, especially in the manufacture of ball heads for hip replacements. The experience and the feedbacks gathered in more than 30-year clinical use of alumina, and 15-year use of zirconia are reviewed. The results of in vitro and in vivo studies on the biocompatibility of alumina and zirconia ceramics are analyzed as well as the studies on carcinogenicity. (Journal of Applied Biomaterials & Biomechanics 2003; 1: 19-32).

Growth of osteoblast-like cells on porous hydroxyapatite ceramics: an in vitro study.

Blocks of two porous synthetic hydroxyapatites (HA) with porosity fraction of 30-40 and 50-60 vol%, respectively and a coralline derived porous HA were evaluated in vitro in presence of the osteogenic line MC3T3-E1 and of L929 fibroblasts. The two tested biomaterials did not affect cellular proliferation (MTT test), but the contact inhibited alkaline phosphatase activity. Porous aggregates resulted perfectly biocompatible in the tests performed, since observations performed by light microscopy did not show any cell morphological change, osteoblast presented a stellar shape and typical pseudopodes. SEM observations showed intercellular matrix containing fibers on HA-based porous aggregates.

Volumetric determination of the wear of ceramics for hip joints.

Osteolysis relating to the reaction cascade to wear debris is the main cause of the failure of arthroprostheses. New materials are still under development to minimise the wear of joints and to improve in this way the performance of total joint replacements. Testing the wear performance of very low wear materials is a rather sophisticated technique. Currently, the worn volume is calculated from the weight variations of the sample, observed from wear testing. This method may be limited especially when very low weight differences are to be evaluated on high hardness, high-density materials like CoCr alloys or ceramics like alumina or zirconia. In the present work, the tribological behaviour of ceramic biomaterials like alumina, Y-TZP and alumina-zirconia composites was evaluated by a pin-on-disc apparatus under different testing conditions. The worn volume was calculated by the use of 3-D (three-dimensional) optical profilometry data. Comparison between 3-D optical profilometry and gravimetric wear data shows the better accuracy of the profilometric method in the determination of wear rate in the range of 10(-7) mm3 (mN(-1)) or lower.

Histologic and ultrastructural analysis in a case of massive failure of Zirconia ball head.

The in vivo histological and ultrastructural analysis of periprosthetic tissue collected at time of revision surgery for failure of a 28 mm yttria-tetragonal zirconium oxide polycrystal (YTZP) ball head, 2 years after implantation is reported. Histologic analysis showed Zirconia particles, rounded to polygonal ranging from 2m to more than 10m intra or extra cellular in a stroma without vessels with few giant cells. Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) showed the different shape from rounded to polygonal of Zirconia. SEM analysis of the internal part of Zirconia ball head showed the presence of different fracture lines especially in the internal surface (Hip International 2002; 4: 388-93).

Surface analysis of a femoral stem after failed total hip replacement.

We analysed the surface of a Ti alloy femoral stem in a cementless total hip replacement with early failure. A specific protocol consisting of non destructive and destructive tests was used in the evaluation of the retrieved stem. The tests confirmed that implant fretting due to bone abrasion constitutes an early phase of loosening.

Analysis of a failed alumina THR ball head.

The favourable properties, on which is based the successful history of the use of alumina in orthopaedic surgery, are due to the tough control made by manufacturers on the whole process from raw materials purity to the quality controls. The minimum requirements of a medical grade alumina are stated from 1981 in ISO 6474 standard. Nevertheless, due to the voluntary character of standards, and lack of national and international laws, it was possible in the past to introduce into the market materials with characteristics not in compliance with the standard ISO 6474. A THR implanted on a fifty years old patient was revised three years after implantation, due to the failure of the alumina ball head. To understand the causes of such an early failure, the fragments of the retrieved ball head were submitted to a series of non destructive and destructive controls. The results show that the poor quality of the design and manufacture of the implant was the origin of the failure.

In vitro evaluation of the mutagenic and carcinogenic power of high purity zirconia ceramic.

Tetragonal zirconia polycrystal (TZP) is a new interesting ceramic for the manufacture of medical devices. Its wide use in orthopedic and odontoiatric implants was limited till now by the high chemical and radiochemical impurities of the raw materials. Purification processes now available allow to obtain high purity ceramic grade powders suitable for TZP ceramics manufacture, even if their possible mutagenic and transforming effects are still unclear. The aim of this work is to study in vitro the mutagenic and oncogenic effects of a new zirconia ceramic stabilized by yttria (Y-TZP). This ceramic was sintered from high purity powders obtained by a process developed under a project carried out within the Brite EuRam programme. For comparison, ceramics made from unpurified zirconia powder were also tested. Fibroblasts irradiated by a linear accelerator were used as positive control. The results obtained show that Y-TZP ceramic does not elicit either mutagenic or transforming effect on C3H/10T(1/2) (10T(1/2)) cells and demonstrate that ceramic from high purity powders can be considered suitable for biomedical applications from the point of view of the effects of its radioactive impurity content.

Zirconia as a ceramic biomaterial.

Zirconia ceramics have several advantages over other ceramic materials, due to the transformation toughening mechanisms operating in their microstructure that can give to components made out of them, very interesting mechanical properties. The research on the use of zirconia ceramics as biomaterials started about twenty years ago, and now zirconia (Y-YZP) is in clinical use in THR, but developments are in progress for application in other medical devices. Recent developments have concentrated on the chemistry of precursors, in forming and sintering processes, and on surface finish of components. Today's main applications of zirconia ceramics is in THR ball heads. This review takes into account the main results achieved up to now, and is focused on the role that microstructural characteristics play on the TZP ceramics behaviour in ball heads, namely mechanical properties and their stability, wear of the UHMWPE paired to TZP, and their influence on biocompatibility.

Y-TZP ceramics for artificial joint replacements.

Due to their excellent mechanical properties, Yttria-stabilized Tetragonal Zirconia Polycrystal ceramics (Y-TZP) are used in ball heads for Total Hip Replacements. It is known that Y-TZP materials may show strength degradation due to ageing or to hydrothermal treatment. Also high wear of UHMWPE sockets coupled to steam sterilized Y-TZP ball heads after a short implantation period was recently reported. This effect may be related to ball head surface phase transformation, due to corrosive attack. The aim of this study is the evaluation of Y-TZP ceramics stability. Y-TZP made out of Yttria coated powders were aged at 140 degrees C under 0.2 MPa water pressure, in Ringer's solution at 37 degrees C, in NZW rabbits. Samples made out Yttria coated powders show lower strength degradation than samples made out coprecipitated powders, and UHMWPE discs coupled to Y-TZP rings made out coated powders do not show increase in wear after repeated sterilization cycles of the ceramic rings.

New Y-TZP powders for medical grade zirconia.

There is interest in using zirconia for biomedical applications as ball heads for total hip prostheses. Two potential types are under discussion: partially stabilized zirconia (PSZ) and tetragonal zirconia polycrystals (TZP) materials. Because of its enhanced material properties, TZP stabilized with yttria is favourable. To eliminate high amounts of natural radioactive impurities, the precursors are purified. The kind of precursor and purification method determine the powder impurity level. The disadvantage of Y-TZP is that the hydrothermal decomposition reaction method is that it depends very strongly on the grain size and the distribution of the stabilizing yttria within the zirconia grains. Thermodynamical and kinetic investigations on high purity coprecipitated and yttria-coated zirconia powders show different behaviours. Y-TZP materials based on yttria-coated zirconia powders show excellent mechanical strength of more than 1000 MPa, a Weibull modulus of up to 20 a! nd a fracture toughness of 9 MPa radical m. The material properties of Y-TZP ceramics based on coprecipitated powders and prepared under the same conditions are less attractive. It is expected that materials based on yttria-coated zirconia will show enhanced properties compared to materials derived from coprecipitated powders. Therefore Y-TZP materials derived from yttria-coated powders are very attractive as medical grade zirconia.