E.M. Brach del Prever

Oxidation in orthopaedic UHMWPE sterilized by gamma-radiation and ethylene oxide

Ten new polyethylene prosthetic components (PEs), ethylene oxide (EtO)- and gamma-sterilized, were studied by means of infrared (IR) analysis in order to evaluate oxidation. Using attenuate total reflection infrared spectroscopy the authors demonstrate that all samples show surface oxidation, formed during processing and shaping, related to mechano-degradation. By means of Fourier transform infrared (FTIR) microscopy and derivatization techniques, the EtO-sterilized PEs present different behaviour in comparison to the gamma-radiated. The former show low levels of depth oxidation that could be related to the degradation which occurred during preparation of slices for IR analysis. The gamma-sterilized PEs show higher oxidation levels, variable from sample to sample, on the surface and in the bulk. The authors demonstrate that oxidation is described both by carbonyl species distribution and by hydroperoxide concentration. The hydroperoxides could be responsible for oxidative PEs ageing in in vivo service. The different oxidation levels and distribution could depend on the conditions of gamma-sterilization, in particular on the rate of the dose absorbed, not previously reported for ready-to-implant PEs. Chain scission of gamma-radiated UHMWPE, estimated by IR analysis, results in reduction of molecular weight and consequently in less abrasive resistance. The scheme of UHMWPE oxidation due to gamma-sterilization demonstrates the inhomogeneous distribution of reactive species in PEs responsible for the unpredictable performance in vivo.

In vivo UHMWPE biodegradation of retrieved prosthesis.

Sixty-two ultra high molecular weight polyethylene prosthetic components (PEs) (31 tibial plateaux and 31 cups), sterilised by gamma rays or ethylene oxide (EtO), were retrieved after 1-12 years depending on different medical reasons and were studied by FTIR spectroscopy with derivatisation of oxidised species. Esters, acids and hydroperoxides were found under the surface of the EtO sterilised PEs up to 2 mm depth. The behaviour of gamma ray sterilised PEs is more complex due to the oxidation following the sterilisation process. Ester and acid formation might arise from the diffusion of components of synovial liquid or from the oxidation process, whereas hydroperoxide formation is thought to be due to the oxidation. Abrasion and delamination process is discussed considering the topological distribution of degradation products.

Analysis of products diffused into UHMWPE prosthetic components in vivo.

Ten UHMWPE hip inserts, five ethylene oxide and five gamma-ray sterilised in air, were retrieved during surgical revision after aseptic failure. Time in situ varied from 6 to 23 years. First implant was carried out for degenerative arthritis in all cases. The retrieved inserts were cut into two parts perpendicular to the articulate surface and a series of 150 microm thick slices were obtained from the cross-section. These were studied by FTIR microscopy and the absorbed products were extracted with cyclohexane for identification by GC/MS and Py/GC/MS. All retrieved UHMWPE components, independent of the sterilisation method, showed species adsorbed on the surface, which were mainly synovial liquid protein components. In addition, species such as cholesterol, fatty esters of cholesterol and squalene, also originating from synovial liquid, were found in the bulk. The concentration of the different species varies depending on the individual patient.

Oxidation of orthopaedic UHMWPE

Retrieved EtO sterilised acetabular cups usually show much less degradation than gamma-ray sterilised cups. Some of our retrieved EtO sterilised cups did, however, reveal unexpected bulk oxidation. It was observed that this oxidation was always accompanied by whitening of the material. This whitening was found to be due to a break-up of the compression moulded material into its original particles. It was noticed that there was no oxidation in all parts, where the break-up and whitening appeared. The oxidation did, however, occur exclusively in the parts where there was a badly consolidated material. Upon examining shelf aged, unsterilised samples, it was found that the degradation was also present here. This shows that the observed phenomenon is not due to the service in vivo and that it must originate from the processing step. Just as for the retrieved samples, the shelf aged cups only showed oxidation in the bulk and not at the surface. It was concluded that the material used for the cups had been badly fused together during the compression moulding and that the machining had created a bad stress situation in the cups leading to a break-up of the particles. The mechanism that initiates the oxidation is not known, but it is believed that the distribution depends on how the internal stresses have acted to break up the structure. In the areas where the particles have been separated, there is probably a higher availability of oxygen than what is normally observed in UHMWPE.

Interplay between surface properties of standard, vitamin E blended and oxidised ultra high molecular weight polyethylene used in total joint replacement and adhesion of Staphylococcus aureus and Escherichia coli

We have assessed the different adhesive properties of some of the most common bacteria associated with periprosthetic joint infection on various types of ultra high molecular Weight Polyethylene (UHMWPE). Quantitative in vitro analysis of the adhesion of biofilm producing strains of Staphylococcus aureus and Escherichia coli to physically and chemically characterised standard UHMWPE (PE), vitamin E blended UHMWPE (VE-PE) and oxidised UHMWPE (OX-PE) was performed using a sonication protocol. A significant decreased bacterial adhesion was registered for both strains on VE-PE, in comparison with that observed on PE, within 48 hours of observation (S. aureus p = 0.024 and E. coli p = 0.008). Since Vitamin E reduces bacterial adhesive ability, VE-stabilised UHMWPE could be valuable in joint replacement by presenting excellent mechanical properties, while reducing bacterial adhesiveness.

Study of neurinomas with ultrasound contrast media: review of a case series to identify characteristic imaging patterns

PurposeThe aim of this study was to evaluate whether there exists a characteristic distribution pattern of vessels within neurinomas that may be used to characterise this type of lesion by employing a contrast-specific ultrasound technique.Materials and methodsBetween January 2003 and May 2010, 66 suspected neurinomas were evaluated according to their sonographic features (solid fusiform mass with well-defined margins located in direct continuity with the nerve that was not always discernible and heterogeneous as a result of the presence of small cystic areas or calcifications). The lesions were examined using a sonographic contrast medium consisting of sulphur hexafluoride microbubbles and equipment with dedicated contrast-specific software [contrast tuned imaging (CnTI)]. Of these lesions, five were excluded from the analysis because the definitive diagnosis was not available (in two cases, the follow-up was still in progress, whereas in the remaining three, there was no follow-up). Our study, therefore, is based on 61 surgically excised lesions that were confirmed to be neurinomas by histology, which is regarded as the gold standard.ResultsIn 41/61 cases (67.2%), we identified an enhancement pattern that we termed reticular owing to the interweaving of blood vessels, of which two subtypes were identified depending on whether the interwoven vessels were densely or sparsely packed: loose-knit reticular in 18/41, and tight-knit reticular in 23/41. In 20/61 (32.8%) cases, we observed a vascular pattern of diffuse heterogeneous enhancement, which was divided into two subtypes based on the presence of one (7/20) or more (13/20) avascular areas.ConclusionsResults showed that all neurinomas studied could be divided into two groups according to the type of enhancement pattern observed: reticular or diffuse heterogeneous.RiassuntoObiettivoScopo dello studio è valutare, mediante l’impiego di una tecnica ecografica contrasto-specifica, se esiste una distribuzione caratteristica dei vasi all’interno dei neurinomi che possa essere usata per una caratterizzazione del tipo di lesione.Materiali e metodiNel periodo compreso tra gennaio 2003 e maggio 2010 sono state valutate nel nostro dipartimento 66 lesioni sospette per neurinoma in base alle loro caratteristiche ecografiche (formazioni solide, fusiformi, a margini netti, in diretta continuità con la fibra nervosa, non sempre riconoscibile, disomogenee per l’eventuale presenza di piccole aree similcistiche o calcificazioni), ed esaminate con mezzo di contrasto (MdC) ecografico, costituito da microbolle a base di esafluoruro di zolfo e apparecchiatura dotata di software dedicato Contrast Tuned Imaging (CnTI) contrasto specifico. Di queste lesioni, 5 sono state escluse dall’analisi in quanto non era disponibile una diagnosi definitiva (n=2 follow-up in corso; n=3 assenza di follow-up). Pertanto il nostro studio si basa unicamente sulle 61 lesioni asportate chirurgicamente e confermate come neurinomi all’esame istologico, considerato come gold standard.RisultatiIn 41/61 (67,2%) casi abbiamo identificato una distribuzione del mezzo di contrasto definita “a reticolo” in base all’intreccio formato dalle strutture vascolari, in cui si riconoscono due sottotipi: “reticolo a maglie larghe” in 18/41 e “reticolo a maglie strette” in 23/41, distinti in base all’aspetto dell’incrocio dei vasi, se più rado o più fitto. In 20/61 (32,8%) casi abbiamo osservato un diverso pattern di vascolarizzazione, denominato “impregnazione diffusa disomogenea”, a sua volta suddiviso in due sottotipi in base alla presenza di una (7/20) o più aree avascolari (13/20).ConclusioniI risultati ottenuti in questo studio hanno dimostrato che tutti i neurinomi analizzati possono essere distinti in due gruppi, in base al tipo di pattern vascolare riscontrato: di tipo reticolare o ad impregnazione diffusa disomogenea.

Ultra high molecular weight polyethylene is cytotoxic and causes oxidative stress, even when modified

Ultra High Molecular Weight (UHMW) Polyethylene (PE) is the most used biomaterial for articulating surface of total joint replacements (TJR). Since its introduction decades ago, many efforts have been made to improve its properties and to understand its behaviour with the final goal to provide a longer duration of the implants. Mechanical abrasion with particles production is an unavoidable process, but catastrophic PE wear with a huge quantity of PE reactive debris production was observed in the last years, with consequent severe periprosthetic osteolysis and aseptic loosenings. Now it is well known that the severe PE particle disease is due to UHMWPE oxidative degradation caused by a ysterilization in air (1-4). In order to solve this problem, the evolution of the conventional UHMWPE drove to alternative sterilization methods (ethylene oxide and gas plasma) and to the development of new PE derivatives with a supposed increased resistance to abrasion in vivo, such as the crosslinked PE (X-PE) and the vitamin Estabilized PE (E-PE), Unfortunately, particle disease and periprosthetic osteolysis still remain an unsolved problem (5-9). The osteolysis is an inflammatory process caused by a foreign body (10), wherein the particles trigger monocyte recruitment and macrophage activation, leading to chronic inflammation, with release of cytokines and proteases, and bone reabsorption (8). It is well recognized that PE particles induce different reactions according to dimension (fragments larger than 10 J.1m produce foreign body-induced giant cell granuloma, whereas smaller fragments are phagocytized), number, shape, superficial hydrophobicity and oxidation (11-14). The majority of the studies have been focused on how conventional and new PEs develop debris particles different in sizes and behaviours, reacting in different ways with human cells and conducting to unpredictable clinical results (7, 15-17). But beside the shape and the dimension of a PE particle, the chemico-physical properties of its surface might playa fundamental role in stimulating the inflammatory reaction, the cytotoxicity and the apoptosis. In particular, it has been suggested that PE particles per se do not cause any response although macrophages are activated, probably due to the superficial characteristics of PE and macrophage binding receptors. Different approaches have shown that some markers of inflammation and oxidative stress were induced after exposure to UHMWPE, in particular to their debris: among them, lactate dehydrogenase (LDH) release and lipid peroxidation (19) and cytokines production (20) have been observed. The mechanisms by which these events occur are not still well elucidated. Some authors demonstrated that in particular the oxidized UHMWPE is toxic in different cellular models: Reno et al. (21) showed that oxidized UHMWPE reduced proliferation in human fibroblasts and induced a strong release of gelatinase B (matrix metalloproteinase 2, MMP-2), and the surface oxidation of UHMWPE has been correlated to increased apoptosis and necrosis in human granulocytes (22). Moreover, the oxidation of UHMWPE has been strongly related to the development of inflammation around the implants (23) and Fiorito et al. (24) demonstrated that, in this inflammatory status, the production of reactive oxygen species (ROS) by inflamed synovial cells plays a very crucial role. The supplementation ofX-PE and E-PE hasbeen shown

Biocompatibility and osteogenetic characteristics of new biocompatible glasses

A fibre-shaped glass with qualities of biocompatibility and biodegradation could be promising for reconstructive bone surgery in orthopaedics and neurosurgery. New highly biocompatible glasses, originally made by the Italian Group of Study on Biocompatible Glass, are obtained both in cylinder and fibre shapes due to their original chemical composition (Glassfiber). This is the only glass which is also available as a continuous filament. Hydrolytic in vitro and in vivo tests demonstrate that these glasses present both good biocompatibility and adjustable biodegradation in relation to their chemical composition. The advantages of bioactive glass also being available as a continuous filament are suggested.

Biology of Primary Fracture Healing. From Experimentation with Animals to Clinical Application. A Review.

The specific radiological manifestations of primary bone healing have been known for over fifty years. In 1914, Lane (22), referred to it is as “bone healing by primary intention” and in 1949, Danis (10), described it as “soudure autogene”, or autogeneous welding. It was also known that rigid internal fixation was a “sine qua non” condition to obtain the specific pattern of healing which is characterized by the absence of callus. It has not been clear,though, whether the effect of compression is biological, or whether the callus-less healing occurs simply due to the stabilizing effect (8). Despite the uncertainty as to the cause of the beneficial effect of rigid fixation, the clinical use of compression plates gained broad recognition since their introduction by Danis in 1949 (10). Venable in 1951 (34), Boreau and Hermann in 1952 (7), Bagby and Janes in 1957 (5) described similar fixation devices. In 1955 Yamagishi and Yoshimura (37) published an experimental paper in which a moderate intermittent compression was considered to be the ideal biomechanical condition for fracture healing. According to the modern philosophy of the Russian Ilizarov, this concept is fun damental. However in 1958 Bagby and Janes (6) carried out experiments on dog femurs and concluded that a steady compression does not necessary stimulate the osteogenesis,although it is a main factor in increasing stability. In the sixties a number of histolo gical observations on primary bone healing in various species including humans were reported (2,24,26,29,32,33). Most of the work in this field came from the Work Group for the Study of Osteosyn-thesis, which was founded in Switzerland by M.E. Muller,M.Allgover and H. Willenegger in 1958. Laboratory facilities for the experimental work on the animal were provided in Davos in the “Laborato- rimn fur experimentelle Chirurgie” headed by Stephan Perren. Most of the work described in this paper in detail on the histology of primary bone healing was performed there. Further research in the same laboratory, working on sheep, showed that a pattern of secondary healing with callus was produced when internal fixation allowed for some interfragmentary motion (no compression). The amount of callus observed corresponded to the deformability of the implant and consequently to interfragmentary motion (17).