1,720,960 research outputs found
Effect of long-term physiological activity on the long-term stem stability of cemented hip arthroplasty: in vitro comparison of three commercial bone cements
No full textLong-term endurance of the cement mantle is fundamental for the survival of cemented hip prostheses. Current protocols to characterize bone cements are unsuitable to predict the actual clinical outcome. The aim of this study was to assess if it is possible to rank cement types having diverse clinical outcome by using a simplified in vitro physiological test. Composite femurs were implanted with identical stems (Lubinus-SPII), using different commercial cement types: CMW1 to represent cement with poor clinical outcome; Simplex-P and Cemex-RX to represent cements with a positive clinical outcome. Implanted femurs were subjected to a validated protocol that simulated a demanding but physiological loading spectrum. Inducible micromotions and permanent migrations were recorded throughout the test. After test completion, the cement mantles were sectioned and inspected with dye penetrants to quantify the fatigue-induced cracks. Micromotions did not differ significantly between cement types (possibly because a successful prosthesis was chosen that is very stable in the host bone). Significant differences were observed in terms of cement cracks: CMW1 induced significantly more numerous and larger cracks than Simplex-P and Cemex-RX; no difference was observed between Simplex-P and Cemex-RX. This indicates that this protocol: (a) can discriminate between 'good' and 'bad' cements and (b) yields consistent results when comparable cements are tested. The proposed protocol overcomes the limitations of existing standardized material tests for bone cements. New cements can be assessed in comparison with other cements with known (positive/negative) clinical outcome, tested with the same protocol
A pictographic atlas for classifying damage modes on polyethylene bearings
Full text linkEvaluation of medical devices retrieved after in vivo service provides unique evidence related to the physiological environment in which the biomaterials performed. This study implements a training procedure for evaluating polyethylene bearings of joint prostheses obtained after pre-clinical tests or explanted after in vivo function. A total of 161 damage regions on 45 bearings were evaluated by four observers. An illustrated Damage Mode Atlas was developed as a reference guide, inclusive of both photographs and concise written descriptions of 16 specific damage modes that are typical for polyethylene bearings. Utilizing the Damage Mode Atlas to train new researchers improved the damage pattern analysis, including more accurate identification of damage modes and improved inter-rater reliability. This Damage Mode Atlas is a useful supplementary tool for conducting Stage II non-destructive analysis of explanted polyethylene bearings used for joint replacement, in accordance with international guidelines for evaluating explanted medical devices
Oxidation of differently sterilized hylamer acetabular cups after in vivo wear.
No full textThe aim of this work was to investigate the oxidation profile, the oxidation products and their distribution in differently sterilized Hylamer acetabular cups explanted after in vivo wear. A microtome was used to obtain 200 Dm sections from spherical hearing portion of explanted Hylamer acetabular cups gamma ray sterilized in air. The thin sections were soaked in boiling exane and the extracted PE sections were scanned through their thickness in 0.2 mm deep increments using FTIR analysis. An explanted Hylamer cup sterilized in N2 was used as control. DSC measurements were also performed in order to correlate the oxidation with the crystallinity of PE. The cups sterilized in air show severe oxidation in the back and in the bulk with the highest oxidation index (OI = 6.3) at 1 mm from the back surface, while no sign of oxidation was found at the hearing surface. An high concentration of esters probably due to biological environmental oxidation was found on the back of the cups. In the bulk the oxidation was prevalently due to chetons, that are associated with an oxidation due to the sterilization with gamma ray in the presence of oxygen. In fact in the control cup the OI was lower and the presence of chetons as negligible. The oxidation profile was similar to that obtained by other author: maximum OI few mm from the hearing surface. The absence of oxidation at the hearing surface of the air sterilized cups could be due to the wear. In fact if wear progresses faster than oxidation, PE will be removed before its oxidation.
The sections of PE sterilized in air with higher OI were delaminated and highly crystalline. Moreover, we have found a good correlation between oxidation profile and crystallinity profile. A possible cause of the poor wear resistance of Hylamer cups could be the high tendency to oxidation specially if they were sterylized in air
Combined wear behaviour and long-term implant-bone fixation of total knee replacement: a novel in vitro set-up
No full textThe success of a total knee replacement (TKR) strongly depends on the prosthetic design; this includes on one hand the best choice of the bearing materials to minimize wear, on the other hand a good orientation of the prosthetic components with respect to the loading directions. The aim of this study was to investigate the feasibility of a new experimental setup combining two fundamental aspects for the long-term success of knee implants: wear and micromotions. A novel procedure was used to simulate working conditions as close as possible to in vivo ones and to measure implant-bone micromotion, by means of fixing the femoral component of the prosthesis to the distal part of a synthetic femur to be tested through a knee simulator. Gravimetric wear of the tibial specimens was assessed at regular intervals. Implant-bone inducible micromotions and permanent migrations were measured at three locations throughout the test. Wear patterns on tibial specimens were characterized through a standardized protocol based on digital image analysis; fatigue damage in the cement was quantified. Some initial conditioning was noticed both in the wear process and microcracking distribution within the cement mantle. Similarity in wear tracks observed on tibial inserts and other retrieval studies, coupled with clinically consistent migration patterns for TKR, supports the efficacy of the new in vitro method presented
Vibrational spectroscopy study of the oxidation of Hylamer UHMWPE explanted acetabular cups sterilized differently.
No full textUltra-high-molecular-weight polyethylene (UHMWPE) has been used for over 40 years for acetabular cups in total hip joint prosthesis. Hylamer is a hot isostatically pressed material with high crystallinity. Early loosening due to extensive oxidation and phase transformation has been observed for this material. To analyze the reasons for its high tendency to oxidize, we have examined by FT-IR spectroscopy explanted acetabular cups γ-sterilized in different ways. The oxidation and wear rate observed were: Hylamer cups γ-sterilized in air with a long shelf life > Hylamer cups γ-sterilized in air with short shelf life Hylamer cups γ-sterilized in nitrogen. Our data indicate the important role of the shelf life on the oxidation of the cups: the samples γ-sterilized in air characterized by a shelf life greater than 3 years showed severe oxidation, a high wear rate, and marked debris production with delamination and the formation of a brittle zone in the more oxidated regions. In these regions we observed an increase in crystallinity, which was probably due to the decrease in the molecular weight of PE. The high oxidation was probably due to the modifications induced by the material treatment
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Vibrational spectroscopy study of the oxidation of differently sterilised UHMWPE explanted acetabular cups.
No full textUltra high molecular weight polyethylene (UHMWPE) is used from more than 40 years as acetabular cup in total hip joint prosthesis. In order to improve the longevity of the implants, in 1991 HylamerTM was patented and marketed by the DePuy-DuPont Orthopaedics joint venture. HylamerTM is a hot isostatically pressed material with high crystallinity (65-71%) and density. Despite the good pre-clinical results, since 1996 some Authors have shown early loosening due to extensive oxidation and phase transformation. In order to analyze the reasons of the high tendency to oxidation of this type of cups, we have examined differently y- sterilised (air and N2) explanted acetabular cups at different distances from the surface using FT-IR spectroscopy. The oxidation is reported as oxidation index (Ol), calculated from the ratio between the area of the carbonyl peak (1670-1850 cm-1) and the area of the reference peak (1327-1394 cm-1).
The results obtained indicate that the air-sterilised acetabular cups are more oxidated than the N2 ones. The oxidation of the N2-sterilised cups is only due to the in vivo environment (presence of the typical esther band at 1738 cm-1) while the oxidation of the air-sterilised cups is due both to the environment and the y rays (presence of the cheton band at 1717 cm-1). In the more oxidated sections of the air-sterilised cups we have observed a PE delamination. Moreover, a correlation between Ol and crystallinity of the cups (calculated by differential scanning calorimetrie measurements) can be observed.
Our results show how sterilization method can change the PE properties. In particular, the cups sterilized in air demonstrated a severe oxidation caused by both sterilization and in vivo permanence. Oxidation has been associated to a great crystallinity increase together with a deterioration of the material properties
Effect of undersizing on the long-term stability of the Exeter hip stem: a comparative in vitro study
No full textBACKGROUND: Even for clinically successful hip stems such as the Exeter-V40 occasional failures are reported. It has been reported that sub-optimal pre-operative planning, leading to implant undersizing and/or thin cement mantle, can explain such failures. The scope of this study was to investigate whether stem undersizing and a thin cement mantle are sufficient to cause implant loosening. METHODS: A comparative in vitro study was designed to compare hip implants prepared with optimal and smaller than optimal stem size. Exeter-V40, a highly polished cemented hip stem, was used in both cases. Tests were carried out simulating 24years of activity of active hip patients. A multifaceted approach was taken: inducible and permanent micromotions were recorded throughout the test; cement micro-cracks were quantified using dye penetrants and statistically analyzed. FINDINGS: The implants with an optimal stem size withstood the entire mechanical test, with low and stable inducible micromotions and permanent migrations during the test, and with moderate fatigue damage in the cement mantle after test completion. Conversely, the undersized specimens showed large and increasing micromotions, and failed after few loading cycles, because of macroscopic cracks in the proximal part of the cement mantle. While results for the optimal stem size are typical for stable hip stems, those for the undersize stem indicate a critical scenario. INTERPRETATION: These results confirm that even a clinically successful hip prosthesis such as the Exeter-V40 is prone to early loosening if a stem smaller than the optimal size is implanted
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
