Mechanism of loosening of the Souter-Strathclyde total elbow replacement evidence from revision surgery

Nine Souter-Strathclyde humeral and ulnar components retrieved from revision surgery for aseptic loosening were examined macro- and microscopically. The wear patterns were compared and photographed. Humeral components demonstrated no evidence of wear. All ulnar components exhibited similar wear patterns. Six of the nine exhibited macroscopic evidence taking the form of deep linear grooves on either the medial or lateral articulating surfaces. Microscopic examinations revealed wear on all nine, exhibited as disruption of the polyethylene machining lines on the articular surfaces, but almost complete preservation on the central gliding ridge. We believe our observations are explained by 'rocking' of the humeral component on the ulnar as a result of the congruent surfaces of the Souter-Strathclyde prosthesis, which resist rotational and translational movements, characteristic of the normal elbow.

In vitro study investigating the mechanical properties of acrylic bone cement containing calcium carbonate nanoparticles

A successful total hip replacement has an expected service life of 10-20 years with over 75% of failures due to aseptic loosening which is directly related to cement mantle failure. The aim of the present study was to investigate the addition of nanoparticles of calcium carbonate to acrylic bone cement. It was anticipated that an improvement in mechanical performance of the resultant nanocomposite bone cement would be achieved. A design of experiment approach was adopted to maximise the mechanical properties of the bone cement containing nanoparticles of calcium carbonate and to determine the constituents and preparation methods for which these occur. The selected conditions provided improvements of 21% in energy to maximum load, 10% in elastic modulus, 7% in bending strength and 8% in bending modulus when compared with bone cement without nanoparticles. Although cement containing nanoCaCO(3) coated in sodium citrate also enhanced the energy to maximum load by 28% and the elastic modulus by 14% when compared with control cement, it is not recommended as a factor in the production of nanocomposite bone cement due to reduction in the bending properties of the final bone cement.

The influence of wear paths produced by hip replacement patients during normal walking on wear rates

Variation in wear paths is known to greatly affect wear rates in vitro, with multidirectional paths producing much greater wear than unidirectional paths. This study investigated the relationship between multidirectional motion at the hip joint, as measured by aspect ratio, sliding distance, and wear rate for 164 hip replacements. Kinematic input from three-dimensional gait analysis was used to determine the wear paths. Activity cycles were determined for a subgroup of 100 patients using a pedometer study, and the relationship between annual sliding distance and wear rate was analyzed. Poor correlations were found between both aspect ratio and sliding distance and wear rate for the larger group and between annual sliding distance and wear rate for the subgroup. However, patients who experienced a wear rate <0.08 mm/year showed a strong positive correlation between the combination of sliding distance, activity levels, and aspect ratio and wear rate (adjusted r(2) = 55.4%). This group may represent those patients who experience conditions that most closely match those that prevail in simulator and laboratory tests. Although the shape of wear paths, their sliding distance, and the number of articulation cycles at the hip joint affect wear rates in simulator studies, this relationship was not seen in this clinical study. Other factors such as lubrication, loading conditions and roughness of the femoral head may influence the wear rate.

Evaluation of an accelerated aging medium for acrylic bone cement based on analysis of nanoindentation measurements on laboratory-prepared and retrieved specimens

The thrust of the study was a critical evaluation of the efficacy of a medium (30% v/v H(2)O(2), at 60 degrees C) that has been suggested in a literature report as being suitable for simulating the oxidative aging process, seen in vivo, in the acrylic bone cement mantles of total hip and knee joint replacements. For this purpose, quasi-static and dynamic nanoindentation measurements were used to obtain material properties--elastic modulus, E; hardness, H; and the variation of the storage and loss moduli with the frequency of the applied indenting force--of PalacosR acrylic bone cement specimens after various periods of immersion (7, 14, 21, and 28 days) in the aging solution, and of specimens prepared from cement mantles retrieved from cemented total hip joint replacements after various times in vivo (0.92-21 years). Also, best-fit relationships were obtained between E and time in the H(2)O(2) solution (t), H and t, E and in vivo time (T), and H and T. This body of results points to the possibility that the aging solution is effective, although the evidence is not conclusive.

Segregation of Beaufort Sea beluga whales during the open-water season

Population segregation by habitat use occurs because energy requirements and survival strategies vary with age, sex, size, and reproductive stage. From late summer to early fall in 1993, 1995, and 1997, relative length (age), sex, and reproductive status of satellite-tagged beluga whales ( Delphinapterus leucas (Pallas, 1776)) in the eastern Beaufort Sea were tested for habitat segregation. We used (i) resource selection function models to evaluate how belugas used areas of varying sea ice concentration and shelf habitat and (ii) distance analysis to measure the selection of areas varying in distance to mainland and island coastlines. Resource selection functions and distance analysis established that habitat selection differed with length, sex, and reproductive status of whales: (i) females with calves and smaller males selected open-water habitats near the mainland; (ii) large males selected closed sea ice cover in and near the Arctic Archipelago; and (iii) smaller males and two females with calves (not newborn) selected habitat near the ice edge. The segregation of habitat use according to sex, age, and reproductive status relates to the different resources required at different life stages and may represent characteristics of beluga social structure. We discuss our results in the context of two common sexual segregation hypotheses and conclude that summer habitat segregation of belugas reflects differences in foraging ecology, risk of predation, and reproduction.

Critical comparison of two methods for the determination of nanomechanical properties of a material: Application to synthetic and natural biomaterials

Two methods used for determining the elastic modulus (E) and hardness (H) of a material--the original version of the well-known Oliver-Pharr Method, OOPM, and a variant of it called the Modified Slopes Method, MSM--were critically compared. The nanoindentation test results, of indenter load-versus-indenter displacement, were recorded for six series of specimens, three of commercially-available acrylic bone cements (Palacos R and Cemex XL) and three of bones (human, bovine, and mouse). In the first series, the specimens were prepared from Palacos R cement mantles retrieved from cemented total hip joint replacements after 11 months, 11 years, and 21 years in vivo. In the second and third series, the specimens were fabricated from hand- and vacuum-mixed dough of Cemex XL cement, respectively. In the fourth, fifth, and sixth series, the specimens were prepared from fresh frozen cortical bone of human tibia, plexiform bone from fresh bovine tibia, and femora from inbred mice, respectively. It was found that, for a given material, the values of E or H computed using OOPM and MSM are not significantly different. However, the recommendation is that MSM is preferable because it is straightforward-only the nanoindentation measurements and values of constants that depend on the geometry of the indenter used are needed. In contrast, when the OOPM is used, there is a critical input (the indenter tip area function), whose computation is problematic. The article also includes a succinct discussion of factors that affect the values of material properties computed from nanoindentation measurements, such as the loading rate and the surface roughness of the test specimen.

A comparison of different biogeographical classifications of Europe, Great Britain and Spain

Various biogeographical and bioclimatic classifications of a number of regions, countries and continents have been created to meet different objectives. A policy maker might ask the question 'why is there no single accepted classification and how do the different classifications compare with one another?' In order to answer these two questions three classifications created by different methods for Great Britain and two for Spain are compared using the Kappa statistic. All of the classifications were created from data on cellular grids with a set window size. Further non-statistical comparisons are made with other classifications. The biogeographic classifications studied in this paper produced three different types of zone: those that were always identified whatever the method; those that were broadly similar but where the boundaries differed; and those that were unique to a particular classification. These different types of zone are likely to exist for any comparison between classifications of a particular region. The extent of the geographic window from which data were obtained had a major effect on the classification of grid cells at the edges of the window. For example, the few grid cells in the south of England, with characteristics of continental Europe, are not detected if data from Great Britain alone are used for the classification. We conclude that the data window should always be larger than the area for which the classification is being made. The objective Kappa statistic, although useful, was not capable of discerning similarities and dissimilarities that appear obvious to the subjective human eye. Although the details of the classifications differed there were broad similarities between the classifications and these differences reflect important divisions along major environmental axes that have been inferred by earlier biogeographers. As the divisions are real there is a sound basis for their use in future land use or environmental policy.

Phase II trial of topotecan and cisplatin in persistent or recurrent squamous and nonsquamous carcinomas of the cervix

OBJECTIVE

Cisplatin is a standard treatment in advanced, recurrent cervical cancer. Because topotecan is an established treatment in gynecologic malignancies such as ovarian cancer and exhibits nonoverlapping toxicity with cisplatin, a phase II trial was conducted to evaluate the tolerability and antitumor activity of a cisplatin/topotecan doublet in persistent or recurrent cervical cancer patients.

METHODS

Patients with bidimensionally measurable persistent or recurrent squamous cell and non squamous cell cervical cancer and adequate bone marrow were enrolled. Patients received 50 mg/m(2) of cisplatin intravenously over 1 h on Day 1 and 0.75 mg/m(2) of topotecan intravenously over 30 min on Days 1, 2, and 3 of 21-day cycles for six cycles or until disease progression. Tumor response and regimen toxicity were assessed using established Gynecologic Oncology Group criteria.

RESULTS

Thirty-two of 35 enrolled patients were evaluable for toxicity and tumor response. All but 2 evaluable patients had received previous radiotherapy. No patient received prior chemotherapy. The cisplatin/topotecan doublet was well tolerated, with 77 and 78% of courses given without interruption or delay and at full doses, respectively. As anticipated, the most common toxicity was hematologic, with grade 3/4 neutropenia and thrombocytopenia reported in 30 and 10% of cycles, respectively. The overall response rate was 28% (9/32), with 3 complete and 6 partial responses. The antitumor response in nonirradiated fields (30%) was similar to the response observed in previously irradiated fields (33%), suggesting good drug penetration. Median duration of response was 5 months (range, 2 to 15+ months). An additional 9 (28%) patients achieved stable disease. Median survival was 10 months, with 3 patients in lasting remission.

CONCLUSIONS

These results demonstrate that the cisplatin/topotecan combination is safe, well tolerated, and active in persistent or recurrent cervical cancer patients. A phase III, multicenter trial is under way (cisplatin/topotecan versus cisplatin) based on these favorable results to confirm the safety and efficacy profile in this patient population.

Inequalities in health: evaluation and effectiveness in practice

This paper details the findings from a project that assessed the contribution made by nurses, midwives and health visitors to targeting health and social need. This is an important theme within the Northern Ireland Regional Strategy entitled 'Health and well-being into the next millennium: a regional strategy for health and social well-being 1997-2002', which is concerned with addressing inequalities in health status and social well-being. In response to this initial survey, the paper also highlights the second phase of the project that was the development of an evaluation manual specifically designed to assist health-care practitioners in establishing evaluation frameworks and in applying evaluation techniques and methods. The paper describes four research case studies that are intended to illustrate the kinds of evaluation methods necessary to cover the stages of evaluation, needs assessment, structure, process and outcome, and to reflect the experience of applied evaluation as it occurs in practice as opposed to how it appears in textbooks.

Bone cement mixing. Theatre staff's views and opinions

Acrylic bone cement has not substantially changed since it was first introduced more than 30 years ago, however the method by which it is mixed has evolved greatly (Dunne 1996).