Performance of the resurfaced hip. Part 1: the influence of the prosthesis size and positioning on the remodelling and fracture of the femoral neck

Hip resurfacing is an established treatment for osteoarthritis in young active patients. Failure modes include femoral neck fracture and prosthesis loosening, which may be associated with medium-term bone adaptation, including femoral neck narrowing and densification around the prosthesis stem.Finite element modelling was used to indicate the effects of prosthesis sizing and positioning on the bone remodelling and fracture strength under a range of normal and traumatic loads, with the aim of understanding these failure modes better.The simulations predicted increased superior femoral neck stress shielding in young patients with small prostheses, which required shortening of the femoral neck to give an acceptable implant–bone interface. However, with a larger prosthesis, natural femoral head centre recreation in the implanted state was possible; therefore stress shielding was restricted to the prosthesis interior, and its extent was less sensitive to prosthesis orientation. With valgus orientation, the implanted neck strength was, at worst, within 3 per cent of its intact strength.The study suggests that femoral neck narrowing may be linked to a reduction in the horizontal femoral offset, occurring if the prosthesis is excessively undersized. As such, hip resurfacing should aim to reproduce the natural femoral head centre, and, for valgus prosthesis orientation, to avoid femoral neck fracture

Business improvement districts in urban freight sustainability initiatives: a case study approach

The paper extends research into the importance of freight transport partnerships by considering the role of Business Improvement Districts (BIDs) in supporting sustainable urban freight initiatives. A review of the freight transport-related work that has been carried out in BIDs in central London is included. A detailed case study of a freight project in the Baker Street Quarter (BSQ) Partnership provides insight into work carried out in the multi-tenanted office and hotel sectors. The findings of this research in terms of freight transport and logistics activity patterns at the businesses studied together with the potential freight transport solutions identified are discussed

Quantum materials with strong spin-orbit coupling : challenges and opportunities for materials chemists

ASG acknowledges funding through an EPSRC Early Career Fellowship EP/T011130/1.Spin-orbit coupling is a quantum effect that can give rise to exotic electronic and magnetic states in the compounds of the 4d and 5d transition metals. Exploratory synthesis, chemical tuning and structure-property characterisation of such compounds is an increasingly active area of research with both fundamental and application-related outlooks, but requires great care with regards to the chemistry of these materials that has not always been considered. This Perspective will give an accessible introduction to topical materials with strong spin-orbit coupling, their crystal chemistry, and their structure-property relationships, which overlaps with the contemporary investigation of some of the same materials within different communities. It will also outline some of the challenges faced in their synthesis and characterisation, and the contributions that materials chemists can make to overcoming these.Publisher PDFPeer reviewe

Does a PEEK femoral TKA implant preserve intact femoral surface strains compared with CoCr? A preliminary laboratory study

BACKGROUND: Both the material and geometry of a total knee arthroplasty (TKA) component influence the induced periprosthetic bone strain field. Strain, a measure of the local relative deformation in a structure, corresponds to the mechanical stimulus that governs bone remodeling and is therefore a useful in vitro biomechanical measure for assessing the response of bone to new implant designs and materials. A polyetheretherketone (PEEK) femoral implant has the potential to promote bone strains closer to that of natural bone as a result of its low elastic modulus compared with cobalt-chromium (CoCr).QUESTIONS/PURPOSES: In the present study, we used a Digital Image Correlation (DIC) technique to answer the following question: Does a PEEK TKA femoral component induce a more physiologically normal bone strain distribution than a CoCr component? To achieve this, a DIC test protocol was developed for periprosthetic bone strain assessment using an analog model; the protocol aimed to minimize errors in strain assessment through the selection of appropriate analysis parameters.METHODS: Three synthetic bone femurs were used in this experiment. One was implanted with a CoCr femoral component and one with a PEEK femoral component. The third (unimplanted) femur was intact and used as the physiological reference (control) model. All models were subjected to standing loads on the corresponding polyethylene (ultrahigh-molecular-weight polyethylene) tibial component, and speckle image data were acquired for surface strain analysis using DIC in six repeat tests. The strain in 16 regions of interest on the lateral surface of each of the implanted bone models was plotted for comparison with the corresponding strains in the intact case. A Wilcoxon signed-rank test was used to test for difference at the 5% significance level.RESULTS: Surface analog bone strain after CoCr implantation indicated strain shielding (R2 = 0.6178 with slope, ? = 0.4314) and was lower than the intact case (p = 0.014). The strain after implantation with the PEEK implant deviated less from the intact case (R2 = 0.7972 with slope ? = 0.939) with no difference (p = 0.231).CONCLUSIONS: The strain shielding observed with the contemporary CoCr implant, consistent with clinical bone mineral density change data reported by others, may be reduced by using a PEEK implant.CLINICAL RELEVANCE: This bone analog in vitro study suggests that a PEEK femoral component could transfer more physiologically normal bone strains with a potentially reduced stress shielding effect, which may improve long-term bone preservation. Additional studies including paired cadaver tests are necessary to test the hypothesis further

Orbital molecules in vanadium oxide spinels

Orbital molecules are clusters of transition metal cations, formed by orbital ordering in materials with extended structures that allow direct d-orbital interactions. Vanadium oxides exhibit an especially rich variety of orbital molecule states, with dimers and trimers identified in numerous systems. VO₂, in which V-V dimerisation accompanies a metal-insulator transition, is a particularly well-known example. Materials of general composition AB₂O₄ often adopt the spinel structure. As this structure features edge-sharing chains of BO₆ octahedra it is a good motif for orbital molecule formation, and the choice of A-site cation allows both the B-site oxidation state and the B-B separation to be varied. Unusually large V₇ ‘heptamer’ orbital molecules had been reported to form in the spinel AlV₂O₄ below an ordering transition at 700 K. Atomic pair distribution function analysis was used to investigate the V-V bonding in this material and reveals that the heptamers are actually ordered pairs of V₃ trimers and V₄ tetramers. Furthermore, these orbital molecules persist into a structurally disordered phase above the 700 K transition and remain well-defined to temperatures of at least 1100 K. Analogous behaviour is found in GaV₂O₄, a newly-synthesised spinel. It is isoelectronic with AlV₂O₄ and crystallographic and local-structure characterisation, complemented by magnetic and transport property measurements, reveals that it has the same V₃ and V₄ orbital molecule states but with a lower ordering temperature, of 415 K. In addition, quasi-elastic neutron scattering indicates that the orbital molecules in the high-temperature phase of GaV₂O₄ have static, rather than dynamic, disorder. By contrast, ZnV₂O₄ has an antiferromagnetic ground state without ordered orbital molecules. The nature of the orbital ordering in this state has been contentious, and has been investigated using X-ray total scattering for the first time. The ground state has a tetragonal structure consistent with long-range ferro-orbital ordering, and V-V bonding is not evident in either its average or local structures. The variation of electronic ordering in ZnₓGa₁₋ₓV₂O₄ solid solutions has also been explored. Whilst the structural and electronic perturbations induced by doping rapidly suppress the long-range ordering found in the two end members, local V-V bonding is remarkably stable with respect to these perturbations and is found in phases with x ≤ 0.875. Powder neutron diffraction and magnetometry measurements suggest that disordered orbital molecules are also present in Li₀.₅Ga₀.₅V₂O₄, another newly-synthesised material. A particularly interesting vanadium oxide is LiV₂O₄, which is one of very few delectron systems in which heavy-fermion behaviour has been found. Although V-V orbital interactions have been implicated in the microscopic origin of this behaviour, no orbital molecule-like distortions are found in the local structure of the heavy-fermion phase. LiV₂O₄ also exhibits a pressure-induced metal-insulator transition, and powder X-ray diffraction under low temperature-high pressure conditions reveals a concurrent cubic-monoclinic structural distortion that may be the result of orbital molecule ordering

Interdisciplinarity and insularity in the diffusion of knowledge: an analysis of disciplinary boundaries between philosophy of science and the sciences

Two fundamentally different perspectives on knowledge diffusion dominate debates about academic disciplines. On the one hand, critics of disciplinary research and education have argued that disciplines are isolated silos, within which specialists pursue inward-looking and increasingly narrow research agendas. On the other hand, critics of the silo argument have demonstrated that researchers constantly import and export ideas across disciplinary boundaries. These perspectives have different implications for how knowledge diffuses, how intellectuals gain and lose status within their disciplines, and how intellectual reputations evolve within and across disciplines. We argue that highly general claims about the nature of disciplinary boundaries are counterproductive, and that research on the nature of specific disciplinary boundaries is more useful. To that end, this paper uses a novel publication and citation network dataset and statistical models of citation networks to test hypotheses about the boundaries between philosophy of science and 11 disciplinary clusters. Specifically, we test hypotheses about whether engaging with and being cited by scientific communities outside philosophy of science has an impact on one’s position within philosophy of science. Our results suggest that philosophers of science produce interdisciplinary scholarship, but they tend not to cite work by other philosophers when it is published in journals outside of their discipline. Furthermore, net of other factors, receiving citations from other disciplines has no meaningful impact—positive or negative—on citations within philosophy of science. We conclude by considering this evidence for simultaneous interdisciplinarity and insularity in terms of scientific trading theory and other work on disciplinary boundaries and communication