Birmingham hip resurfacing: a systematic review of outcomes at minimum 10-years follow-up.

Although controversy surrounding the use of metal-on-metal (MoM) arthroplasty implants continues to exist, satisfactory clinical and radiological outcomes have been reported following Birmingham Hip Resurfacing (BHR) at long-term follow-up, leading to an Orthopaedic Data Evaluation Panel (ODEP) rating of 13A. The purpose of this study was to systematically review the literature to evaluate the functional outcomes, radiological outcomes and revision rates following BHR at a minimum of 10 years follow-up. Using the PRISMA guidelines, two independent reviewers performed a literature search using Pubmed, Embase and Scopus databases. Only studies reporting on outcomes of BHR with a minimum of 10 years' follow-up were considered for inclusion. A total of 12 studies including 7132 hips (64.8% males), with mean follow-up of 11.5 years (10-15.3), met our inclusion criteria. Of included patients, 94.3% of patient underwent BHR for osteoarthritis at a mean age was 52.0 years (48-52). At final follow-up, 96% of patients reported being satisfied with their BHR, with mean Harris Hip Scores of 93.6 and Oxford Hip Scores of 16.5. Rates of radiological femoral neck narrowing of greater than 10% and non-progressive radiological loosening were reported as 2.0% and 3.8% respectively. At final follow-up, the overall revision rate was 4.9% (334/7132), deep infection rate was 0.4%, metal allergy/insensitivity rate was 1.6%, metal reaction rate was 0.3%, rate of peri-prosthetic fracture was 0.9% and aseptic loosening rates were 1.6%. This systematic review demonstrates that BHR results in satisfactory clinical outcomes, acceptable implant survivorship, low complication rates and modest surgical revision rates in the long-term at minimum 10-year follow-up.

The origins of high hardening and low ductility in magnesium.

Magnesium is a lightweight structural metal but it exhibits low ductility-connected with unusual, mechanistically unexplained, dislocation and plasticity phenomena-which makes it difficult to form and use in energy-saving lightweight structures. We employ long-time molecular dynamics simulations utilizing a density-functional-theory-validated interatomic potential, and reveal the fundamental origins of the previously unexplained phenomena. Here we show that the key 〈c + a〉 dislocation (where 〈c + a〉 indicates the magnitude and direction of slip) is metastable on easy-glide pyramidal II planes; we find that it undergoes a thermally activated, stress-dependent transition to one of three lower-energy, basal-dissociated immobile dislocation structures, which cannot contribute to plastic straining and that serve as strong obstacles to the motion of all other dislocations. This transition is intrinsic to magnesium, driven by reduction in dislocation energy and predicted to occur at very high frequency at room temperature, thus eliminating all major dislocation slip systems able to contribute to c-axis strain and leading to the high hardening and low ductility of magnesium. Enhanced ductility can thus be achieved by increasing the time and temperature at which the transition from the easy-glide metastable dislocation to the immobile basal-dissociated structures occurs. Our results provide the underlying insights needed to guide the design of ductile magnesium alloys.

A growing challenge: The rise of femoral periprosthetic fractures - An 11-year observational study.

INTRODUCTION: The demand for joint arthroplasty has risen as our elderly population increases and ages. With this so to has the number of patients suffering periprosthetic fractures (PPF). The aim of our study was to quantify the burden of PPF and provide an up to date reference of the epidemiology of PPF in Ireland. We also sought to assess length of stay (LOS), resource utilisation and mortality associated with this cohort of patients. METHODS: An eleven-year retrospective observational study was conducted of a consecutive series of patients treated for a femoral PPF. Costs were obtained from activity based tariffs provided by the hospital inpatient enquiry system and mortality was confirmed using the national death events publication system. RESULTS: Over the 11-year study period 174 procedures for a femoral PPF were performed. Mean age of patients was 77.6 years (SD 11.1 years) with 44.7% male. Median ASA grade was 3 (range 1-4) and mean LOS was 19 days. There was a 700% increase in patients undergoing surgery for a PPF over the study period. The mean cost of care was €24,413 in 2017. Thirty-day mortality was 2.9% while one-year mortality was 12.4%. CONCLUSIONS: PPF occur in an elderly comorbid cohort of patients. Care of these patients now makes up a considerable part of the orthopaedic workload and consumes a significant portion of healthcare resources. Patients should be treated in tertiary referral centres with surgeons skilled in their management. Better access to rehabilitation is needed.

Mechanism and energetics of 〈c + a〉 dislocation cross-slip in hcp metals.

Hexagonal close-packed (hcp) metals such as Mg, Ti, and Zr are lightweight and/or durable metals with critical structural applications in the automotive (Mg), aerospace (Ti), and nuclear (Zr) industries. The hcp structure, however, brings significant complications in the mechanisms of plastic deformation, strengthening, and ductility, and these complications pose significant challenges in advancing the science and engineering of these metals. In hcp metals, generalized plasticity requires the activation of slip on pyramidal planes, but the structure, motion, and cross-slip of the associated [Formula: see text] dislocations are not well established even though they determine ductility and influence strengthening. Here, atomistic simulations in Mg reveal the unusual mechanism of [Formula: see text] dislocation cross-slip between pyramidal I and II planes, which occurs by cross-slip of the individual partial dislocations. The energy barrier is controlled by a fundamental step/jog energy and the near-core energy difference between pyramidal [Formula: see text] dislocations. The near-core energy difference can be changed by nonglide stresses, leading to tension-compression asymmetry and even a switch in absolute stability from one glide plane to the other, both features observed experimentally in Mg, Ti, and their alloys. The unique cross-slip mechanism is governed by common features of the generalized stacking fault energy surfaces of hcp pyramidal planes and is thus expected to be generic to all hcp metals. An analytical model is developed to predict the cross-slip barrier as a function of the near-core energy difference and applied stresses and quantifies the controlling features of cross-slip and pyramidal I/II stability across the family of hcp metals.

Cast aluminium single crystals cross the threshold from bulk to size-dependent stochastic plasticity.

Metals are known to exhibit mechanical behaviour at the nanoscale different to bulk samples. This transition typically initiates at the micrometre scale, yet existing techniques to produce micrometre-sized samples often introduce artefacts that can influence deformation mechanisms. Here, we demonstrate the casting of micrometre-scale aluminium single-crystal wires by infiltration of a salt mould. Samples have millimetre lengths, smooth surfaces, a range of crystallographic orientations, and a diameter D as small as 6 µm. The wires deform in bursts, at a stress that increases with decreasing D. Bursts greater than 200 nm account for roughly 50% of wire deformation and have exponentially distributed intensities. Dislocation dynamics simulations show that single-arm sources that produce large displacement bursts halted by stochastic cross-slip and lock formation explain microcast wire behaviour. This microcasting technique may be extended to several other metals or alloys and offers the possibility of exploring mechanical behaviour spanning the micrometre scale.

Computational Design of Strain in Core-Shell Nanoparticles for Optimizing Catalytic Activity.

Surface strains in core-shell nanoparticles modify catalytic activity. Here, a continuum-based strategy enables accurate surface-strain-based screening and design of core-shell systems using minimal input as a means to enhance catalytic activity. The approach is validated here for Pt shells on Cu(x)Pt(1-x) cores and used to interpret experimental results on the oxygen reduction reaction in the same system. The analysis shows that precise control of particle sizes and shell thicknesses is required to achieve peak activity, rationalizing the limited increases in activity observed in experiments. The method is also applied to core-shell nanorods to demonstrate its wide applicability.

Atomic mechanism and prediction of hydrogen embrittlement in iron.

Hydrogen embrittlement in metals has posed a serious obstacle to designing strong and reliable structural materials for many decades, and predictive physical mechanisms still do not exist. Here, a new H embrittlement mechanism operating at the atomic scale in α-iron is demonstrated. Direct molecular dynamics simulations reveal a ductile-to-brittle transition caused by the suppression of dislocation emission at the crack tip due to aggregation of H, which then permits brittle-cleavage failure followed by slow crack growth. The atomistic embrittlement mechanism is then connected to material states and loading conditions through a kinetic model for H delivery to the crack-tip region. Parameter-free predictions of embrittlement thresholds in Fe-based steels over a range of H concentrations, mechanical loading rates and H diffusion rates are found to be in excellent agreement with experiments. This work provides a mechanistic, predictive framework for interpreting experiments, designing structural components and guiding the design of embrittlement-resistant materials.

Diffusion on demand to control precipitation aging: application to Al-Mg-Si alloys.

We demonstrate experimentally that a part-per-million addition of Sn solutes in Al-Mg-Si alloys can inhibit natural aging and enhance artificial aging. The mechanism controlling the aging is argued to be vacancy diffusion, with solutes trapping vacancies at low temperature and releasing them at elevated temperature, which is supported by a thermodynamic model and first-principles computations of Sn-vacancy binding. This "diffusion on demand" solves the long-standing problem of detrimental natural aging in Al-Mg-Si alloys, which is of great scientific and industrial importance. Moreover, the mechanism of controlled buffering and release of excess vacancies is generally applicable to modulate diffusion in other metallic systems.

Stress-gradient plasticity.

A new model, stress-gradient plasticity, is presented that provides unique mechanistic insight into size-dependent phenomena in plasticity. This dislocation-based model predicts strengthening of materials when a gradient in stress acts over dislocation source-obstacle configurations. The model has a physical length scale, the spacing of dislocation obstacles, and is validated by several levels of discrete-dislocation simulations. When incorporated into a continuum viscoplastic model, predictions for bending and torsion in polycrystalline metals show excellent agreement with experiments in the initial strengthening and subsequent hardening as a function of both sample-size dependence and grain size, when the operative obstacle spacing is proportional to the grain size.

Engineering size-scaling of plastic deformation in nanoscale asperities.

Size-dependent plastic flow behavior is manifested in nanoindentation, microbending, and pillar-compression experiments and plays a key role in the contact mechanics and friction of rough surfaces. Recent experiments using a hard flat plate to compress single-crystal Au nano-pyramids and others using a Berkovich indenter to indent flat thin films show size scaling into the 100-nm range where existing mechanistic models are not expected to apply. To bridge the gap between single-dislocation nucleation at the 1-nm scale and dislocation-ensemble plasticity at the 1-microm scale, we use large-scale molecular dynamics (MD) simulations to predict the magnitude and scaling of hardness H versus contact size l(c) in nano-pyramids. Two major results emerge: a regime of near-power-law size scaling H approximately l(c)(-eta) exists, with eta(MD) approximately 0.32 compared with eta(expt) approximately 0.75, and unprecedented quantitative and qualitative agreement between MD and experiments is achieved, with H(MD) approximately 4 GPa at l(c) = 36 nm and H(expt) approximately 2.5 GPa at l(c) = 100 nm. An analytic model, incorporating the energy costs of forming the geometrically necessary dislocation structures that accommodate the deformation, is developed and captures the unique magnitude and size scaling of the hardness at larger MD sizes and up to experimental scales while rationalizing the transition in scaling between MD and experimental scales. The model suggests that dislocation-dislocation interactions dominate at larger scales, whereas the behavior at the smallest MD scales is controlled by nucleation over energy barriers. These results provide a basic framework for understanding and predicting size-dependent plasticity in nanoscale asperities under contact conditions in realistic engineered surfaces.

Strength can be controlled by edge dislocations in refractory high-entropy alloys.

Energy efficiency is motivating the search for new high-temperature (high-T) metals. Some new body-centered-cubic (BCC) random multicomponent "high-entropy alloys (HEAs)" based on refractory elements (Cr-Mo-Nb-Ta-V-W-Hf-Ti-Zr) possess exceptional strengths at high temperatures but the physical origins of this outstanding behavior are not known. Here we show, using integrated in-situ neutron-diffraction (ND), high-resolution transmission electron microscopy (HRTEM), and recent theory, that the high strength and strength retention of a NbTaTiV alloy and a high-strength/low-density CrMoNbV alloy are attributable to edge dislocations. This finding is surprising because plastic flows in BCC elemental metals and dilute alloys are generally controlled by screw dislocations. We use the insight and theory to perform a computationally-guided search over 107 BCC HEAs and identify over 106 possible ultra-strong high-T alloy compositions for future exploration.

Yield strength and misfit volumes of NiCoCr and implications for short-range-order.

The face-centered cubic medium-entropy alloy NiCoCr has received considerable attention for its good mechanical properties, uncertain stacking fault energy, etc, some of which have been attributed to chemical short-range order (SRO). Here, we examine the yield strength and misfit volumes of NiCoCr to determine whether SRO has measurably influenced mechanical properties. Polycrystalline strengths show no systematic trend with different processing conditions. Measured misfit volumes in NiCoCr are consistent with those in random binaries. Yield strength prediction of a random NiCoCr alloy matches well with experiments. Finally, we show that standard spin-polarized density functional theory (DFT) calculations of misfit volumes are not accurate for NiCoCr. This implies that DFT may be inaccurate for other subtle structural quantities such as atom-atom bond distance so that caution is required in drawing conclusions about NiCoCr based on DFT. These findings all lead to the conclusion that, under typical processing conditions, SRO in NiCoCr is either negligible or has no systematic measurable effect on strength.

Cyclical ischaemic preconditioning modulates the adaptive immune response in human limb ischaemia-reperfusion injury.

BACKGROUND: Reperfusion injury (RI) has significant local and systemic consequences. Ischaemic preconditioning (IPC) modulates RI and the innate immune response. This study examined whether IPC attenuates RI-mediated changes in lymphocyte populations and function following elective surgery. METHODS: Twenty-five patients sustaining 1 h of tourniquet ischaemia during cruciate ligament reconstruction were randomized before surgery to three 5-min ischaemia cycles separated by 5 min of reperfusion, or to a control group. Systemic levels of interleukin (IL) 4 and interferon (IFN) gamma, and surface expression of CD45ro/ra, CD62L and CD95 were measured. T cells were examined systemically and in stimulated serum co-culture to determine CD4/CD8 and Th1/Th2 shifts through intracellular cytokine production. RESULTS: CD4 CD45ro cell numbers increased after RI without IPC, whereas CD8 cells expressing CD45ro and CD95 increased with IPC. Preconditioned serum in co-culture attenuated increases in CD4 and decreases in CD8 numbers, a process prevented by inhibition of antigen activation. Following RI, systemic IL-2 levels were significantly lower after IPC, whereas co-culture with post-RI serum increased proinflammatory intracellular cytokine production. CONCLUSION: IPC modulated T cell responses in limb RI through reduced activation and proinflammatory cytokine production by CD4 cells, while preventing CD4/CD8 derangement. IPC prevented lymphocyte-directed immune dysfunction.

Mechanistic origin and prediction of enhanced ductility in magnesium alloys.

Pure magnesium exhibits poor ductility owing to pyramidal [Formula: see text] dislocation transformations to immobile structures, making this lowest-density structural metal unusable for many applications where it could enhance energy efficiency. We show why magnesium can be made ductile by specific dilute solute additions, which increase the [Formula: see text] cross-slip and multiplication rates to levels much faster than the deleterious [Formula: see text] transformation, enabling both favorable texture during processing and continued plastic straining during deformation. A quantitative theory establishes the conditions for ductility as a function of alloy composition in very good agreement with experiments on many existing magnesium alloys, and the solute-enhanced cross-slip mechanism is confirmed by transmission electron microscopy observations in magnesium-yttrium. The mechanistic theory can quickly screen for alloy compositions favoring conditions for high ductility and may help in the development of high-formability magnesium alloys.

Diathermy versus scalpel incisions for hemiarthroplasty for hip fracture: a randomised prospective trial.

As the age profile of our population expands, we can expect subsequent increase in patients presenting with intracapsular fracture. The onus remains on the surgeon to make all reasonable efforts to find new and innovative means of reducing associated morbidity and mortality of the treatment of these injuries. This challenge is particularly relevant in the elderly and in patients with multiple co-morbidities. In this study, 100 patients were randomly allocated into two groups. One group had dissection to the level of the hip joint under direct diathermy control; the other group had dissection using a scalpel with supplementary electrocautery. Intraoperative total blood loss prior to dissection of the abductors was measured by collecting blood using wound swabs using a local protocol and results were statistically analysed using PROC GLM SAS. We demonstrate a clear advantage in the use of diathermy to create a hip incision showing a significant reduction in wound-related blood loss and a reduction, whilst not statistically significant, in total operative blood loss using diathermy incision. Larger randomised prospective trials are necessary to study the effects of this intervention in a larger patient population so that these end-points can be adequately assessed.

A Simple and Easy Intramedullary Lavage Method to Prevent Embolism During and After Reamed Long Bone Nailing.

Reaming of the long bones is widely practiced because it allows for improved healing and early mobilization in patients needing surgical debridement of bone tissue. The insertion of reamed intramedullary nails can cause complications such as bone necrosis, cortical blood supply damage, and fat or bone marrow embolism. We describe a novel way to limit the amount of material in the canal before nail insertion to limit the chances of embolism.

Early results of the LPS™ limb preservation system in the management of periprosthetic femoral fractures.

INTRODUCTION: Achieving skeletal fixation in the presence of progressive bone loss is a surgical challenge, especially in cases of periprosthetic fracture (PPF). Unpredictable fracture patterns and preexisting bone loss frequently combine in this patient group. Megaprosthetic arthroplasty allows for immediate mobilisation and shorter periods of rehabilitation. We describe the clinical outcomes of a cohort of LPS™ megaprostheses performed for PPF by a single surgeon at our institution. METHODS: Between July 2013 and November 2015, 23 patients underwent endoprosthetic femoral replacement of which 16 were performed for PPF or bone loss. Patient demographics, surgical indication, operative details, implant composition, blood loss, survival, and revision surgery details were recorded in a prospectively maintained database. Patients underwent serial clinical and X-ray evaluations at 6 weeks, 3 months and 6 months post surgery with yearly reviews thereafter. RESULTS: The PPF cohort consisted of 9 males and 7 females with a mean age of 75 and a mean follow up of 19.2 months. The mean Oxford score prior to fracture was 41 (range 12-48), and 39 (range 13-48, p = 0.6) post megaprosthesis insertion. Postoperative dislocation of the megaprosthesis occurred in two patients (12.5%), with no postoperative infections recorded. CONCLUSION: We report minimal postoperative changes in functional outcome scores. The results of revision arthroplasty with LPS™ proximal femur megaprosthesis were satisfactory in 15/16 patients at a mean follow-up of 19.2 months. We recommend the use of megaprostheses in patients with markedly deficient bone stock for whom other available reconstructive procedures are unavailable.

Medium term review of the ASR implant system: A single surgeon series.

INTRODUCTION: Both ASR hip resurfacings and stemmed ASR XL arthroplasties have failed at high rates in several published series. We assessed a single surgeon series of these arthroplasties looking to identify factors associated with their failure. METHODS: All surgeries were performed by one surgeon. Patients were evaluated clinically, radiologically and with serial cobalt and chromium ion analysis. RESULTS: 274 implants were analysed - 152 ASR resurfacings and 122 ASR XL implants. Thirty revisions were performed. CONCLUSION: The failure rate of the ASR implant in our series is unacceptably high - its use in routine hip arthroplasty cannot be supported.

Mechanical work makes important contributions to surface chemistry at steps.

The effect of mechanical strain on the binding energy of adsorbates to late transition metals is believed to be entirely controlled by electronic factors, with tensile stress inducing stronger binding. Here we show, via computation, that mechanical strain of late transition metals can modify binding at stepped surfaces opposite to well-established trends on flat surfaces. The mechanism driving the trend is mechanical, arising from the relaxation of stored mechanical energy. The mechanical energy change can be larger than, and of opposite sign than, the energy changes due to electronic effects and leads to a violation of trends predicted by the widely accepted electronic 'd-band' model. This trend has a direct impact on catalytic activity, which is demonstrated here for methanation, where biaxial tension is predicted to shift the activity of nickel significantly, reaching the peak of the volcano plot and comparable to cobalt and ruthenium.

Intrapartum fever, epidural analgesia and histologic chorioamnionitis.

OBJECTIVE: Our objective was to determine whether epidural analgesia and histologic chorioamnionitis were independent predictors of intrapartum fever. STUDY DESIGN: This secondary analysis, retrospective cohort study included term parturients with placental examination during 2005. Logistic regression used fever (⩾38 °C) as the dependent variable. Significance was defined as P⩽0.05. RESULT: There were 488 (76%) of 641 term parturients with placental examination and epidural. Independent predictors of intrapartum fever were epidural odds ratio (OR)=3.4, confidence interval (CI): 1.70, 6.81, histologic chorioamnionitis OR=3.18, 95% CI: 2.04, 4.95, birthweight OR=2.07, 95%CI: 1.38, 3.12, vaginal exams OR=1.15, 95% CI:1.06, 1.24, duration ruptured membranes OR=1.03, 95% CI: 1.01,1.05, parity⩾1 OR=0.44: 0.29, 0.66 and thick meconium OR=0.35: 95%CI: 0.24, 0.85. CONCLUSION: Epidural analgesia and histologic chorioamnionitis were independent predictors of intrapartum fever. Modification of labor management may reduce the incidence of intrapartum fever.