Biomechanical Effects of a Cross Connector in Sacral Fractures – A Finite Element Analysis

Background: Spinopelvic fractures and approaches of operative stabilization have been a source of controversial discussion. Biomechanical data support the benefit of a spinopelvic stabilization and minimally invasive procedures help to reduce the dissatisfying complication rate. The role of a cross connector within spinopelvic devices remains inconclusive. We aimed to analyze the effect of a cross connector in a finite element model (FE model). Study Design: A FE model of the L1-L5 spine segment with pelvis and a spinopelvic stabilization was reconstructed from patient-specific CT images. The biomechanical relevance of a cross connector in a Denis zone I (AO: 61-B2) sacrum fracture was assessed in the FE model by applying bending and twisting forces with and without a cross connector. Biomechanical outcomes from the numerical model were investigated also considering uncertainties in material properties and levels of osseointegration. Results: The designed FE model showed comparable values in range-of-motion (ROM) and stresses with reference to the literature. The superiority of the spinopelvic stabilization (L5/Os ilium) ± cross connector compared to a non-operative procedure was confirmed in all analyzed loading conditions by reduced ROM and principal stresses in the disk L5/S1, vertebral body L5 and the fracture area. By considering the combination of all loading cases, the presence of a cross connector reduced the maximum stresses in the fracture area of around 10%. This difference has been statistically validated (p < 0.0001). Conclusion: The implementation of a spinopelvic stabilization (L5/Os ilium) in sacrum fractures sustained the fracture and led to enhanced biomechanical properties compared to a non-reductive procedure. While the additional cross connector did not alter the resulting ROM in L4/L5 or L5/sacrum, the reduction of the maximum stresses in the fracture area was significant. © Copyright © 2021 Gierig, Liu, Weiser, Lehmann, Wriggers, Marino and Saul

Bone Healing Gone Wrong : Pathological Fracture Healing and Non-Unions—Overview of Basic and Clinical Aspects and Systematic Review of Risk Factors

Bone healing is a multifarious process involving mesenchymal stem cells, osteoprogenitor cells, macrophages, osteoblasts and -clasts, and chondrocytes to restore the osseous tissue. Particularly in long bones including the tibia, clavicle, humerus and femur, this process fails in 2–10% of all fractures, with devastating effects for the patient and the healthcare system. Underlying reasons for this failure are manifold, from lack of biomechanical stability to impaired biological host conditions and wound-immanent intricacies. In this review, we describe the cellular components involved in impaired bone healing and how they interfere with the delicately orchestrated processes of bone repair and formation. We subsequently outline and weigh the risk factors for the development of non-unions that have been established in the literature. Therapeutic prospects are illustrated and put into clinical perspective, before the applicability of biomarkers is finally discussed

Limit on the Fierz Interference Term b from a Measurement of the Beta Asymmetry in Neutron Decay

In the standard model of particle physics, the weak interaction is described by vector and axial-vector couplings only. Non-zero scalar or tensor interactions would imply an additional contribution to the differential decay rate of the neutron, the Fierz interference term. We derive a limit on this hypothetical term from a measurement using spin polarized neutrons. This method is statistically less sensitive than the determination from the spectral shape but features much cleaner systematics. We obtain a limit of b = 0.017(21) at 68.27 C.L., improving the previous best limit from neutron decay by a factor of four.Comment: Phys. Rev. Lett., https://journals.aps.org/prl

Cilostazol promotes blood vessel formation and bone regeneration in a murine non-union model

Non-unions represent a major complication in trauma and orthopedic surgery. Many factors contribute to bone regeneration, out of which an adequate vascularization has been recognized as crucial. The phosphodiesterase-3 (PDE-3) inhibitor cilostazol has been shown to exert pro-angiogenic and pro-osteogenic effects in a variety of preclinical studies. Hence, we herein investigated the effects of cilostazol on bone regeneration in an atrophic non-union model in mice. For this purpose, a 1.8 mm femoral segmental defect was stabilized by pin-clip fixation and the animals were treated daily with 30 mg/kg body weight cilostazol or saline (control) per os. At 2, 5 and 10 weeks after surgery the healing of femora was analyzed by X-ray, biomechanics, photoacoustic imaging, and micro-computed tomography (µCT). To investigate the cellular composition and the growth factor expression of the callus tissue additional histological, immunohistochemical and Western blot analyses were performed. Cilostazol-treated animals showed increased bone formation within the callus, resulting in an enhanced bending stiffness when compared to controls. This was associated with a more pronounced expression of vascular endothelial growth factor (VEGF), a higher number of CD31-positive microvessels and an increased oxygen saturation within the callus tissue. Furthermore, cilostazol induced higher numbers of tartrate-resistant acidic phosphate (TRAP)-positive osteoclasts and CD68-positive macrophages. Taken together, these findings demonstrate that cilostazol is a promising drug candidate for the adjuvant treatment of atrophic non-unions in clinical practice

Significant effusion in the joints of the lower extremity after running an ultramarathon in extreme conditions

Introduction: The “Brocken challenge” ultramarathon takes place in the cold of February over 80 km with 1,900 m of elevation change. The purpose of this study was to evaluate the effects of an ultramarathon under extreme conditions on the lower extremities. Methods: Out of the 182 starters, 44 athletes were included into the study (n=44). We examined these athletes using a questionnaire, by measuring circumferences of their lower extremities and by standardized sonographic measurement of joint effusion of knee and ankle joints before and after the run. Results: After the run, the right leg and both feet significantly increased in circumference. Knee joints on both sides and the left ankle joint showed significantly more effusion after the run (right knee: 84%, right ankle: 43%; left knee: 80%, left ankle: 48%). Heavier and less trained athletes showed significantly more effusion in sonographic assessment of the knee and ankle. Neither swelling, nor effusion had a measurable influence on finishing time. Conclusions: Running an ultramarathon in the cold overloads the fluid draining capacity in the muscles and joints of the legs especially in heavier and less trained athletes without measurable immediate effect on performance

The Astropy Problem

The Astropy Project (http://astropy.org) is, in its own words, "a community effort to develop a single core package for Astronomy in Python and foster interoperability between Python astronomy packages." For five years this project has been managed, written, and operated as a grassroots, self-organized, almost entirely volunteer effort while the software is used by the majority of the astronomical community. Despite this, the project has always been and remains to this day effectively unfunded. Further, contributors receive little or no formal recognition for creating and supporting what is now critical software. This paper explores the problem in detail, outlines possible solutions to correct this, and presents a few suggestions on how to address the sustainability of general purpose astronomical software

Production of charged pions, kaons and protons at large transverse momenta in pp and Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV

Transverse momentum spectra of $\pi^{\pm}, K^{\pm}$ and $p(\bar{p})$ up to $p_T$ = 20 GeV/c at mid-rapidity, |y| $\le$ 0.8, in pp and Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV have been measured using the ALICE detector at the LHC. At intermediate $p_T$ (2-8 GeV/c) an enhancement of the proton-to-proton ratio, (p + \bar{p})/(\pi^+ + \pi^-\(), with respect to pp collisions is observed and the ratio reaches 0.80 in central Pb-Pb collisions. The measurement of the nuclear modification factors for \(\pi^{\pm}, K^{\pm} and $p(\bar{p})$ indicates that within the systematic and statistical uncertainties they are the same at high $p_T$ (> 10 GeV/c), suggesting that the chemical composition of leading particles from jets in the medium is similar to that of vacuum jets.publishedVersio

Charmonium and e+e−e^+e^- pair photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV

The ALICE Collaboration at the LHC has measured the $J/\psi$ and $\psi$' photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. The charmonium is identified via its leptonic decay for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 23 ${\mu}b^{-1}$, The cross section for coherent and incoherent $J/\psi$ production in the rapidity interval -0.9 < y < 0.9, are $d\sigma_{J/\psi}^{coh}/dy = 2.38^{+0.34}_{-0.24}(sta+sys)$ mb and $d\sigma_{J/\psi}^{inc}/dy = 0.98^{+0.19}_{-0.17}(sta+sys)$ mb, respectively. The results are compared to theoretical models for $J/\psi$ production and the coherent cross section is found to be in good agreement with those models which include nuclear gluon shadowing consistent with EPS09 parametrization. In addition the cross section for the process $\gamma\gamma \to e^+e^-$ has been measured and found to be in agreement with the STARLIGHT Monte Carlo predictions.publishedVersio

Measurement of the Cross Section for Electromagnetic Dissociation with Neutron Emission in Pb-Pb Collisions at √sNN = 2.76 TeV

The first measurement of neutron emission in electromagnetic dissociation of 208Pb nuclei at the LHC is presented. The measurement is performed using the neutron Zero Degree Calorimeters of the ALICE experiment, which detect neutral particles close to beam rapidity. The measured cross sections of single and mutual electromagnetic dissociation of Pb nuclei at √sNN = 2.76 TeV with neutron emission are σ_single EMD = 187.2±0.2 (stat.) +13.8−12.0 (syst.) b and σ_mutual EMD = 6.2 ± 0.1 (stat.) ±0.4 (syst.) b respectively. The experimental results are compared to the predictions from a relativistic electromagnetic dissociation model.publishedVersio