Pelvic ring fractures: External fixation comparative numerical structural analysis

External fixation (EF) is commonly practiced for pelvic ring fractures management. Many parameters influence mechanical performances of external fixators. Our virtual 3D model of the pelvic ring introduces the advantage of differentiating the mechanical properties of cortical and cancellous bone along with the complex boundary conditions of major ligaments. We assessed stiffness variations by increasing fixator pins depth and we evaluated dislocation related to load intensity and sitting angle

Spiral-Wave Turbulence and Its Control in the Presence of Inhomogeneities in Four Mathematical Models of Cardiac Tissue

Regular electrical activation waves in cardiac tissue lead to the rhythmic contraction and expansion of the heart that ensures blood supply to the whole body. Irregularities in the propagation of these activation waves can result in cardiac arrhythmias, like ventricular tachycardia (VT) and ventricular fibrillation (VF), which are major causes of death in the industrialised world. Indeed there is growing consensus that spiral or scroll waves of electrical activation in cardiac tissue are associated with VT, whereas, when these waves break to yield spiral- or scroll-wave turbulence, VT develops into life-threatening VF: in the absence of medical intervention, this makes the heart incapable of pumping blood and a patient dies in roughly two-and-a-half minutes after the initiation of VF. Thus studies of spiral- and scroll-wave dynamics in cardiac tissue pose important challenges for in vivo and in vitro experimental studies and for in silico numerical studies of mathematical models for cardiac tissue. A major goal here is to develop low-amplitude defibrillation schemes for the elimination of VT and VF, especially in the presence of inhomogeneities that occur commonly in cardiac tissue. We present a detailed and systematic study of spiral- and scroll-wave turbulence and spatiotemporal chaos in four mathematical models for cardiac tissue, namely, the Panfilov, Luo-Rudy phase 1 (LRI), reduced Priebe-Beuckelmann (RPB) models, and the model of ten Tusscher, Noble, Noble, and Panfilov (TNNP). In particular, we use extensive numerical simulations to elucidate the interaction of spiral and scroll waves in these models with conduction and ionic inhomogeneities; we also examine the suppression of spiral- and scroll-wave turbulence by low-amplitude control pulses. Our central qualitative result is that, in all these models, the dynamics of such spiral waves depends very sensitively on such inhomogeneities. We also study two types of control schemes that have been suggested for the control of spiral turbulence, via low amplitude current pulses, in such mathematical models for cardiac tissue; our investigations here are designed to examine the efficacy of such control schemes in the presence of inhomogeneities. We find that a local pulsing scheme does not suppress spiral turbulence in the presence of inhomogeneities; but a scheme that uses control pulses on a spatially extended mesh is more successful in the elimination of spiral turbulence. We discuss the theoretical and experimental implications of our study that have a direct bearing on defibrillation, the control of life-threatening cardiac arrhythmias such as ventricular fibrillation

Arthroscopic reduction and fixation of partial posterior wall acetabular fractures

BACKGROUND AND AIM: Reduction and fixation of partial posterior wall fracture is usually performed with an open posterolateral approach. When the fragment may be fixed without a plate (with screws only), reduction and fixation may be also achieved via hip arthroscopy. To our knowledge no study described this technique. Aim of our study is to describe the surgical technique and to present the achieved outcomes and the occurred complications. METHODS: Six cases of arthroscopic fixation of partial posterior wall fracture have been reviewed for the purpose of this study. Patients were treated arthroscopically if the fragment was not bigger than 25% of the posterior wall. Patient demographic, injury, and surgical variables as well as complications were recorded and retrospectively evaluated. Radiographic outcome was scored according to Matta's criteria on postoperative radiographs and clinical outcomes were evaluated with the modified Harris hip score. RESULTS: Fracture reduction was classified as anatomic on post-operative x-rays in all patients. The mean clinical score was 98 points at one year follow-up. No patient developed symptomatic femoral head AVN, none had heterotopic ossification. In one patients a screw breakage occurred without clinical complications. CONCLUSIONS: Arthroscopic reduction and fixation of partial posterior wall fracture is an effective treatment and showed good outcomes if a careful patients' selection is done