A Method for Evaluation the Fatigue Microcrack Propagation in Human Cortical Bone Using Differential X-ray Computed Tomography.

Fatigue initiation and the propagation of microcracks in a cortical bone is an initial phase of damage development that may ultimately lead to the formation of macroscopic fractures and failure of the bone. In this work, a time-resolved high-resolution X-ray micro-computed tomography (CT) was performed to investigate the system of microcracks in a bone sample loaded by a simulated gait cycle. A low-cycle (1000 cycles) fatigue loading in compression with a 900 N peak amplitude and a 0.4 Hz frequency simulating the slow walk for the initialization of the internal damage of the bone was used. An in-house developed laboratory X-ray micro-CT imaging system coupled with a compact loading device were employed for the in situ uni-axial fatigue experiments reaching a µ2µm effective voxel size. To reach a comparable quality of the reconstructed 3D images with the SEM microscopy, projection-level corrections and focal spot drift correction were performed prior to the digital volume correlation and evaluation using differential tomography for the identification of the individual microcracks in the microstructure. The microcracks in the intact bone, the crack formation after loading, and the changes in the topology of the microcracks were identified on a volumetric basis in the microstructure of the bone.

A comprehensive interdisciplinary view at the Return to Sport after COVID-19 infection.

The COVID-19 pandemic has affected the whole world. It applies to all age and social groups. It is no different with athletes. So far, we cannot say for sure what the long-term consequences of SARS-CoV-2 infection are. Recent evidence, however, suggests that we should be very careful when returning to sports. After self-isolation, the athlete should undergo a Preparticipation Physical Examination and then pay attention to the gradual dosing of the load to prevent complications. Lifestyle changes and care for the mental health of athletes are also necessary during the illness. In this work, we present a comprehensive methodology for returning to sports after COVID-19 for medical and coaching teams caring for athletes divided according to the course of the disease. In scientific literature, similar algorithms are called "Return to Play" or "Return to Sport". Creating an exact algorithm can make the Return to Play process more efficient and safer. However, increased attention still needs to be paid to certain organ systems and specific symptoms that could indicate long-term consequences to the new type of coronavirus.