Structural and ultrastructural changes in striated skeletal muscle tissue following high-energy injuries in the early post-traumatic period

BACKGROUND: With the sharp increase in mine-explosive injuries, one of the key tasks of modern histology is to assess the morphogenesis of high-energy limb tissue damage. AIM: This study aimed to characterize striated skeletal muscle tissue in the zone of mine-explosive limb segment avulsion during the early post-traumatic period (days 1–4). METHODS: Histological methods (hematoxylin and eosin staining and Martius Scarlet Blue [MSB] staining for fibrin age determination), immunohistochemical and immunofluorescence techniques (antibodies to CD3, CD20, CD31 [Platelet Endothelial Cell Adhesion Molecule-1], CD68, and NETs [Neutrophil Extracellular Traps]), transmission electron microscopy, and morphometric analyses were applied. RESULTS: Post-traumatic pathological changes affected both muscle tissue (necrosis, fiber fragmentation, traumatic edema) and endomysial and perimysial connective tissue (traumatic edema, fibrin infiltration). Disruption of the cytoskeletal structure (sarcomeres), loss of myosatellite cells, and endothelial cell death in capillaries were observed. Local hemodynamic disturbances manifested as mosaic thrombosis, embolism, and hemorrhage. Within the first 24 hours, arterial and arteriolar spasms led to reduced tissue perfusion. Partial resolution of the spasms by day 4 likely corresponded to the second stage of traumatic shock (the torpid phase). Among leukocytes, CD68+ macrophages were the first to respond, with extravasation beginning on day 2 after injury. A similar trend was observed for CD3+ T cells. CD20+ B cells showed no morphological signs of reactivity during this period. NET formation was observed both intravascularly and in the extravascular compartment. CONCLUSION: Structural and ultrastructural changes in skeletal muscle tissue within the first 4 days after mine-explosive injury have been characterized.