Frequently, however, the more destructive injury occurs after impact and its mechanisms are less visible.
Secondary injury begins after impact and can continue for hours, even days.
Toxic substances, normally released by cells in very small amounts, flood the liquid spaces between cells after injury. At high concentrations, these substances initiate a cascade of complex neurochemical and pathophysiological events that can permanently injure neighboring cells. The formation of oxygen-free radicals is of particular concern following traumatic injury. These elements target primarily the fatty acids of cell membranes and cause lipid peroxidation, which damages neuronal, glial, and vascular cell membranes in a geometrically progressing fashion. Left unchecked, lipid peroxidation spreads over the entire surface of the cell membrane, leading to cell death.