Cellular Events and Pathophysiology of SCI.

Spinal cord injury (SCI) has occurred in 2.5 million people worldwide, and 130,000 new cases are reported each year. SCI most commonly consists of a compression injury with hemorrhage into gray matter and loss of neurons, oligodendroglia, and astrocytes, followed by invasion of lymphocytes and macrophages; cavitation of the cord follows, then Wallerian degeneration of ascending and descending tracts and loss of neuronal circuitry, culminating in glial scar perpendicular to the direction of the axon. Onset of necrosis occurs within 24 hours. Spontaneous repair is incomplete and involves limited sprouting of axons and new spinal circuits that bypass the lesion and move into descending tracts, resulting in indirect connections with lumbar motor neurons.