The spinal cord contains the nervous system structures serving motor, sensory, and autonomic functions of the body. A spinal cord injury is thus an injury affecting these structures, resulting in transitory or permanent motor, sensory, or autonomic dysfunction. Patients with spinal cord injuries often have permanent neurologic deficits and disabilities. Causes of spinal cord injury include direct trauma from motor vehicle collisions, falls, sports injuries, or gunshot wounds; compression secondary to bony fragments or osteoporosis, abscess, hematoma, or disk material; and ischemia secondary to compromise of spinal arteries. Men are more likely to have spinal cord injuries than women. The average age for spinal cord injuries is 42. There are approximately 17 000 new spinal cord injuries each year in the United States.

Clinical presentation is related to the level of spinal cord injury. Classification of spinal cord injuries is typically performed based on the American Spinal Injury Association (ASIA) grading system, with grade A being a complete injury and grades B through D representing less severe injuries. Injuries may also be defined by the level of the vertebral injury (eg, C5 or L1), but it should be noted that the vertebral level is not the same as the spinal cord level, due to the vertebral column extending beyond the length of the spinal cord, which ends at L2-L3.

Other descriptors include tetraplegia, referring to an injury in the cervical region with associated loss of muscle strength in all 4 extremities, and paraplegia, with an injury to the spinal cord in the thoracic, lumbar, or sacral segments leading to loss of muscle strength in the lower extremities.

Injury at the level of C4 or above will result in impairment of respiratory function and need for intubation because of diaphragm paralysis due to compromise of the phrenic nerve, consisting of nerve roots from C3-C5. Lower cervical and upper thoracic injuries may also involve some degree of respiratory dysfunction due to paralysis of many intercostal / chest wall muscles.

Initially, spinal cord injury results in flaccid paralysis, change in sensation, loss of reflexes, and/or loss of bowel / bladder function. When accompanied by hypotension and bradycardia, this is often referred to as "spinal shock."

Over a period of days to weeks after a severe injury, the examination findings will change to spastic extremities, brisk reflexes, and urinary retention, often requiring catheterization.

Disruption of the autonomic nervous system, more specifically sympathetic function, occurs if the cervical or thoracic cord is injured. In settings of severe injury, after spinal shock wears off, autonomic dysreflexia can occur, which results in episodic sweating, flushing, hypertension, and reflexive bradycardia.