Spinal cord injuries causes myelopathy or damage to white matter or myelinated fiber tracts that carry signals to and from the brain. It also damages gray matter in the central part of the spine, causing segmental losses of interneurons and motorneurons. Spinal cord injury can occur from many causes, including:

• Trauma such as automobile crashes, falls, gunshots, diving accidents, war injuries, etc.
• Tumor such as meningiomas, ependymomas, astrocytomas, and metastatic cancer.
• Ischemia resulting from occlusion of spinal blood vessels, including dissecting aortic aneurysms, emboli, arteriosclerosis.
• Developmental disorders, such as spina bifida, meningomyolcoele, and other.
• Neurodegenerative diseases, such as Friedreich's ataxia, spinocerebellar ataxia, etc.
• Demyelinative diseases, such as Multiple Sclerosis.
• Transverse myelitis, resulting from spinal cord stroke, inflammation, or other causes.
• Vascular malformations, such as arteriovenous malformation (AVM), dural arteriovenous fistula (AVF), spinal hemangioma, cavernous angioma and aneurysm.

Stages

a) Stage of spinal shock - i.e., sensation and motor power localized below the vertical height of the lesion are lost. This stage lasts for 2 to 3 weeks in humans, and hours to days in lower animals due to a lesser degree of encephalitis.
b) Stage of recovery - after a period typically ranging from 2 to 3 weeks of injury, the nerves partially recover, and the return of segmental reflexes produce paraplegia-in-flexion.
c) Stage of reflex failure - after a period of days the recovered reflexes again start to give way due to complete degeneration of nerve cells.

Classification

The American Spinal Injury Association or ASIA defined an international classification based on neurological levels, touch and pinprick sensations tested in each dermatome, and strength of ten key muscles on each side of the body, i.e. shoulder shrug (C4), elbow flexion (C5), wrist extension (C6), elbow extension (C7), hip flexion (L2). Traumatic spinal cord injury is classified into five types by the American Spinal Injury Association and the International Spinal Cord Injury Classification System.

• A indicates a "complete" spinal cord injury where no motor or sensory function is preserved in the sacral segments S4-S5. Since the S4-S5 segment is the lower segmental, absence of motor and sensory function indicates "complete" spinal cord injury.
• B indicates an "incomplete" spinal cord injury where sensory but not motor function is preserved below the neurological level and includes the sacral segments S4-S5. This is typically a transient phase and if the person recovers any motor function below the neurological level, that person essentially becomes a motor incomplete, i.e. ASIA C or D.
• C indicates an "incomplete" spinal cord injury where motor function is preserved below the neurological level and more than half of key muscles below the neurological level have a muscle grade of less than 3.
• D indicates an "incomplete" spinal cord injury where motor function is preserved below the neurological level and at least half of the key muscles below the neurological level have a muscle grade of 3 or more.
• E indicates "normal" where motor and sensory scores are normal. Note that it is possible to have spinal cord injury and neurological deficit with completely normal motor and sensory scores.