Understanding spinal cord injury

The level of injury describes the lowest segment of the spinal cord still working normally, and completeness describes whether any signal passes below it. Together they determine what recovery is realistically possible, which is why the ASIA classification is done carefully and repeated.

Injuries are described by the vertebral level — C for cervical (neck), T for thoracic (chest), L for lumbar. Higher injuries affect more of the body: a C5 injury affects arms and legs, a T10 injury affects the legs and trunk below that point.

The vertebral level and the neurological level are not always the same, because the spinal cord is shorter than the spinal column. A fracture of the T12 vertebra can produce a neurological level several segments lower, which is why the neurological examination rather than the X-ray defines the injury.

An incomplete injury means some signal still crosses the damaged segment, and that changes the prognosis substantially. Whether any sensation or movement remains in the lowest segments — sacral sparing — is the single most consequential finding in the examination.

Sacral sparing is tested specifically — sensation around the anus and voluntary anal contraction — because it is the most reliable indicator that some pathway remains intact. It is an uncomfortable examination and it is the one that most changes the prognosis.

The grade can change over the first weeks as swelling settles. An assessment done in the acute phase is less reliable, and a prognosis given on it should be treated as provisional.

Spinal shock, a period of absent reflexes immediately after injury, can make a functionally incomplete injury look complete. Classification is therefore repeated at intervals, and a grade assigned in the first days should never be presented to a family as a final answer.

The difference between C5 and C6 is the difference between needing assistance for most self-care and being able to feed, groom and manage a manual wheelchair independently, because C6 preserves wrist extension and with it a functional tenodesis grip.

This is why a single segment of recovery matters so much in cervical injury, and why upper limb rehabilitation is prioritised there over almost everything else.