Spinal cord injury

Why it matters

In 2021 about 14.5 million people worldwide were living with a spinal cord injury, roughly half with injuries at neck level and half below it ^[1]. The highest prevalence was in men aged 50 to 64 ^[1].

What it is

A spinal cord injury interrupts communication between the brain and the parts of the cord below the damage ^[2]. What is lost depends on the level and on how much of the cord's cross-section is damaged ^{[3, 4]}.

When it does not behave

The level decides which functions are affected ^{[5, 6, 3]}:

• The phrenic nerve leaves the cord at C3 to C5, so damage below the mid-cervical level does not stop the diaphragm ^[5].
• The micturition reflex may survive an injury causing paraplegia or quadriplegia, but voluntary control needs an intact cord and pudendal nerve, and catheterisation may be needed ^[6].
• Upper motor neuron damage brings weakness, strong tendon reflexes and spasticity, while lower motor neuron damage brings flaccid paralysis and lost reflexes ^[3].

How we see and measure it

The International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) test sensation at a key point in each dermatome and strength in key muscles on both sides ^{[7, 8]}. From these come the sensory and motor levels, the neurological level of injury, and the ASIA Impairment Scale (AIS) grade ^[4]:

• AIS A, neurologically complete: no sacral sparing, meaning no light touch or pinprick at S4–5, no deep anal pressure and no voluntary anal contraction ^[9].
• An injury is incomplete when there is sensory or motor sparing in the lowest sacral segments ^[4].
• A sensory incomplete injury can be graded AIS C if there is motor function more than three segments below the motor level ^[9].
• Among motor incomplete injuries, AIS D means at least half of the key muscles below the neurological level have a grade of 3 or more; otherwise it is AIS C ^[4].
• AIS E is for people with a documented spinal cord injury whose follow-up examination is intact ^[8].

ISNCSCI motor score^[7]

$$\mathrm{MS} = \mathrm{UEMS} + \mathrm{LEMS},\quad \mathrm{UEMS} = \sum_{C5}^{T1} (R + L),\quad \mathrm{LEMS} = \sum_{L2}^{S1} (R + L)$$

Each of the ten key muscles is graded 0 to 5 on each side. The upper-limb motor score adds the five arm muscles (C5 to T1) on both sides, up to 50; the lower-limb score adds the five leg muscles (L2 to S1), up to 50.

Variables of ISNCSCI motor score

Symbol	Meaning	Unit
$\mathrm{UEMS}$	upper extremity motor score	dimensionless
$\mathrm{LEMS}$	lower extremity motor score	dimensionless
$\mathrm{MS}$	sum of the two motor scores	dimensionless

Valid when

• A scoring convention for examination after spinal cord injury, done by trained examiners
• For learning only: this site does not score or interpret anyone’s examination

Worked example^[7]

Full strength in all ten key muscles on both sides gives 50 + 50.

uems = 50 , lems = 50 → ms = 100

Frontier

Research is trying to restore movement by stimulating the lumbar cord, by linking cortical recordings to that stimulation, and by guiding regenerating axons. Each entry shows its evidence tier and what it does not show ^{[10, 11, 2, 12]}.

• T1T1 peer-reviewed human studyStimulation timed to the intended step restores walking2018-10 · as of 2026-10-02 · trial

  Trains of spatially selective stimulation were delivered to the lumbosacral cord at the moment each leg movement was intended. In people injured more than four years earlier, adaptive control of paralysed muscles returned within a week; after months of rehabilitation some regained voluntary control without stimulation.

  What it does not show: A small group with incomplete or chronic injuries; walking needed the implant and assistance, and results do not predict any one person's recovery.

  Sources and details
• T1T1 peer-reviewed human studyActivity-specific stimulation after complete paralysis2022-02 · as of 2026-10-02 · trial

  A new paddle lead was arranged to target the dorsal roots for leg and trunk movements, with software for activity-specific stimulation programs. Within a single day, three people with complete sensorimotor paralysis could stand, walk, cycle, swim and control trunk movements with stimulation.

  What it does not show: Three participants; the movements need the stimulation programs to run, and the cord injury itself is not healed.

  Sources and details

• T2T2 peer-reviewed animal or in-vitro studyRegrowing the right axons to the right place restores walking in mice2023-09 · as of 2026-10-02 · research

  After identifying the neuron types that restore walking after incomplete injury, the team guided their cut axons back to their natural target region. In mice with complete spinal cord injury this led to substantial recovery of walking, whereas regrowth simply across the lesion had no effect.

  What it does not show: Mice, not people. No human treatment exists from this work.

  Sources and details

Common misconceptions

Check yourself

What makes an injury AIS A?

No sacral sparing: no light touch or pinprick at S4–5, no deep anal pressure and no voluntary anal contraction ^[9].

Why can someone with an injury at C6 still breathe with the diaphragm?

The phrenic nerve leaves the cord at C3 to C5, above the injury ^[5].

Read next

• Incomplete cord syndromes.
• Lesion explorer.
• Brain–spine interfaces.