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Classification of spinal cord injury (ISNCSCI and AIS)

In spinal cord injury, "complete" or "incomplete" is decided only by the lowest sacral segments (S4–5): if there is sensation or motor control there, the injury is incomplete — even if the limbs are paralysed.

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Why it matters in the exam

The exam presents ISNCSCI examination results and asks for the neurological level and the AIS grade. Sensory level: the lowest dermatome with normal light touch and pinprick. Motor level: the lowest key muscle with strength of at least 3, provided the muscles above it have strength 5; in regions without a key muscle (C1–C4, T2–L1, S2–S5) the motor level equals the sensory level. The neurological level (NLI) is the highest of the four levels (sensory and motor, right and left).

Key muscles: C5 elbow flexors, C6 wrist extensors, C7 elbow extensors, C8 middle finger flexor, T1 little finger abductor; L2 hip flexors, L3 knee extensors, L4 ankle dorsiflexors, L5 long toe extensor, S1 ankle plantar flexors. AIS A — complete: no sensation and no movement at S4–5 (including deep anal pressure and voluntary anal contraction). AIS B — sensory incomplete: sacral sensation, no movement below the level (and not more than three levels below the motor level). AIS C — motor incomplete, and fewer than half of key muscles below the NLI have strength 3 or more. AIS D — at least half have strength 3 or more. AIS E — normal.

A reliable examination for prognosis is done about 72 hours after injury, after spinal shock, whose end is marked by the return of the bulbocavernosus reflex. Predictors of walking: incomplete injury, and especially preserved pinprick in the sacral segments in AIS B. Incomplete syndromes: central cord syndrome — the common one, in an older person with cervical stenosis and hyperextension, arms weaker than legs and a relatively good prognosis; Brown-Séquard — weakness and loss of position sense on the same side and loss of pain and temperature on the opposite side, with the best prognosis for walking; anterior cord syndrome — paralysis and loss of pain and temperature with preserved position sense, and the worst prognosis. The zone of partial preservation (ZPP) describes segments with partial function below the level.

Key points

• Completeness is decided by S4–5.
• Motor level — strength 3 with strength 5 above.
• NLI — the highest of the four levels.
• C versus D — half of key muscles at strength 3.
• Brown-Séquard — good prognosis; anterior cord — poor.

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Sources

• International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI), ASIA/ISCoS, revised 2019 — Levels, AIS grades and zone of partial preservation
• Braddom's Physical Medicine and Rehabilitation, 6th edition (2021) — Spinal Cord Injury

Sources are given for further reading; the text is written afresh and not copied from them.

Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.