The ASIA Impairment Scale (AIS) classifies a patient as Grade B when:

• A Normal motor and sensory function below the neurological level
• B Sensory but no motor function is preserved below the neurological level including S4–S5 (sacral sparing) ✓
• C Motor function preserved below neurological level — majority of key muscles graded <3/5
• D Motor function preserved below neurological level — majority of key muscles graded ≥3/5

Explanation

ASIA Impairment Scale: Grade A = complete (no motor or sensory function below neurological level, including S4–S5); Grade B = sensory incomplete (sensory preserved below including S4–S5, no motor function); Grade C = motor incomplete (motor preserved below, majority of key muscles <3/5); Grade D = motor incomplete (majority of key muscles ≥3/5); Grade E = normal. Sacral sparing (voluntary anal contraction, perianal sensation, or big toe/heel proprioception) is critical — its presence converts a Grade A to Grade B. Sacral sparing predicts potential for neurological recovery and drives rehabilitation goals.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.