The ASIA Impairment Scale (AIS) grade B spinal cord injury is defined as:

• A Motor incomplete: >50% key muscles below injury level have muscle grade <3
• B Normal motor function but abnormal sensory below injury level
• C Sensory incomplete: sensory but no motor function preserved below neurological level, including sacral segments S4-S5 ✓
• D Complete injury: no sensory or motor function in sacral segments S4-S5

Explanation

ASIA Impairment Scale: AIS A = complete (no sensory/motor at S4-S5); AIS B = sensory incomplete (sensory but no motor preserved below neurological level, including S4-S5); AIS C = motor incomplete (motor function preserved, >50% key muscles below NLI grade <3); AIS D = motor incomplete (>50% key muscles ≥3); AIS E = normal. Sacral sparing at S4-S5 (perianal sensation, voluntary anal contraction) determines complete vs incomplete injury. AIS B implies some sensory preservation — including sacral segments — without useful motor function.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.