ASIA impairment scale for spinal injury

The American Spinal Injury Association Impairment Scale (AIS) was developed by the American Spinal Injury Association (ASIA) in 2006, was revised in 2011, and remains the most widely used neurologic classification of spinal cord injury.

Classification

The scale divides spinal cord injuries into 5 categories:

• A: complete

  • no sensory or motor function at the most caudal sacral segments (S4-S5) as measured by perianal light touch or pinprick sensation, deep anal pressure sensation, and voluntary anal sphincter contraction

• B: incomplete sensory

  • sensory but not motor function is preserved below the neurological level including sensory sacral sparing, AND no motor function is preserved more than three levels below the motor level on either side of the body

• C: incomplete motor

  • motor function is preserved below the neurological level, and more than half of key muscles below the neurological level have a muscle grade of less than 3 strength

• D: incomplete motor

  • motor function is preserved below the neurological level, and at least half of key muscles below the neurological level have a muscle grade of 3 or more strength

• E: normal

  • prior injury now with normal motor and sensory testing

The neurological level of injury is the lowest (most caudal) segment above which there is preserved sensation and at least antigravity (grade 3) motor function on both sides of the body. The motor and sensory levels are specified separately for each side and can either be at or below (more caudal) than the single overall neurological level. The motor level is the lowest of ten key myotomes (C5-T1 and L2-S1) that have at least grade 3 (antigravity) function and above which there is grade 5 (normal) function. The sensory level is the lowest of 28 dermatomes (C2 to S4-5) that is intact to both pinprick and light touch sensations.

Clinical syndromes

Incomplete spinal cord injuries can optionally be differentiated by syndrome:

• central cord syndrome

• Brown-Sequard syndrome

• anterior cord syndrome

• conus medullaris syndrome

• cauda equina syndrome

Muscle strength grading

• 0: total paralysis

• 1: palpable or visible contraction

• 2: active movement, full range of motion, gravity eliminated

• 3: active movement, full range of motion, against gravity

• 4: active movement, full range of motion, against gravity and provides some resistance

• 5: active movement, full range of motion, against gravity and provides normal resistance

• 5*: muscle able to exert, in the examiner’s judgment, sufficient resistance to be considered normal if identifiable inhibiting factors were not present