3.1 ASIA Examination & Impairment Scale
Key Takeaways
- The ISNCSCI protocol provides a standardized clinical framework for classifying spinal cord injury severity, sensory levels, motor levels, and completeness.
- Neurologic Level of Injury (NLI) is defined as the most caudal spinal segment possessing intact sensory (2/2) AND motor function (>=3/5), provided all rostral motor levels are 5/5.
- ASIA Impairment Scale (AIS) ranges from AIS A (complete sacral motor and sensory loss) to AIS E (normal motor and sensory function).
- Sensory testing evaluates 28 key sensory points bilaterally for light touch and pinprick; motor testing evaluates 10 key muscle groups bilaterally.
- Zone of Partial Preservation (ZPP) refers to dermatomes and myotomes caudal to the sensory/motor level that remain partially innervated in complete (AIS A) injuries.
3.1 ASIA Examination & Impairment Scale
The International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI), established by the American Spinal Injury Association (ASIA), represents the universal clinical framework for assessing and categorizing spinal cord injury (SCI). Accurate completion and interpretation of the ISNCSCI exam is a foundational competency in Physical Medicine and Rehabilitation (PM&R) and a heavily weighted topic on the ABPMR board examination. Classification dictates clinical prognosis, guides rehabilitation goal setting, directs medical interventions, and establishes eligibility for clinical trials.
The Sensory Examination
The sensory exam systematically evaluates 28 key sensory points corresponding to dermatomes C2 through S4-S5 bilaterally. Two distinct sensory modalities are tested at each point:
- Light Touch (LT): Assesses the dorsal column-medial lemniscal pathway using a light cotton wisp touch.
- Pinprick (PP): Assesses the lateral spinothalamic tract using a clean safety pin to test sharp/dull discrimination.
Sensory Scoring Scale
Each key sensory point is scored for both light touch and pinprick:
- 0 (Absent): Sensation is absent or the patient cannot accurately distinguish sharp from dull.
- 1 (Impaired/Altered): Sensation is present but altered, duller, hyperesthetic, or qualitatively different compared to intact facial sensation.
- 2 (Normal): Sensation is identical to normal intact facial sensation.
- NT (Not Testable): The key point cannot be tested (e.g., due to cast, burn, dressing, or amputation).
Deep Anal Pressure (DAP)
Evaluation of Deep Anal Pressure (DAP) is performed by inserting a gloved finger into the rectum and applying pressure against the anal sphincter wall. DAP is recorded as Present or Absent. Presence of DAP (or any light touch/pinprick at S4-S5) confirms sacral sensory sparing, distinguishing sensory incomplete from complete injury.
The Motor Examination
The motor exam evaluates 10 key muscle groups bilaterally, representing segmental motor innervation from C5 through T1 in the upper extremities and L2 through S1 in the lower extremities.
| Level | Key Motor Muscle | Primary Action Tested |
|---|---|---|
| C5 | Elbow flexors | Biceps brachii, brachialis |
| C6 | Wrist extensors | Extensor carpi radialis longus and brevis |
| C7 | Elbow extensors | Triceps brachii |
| C8 | Finger flexors | Flexor digitorum profundus (middle finger) |
| T1 | Small finger abductors | Abductor digiti minimi |
| L2 | Hip flexors | Iliopsoas |
| L3 | Knee extensors | Quadriceps femoris |
| L4 | Ankle dorsiflexors | Tibialis anterior |
| L5 | Long toe extensors | Extensor hallucis longus |
| S1 | Ankle plantarflexors | Gastrocnemius, soleus |
Motor Grading Scale
Key muscles are graded using the standard 0 to 5 Medical Research Council scale:
- 0: Total paralysis.
- 1: Palpable or visible muscle contraction without joint movement.
- 2: Active movement through full Range of Motion (ROM) with gravity eliminated.
- 3: Active movement through full ROM against gravity.
- 4: Active movement through full ROM against moderate resistance.
- 5: Normal active movement against full resistance.
- NT: Not testable (e.g., severe pain, cast, or spasticity preventing testing).
Voluntary Anal Contraction (VAC)
The examiner instructs the patient to voluntarily squeeze the anal sphincter around the examiner's finger. VAC is documented as Present or Absent. Presence of VAC establishes motor incomplete status regardless of rostral muscle strength.
Determining Neurologic Levels
Interpretation of the ISNCSCI exam requires establishing four specific levels:
- Sensory Level: The most caudal dermatome with normal scores (2/2 for LT and PP) bilaterally.
- Motor Level: The most caudal myotome with a muscle grade of at least 3/5, provided that all rostral key muscles are fully normal (5/5).
- Non-Key Muscle Levels (C2-C4, T2-L1, S2-S5): In segments without key muscles, the motor level is assumed identical to the sensory level if sensory function is normal.
- Neurologic Level of Injury (NLI): The lowest segment of the spinal cord with intact sensory and motor function bilaterally (sensory 2/2 and motor >=3/5 with 5/5 strength above).
- Overall Completeness: Determined by sacral sparing (presence of S4-S5 LT/PP, DAP, or VAC).
ASIA Impairment Scale (AIS) Categories
| AIS Category | Classification | Diagnostic Definition & Criteria |
|---|---|---|
| AIS A | Complete | No sensory or motor function is preserved in sacral segments S4-S5 (No DAP, No VAC, No S4-S5 LT/PP). |
| AIS B | Sensory Incomplete | Sensory but NOT motor function is preserved below NLI including sacral segments S4-S5 (LT/PP at S4-S5 or DAP present), AND no motor function is preserved >3 levels below motor level on either side. |
| AIS C | Motor Incomplete | Motor function is preserved at sacral segments (VAC present) OR meets AIS B criteria with motor function >3 levels below motor level. More than half (50%+) of key muscles below single NLI have grade < 3/5. |
| AIS D | Motor Incomplete | Motor function is preserved below single NLI, AND at least half (50%+) of key muscles below single NLI have grade >= 3/5. |
| AIS E | Normal | Sensory and motor function are graded normal (2/2 sensory, 5/5 motor) in all segments in an individual with prior SCI deficits. |
Zone of Partial Preservation (ZPP)
The Zone of Partial Preservation (ZPP) refers to dermatomes and myotomes caudal to the sensory or motor level that remain partially innervated.
- In Complete SCI (AIS A): ZPP represents the most caudal segment with any preserved sensory or motor function.
- In Incomplete SCI (AIS B, C, D): ZPPs are recorded for sensory (if DAP/sacral sensation absent) or motor (if VAC absent) on each side where voluntary function persists caudal to the motor/sensory level.
A patient with traumatic SCI has C5 5/5 biceps strength and C6 5/5 wrist extensors bilaterally. C7 triceps strength is 1/5 on the right and 0/5 on the left. C8 and T1 key muscles are 0/5 bilaterally. Light touch and pinprick are 2/2 through C6 bilaterally, 1/2 at C7, and 0/2 at C8-S5. Deep anal pressure and voluntary anal contraction are absent. What is the ASIA Impairment Scale (AIS) grade and Neurologic Level of Injury (NLI)?
A 28-year-old male involved in a motor vehicle collision undergoes ISNCSCI examination. His sensory level is C6 bilaterally. His motor level is C6 bilaterally (C6 wrist extensors 5/5, C7 triceps 2/5, C8 finger flexors 0/5). Sensation to light touch and pinprick is present at S4-S5, and deep anal pressure (DAP) is preserved. Voluntary anal contraction (VAC) is absent. All key muscles more than three levels below the motor level are 0/5. Which AIS classification applies to this patient?
Which of the following muscle groups is designated as the key motor muscle for assessing the L4 spinal cord segment during the ISNCSCI examination?