Comprehensive Analysis of the ASIA Impairment Scale (AIS) and International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI)

📎 ASIA-ISCOS-IntlWorksheet_2019.pdf

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The ASIA Impairment Scale (AIS) and the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) are standardized tools designed to assess and classify spinal cord injuries (SCI). These tools are essential for orthopedic residents and practitioners to accurately evaluate the extent of SCI, guide clinical management, predict outcomes, and facilitate communication among healthcare professionals. This comprehensive guide will cover the detailed procedures for motor and sensory testing, the interpretation of results, and the systematic classification of spinal cord injuries.

1. Components of the ASIA Form:

The ASIA form is an essential tool for the standardized assessment of motor and sensory functions. It allows for the precise evaluation of neurological impairment in patients with SCI, ensuring accurate documentation and classification.

Motor and Sensory Examination:

• Motor Examination:
  • The motor examination evaluates key muscle groups in the upper and lower extremities on both sides of the body. Each muscle group is assigned a motor score based on the patient's ability to perform specific movements against resistance. The grading scale is as follows:
    • 0: Total paralysis - No muscle contraction is detected.
    • 1: Palpable or visible muscle contraction - Slight muscle contraction is present, but there is no movement of the joint.
    • 2: Active movement, gravity eliminated - The muscle can move through its full range of motion when gravity is eliminated (e.g., moving a limb in a horizontal plane).
    • 3: Active movement against gravity - The muscle can move through its full range of motion against gravity, but not against any resistance.
    • 4: Active movement against some resistance - The muscle can move through its full range of motion against gravity and some resistance but is not considered normal strength.
    • 5: Normal active movement against full resistance - The muscle can move through its full range of motion against gravity and full resistance, indicating normal strength.
    • NT: Not testable - The muscle cannot be tested due to factors such as immobilization, severe pain, amputation, or contracture of more than 50% of the normal range of motion (ROM).
• Sensory Examination:
  • The sensory examination assesses two types of sensations—light touch (LT) and pin prick (PP)—at 28 key dermatomes on both sides of the body. Sensory testing helps determine the extent of sensory impairment and is graded as follows:
    • 0: Absent sensation - The patient cannot feel any sensation in the tested area.
    • 1: Altered sensation - The patient reports decreased or heightened sensation or any form of hypersensitivity.
    • 2: Normal sensation - The patient has normal sensation compared to a non-injured reference area.
    • NT: Not testable - Sensation cannot be tested due to factors such as bandages, severe pain, or non-SCI conditions.
• Voluntary Anal Contraction (VAC) and Deep Anal Pressure (DAP):
  • These tests are critical for determining whether an injury is complete or incomplete:
    • VAC: Tests the presence of voluntary muscle contraction in the anal sphincter, assessing motor function in the most caudal segment of the sacral cord.
    • DAP: Tests sensory function by applying deep pressure to the anal region to assess the integrity of the sacral segments.

2. Determining Motor and Sensory Levels:

• Motor Level:
  • The motor level is determined by identifying the lowest key muscle function with a grade of at least 3 (active movement against gravity) provided that all key muscle functions above that level are graded as 5 (normal strength). This ensures that the motor level reflects the most caudal segment with intact motor function.
• Sensory Level:
  • The sensory level is defined as the most caudal, intact dermatome for both light touch and pin prick sensations. This indicates the lowest spinal level with preserved sensory function. Sensory testing involves careful assessment of each dermatome to detect any abnormalities or asymmetries.

3. Neurological Level of Injury (NLI):

• The Neurological Level of Injury (NLI) is defined as the most caudal segment of the spinal cord with intact sensation and antigravity muscle function (motor score of 3 or more), provided that there is normal (intact) sensory and motor function above this level. The NLI represents the most rostral of the sensory and motor levels, providing a clear demarcation of the extent of spinal cord involvement.

4. Classification of Spinal Cord Injury:

Spinal cord injuries are classified as either complete or incomplete based on the preservation of sensory and motor functions:

• Complete Injury (AIS A):
  • This classification is assigned when there is no sensory or motor function preserved in the sacral segments S4-5. A complete injury indicates total loss of function below the level of injury, with no evidence of sacral sparing. This means that there is no voluntary anal contraction, and both light touch and pin prick sensations are absent in the S4-5 dermatome.
• Incomplete Injury (AIS B-E):
  • Incomplete injuries are classified based on the extent of sensory and motor preservation below the neurological level of injury, including the sacral segments:
    • AIS B (Sensory Incomplete): Sensory but not motor function is preserved below the neurological level, including the sacral segments S4-5 (light touch or pin prick at S4-5 or deep anal pressure), with no motor function preserved more than three levels below the motor level on either side of the body.
    • AIS C (Motor Incomplete): Motor function is preserved below the neurological level, with more than half of the key muscles below the NLI having a muscle grade of less than 3. This indicates some motor preservation, but it is insufficient for functional movement.
    • AIS D (Motor Incomplete): Motor function is preserved below the neurological level, with at least half of the key muscles below the NLI having a muscle grade of 3 or more. This suggests a greater degree of motor preservation, with potential for functional recovery.
    • AIS E (Normal): Sensory and motor functions are graded as normal in all segments, and the individual had prior deficits. AIS E is used in follow-up testing when an individual with a documented SCI has recovered normal function.

5. Zone of Partial Preservation (ZPP):

• The Zone of Partial Preservation (ZPP) is applicable only in cases where no motor or sensory function is preserved in the lowest sacral segments (S4-5). The ZPP refers to the most caudal segments with some preserved motor or sensory function. This concept is crucial for understanding the extent of injury and potential for recovery in individuals with complete injuries. The ZPP is recorded separately for motor and sensory functions and provides valuable information about the remaining functional capacity below the level of injury.

6. Steps in Classification:

The classification process using the AIS and ISNCSCI is systematic and involves several steps to ensure accurate determination of the injury grade:

1. Determine Sensory Levels for Right and Left Sides:
   • Assess and record the most caudal intact dermatome for both light touch and pin prick sensations on each side of the body. This requires careful testing and comparison with a reference area to ensure consistency.
2. Determine Motor Levels for Right and Left Sides:
   • Identify the lowest key muscle function that has a grade of at least 3 on supine testing, provided that the key muscle functions represented by segments above that level are judged to be intact (graded as 5). This step ensures that the motor level reflects the most caudal segment with functional motor capacity.
3. Determine the Neurological Level of Injury (NLI):
   • The NLI is the most caudal segment of the spinal cord with intact sensory and motor function above it. This level is determined by combining the sensory and motor levels, providing a comprehensive assessment of the extent of spinal cord involvement.
4. Determine Whether the Injury is Complete or Incomplete:
   • Based on the presence or absence of sacral sparing (voluntary anal contraction and deep anal pressure), determine if the injury is complete (AIS A) or incomplete (AIS B-E). Sacral sparing is a critical factor in differentiating between complete and incomplete injuries and has significant implications for prognosis and rehabilitation.
5. Assign the ASIA Impairment Scale (AIS) Grade:
   • Based on the motor and sensory findings, assign an appropriate AIS grade (A-E) to classify the injury. This grade reflects the overall severity of the injury and guides clinical decision-making.
6. Determine the Zone of Partial Preservation (ZPP):
   • If applicable, record the most caudal level with some preserved motor or sensory function in cases of complete injury. The ZPP provides additional information about the extent of neurological preservation and potential for recovery.

Motor and Sensory Testing for Cervical, Lumbar, and Sacral Nerve Roots

Motor and sensory testing of the cervical, lumbar, and sacral nerve roots is essential for assessing the level and extent of neurological impairment in spinal cord injuries or nerve root compressions. Each nerve root controls specific muscles and actions, which are evaluated during motor testing, while sensory testing assesses the dermatomes associated with these nerve roots.

Cervical Nerve Roots

C5 Nerve Root:

• Muscles Involved: Deltoid and Biceps
• Actions: Shoulder abduction, Elbow flexion
• Motor Testing Procedure:
  • Shoulder Abduction: Ask the patient to raise their arm sideways to shoulder level against resistance. Place your hand on the patient's arm just above the elbow and instruct them to push against your hand while you resist the movement.
  • Elbow Flexion: Ask the patient to bend their elbow while keeping the arm close to the body. Provide resistance by holding the forearm and instructing the patient to pull towards their shoulder.
• Dermatome Area: Lateral arm (over the deltoid region)
• Sensory Testing Procedure: Use a cotton swab or a piece of gauze to lightly touch the lateral aspect of the upper arm. Then, use a pin to gently prick the same area. Ask the patient to report if they feel the touch and whether it feels normal, decreased, or painful.

C6 Nerve Root:

• Muscles Involved: Biceps, Wrist Extensors (extensor carpi radialis longus and brevis)
• Actions: Elbow flexion, Wrist extension
• Motor Testing Procedure:
  • Elbow Flexion: Ask the patient to bend the elbow against resistance as with C5.
  • Wrist Extension: Ask the patient to extend their wrist upward as if making a "stop" sign. Apply resistance by pushing down on the dorsum of the hand while instructing the patient to resist.
• Dermatome Area: Lateral forearm and thumb
• Sensory Testing Procedure: Perform light touch and pinprick tests on the lateral forearm, thumb, and index finger. Ask the patient to compare sensations between both sides of the body.

C7 Nerve Root:

• Muscles Involved: Triceps, Wrist Flexors, Finger Extensors
• Actions: Elbow extension, Wrist flexion, Finger extension
• Motor Testing Procedure:
  • Elbow Extension: Ask the patient to straighten their elbow against resistance. Apply resistance by holding the forearm and instructing the patient to push away from their body.
  • Wrist Flexion: Ask the patient to flex the wrist downward. Apply resistance by pushing up on the palm of the hand while instructing the patient to resist.
  • Finger Extension: Ask the patient to extend all fingers (straighten them out). Apply resistance by pressing on the dorsal aspect of the fingers while instructing the patient to keep them straight.
• Dermatome Area: Middle finger
• Sensory Testing Procedure: Perform light touch and pinprick tests on the pad of the middle finger. Ask the patient to indicate if the sensation feels normal or altered.

C8 Nerve Root:

• Muscles Involved: Finger Flexors (flexor digitorum superficialis and profundus), Interossei (small muscles of the hand)
• Actions: Finger flexion, Finger abduction/adduction
• Motor Testing Procedure:
  • Finger Flexion: Ask the patient to make a fist. Apply resistance by trying to open the fingers while the patient keeps them tightly closed.
  • Finger Abduction: Ask the patient to spread their fingers apart. Apply resistance by trying to push the fingers together while the patient resists.
  • Finger Adduction: Ask the patient to bring the fingers together. Apply resistance by trying to separate the fingers while the patient resists.
• Dermatome Area: Medial forearm, ring finger, and little finger
• Sensory Testing Procedure: Test the medial aspect of the forearm and both the ring and little fingers using light touch and pinprick methods. Compare sensations between both sides of the body.

T1 Nerve Root:

• Muscles Involved: Interossei (small muscles of the hand)
• Actions: Finger abduction/adduction
• Motor Testing Procedure:
  • Finger Abduction/Adduction: Similar to C8, assess finger abduction and adduction using resistance. Ask the patient to spread their fingers apart and then bring them together, applying resistance in both directions.
• Dermatome Area: Medial arm (just above the elbow)
• Sensory Testing Procedure: Perform light touch and pinprick tests on the medial upper arm near the elbow. Ask the patient if the sensation feels normal or altered compared to the other side.

Lumbar and Sacral Nerve Roots

L2 Nerve Root:

• Muscles Involved: Iliopsoas
• Actions: Hip flexion
• Motor Testing Procedure:
  • Hip Flexion: Ask the patient to lift their thigh up towards their abdomen while keeping their knee bent. Place your hand on the patient’s thigh and apply downward resistance while instructing the patient to resist by pushing upwards.
• Dermatome Area: Anterior thigh
• Sensory Testing Procedure: Lightly touch the anterior thigh with a cotton swab or use a pin to perform a pinprick test. Ask the patient to report the sensation and compare it to the other side for symmetry.

L3 Nerve Root:

• Muscles Involved: Quadriceps
• Actions: Knee extension
• Motor Testing Procedure:
  • Knee Extension: Ask the patient to straighten their leg at the knee. Place your hand on the shin and provide resistance by pushing down while instructing the patient to push against your hand.
• Dermatome Area: Anteromedial thigh and medial knee
• Sensory Testing Procedure: Perform light touch and pinprick tests over the anteromedial thigh and medial knee area. Compare the sensation between both sides.

L4 Nerve Root:

• Muscles Involved: Tibialis anterior
• Actions: Ankle dorsiflexion
• Motor Testing Procedure:
  • Ankle Dorsiflexion: Ask the patient to bring their foot upwards towards their head (dorsiflex the ankle). Apply resistance on the dorsum of the foot and instruct the patient to resist your pressure.
• Dermatome Area: Medial aspect of the leg, including the medial malleolus
• Sensory Testing Procedure: Lightly touch or use a pin to test the medial aspect of the lower leg and ankle. Ask the patient to describe the sensation and compare it to the opposite side.

L5 Nerve Root:

• Muscles Involved: Extensor hallucis longus
• Actions: Great toe extension
• Motor Testing Procedure:
  • Great Toe Extension: Ask the patient to extend (lift up) their big toe. Apply resistance to the top of the big toe and instruct the patient to resist your pressure.
• Dermatome Area: Lateral leg, dorsum of the foot, and middle three toes
• Sensory Testing Procedure: Perform light touch and pinprick tests on the lateral leg, dorsum of the foot, and middle three toes. Compare the sensation to the contralateral side.

S1 Nerve Root:

• Muscles Involved: Gastrocnemius and Soleus
• Actions: Ankle plantarflexion
• Motor Testing Procedure:
  • Ankle Plantarflexion: Ask the patient to point their foot downwards (like pressing on a gas pedal). Apply resistance on the bottom of the foot and instruct the patient to push down against your hand.
• Dermatome Area: Lateral foot and sole
• Sensory Testing Procedure: Lightly touch or use a pin to test the lateral aspect of the foot and the sole. Ask the patient to describe the sensation and compare it to the other foot.

Procedure for Examination:

1. Position the Patient: Ensure the patient is seated or lying down comfortably. The limb being tested should be supported adequately to relax the muscles and allow for accurate assessment.
2. Motor Testing:
   • Explain Each Movement: Clearly explain each movement you want the patient to perform and demonstrate if necessary to ensure understanding.
   • Apply Resistance: Use your hand to apply resistance to the limb or muscle being tested. Instruct the patient to perform the action against your resistance, ensuring consistent pressure is applied.
   • Grade Muscle Strength: Use the 0 to 5 scale to grade muscle strength, noting any asymmetries or abnormalities. Document the findings accurately for each muscle group tested.
3. Sensory Testing:
   • Use Light Touch and Pinprick: Assess each dermatome using light touch (cotton swab or gauze) and pinprick (safety pin or similar object). Ensure the patient’s eyes are closed during testing to focus on the sensation.
   • Ask the Patient to Report Sensations: Encourage the patient to describe what they feel and compare sensations on both sides of the body to identify any differences or deficits.
   • Document Findings: Record the sensory scores for each dermatome, noting any areas of altered or absent sensation.

Conclusion:

The ASIA Impairment Scale (AIS) and the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) are vital tools for accurately assessing and classifying spinal cord injuries. By providing a standardized approach to motor and sensory testing, these tools ensure consistent and reliable evaluation of SCI, guiding prognosis, rehabilitation, and clinical management. For orthopedic residents and practitioners, mastering the use of the ASIA form and understanding the implications of each finding are crucial for optimizing patient outcomes and advancing clinical expertise in the management of spinal cord injuries. Proper usage of these tools involves a systematic approach to testing, thorough understanding of sacral sparing, and precise application of classification criteria, all of which are essential for effective clinical practice.