Excerpt from Spinal Cord Injury: Definition, Epidemiology, Pathophysiology

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Spinal cord injury (SCI) is an insult to the spinal cord resulting in a change, either temporary or permanent, in its normal motor, sensory, or autonomic function. The International Standards for Neurological and Functional Classification of Spinal Cord Injury is a widely accepted system describing the level and the extent of injury based on a systematic motor and sensory examination of neurologic function. The following terminology has developed around classification of SCI:

• Tetraplegia (replaced the term quadriplegia) - Injury to the spinal cord in the cervical region with associated loss of muscle strength in all 4 extremities
• Paraplegia - Injury in the spinal cord in the thoracic, lumbar, or sacral segments, including the cauda equina and conus medullaris

SCI can be sustained through different mechanisms with the following 3 common abnormalities leading to tissue damage:

• Destruction from direct trauma
• Compression by bone fragments, hematoma, or disk material
• Ischemia from damage or impingement on the spinal arteries

Edema could ensue subsequent to any of these types of damage. The different clinical presentations of the above causes of tissue damage are explained further below.

Spinal shock

Spinal shock is a state of transient physiological (rather than anatomical) reflex depression of cord function below the level of injury with associated loss of all sensorimotor functions. An initial increase in blood pressure is noted due to the release of catecholamines, followed by hypotension. Flaccid paralysis, including of the bowel and bladder, is observed, and sometimes sustained priapism develops. These symptoms tend to last several hours to days until the reflex arcs below the level of the injury begin to function again (eg, bulbocavernosus reflex, muscle stretch reflex [MSR]).

Neurogenic shock

Neurogenic shock is manifested by the triad of hypotension, bradycardia, and hypothermia. Shock tends to occur more commonly in injuries above T6, secondary to the disruption of the sympathetic outflow from T1-L2 and to unopposed vagal tone, leading to decrease in vascular resistance with associated vascular dilatation. Neurogenic shock needs to be differentiated from spinal and hypovolemic shock. Hypovolemic shock tends to be associated with tachycardia.

Autonomic dysreflexia

See the article Autonomic Dysreflexia.

In a recent study showing high incidence of autonomic dysfunction, including orthostatic hypotension and impaired cardiovascular control, assessment of autonomic function was recommended as a routine along with American Spinal Injury Association (ASIA) assessment.

Motor strengths and sensory testing

The extent of injury is defined by the ASIA Impairment Scale (modified from the Frankel classification), using the following categories:

• A - Complete: No sensory or motor function is preserved in sacral segments S4-S5.
• B - Incomplete: Sensory, but not motor, function is preserved below the neurologic level and extends through sacral segments S4-S5.
• C - Incomplete: Motor function is preserved below the neurologic level, and most key muscles below the neurologic level have muscle grade less than 3.
• D - Incomplete: Motor function is preserved below the neurologic level, and most key muscles below the neurologic level have muscle grade greater than or equal to 3.
• E - Normal: Sensory and motor functions are normal.

Perform rectal examination to check motor function or sensation at the anal mucocutaneous junction. The presence of either is considered sacral-sparing.

Definitions of complete and incomplete SCI are based on the above ASIA definition with sacral-sparing.

• Complete - Absence of sensory and motor functions in the lowest sacral segments
• Incomplete - Preservation of sensory or motor function below the level of injury, including the lowest sacral segments

Sacral-sparing is evidence of the physiologic continuity of spinal cord long tract fibers with the sacral fibers located more at the periphery of the cord. Indication of the presence of sacral fibers is of significance in defining the completeness of the injury and the potential for some motor recovery. This finding tends to be repeated and better defined after the period of spinal shock.

With the ASIA classification system, the terms paraparesis and quadriparesis now have become obsolete. The ASIA classification using the description of the neurologic level of injury is used in defining the type of SCI (eg, C8 ASIA A with zone of partial preservation of pinprick to T2). See the entire ASIA Impairment Scale (requires Acrobat reader).

Other classifications of SCI include the following:

• Central cord syndrome often is associated with a cervical region injury leading to greater weakness in the upper limbs than in the lower limbs with sacral sensory sparing.
• Brown-Séquard syndrome often is associated with a hemisection lesion of the cord, causing a relatively greater ipsilateral proprioceptive and motor loss with contralateral loss of sensitivity to pain and temperature.
• Anterior cord syndrome often is associated with a lesion causing variable loss of motor function and sensitivity to pain and temperature, while proprioception is preserved.
• Conus medullaris syndrome is associated with injury to the sacral cord and lumbar nerve roots leading to areflexic bladder, bowel, and lower limbs, while the sacral segments occasionally may show preserved reflexes (eg, bulbocavernosus and micturition reflexes).
• Cauda equina syndrome is due to injury to the lumbosacral nerve roots in the spinal canal leading to areflexic bladder, bowel, and lower limbs.

Muscle strengths are graded using the following Medical Research Council (MRC) scale of 0-5:

• 5 - Normal power
• 4+ - Submaximal movement against resistance
• 4 - Moderate movement against resistance
• 4- - Slight movement against resistance
• 3 - Movement against gravity but not against resistance
• 2 - Movement with gravity eliminated
• 1 - Flicker of movement
• 0 - No movement

Muscle strength always should be graded according to maximum strength attained, no matter how briefly that strength is maintained during the examination. The muscles are tested with the patient supine.

The following key muscles are tested in patients with SCI, and the corresponding level of injury is indicated:

• C5 - Elbow flexors (biceps, brachialis)
• C6 - Wrist extensors (extensor carpi radialis longus and brevis)
• C7 - Elbow extensors (triceps)
• C8 - Finger flexors (flexor digitorum profundus) to the middle finger
• T1 - Small finger abductors (abductor digiti minimi)
• L2 - Hip flexors (iliopsoas)
• L3 - Knee extensors (quadriceps)
• L4 - Ankle dorsiflexors (tibialis anterior)
• L5 - Long toe extensors (extensors hallucis longus)
• S1 - Ankle plantar flexors (gastrocnemius, soleus)

Sensory testing is performed at the following levels:

• C2 - Occipital protuberance
• C3 - Supraclavicular fossa
• C4 - Top of the acromioclavicular joint
• C5 - Lateral side of antecubital fossa
• C6 - Thumb
• C7 - Middle finger
• C8 - Little finger
• T1 - Medial side of antecubital fossa
• T2 - Apex of axilla
• T3 - Third intercostal space (IS)
• T4 - 4th IS at nipple line
• T5 - 5th IS (midway between T4 and T6)
• T6 - 6th IS at the level of the xiphisternum
• T7 - 7th IS (midway between T6 and T8)
• T8 - 8th IS (midway between T6 and T10)
• T9 - 9th IS (midway between T8 and T10)
• T10 - 10th IS or umbilicus
• T11 - 11th IS (midway between T10 and T12)
• T12 - Midpoint of inguinal ligament
• L1 - Half the distance between T12 and L2
• L2 - Mid-anterior thigh
• L3 - Medial femoral condyle
• L4 - Medial malleolus
• L5 - Dorsum of the foot at third metatarsophalangeal joint
• S1 - Lateral heel
• S2 - Popliteal fossa in the midline
• S3 - Ischial tuberosity
• S4-5 - Perianal area (taken as one level)

Sensory scoring is for light touch and pinprick, as follows:

• 0 - Absent
• 1 - Impaired or hyperesthesia
• 2 - Intact

A score of zero is given if the patient cannot differentiate between the point of a sharp pin and the dull edge.

Motor level - Determined by the most caudal key muscles that have muscle strength of 3 or above while the segment above is normal (= 5)

Motor index scoring - Using the 0-5 scoring of each key muscle with total points being 25/extremity and a total possible score of 100

Sensory level - Most caudal dermatome with a normal score of 2/2 for both pinprick and light touch

Sensory index scoring - Total score from adding each dermatomal score with possible total score (= 112 each for pinprick and light touch)

Neurologic level of injury - Most caudal level at which both motor and sensory levels are intact, with motor level as defined above and sensory level defined by a sensory score of 2

Zone of partial preservation - This index is used only when the injury is complete. All segments below the neurologic level of injury with preservation of motor or sensory findings

Skeletal level of injury - Level of greatest vertebral damage on radiograph

Lower extremities motor score (LEMS) - Uses the ASIA key muscles in both lower extremities with a total possible score of 50 (ie, maximum score of 5 for each key muscle L2, L3, L4, L5, and S1 per extremity). A LEMS score of 20 or less indicates patients are likely to be limited ambulators. A LEMS of 30 or more suggests that patients are likely to be community ambulators.

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