CLASSIFICATION OF SPINAL CORD INJURY

LEVEL OF INJURY—ASIA IMPAIRMENT SCALE

The most common method of classifying impairment from SCI is the American Spinal Injury Association (ASIA) impairment scale. The classification is based upon assessment of strength and sensation to light touch and pinprick in defined myotomes and dermatomes. Key muscle groups and sensory points are shown in Figure 16.1. The ASIA impairment scale has been modified over the years, originally based on the classification system defined by Frankel. For a child, completing the ASIA examination requires a certain level of maturity in being able to follow motor commands and respond appropriately to sensory stimulation. The examiner must take this into account when assessing children. Other factors that may limit examination (eg, long bone fractures or decreased level of consciousness) need to be taken into account as well. The motor examination scores strength on a six-point scale: 0 to 5. For each strength grade, the joint being assessed must be moved through a full available range of motion. A strength grade of 0 is given for total paralysis. A 1 is given for a visible or palpable contraction that cannot move the joint through its available range of motion with gravity removed. A grade 2 is given if the muscle group can move the joint through its range of motion with gravity removed. The joint is positioned parallel to the ground to limit the effect of gravity. A grade 3 is given when the patient can move the joint through a full available range of motion against gravity but cannot bear any additional resistance. If a patient can bear additional resistance, he or she is given a grade 4, and a grade 5 is given for normal strength. Motor scores are documented on the ASIA form and summed for a total motor score. A rectal exam must be performed to assess for voluntary contraction, and is scored as yes/no. As individual muscles are almost always innervated by multiple spinal cord levels, a strength grade of 3 is considered normal for a muscle group if the level above has grade 5 strength. This implies that the grade 3 muscle group is only partially innervated and the more proximal innervation level is intact.

Sensory examination is performed using pinprick and light touch at key points, and it is graded as 0 for absent, 1 for impaired, and 2 for normal. These results are summed as well for total light touch and pinprick scores. Again, a rectal exam is necessary to assess anal sensation, also scored yes/no.

The ASIA neurologic level is the most caudal segment with intact motor and sensory exam. In addition to the level is whether the injury is complete or incomplete. With a complete injury, there is no motor or sensory function in the lowest sacral segment (ie, no anal sensation or voluntary anal contraction). A complete injury is classified as ASIA-A. Incomplete injuries are classified as B to E, as listed in Figure 16.1. While an "E" is described as normal sensory and motor function, this is in the context of a previously abnormal examination.

Paraplegia affects the lower extremities and, to varying degrees, the trunk. It does not affect the upper extremities; thus, T2 must be normal and any deficits are below that sensory and motor level. The preferred term from ASIA for involvement of all four extremities is tetraplegia, though quadriplegia is much more commonly used. Any injury that affects motor and/or sensation at or above the T2 level is tetraplegia. In addition, a number of syndromes have been described based upon the patterns seen after specific areas of the spinal cord have been injured.

CENTRAL CORD SYNDROME

The central cord syndrome was first described in 1954 (10). As its name implies, this is damage to the central area of the spinal cord. This most commonly happens in

American Spinal Injury Association Exam Sheet

the cervical region at the lower cervical levels because of the high amount of normal motion at these segments and is often due to a hyperextension injury Disruption of decussating spinothalamic fibers at the site of the lesion results in impaired pain and temperature sensation at those dermatomes and may also be associated with the development of neuropathic pain. Dermatomes above and below the lesion may have normal sensation. As a lesion enlarges, damage may extend into the anterior horn cells and medial corticospinal tracts, causing weakness. Reflexes may be lost at the level of the lesion as well, with possible hyperreflexia at lower levels. As this is primarily a cervical syndrome, there are typically motor and sensory changes in the arms, with relative sparing of the legs, bowel, and bladder function.

BROWN-SEQUARD SYNDROME

Brown-Sequard syndrome results from a hemisection of the spinal cord. This is most commonly seen with low-speed penetration wounds, such as a stabbing. Corticospinal tracts and the dorsal columns cross in the brainstem, so their damage in this type of lesion leads to ipsilateral weakness and loss of vibration and position sense. The lateral spinothalamic tracts cross soon after entering the spinal cord, thus causing contralateral loss of pain and temperature sensation.

ANTERIOR CORD SYNDROME

The anterior (or ventral) cord syndrome is most commonly related to a vascular insult, causing infarction of the ventral spinal cord or a hyperflexion injury to the spinal cord. This injury includes damage to the corticospinal, spinothalamic, and descending autonomic tracts to the bladder. This syndrome results in paralysis, loss of pain and temperature sensation, and urinary incontinence. Vibratory and position sense, whose tracts are in the dorsal columns, are most often spared.

CAUDA EQUINA AND CONUS MEDULLARIS SYNDROME

Compressive injuries in the lower lumbar and sacral vertebral levels may result in damage to the cauda equina, as the spinal cord proper has terminated at a higher level. This results in scattered symptoms, depending upon which nerve roots are damaged. The cauda equina syndrome results in damage to the axon of lower motor neurons, leading to a flaccid paralysis. Conus medullaris syndrome shares many of the same features of cauda equina compression and represents damage to the bulbous, caudal portion of the spinal cord, which terminates

near the LI level. A large, nonselective lesion at this level may damage the most distal portions of the spinothalamic, corticospinal, and autonomic tracts as well as the descending nerve roots resulting in both upper and lower motor neuron findings.

SPINAL CORD CONCUSSION

Spinal cord concussions are an uncommon injury. These are transient injuries with full recovery. These are defined by four criteria:

1. Spinal injury with immediate neurological deficit of varying degree

2. Neurologic deficit corresponding to the level of spinal injury

3. Complete neurologic recovery within 72 hours (ASIA-E)

4. No evidence of injury on imaging

These injuries are most commonly at the cervical levels. While spinal cord concussion has been reported across the age span, it is more likely to occur in children. Long-term prognosis seems excellent, though data is very limited. The mechanism of the concussion is unknown (11).

 
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