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Spinal Cord Injury: Progress, Promise, and Priorities
TABLE 2-3 ASIA Impairment Scale
Level of Impairment
No motor or sensory function preserved in the lowest sacral segments (S4 and S5)
Sensory but no motor function preserved, including the lowest sacral segments (S4-S5)
Motor function present below the injury, but the strengths of more than half of the key muscles are graded < 3 of 5
Motor function present below the injury, but the strengths of more than half of the key muscles are graded ≥ 3 of 5
Motor and sensory functions in key muscles and dermatomes are normal
SOURCE: Reprinted with permission, from ASIA, 2000. Copyright 2000 by ASIA.
hand, leaves a person with some sensory or motor function below the site of injury and in the lowest sacral region. It is important to assess sacral sensation when investigating the completeness of an injury, because there is the potential for partial function to be preserved in this area and this may be the only evidence of neurological function below an injury.
The ASIA Impairment Scale provides clinicians with a standard way of grading the functional severity of a spinal cord injury (Table 2-3). The scale has one grade for complete injuries (ASIA A), three others grades for incomplete injuries (ASIA B through ASIA D), and another for no impairment from the injury (ASIA E). To assign one of the three grades for incomplete injuries (ASIA B through ASIA D), clinicians determine the degree of muscle strength (on a scale from 0 to 5, with 0 being total paralysis and 5 being active movement against full resistance) of the key muscles below the neurological level of the injury. The assignment is based on the extent to which more than half of the key muscles have a muscle strength grade of 3 or higher.
The zone of partial preservation applies only to complete injuries (ASIA A). It refers to the area of the spinal cord that still retains some motor or sensory function above the level of S5 (and below the level of injury). For example, a person might be classified as having a zone of partial preservation at T1 to T3, meaning that he or she has some degree of sensory or motor function at that level of the thoracic spinal cord, even though the injury is complete. A zone of partial preservation is likely due to the presence of intact fiber pathways. About 65 percent of individuals with neuro-