Complete Versus Incomplete Injury
Most clinicians commonly describe injuries as “complete” or “incomplete.” Traditionally, “complete” spinal cord injury means having no voluntary motor or conscious sensory function below the injury site. However, this definition is often difficult to apply. The following three examples illustrate the weaknesses and ambiguity of the traditional definition. The ASIA committee considered these questions when it formulated the classification system for spinal cord injury in 1992.
- Zone of partial preservation. Some people have some function for several segments below the injury site but below which no motor and sensory function was present. This is, in fact, rather common. Many people have zones of partial preservation. Is such a person “complete” or “incomplete,” and at what level?
- Lateral preservation. A person may have partial preservation of function on one side but not the other or at a different level. For example, if a person has a C4 level on one side and a T1 level on the other side, is the person complete and at what level?
- Recovery of function. A person may initially have no function below the injury level but recovers substantial motor or sensory function below the injury site. Was that person a “complete” spinal cord injury and became “incomplete”? This is not a trivial question, because if one has a clinical trial that stipulates “complete” spinal cord injuries, a time must be stipulated for when the status was determined.
Most clinicians would regard a person as complete if the person has any level below which no function is present. The ASIA Committee decided to take this criterion to its logical limit, i.e. if the person has any spinal level below which there is no neurological function, that person would be classified as a “complete” injury. This translates into a simple definition of “complete” spinal cord injury: a person is a “complete” if they do not have motor and sensory function in the anal and perineal region representing the lowest sacral cord (S4-S5).
The decision to make the absence and presence of function at S4-5 the definition for “complete” injury not only resolved the problem of the zone of partial preservation and lateral preservation of function, but it also resolved the issue of recovery of function. As it turns out, very few patients who have loss of S4/5 function recovered such function spontaneously. As shown in Figure 3 below, while this simplifies the criterion for assessing whether an injury is “complete,” the ASIA classification committee decided that both motor and sensory levels should be expressed on each side separately, as well as the zone of partial preservation.
Figure 3. Neurological level, completeness, and zone of partial preservation.
In the end, the whole issue of “complete” versus “incomplete” injury may be a moot issue. The absence of motor and sensory function below the injury site does not necessarily mean that there are no axons that cross the injury site. Many clinicians equate a “complete” spinal cord injury with the lack of axons crossing the injury site. However, much animal and clinical data suggest that an animal or person with no function below the injury site can recover some function when the spinal cord is reperfused (as in the case of an arteriovenous malformation causing ischemia to the cord), decompressed (in the case of a spinal cord that is chronically compressed), or treated with a drug such as 4-aminopyridine. The labeling of a person as being “complete” or “incomplete,” in my opinion, should not be used to deny a person hope or therapy.