The American Spinal Injury Association (ASIA) International Classification of Spinal Cord Injury, neurological level of injury and completeness of injury are often used to indicate human neurological recovery.
ASIA International Standards for Neurological Classification of Spinal Cord Injury consists of 1) 5 category ASIA Impairment Scale (AIS A-E), 2) motor score and 3) sensory score (ASIA 2002). Twenty-eight dermatomes are assessed bilaterally using pinprick and light touch sensation for the sensory score (maximum of 112 for pinprick and 112 for light touch sensation). Ten key muscles are assessed bilaterally with manual muscle testing for the motor score (maximum of 50 for lower limbs and 50 for upper limbs). The results are used in combination with evaluation of anal sensory and motor function as a basis for the determination of the AIS and the 5 categories are summarized below (ASIA 2002).
Table 1: Descriptions of Categories from ASIA Impairment Scale (AIS)
AIS A: Complete injury where no sensory or motor function is preserved in sacral segments S4-S5.
AIS B: Incomplete injury where sensory, but not motor, function is preserved below the neurologic level and extends through sacral segments S4-S5.
AIS C: Incomplete injury where motor function is preserved below the neurologic level, and most key muscles below the neurologic level have muscle grade less than 3 (active full-range movement against gravity).
AIS D: Incomplete injury where 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.
AIS E: Normal sensory and motor functions.
Neurological level of injury is the most caudal level at which both motor and sensory levels are intact and has been shown to change in some individuals over recovery.
Completeness of injury is based on the ASIA standards. The absence of sensory and motor functions in the lowest sacral segments indicates a complete injury and preservation of sensory or motor function below the level of injury, including the lowest sacral segments, indicates an incomplete injury. Sacral-sparing is an important indicator of motor recovery and provides evidence of the physiologic continuity of spinal cord long tract fibers with the sacral fibers at the end of the cord. The requirement of sacral sparing to identify an incomplete injury provides a more rigorous definition and less patients will convert from incomplete to complete injury over time when using this definition.
Stauffer (1976) proposed that individuals with tetraplegia would recover one neurological level, although this has been revised in recent years to qualify that recovery of one neurologic level in subjects with tetraplegia depends on severity, initial level of the injury and the strength of muscles below the level of injury (Dittuno et al. 2005). Dittuno et al. (1992) reported that 70 to 80% of motor-complete tetraplegia subjects with some motor strength at the injury level would recover to the next neurologic level within 3 to 6 months. Although those with complete lesions are generally limited to improvements of one or two levels, subjects with incomplete lesions may exhibit recovery at multiple levels below the injury site (Dittuno et al. 2005). Triceps elbow extension (C7) is a significant determinant for functional independence in self-care for community-living individuals with tetraplegia (Welch et al. 1986).
For those with complete paraplegia, Waters et al. (1992) reported that 73% of 108 patients (T2-L2) did not change in neurological level at one year post-injury compared to the rehabilitation admission assessment. 18% recovered to the next neurological level, while 7% had 2 levels of recovery. For incomplete paraplegia, 78% of 45 cases (T1-L3) had no changes in neurological level between the first and 12th month but there was substantial improvement in motor function particularly within the first 3 months (Waters et al. 1994). 70% of this sample were able to ambulate within 1 or 2 years post-injury (27% without any devices). Patients with initial grade 2 hip flexor and knee extensor motor strength achieved community ambulation. In terms of function, individuals with a T2-T9 injury have some trunk control and may be able to stand using braces and an assistive device such as a walker. Although injuries below T11 have increased potential for ambulation with bracing, successful community ambulation often involves individuals with an injury at the L3 level or below.
Marino et al. (1999) assessed data from 21 Model System SCI systems with 3585 individuals with SCI over the first year of recovery. They found that 10 to 15% of those with initial complete AIS A injuries converted to incomplete injuries. For AIS B injuries, 1/3 converted to AIS C and 1/3 to AIS D or E. For AIS C injuries, over 2/3 converted to AIS D. However, the accurate prediction of AIS conversion can be fraught with problems. Burns et al. (2003) found that individuals with cognitive factors (e.g., traumatic brain injury, alcohol intoxication, analgesic administration, psychological disorders) and communication barriers (e.g., language barriers, ventilatory dependency) had a higher percent of AIS conversion over the first year likely due to an inaccurate initial assessment.