The extent of spinal injury, defined by the American Spinal Injury Association Impairment Scale (modified from the Frankel classification), is categorized as follows: 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 strength 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; and E-Normal: sensory and motor functions are normal. For more information, see the following Web site for the scale: http://www.asia-spinalinjury.org/publications/2006_Classif_worksheet.pdf.