An "incomplete" spinal cord injury involves preservation of motor or sensory function below the level of injury in the spinal cord. To be classed as incomplete, there must be some preservation of sensation or motion in the areas innervated by S4 to S5, e.g. voluntary external anal sphincter contraction. The nerves in this area are connected to the very lowest region of the spinal cord, and retaining sensation and function in these parts of the body indicates that the spinal cord is only partially damaged. Incomplete injury by definition includes a phenomenon known as sacral sparing: some degree of sensation is preserved in the sacral dermatomes, even though sensation may be more impaired in other, higher dermatomes below the level of the lesion. Sacral sparing has been attributed to the fact that the sacral spinal pathways are not as likely as the other spinal pathways to become compressed after injury due to the lamination of fibers within the spinal cord. Spinal cord injury without radiographic abnormality
Spinal cord injury without radiographic abnormality exists when SCI is present but there is no evidence of spinal column injury on radiographs. Spinal column injury is trauma that causes fracture of the bone or instability of the ligaments in the spine; this can coexist with or cause injury to the spinal cord, but each injury can occur without the other. Abnormalities might show up on magnetic resonance imaging (MRI), but the term was coined before MRI was in common use.
Lumbosacral
The effects of injuries at or above the lumbar or sacral regions of the spinal cord (lower back and pelvis) include decreased control of the legs and hips, genitourinary system, and anus. People injured below level L2 may still have use of their hip flexor and knee extensor muscles. Bowel and bladder function are regulated by the sacral region. It is common to experience sexual dysfunction after injury, as well as dysfunction of the bowel and bladder, including fecal and urinary incontinence. Thoracic
In addition to the problems found in lower-level injuries, thoracic (chest height) spinal lesions can affect the muscles in the trunk. Injuries at the level of T1 to T8 result in inability to control the abdominal muscles. Trunk stability may be affected; even more so in higher level injuries. The lower the level of injury, the less extensive its effects. Injuries from T9 to T12 result in partial loss of trunk and abdominal muscle control. Thoracic spinal injuries result in paraplegia, but function of the hands, arms, and neck are not affected.One condition that occurs typically in lesions above the T6 level is autonomic dysreflexia (AD), in which the blood pressure increases to dangerous levels, high enough to cause potentially deadly stroke. It results from an overreaction of the system to a stimulus such as pain below the level of injury, because inhibitory signals from the brain cannot pass the lesion to dampen the excitatory sympathetic nervous system response.