A spinal cord injury (SCI) results from damage to the bundle of nerves that transmits signals between the brain and the rest of the body. Suspecting a complete spinal cord injury demands immediate, precise medical attention due to the profound consequences. This suspicion is raised by specific clinical findings that indicate the communication highway has been entirely disrupted at the point of trauma. Understanding these signs is paramount for initial assessment and predicting potential recovery.
Understanding Complete Versus Incomplete Injury
The initial classification of a spinal cord injury determines whether it is complete or incomplete, a distinction that carries significant weight for diagnosis and prognosis. A complete SCI is characterized by the total and permanent loss of all motor and sensory function below the neurological level of injury.
Conversely, an incomplete SCI involves the preservation of some motor or sensory function below the site of injury, indicating that some neural pathways remain intact. Even minimal preserved function classifies the injury as incomplete, offering a more favorable outlook for recovery. While the initial presentation may suggest a complete injury, the final determination is made only after a thorough neurological examination, often using the American Spinal Injury Association (ASIA) Impairment Scale (AIS).
Total Loss of Movement and Sensation
The most obvious finding that raises suspicion of a complete injury is the absolute absence of body function below the injury site, observed in both the motor and sensory systems. For motor function, a patient will exhibit either paraplegia (paralysis affecting the lower half of the body) or quadriplegia (affecting all four limbs and the trunk), depending on the injury’s location.
There is no voluntary movement in any muscle group below the neurological level of injury, and testing will show a muscle strength grade of zero. This paralysis is coupled with a complete absence of sensation across all skin regions below the injury. The patient cannot perceive light touch, pinprick, temperature changes, or vibration.
The neurological level of injury is the most caudal (lowest) segment of the spinal cord that has normal sensory and motor function bilaterally. Below this level, a complete injury means the abrupt and total cessation of all nerve communication. The complete loss of both motor and sensory function is a prerequisite for considering the injury potentially complete.
The Hallmark Sign: Absence of Sacral Sparing
The finding that definitively raises suspicion of a complete spinal cord injury is the absolute absence of sacral sparing. The sacral segments (S4 and S5) are the most caudal parts of the spinal cord, innervating the perianal area and the anal sphincter. Because the nerve tracts are organized so that sacral fibers are often centrally located, they are sometimes spared even when the outer portions of the cord are damaged.
Sacral sparing refers to the preservation of any sensation or motor function controlled by the S4-S5 segments. This includes the ability to feel light touch or a pinprick in the perianal skin region, the preservation of deep anal pressure sensation, and the presence of a voluntary anal sphincter contraction. The ability to voluntarily tighten the anal muscle proves that a few nerve fibers have survived the trauma.
Therefore, the finding that confirms the suspicion of a complete injury is the total lack of perianal sensation and the absence of voluntary anal contraction. If testing reveals no sensory or motor function in these lowest sacral segments, the injury is classified as an AIS Grade A, or a complete SCI.
Systemic Changes and Spinal Shock
In the immediate aftermath of a severe spinal cord injury, a temporary state known as spinal shock often occurs, which can initially mask the true extent of the damage. Spinal shock involves a temporary loss of all reflex activity, motor function, and sensation below the injury level, resulting in flaccidity and areflexia. This condition can make an incomplete injury appear complete during the initial assessment, as all function is temporarily suppressed.
The sudden loss of communication can also lead to significant autonomic dysfunction, particularly in high-level injuries that disrupt sympathetic nervous system pathways. Patients may experience neurogenic shock, characterized by a low heart rate and low blood pressure due to the loss of vascular tone.
Additionally, the loss of neural control over the pelvic organs results in bladder and bowel dysfunction, presenting as an inability to control urination or defecation. These systemic findings support the suspicion of a severe SCI, but the determination of completeness still relies on detailed motor and sensory testing once spinal shock begins to resolve.