Sensory Impairment Related to Level of Spinal Cord Injury

Segments C5 to T1 innervate the arm and hand, with the anterolateral aspect of the shoulder supplied by C5. The thumb and index finger are good markers for C6, the middle finger for C7, and the ring and little fingers for C8. T1 innervates the medial upper arm adjacent to the axilla. The nipple line is innervated by T4 and the area over the abdomen at the umbilicus by T10.

In the lower extremities, L3 and L4 segments innervate the anterior thigh and pretibial regions, respectively. The second, third, and fourth toes are innervated by L5, while S1 innervates the fifth toe and S2 the posterior medial thigh. The saddle area of the buttocks is innervated by segments S3, S4, and S5.

Paresthesias in the buttocks are an important sign of possible spinal cord dysfunction. Because segments S3, S4, and S5 are the lowest and most peripheral segments in the spinal cord, an extramedullary lesion at any level may first compress these fibers and affect pain and temperature sensation. If the saddle area of the buttocks is not examined for pain and temperature sensation, an early spinal cord lesion may not be suspected. In contrast, if an intramedullary lesion is present, the buttocks region is the last to be affected, with resultant sacral sparing.

Because the various ascending spinal tracts decussate at different levels of the spinal cord, several relatively specific patterns of dissociated sensory loss may be recognized clinically. The Brown-Séquard syndrome implies a hemisection or unilateral lesion of the spinal cord. This is characterized by ipsilateral diminution of touch, vibration, and position sense, and contralateral loss of pain and temperature sensation. Because the descending motor fibers decussate at the distal medulla, damage to these nerve fibers causes ipsilateral loss of function, with associated weakness and hyperreflexia (see Plate 2-18).

The anterior spinal artery syndrome, resulting from compression of this artery, occlusion of its feeders, trauma, or marked hypotension, affects the anterior two thirds of the spinal cord bilaterally, causing loss of pain and temperature sensation at approximately one to two segments below the level of the lesion, accompanied by paraplegia. However, because the posterior columns are preserved, touch, vibration, and position sense is normal bilaterally. The rare posterior spinal artery syndrome is characterized by loss of position sense but preserved pain appreciation and motor function below the lesion.

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