A patient diagnosed with an incomplete spinal cord injury at L1 shows which finding that indicates sacral sparing?

The presence of voluntary anal sphincter tone in a patient with an incomplete spinal cord injury at the L1 level is a key indicator of sacral sparing. Sacral sparing refers to the preservation of some neurological function below the level of injury, particularly involving the sacral segments of the spinal cord. In this context, the anal sphincter is innervated by the sacral nerves (S2-S4), so the ability to voluntarily contract this muscle suggests that not all neurological function has been lost.

This finding can be crucial in assessing the degree of injury and in formulating a plan for rehabilitation and recovery. Preserved function in the anal sphincter implies that there is some intact neural pathway, which can offer insights into the potential for recovery of other functions as well.

In contrast, loss of sensation in the lower extremities typically indicates more significant neurological impairment and does not demonstrate any sparing, while flaccid paralysis and complete loss of reflexes would suggest a more severe injury without any preserved function. Thus, the presence of voluntary anal sphincter tone clearly demonstrates sacral sparing in the context of an incomplete spinal cord injury.