Patterns and significance of the sacral evoked response (the urologist's knee jerk)

Neurological examination may fail to demonstrate any abnormality in patients who have neurogenic bladder dysfunction. Standard clinical methods will include full examination of segmental nerves to the level of S1 but will not include the lower sacral segments which control sphincter function. We describe a simple method of measuring the integrity and function of these segments of the cord. The method and the common patterns of response are described. The stimulus is physiological (not supramaximal), the response is measured with surface mounted electrodes at the urethral and anal sphincters and each measurement is the average response after 100 stimuli.