A discectomy method entails removing at least a portion of a spinal lamina to form an access path in a patient. A surgical instrument is inserted along the path and a distal end of the instrument is placed in operative contact with herniated or bulging disc material of a spinal disc. The instrument is operated to remove the herniated or bulging disc material, to thereby space a remaining portion of the spinal disc from spinal nerves. A tip of an ultrasonic surgical probe is then placed into contact with an outer surface of the remaining portion of the spinal disc, and an ultrasonic mechanical standing wave generated in the probe while maintaining the operative tip in contact with the outer surface to harden the wall surface and thereby reduce chances of disc herniation at the outer surface.