The Mayfield headholder is used to stabilize the head during surgery on the brain.  It consists of a clamp with three sterile pins which insert through the scalp into the outer table of the skull.  Although the device looks painful, it is extremely rare for a patient to ever even notice that the pins were in the skull.  The head holder is affixed to the head when the patient is asleep, and the pinsites show as small punctures in the scalp, and generally heal without any difficults.