n. a surgical procedure in which a spinal nerve root is severed within the spinal canal. A rhizotomy may be performed for the relief of pain or to control muscle spasms. The different types of rhizotomy include anterior rhizotomy, in which an anterior (motor) spinal nerve is cut; posterior rhizotomy, in which a posterior (sensory) spinal nerve is cut; and trigeminal rhizotomy, in which the sensory root fibers of the trigeminal nerve are transected.