This invention relates to a method for operating on a spine, and more particularly to a method for operating on a spine by using a spinal fixation device which comprises the steps of (1) creating a hole on a vertebra; (2) placing said hollow fixation part joined with said cover part into the hole, and leaving the joining end of said hollow fixation part outside of the vertebra and exposed; (3) injecting said medical filling into said cover part via an injecting device and said hollow fixation part; (4) allowing said medical filling to become solidified so that said medical filling and the cover part form a lump; (5) removing said injecting device from said hollow fixation part.