To improve the ease of use by providing a bone cutter, a threaded protractor with a handle and a trephine (perforator) and forming the trephine by providing a blade with a sleeve in a kit for removing a spacer having external surface portion and facing ends from the spine.

The device kit 100 is equipped with a bone cutter 10, an inverse- threaded protractor and trephine 70, and is used by a surgeon to remove a certain quantity of the bone only around a spacer 12 from the axon to replace an intravertebral disk 20. The spacer 12 is furnished with a threaded metal fusion cage and is planted nearly horizontally in the spine 14. An inverse- threaded protractor is intended to remove the spacer 12 from the axon and has a threaded end to be screwed into the hole 34 of the spacer 12. The trephine 70 is designed to cut around the spacer 12 and separate the spacer 12 from the spine 13 and has a ring blade 80.