To easily attach a vertebral arch spacer to a vertebral arch in a vertebral arch plasty.SOLUTION: A vertebral arch spacer 1 comprises: plate-shaped body parts 11, 12 which are arranged between cut surfaces of a vertebral arch which is cut and opened, and are fixed to respective cut surface by a screw 2. The main body parts 11, 12 comprise two open holes 14, 15 penetrating in a plate thickness direction, being arranged at an interval mutually, and allowing the screw 2 to penetrate. At least one of the open holes 14, 15 comprises: a small diameter part whose inner diameter is larger than an outer diameter of a shaft part 24 of the screw 2 and is smaller than an outer diameter of a head part 22； and a large diameter part being continuous to a part of the small diameter part in a peripheral direction and having an aperture in which the head part 22 can penetrate.SELECTED DRAWING: Figure 1【課題】椎弓形成術において簡便に椎弓スペーサを椎弓に取り付ける。【解決手段】切断されて開かれた椎弓の切断面間に配置され各切断面にスクリュ２によって固定される板状の本体部１１，１２を備え、本体部１１，１２が、板厚方向に貫通し、相互に間隔をあけて配置され、スクリュ２をそれぞれ貫通させる２つの貫通孔１４，１５を備え、貫通孔１４，１５の少なくとも一方が、スクリュ２の軸部２４の外径よりも大きくかつ頭部２２の外径よりも小さい内径の小径部と、小径部の周方向の一部に連続し頭部２２を貫通可能な口径の大径部とを備える椎弓スペーサ１である。【選択図】図１
