An extension device for a bone anchor is provided, wherein the bone anchor comprises an anchoring section (100) for anchoring in a bone and a receiving part (200, 200) connected to the anchoring section, the receiving part comprising a central axis (C) and a channel (204) for receiving a rod, wherein sidewalls of the channel form two free legs (205a, 205b), the extension device comprising a first sleeve (1, 1, 1") with a first sleeve axis (c) that is coaxial with the central axis (C), wherein the first sleeve (1, 1, 1") is configured to be detachably coupled to the receiving part (200, 200) and a second sleeve (2, 2, 2", 2) with a second sleeve axis, wherein the second sleeve is positioned within the first sleeve (1, 1, 1"), wherein the first sleeve (1, 1, 1") is configured to be coupled to the receiving part (200, 200) such as to inhibit a translational movement of the first sleeve relative to the receiving part along the central axis and wherein the second sleeve (2, 2, 2", 2) is configured to be coupled to the receiving part so as to hinder or inhibit a rotational movement of the second sleeve (2, 2, 2", 2) relative to the receiving part (200, 200) and wherein the second sleeve (2, 2, 2", 2) is connected to the first sleeve (1, 1, 1") through a coupling member (3) that is configured to advance in the first sleeve (1, 1, 1") together with the second sleeve (2, 2, 2", 2) in an axial direction.本案提供一種骨骼固定器之延長裝置,其中骨骼固定器包括:一固定段(100),供固定於骨骼內;和一容納件(200,200),連接於該固定段,該容納件包括一中心軸線(C)和一槽溝(204),供容納一桿件,其中該槽溝之側壁形成二自由股部(205a,205b);該延長裝置包括:一第一套筒(1,1,1"),具有一第一套筒軸線(c),與該中心軸線(C)共軸,其中該第一套筒(1,1,1")構成可拆卸式聯結於該容納件(200,200);一第二套筒(2,2,2",2),具有一第二套筒軸線,其中該第二套筒係位於該第一套筒(1,1,1")內;其中該第一套筒(1,1,1")構成聯結於該容納件(200,200),以抑制該第一套筒相對於該容納件沿該中心軸線移動;其中該第二套筒(2,2,2",2)構成聯結於該容納件,以阻止或抑制該第二套筒(2,2,2",2)相對於該容納件(200,200)轉動,又其中第二套筒(2,2,2",2)連接於該第一套筒(1,1,1"),透過一聯結構件(3),其構成為在該第一套筒(1,1,1")內連同該第二套筒(2,2,2",2)沿一軸向推進。1‧‧‧第一套筒1a‧‧‧第一套筒前端2‧‧‧第二套筒2a‧‧‧第二套筒前端3‧‧‧聯鎖軸襯12a,12b‧‧‧縱向開縫13‧‧‧結合部17a‧‧‧U形開縫18a,18b‧‧‧自由股部21‧‧‧第二套筒第一段22‧‧
