A polyaxial bone anchoring device is provided including an anchoring element (1) having a shaft (2) for anchoring in the bone and a head (3), the head having a curved outer surface portion； a receiving part (5) having a top end (5a) and a bottom end (5b), a channel (12) for receiving a rod therein, a coaxial bore (51) extending from the top end (5a) in the direction of the bottom end (5b) and a seat portion (52) for receiving the head at the bottom end； a pressure element (6) arranged within the bore, the pressure element (6) having a head contacting surface portion (62, 63, 64) that contacts the curved outer surface portion of the head (3)； wherein the head (3) is pivotable with respect to the receiving part (5) and can be fixed at an angle by exerting pressure via the pressure element (6) onto the head, and wherein the head has an oversize in the curved outer surface portion with respect to the head contacting surface portion (62, 63, 64) such that an interference fit is achieved that clamps the head by the friction between the outer surface portion and the head contacting surface portion. The curved outer surface portion has a largest diameter (E) and the head contacting surface surface (62, 63) contacts the head at least in a region including the largest diameter (E).本案提供一種多軸式骨骼固定裝置，包含：固定元件(1)，有軸部(2)，可供固定於骨骼內，和頭部(3)，頭部有彎曲外表面部；容納件(5)，有頂端(5a)和底端(5b)，容納桿件用之槽溝(12)，從頂端(5a)按底端(5b)方向延伸之共軸腔孔(51)，以及在底端容納頭部用之支座部(52)；壓力元件(6)，配置在腔孔內，壓力元件(6)有頭部接觸表面部(62,63,64)，與頭部(3)之彎曲外表面部接觸；其中頭部(3)相對於容納件(5)樞動，可經由壓力元件(6)施壓於頭部而固定在某一角度，且其中頭部在彎曲外表面部的尺寸大過頭部接觸表面部(62,63,64)，以達成干涉配合，利用外表面部和頭部接觸表面部間之摩擦，夾持頭部。彎曲外表面部有最大直徑(E)，而頭部接觸表面部(62,63)至少在包含最大直徑(E)之區域，與頭部接觸。
