A receiving part for receiving a rod (100) for coupling the rod to a bone anchoring element (1) is provided, the receiving part including a receiving part body (5) with a top end (10), a bottom end (11) and a central axis (M) extending through the top end and the bottom end a channel (13) for receiving the rod, and an accommodation space (12a, 12b) for accommodating a head (3) of the bone anchoring element, the accommodation space having an opening (16) at the bottom end for introduction of the head and a single piece pressure element (6, 6, 6") located at least partly in the accommodation space, the pressure element having top end (61) facing the top end of the receiving part and a bottom end (62) facing the bottom end of the receiving part and a flexible portion (7, 70, 73) to clamp the head wherein the flexible portion comprises a first slit (70) at a distance from the bottom end of the pressure element, the first slit extending partially around the central axis (M) when the pressure element is in the receiving part body (5) and a second slit (73) extending from the bottom end (61) of the pressure element into the first slit (70). A polyaxial bottom loading bone anchoring device comprises a bone anchoring element (1) and a such a receiving part.本案提供一種容納桿件(100)用之容納件,把桿件聯結於骨骼固定元件(1),容納件包含:容納件本體(5),有頂端(10)、底端(11),以及延伸貫穿頂端和底端之中心軸線(M);容納桿件用之槽溝(13);包容空間(12a,12b),供包容骨骼固定元件之頭部(3),包容空間在底端有開口(16),可把頭部引進;單件式壓力元件(6,6,6"),至少部份位在包容空間內,壓力元件有頂端(61)朝向容納件頂端、底端(62)朝向容納件的底端,和撓性部(7,70,73)夾持頭部;其中撓性部包括第一開縫(70),離壓力元件底端一段距離,當壓力元件在容納件本體(5)內時,第一開縫部份圍繞中心軸線(M)延伸;和第二開縫(73),從壓力元件底端(61)延伸入第一開縫(70)。多軸式底部裝載之骨骼固定裝置包括骨骼固定元件(1)和上述容納件。1‧‧‧骨骼固定元件2‧‧‧螺紋幹部3‧‧‧頭部4‧‧‧凹部5‧‧‧容納件本體6‧‧‧壓力元件7‧‧‧封閉元件8a,8b‧‧‧插銷10‧‧‧容納件頂端11‧‧‧容納件底端12‧‧‧腔孔13‧‧‧U形凹部14a,14b‧‧‧自由股部15‧‧‧陰螺紋19a,19b‧‧‧腔孔69a‧‧‧長形凹部70‧‧‧開縫71‧‧‧開縫環73‧‧‧垂直開縫100‧‧‧桿件E‧‧‧頭部最大外徑M‧‧‧容納件本體對稱軸線
