A polyaxial bone anchoring device is provided comprising a bone anchoring element (1) having a shank (2) to be anchored to a bone and a head (3)； a receiving part (5, 5') having a longitudinal axis (C), a charnel (54) for receiving a rod (100) and an accommodation space (52, 51) for pivotably holding the head； a pressure member (7, 7', 7", 7''') positioned in the receiving part and configured to exert pressure onto the head to lock the head in the receiving part； wherein the pressure member (7, 7', 7", 7''') comprises a pressure exerting surface (75) and a deformable portion (77, 78； 77', 78'； 77", 78") having a free end (77a, 78a) wherein the deformable portion is configured to assume at least a first configuration and a second configuration, a locking member (8, 8', 8", 8''') that is insertable into the channel (54) and that is configured to exert a force onto the deformable portion； wherein when the head (3) and the pressure member (7, 7', 7", 7''') and the locking member (8, 8', 8") are in the receiving part (5, 5'), the free end (77a, 78a) of the deformable portion is supported in the receiving part, and wherein the locking member (8, 8', 8") is movable in the channel along the longitudinal direction in such a manner that it first contacts the deformable portion (77, 78； 77', 78'； 77", 78") and exerts a force onto the deformable portion to bring the deformable portion from the first configuration into the second configuration thereby locking the head, and thereafter the locking member (8, 8', 8") comes into contact with the rod (100) and locks the rod.本案提供一種多軸式骨骼固定裝置，包括：一骨骼固定元件(1)，有可固定於骨骼之一幹部(2)，和一頭部(3)；一容納件(5,5')，具有一縱軸線(C)，容納一桿件(100)用之一槽溝(54)，和以樞動方式保持該頭部之一包容空間(52,51)；一壓力構件(7,7',7",7''')，定位於該容納件內，並構成施壓於該頭部，把該頭部鎖定於該容納件內；其中該壓力構件(7,7',7",7''')包括一施壓表面(75)，和一可變形部(77,78；77',78'；77",78")，具有一自由端(77a,78a)，其中該可變形部構成至少可呈一第一組態和一第二組態；一鎖定構件(8,8',8",8''')，可插入於該槽溝(54)內，並構成施力於該可變形部；其中當該頭部(3)和該壓力構件(7,7',7",7''')以及該鎖定構件(8,8',8")在該容納件(5,5')內，該可變形部之自由端(77a,78a)支持在該容納件內；且其中該鎖定構件(8,8
