An extension device (1) for a bone anchor (2), comprising: at least one tab (10a, 10b), which includes: an elongate shaft portion (11a, 11b), that forms part of a channel (14) for providing a stabilization rod to a rod receiving recess (24) of a receiving part (20) of a bone anchor (2), and a coupling portion (12a, 12b), which is provided at a distal end of the elongate shaft portion (11a, 11b) and which is configured to be coupled to the receiving part (20) wherein the coupling portion (12a, 12b) includes a first engagement portion (151a, 151b) for engaging a first engagement face (212a, 212b) of the receiving part and a second engagement portion (111a, 111b) for engaging a second engagement face (213 a, 213b) of the receiving part (20), wherein a spring element (15a, 15b) is provided at the coupling portion (12a, 12b), the spring element exerting a compression force to urge the first and second engagement portions (151a, 151 b 111a, 111 b) in mutually opposite directions towards each other and towards the corresponding first and second engagement faces (212a, 212b 213a, 213b) along a longitudinal axis (L) defined by the extension device (1) and the receiving part (20) when being coupled together.
