An osteosynthesis device is proposed, particularly for spinal support or correction, enabling easier and compact implantation, that can be particularly used in the case of implantation via the anterior approach, and a preassembly method for such a device. In various embodiments, the device comprises implants screwed into two vertebrae (0) and a plate (2) used to hold and displace the spine. In various embodiments, the plate (2) comprises on at least one of its ends at least one longitudinally elongated opening, the opening having firstly at least one part opening onto an edge of the plate, or one part of a sufficiently large size (s210b) to be able to be inserted without disassembly in the fixation means of an implant (1) already screwed into the spine when the fixation means are already assembled.
