A retaining mechanism is disclosed, which comprises a plate including a first surface adapted to engage with an implant and a second opposing surface, the plate having mechanically-weakened areas, such that the plate is compressible from a first dimension to a second reduced dimension via the weakened areas, wherein the plate includes at least one ledge adapted to engage with a recess in the implant to prevent a fixation member inserted into the implant from backing out. A tool is also disclosed for compressing and inserting the retaining mechanism into engagement with the implant, as are respective methods of compression and insertion of the retaining mechanism into engagement with the implant.