The present disclosure relates, in some embodiments, to locking mechanisms for a fastener (e.g., a bone screw) and associated devices, systems, and methods. According to some embodiments, a lockable bone plate assembly may comprise, for example, a bone plate and a bone screw assembly. A bone plate may comprise, in some embodiments, at least one through hole, the at least one through hole having at least one bone plate hole circumferential recess. According to some embodiments, a bone screw assembly may comprise (a) a bone screw, (b) at least one deployable protrusion, and/or (c) a protrusion driver. The present disclosure further relates, in some embodiments, to methods for bone (e.g., vertebral) fixation. For example, a method may comprise contacting at least a portion of a spine (e.g., cervical spine) of a subject with a lockable bone plate assembly.