Expandable fixation assemblies, expandable cranial fixation assemblies, and expandable intervertebral implant assemblies are provided for securing structures to bone and for securing bones and/or bone segments with respect to each other. An expansion member can be moved through at least a portion of an expandable fixation body, thereby causing expansion of the expandable fixation body, such that bone engagement features of the expandable fixation body engage surrounding structure, such as bone.