Devices are disclosed for treating the vertebral column. A fastener having a fastener head comprising a screw lumen and fastener shaft is provided. In some embodiments, an external groove and one or more openings between the screw lumen and an external groove are provided. An expandable member is located at least partially in the external groove and protrudes through the one or more openings into the screw lumen. Alternative fixation systems and screw retaining assemblies are also contemplated.