A fixation system is described that can be secured to a bony structure, such as a pedicle of a vertebrae. For example, the fixation system can include a pedicle screw and a receiver element. The receiver element can have a pair of upper opposing projections with a first channel formed therebetween and shaped to receive a part of a connecting rod. The receiver element can further include a pair of lower opposing projections with a second channel formed therebetween and shaped to mate with the pedicle screw. The fixation system can further include an expanding element that forms a tubular shape when a compressive force is applied along a plurality of flexible arms of the expanding element. The plurality of flexible arms can be self-expanding and bow radially outward when the compressive force is released.