Treating fractures using one or both of an implant, such as an intramedullary nail, and a fastening assembly, such as a lag screw and compression screw assembly. The implant in some embodiments has a proximal section with a transverse aperture having a non-circular cross-section that may be shaped to selectively constrain the fastening assembly within the transverse aperture. Two or more components of the fastening assembly may be received to slide, in a controlled way, in the transverse aperture of the implant, and to cooperate to resist a force moment applied thereto. Without the presence of one of the components, such as the lag screw, another component, such as the compression screw may not resist a force moment applied thereto. In some implementations, an engaging member and a compression device of the fastening assembly are configured so that the compression device interacts with a portion of the implant and a portion of the engaging member to enable controlled movement between first and second bone fragments. This configuration is useful for, among other things, compressing a fracture.
