an implantable anchor having a body extending between a first end and a second end, the body having an outer surface with a cylindrical portion and a tapered tip portion the body being externally threaded from the first end to the second end, the threads having blunt edges, the cylindrical portion having a length and defining an inner longitudinal passage having an inner surface of a cruciate shape along the length of the cylindrical portion, the longitudinal passage including four inner longitudinal ribs; and

separate elongated plug having an outer surface of cruciate shape, the elongated plug including four outer longitudinal grooves, the elongated plug slidably receivable within and mateable with the inner longitudinal passage along the length of the externally threaded cylindrical portion, such that the inner longitudinal ribs of the longitudinal passage are received in the corresponding outer longitudinal grooves of the elongated plug, the elongated plug formed of a material promoting bone growth through the anchor.