Implants for bone fixation or fusion

An implant for bone fixation, the implant comprising:

• an elongate body having a length, a longitudinal axis, a distal end, a proximal end, and a cross-section transverse to the longitudinal axis, the transverse cross-section having an inner circular portion and exactly four ribs, each of the four ribs extending radially outward from the inner circular portion, each of the four ribs having a rectilinear overall cross-sectional profile, being about 1 mm to about 5 mm wide and about 2 mm to about 8 mm high, the ribs being evenly spaced around the inner circular portion, extending at least partially along the length of the elongate body and having a taper at their distal ends, the elongate body comprises square fenestrations located at least near the distal ends of the ribs and configured to allow for bony through-growth, the fenestrations being between about 1 mm and about 5 mm in width, the elongate body having a central lumen extending from the proximal end to the distal end and sized to closely fit over a guide pin, the elongate body having a length between about 20 mm and about 90 mm and an inscribed diameter between about 3 mm and about 14 mm, the inner circular portion and the ribs being made of a metal or a metal alloy and being integrally formed, the elongate body being configured to be implanted across a sacroiliac joint and having an outer surface that is porous, and the elongate body being configured to be impacted into place during implantation.