An assembly tool comprises in an assembled configuration a proximal implant fastener, a distal implant fastener, and a compression member. The assembly tool is operable to hold in the assembled configuration a proximal implant partially engageable with a distal implant during implantation and axial impaction. Axial impaction is exerted through the compression member of the assembly tool. The assembly tool is also operable to securely lock the tapers of proximal and distal implants after impaction by rotating the compression member.