A prosthesis may be used for treatment of an aneurismal body vessel. The prosthesis may include a prosthetic trunk (20) and a prosthetic branch (40). The prosthetic trunk may include a graft body (25), an open first end (21), an open second end (23), and a trunk lumen (29) extending therebetween. The prosthetic branch (40) may include a graft body (45), an open first end (41), an open second end (43), and a branch lumen (49) extending therebetween. The first end of the prosthetic branch may be attached to the prosthetic trunk (20), and the branch lumen may be in fluid communication with the trunk lumen. The prosthetic branch (40) may be movable in relation to the prosthetic trunk (20) between neutral, right biased, and left biased configurations. First and second releasable steering members (70, 90) may be associated with the respective first and second biased configurations and may cooperatively retain the prosthetic branch (40) in the neutral configuration.