An endoluminal prosthesis is provided with an improved fixation system for coupling the endoluminal prosthesis to an inner wall of a lumen and to reduce distal migration. According to an embodiment of the present invention, a laterally protruding member atraumatically engages the ostium of a side or branch vessel. The protruding member may be fixed to a portion of a prosthesis. In one embodiment the protruding member is provided on a modular fixation device for initial fixation within the body lumen with the finger member within the side or branch vessel. A primary endoluminal prosthesis is then fixed to the modular fixation device to bypass a diseased portion of the anatomy.