A catheter system for treating lesions is provided. The system is suitable for treatment of bifurcation lesions, has a low profile and provides substantially predictable translational and rotational positioning. In one embodiment, the system includes a fixed wire balloon catheter and a partially attached guidewire lumen, wherein the guidewire lumen is attached to the catheter at a crotch point. The location of the crotch point is predetermined so as to provide substantially predictable positioning. Several embodiments of the system are described for various types of lesions and vessel configurations.