A modular handle assembly includes a dial rotatably connected to a handle and rotatable about a first rotary axis. A first gear arm extends from the dial and terminates at a first traction surface. A second gear arm is connected to the handle and rotatable about a second rotary axis that is parallel to the first rotary axis. The second gear arm terminates at a second gear tip that presents a second traction surface disposed against the first traction surface such that rotation of the dial in a first rotary direction effectuates rotation of the second gear arm in an opposite direction. A cam is coupled with at least one of the first and second gear tips and presents at least one deflection surface for deflecting a deflection wire during rotation of the dial to steer a distal end of a steerable catheter containing the deflection wire.
