Systems and methods are described for using a robotic system to perform procedures within a cavity using a virtual fixture. The robotic system includes a rigid central stem including an access channel positioned longitudinally along the rigid central stem and a dexterous arm at least partially positioned within the access channel of the central stem. The dexterous arm includes a plurality of individually adjustable segments. A control system receives a positioning command from a manipulator control indicative of a desired movement of a distal end of the dexterous arm. A virtual fixture is defined that is representative of the access channel of the rigid central stem. The position of the dexterous arm is adjusted such that the distal end of the dexterous arm performs the desired movement while the portion of the dexterous arm that is positioned within the first access channel is not moved beyond the defined virtual fixture.