A medical instrument assembly and robotic medical system are provided. The instrument assembly comprises coaxially disposed shafts, and a mechanically drivable interface to which the proximal ends of the shafts are mounted. The drivable interface has first and second actuating elements configured for independently axially rotating the shafts relative to each other, and a third actuating element configured for deflecting the distal end of one of the shafts. The robotic medical system comprises the instrument assembly, a user interface configured for generating at least one command, and a drive unit coupled to the drivable interface. The robotic medical system further comprises an electrical controller configured, in response to the at least one command, for directing the drive unit to drive the first and second actuating elements to independently axially rotate the shafts relative to each other, and to drive the third actuating element to deflect one of the shafts.