An interface joint for interconnecting an electrosurgical generator and an electrosurgical instrument, the interface joint comprising: a housing made of electrically insulating material, the housing having: a first inlet for receiving radiofrequency electromagnetic energy and/or microwave frequency EM energy from the electrosurgical generator, a second inlet for receiving fluid, and an outlet; a flexible shaft for connecting the housing to the electrosurgical instrument, the flexible shaft extending through the outlet and having a longitudinal passage therein, which provides a fluid flow path that is in fluid communication with the second inlet, and which conveys a coaxial transmission line that is connected to the first inlet; an actuation mechanism operably connected to the electrosurgical instrument to control deployment of a fluid delivery structure, the actuation mechanism comprising: an actuation rod extending out of the housing through the outlet, an actuator movably mounted on the housing and connected to the actuation rod; and a shaft rotation mechanism for rotating the flexible shaft relative to the housing, the shaft rotation mechanism comprising a rotation actuator rotatably mounted on the housing and operably coupled to the flexible shaft, and wherein the housing includes an internal watertight branched conduit that provides a fluid flow path between the second inlet and the outlet, the branched conduit comprising: a main conduit fixed to the housing, and a rotating luer lock fitting rotatably mounted to a distal end of the main conduit, wherein the flexible shaft is non-rotatably coupled to the rotating luer lock fitting, and wherein the rotation actuator is operable to rotate the rotating luer lock fitting relative to the main conduit. a housing made of electrically insulating material, the housing having: a first inlet for receiving radiofrequency electromagnetic energy and/or microwave frequency EM energy from the electrosurgical generator, a second inlet for receiving fluid, and an outlet; a first inlet for receiving radiofrequency electromagnetic energy and/or microwave frequency EM energy from the electrosurgical generator, a second inlet for receiving fluid, and an outlet; a flexible shaft for connecting the housing to the electrosurgical instrument, the flexible shaft extending through the outlet and having a longitudinal passage therein, which provides a fluid flow path that is in fluid communication with the second inlet, and which conveys a coaxial transmission line that is connected to the first inlet; an actuation mechanism operably connected to the electrosurgical instrument to control deployment of a fluid delivery structure, the actuation mechanism comprising: an actuation rod extending out of the housing through the outlet, an actuator movably mounted on the housing and connected to the actuation rod; and an actuation rod extending out of the housing through the outlet, an actuator movably mounted on the housing and connected to the actuation rod; and a shaft rotation mechanism for rotating the flexible shaft relative to the housing, the shaft rotation mechanism comprising a rotation actuator rotatably mounted on the housing and operably coupled to the flexible shaft, and wherein the housing includes an internal watertight branched conduit that provides a fluid flow path between the second inlet and the outlet, the branched conduit comprising: a main conduit fixed to the housing, and a rotating luer lock fitting rotatably mounted to a distal end of the main conduit, wherein the flexible shaft is non-rotatably coupled to the rotating luer lock fitting, and wherein the rotation actuator is operable to rotate the rotating luer lock fitting relative to the main conduit. a main conduit fixed to the housing, and a rotating luer lock fitting rotatably mounted to a distal end of the main conduit, wherein the flexible shaft is non-rotatably coupled to the rotating luer lock fitting, and wherein the rotation actuator is operable to rotate the rotating luer lock fitting relative to the main conduit.