An adapter assembly for operably connecting an end effector to an electrosurgical instrument, the adapter assembly comprising: a connector assembly; a drive transfer assembly operably received through the connector assembly and including first, second, and third rotatable shafts (116, 118, 120); a first pusher assembly operably connected to the first rotatable shaft for converting rotational motion from the first rotatable shaft to longitudinal movement to perform a first function; a second pusher assembly operably connected to the second rotatable shaft for converting rotational motion from the second rotatable shaft to longitudinal movement to perform a second function; the first pusher assembly including a first planetary gear assembly and the second pusher assembly including a second planetary gear assembly wherein each of the first and second planetary gear assemblies includes a first planetary gear system (166a, 186a) and a second planetary gear system (166b, 186b), wherein each of the first and second planetary gear systems are configured to reduce a speed of rotation of the first and second rotatable shafts; and a drive member operably connected to the third rotatable shaft for transferring rotational motion from the third rotatable shaft to perform a third function; and an extension assembly operably connected to a distal end of the adapter assembly, the extension assembly including at least one flexible band assembly operably connected to one of the first and second pusher assemblies; characterised in that: the first pusher assembly includes a first drive screw operably connected to the first planetary gear assembly and the second pusher assembly includes a second drive screw operably connected to the second planetary gear assembly wherein the first pusher assembly includes a first pusher member operably received about the first drive screw and the second pusher assembly includes a second pusher member operably received about the second screw member and wherein rotation of the first drive screw causes longitudinal movement of the first pusher member and rotation of the second drive screw causes longitudinal movement of the second pusher member. a connector assembly; a drive transfer assembly operably received through the connector assembly and including first, second, and third rotatable shafts (116, 118, 120); a first pusher assembly operably connected to the first rotatable shaft for converting rotational motion from the first rotatable shaft to longitudinal movement to perform a first function; a second pusher assembly operably connected to the second rotatable shaft for converting rotational motion from the second rotatable shaft to longitudinal movement to perform a second function; the first pusher assembly including a first planetary gear assembly and the second pusher assembly including a second planetary gear assembly wherein each of the first and second planetary gear assemblies includes a first planetary gear system (166a, 186a) and a second planetary gear system (166b, 186b), wherein each of the first and second planetary gear systems are configured to reduce a speed of rotation of the first and second rotatable shafts; and a drive member operably connected to the third rotatable shaft for transferring rotational motion from the third rotatable shaft to perform a third function; and an extension assembly operably connected to a distal end of the adapter assembly, the extension assembly including at least one flexible band assembly operably connected to one of the first and second pusher assemblies; characterised in that: the first pusher assembly includes a first drive screw operably connected to the first planetary gear assembly and the second pusher assembly includes a second drive screw operably connected to the second planetary gear assembly wherein the first pusher assembly includes a first pusher member operably received about the first drive screw and the second pusher assembly includes a second pusher member operably received about the second screw member and wherein rotation of the first drive screw causes longitudinal movement of the first pusher member and rotation of the second drive screw causes longitudinal movement of the second pusher member.