A working insert for an endoscopic hollow shank instrument includes a shank, on whose outer side is arranged a monopolar working electrode axially displaceable relative to the shank. Using fractal geometry, the antenna ground counterpoise has a self-similar structure resulting from the repetition of a design or motif that is replicated using rotation, andor translation, andor scaling. The torque generator is configured to generate torque between said shank link and said thigh link.