Instrument for water jet surgery

A surgical instrument for performing water jet surgical operations comprises a nozzle that can be moved via a hydraulic actuator out of a retracted or passive position into a moved-forward or active position. The actuation is accomplished using hydraulic fluid that is supplied to the instrument head via a tube and/or hose. The fluid (e.g., a sodium chloride solution) that is to be injected into the tissue can be used as the hydraulic fluid that is supplied to the nozzle. High-frequency (HF) current can additionally be applied to the nozzle. The HF current can be conducted to the nozzle via a line extending through the fluid conducting element or via the electrolyte present therein.