A variety of surgical instruments include one or more elements that transmit RF energy to tissue. Some such instruments comprise a pair of jaws that open and close on tissue, with conductive tissue contact surfaces that are operable to weld tissue clamped between the jaws. Some surgical instruments also include a translating tissue cutting element. Some such instruments may be in the form of forceps having a scissor grip. When an electrosurgical instrument includes grasping jaws and tissue severing capabilities it may be desirable to avoid accidental cutting by the knife. Hence, the instrument may include a feature that prevents the knife from firing until the jaws are sufficiently closed upon the tissue. It may also be desirable to prevent the jaws from being opened until the knife has been retracted. One or both of these features can prevent the knife from being extended while the jaws are open.
