A system and method for a modular external interface for a skin penetrating appliance is provided. The modular device prevents internalization of bacteria, other infectious agents, or other unwanted materials from entering the access point for a catheter, Steinman pin, Kirschner wires, or other percutaneous instruments. The modular external interface provides for the hermaticity in the vicinity of the skin-appliance interface with fluid exudate or transudate egressing from the vicinity of the skin-appliance interface. The modular external interface forms a hermetic seal with the external neck of an implanted appliance with a locking feature that joins the main body of the modular external interface together around the neck of the appliance. The modular external interface provides mechanical stability to an implanted appliance so as to speed healing around a semi-permanent implanted appliance, as well as connection points for vacuum lines and drive lines for the insertion of medical devices.