The invention relates to an attachment adapter for attaching additional functions to a surgical tool. The attachment adapter provides a joint or a coupling between two instruments, e.g. a surgical tool and a navigation marker. The attachment adapter comprises an attachment body for attaching a surgical tool to the attachment adapter and a mounting seat with a mechanical coupling for fastening an add-on device to the attachment adapter. The attachment body comprises an elongate part adapted to receive the winding of a line and provided with at least two legs adapted to fit in an astride position on an elongate part of a surgical tool. It also comprises a line securing means adapted for securing a line, wound around the attachment body to join the attachment adapter to the surgical tool, in a locking position.
