A navigation system for placing an implant in orthopaedic surgery is provided, comprising an orientation apparatus and a reference apparatus. The reference apparatus comprises an anchor for fixing the reference apparatus to a predetermined feature of the subjects body and an indicator for indicating at least one reference plane or axis. The orientation apparatus comprises a number of probes for contacting a number of predetermined features of a subjects body and defining a plane. The orientation apparatus and/or the reference apparatus comprises at least one connector for connecting the orientation apparatus and the anchor such that, when connected, relative translation of the connector and the anchor along a predetermined direction with respect to the plane defined by the probes is allowed and relative rotation of the connector and the anchor about that predetermined direction is prevented.
