Support orthopaedic device (1) for a knee joint, comprising a proximal connector (2) and a distal connector (3), articulated among themselves and respectively intended to be associated with a proximal bone (100) and a distal bone (101) of a lower limb connected among themselves by a knee joint. The device comprises a first rod (4a) and a second rod (4b), which are hinged, according to hinging axes normal to a median excursion plane of the orthopaedic device (1), to the proximal connector (2) and to the distal connector (3) so as to form with them an articulated quadrilateral. The articulated quadrilateral is planarly mobile according to a plane parallel to the excursion plane between a configuration corresponding to an extended position of the knee joint and configurations corresponding to bendings of different entity of the knee joint; the relative motion imposed to the proximal and distal connectors (2, 3) by the articulated quadrilateral is consistent with the physiological movement of the knee joint.