Knee orthosis for the support of a knee joint in the case of instability, comprising a part of the thigh (4) that can be fixed on the thigh by means of fixation means (7) with a half of the upper helmet (6) and articulation plates (14) fixed in the upper half helmet (6), a calf part (5) that can be fixed in the calf by means of fixing means (10) with a lower half helmet (9) and elements of splint (12) installed laterally in the lower hull half (9), splint elements (12) that are connected by means of articulation (13) with the respective articulation plate (14) and splint elements (12) in the which in the remote areas of the articulation means (13) the lower hull half (9) is pivotally mounted around a pivoted axis (15) and can be pivoted by means of adjustment (16) towards the calf, the adjustment means (16) being formed from at less a flexible, longitudinally stable traction element (17), one of whose end areas is secured in a part of the articulation means (13) that can be pivoted with respect to the splint elements (12) by a first support ( 18), whose other end zone is held in the lower hull half (9) by a second support (19) and flexible traction element (17) of longitudinal stability that is offset between the first support (18) and the second support (19) around a deflection element (20) installed in the splint element (12).Órtesis de rodilla para el apoyo de una articulación de la rodilla en el caso de una inestabilidad, que comprende una parte de muslo (4) que puede fijarse en el muslo mediante medios de fijación (7) con una mitad de casco superior (6) y placas de articulación (14) fijadas en la mitad de casco superior (6), una parte de pantorrilla (5) que puede fijarse en la pantorrilla mediante medios de fijación (10) con una mitad de casco inferior (9) y elementos de férula (12) instalados lateralmente en la mitad de casco inferior (9), elementos de férula (12) que están unidos mediante medios de articulación (13) con la placa de articulación respectiva (14
