A fail-safe attachment is provided for coupling an exoskeletal prosthesis to a patient limb having a bone anchored mounting post with an external fixation structure (1). The fail-safe attachment comprises a first component (2) adapted for connection to the fixation structure, and a second component (3) adapted for connection to the prosthesis. A safety release mechanism is provided normally retaining the prosthesis in a rigid substantially motion-free interconnected relation to the fixation structure, said safety release mechanism responding to a force overload condition to permit relative movement between the prosthesis and the fixation structure. The safety release mechanism comprises a bending force release mechanism responsive to a bending force overload condition to permit the separation of the second component (3) relative to said first component (2). The bending force release mechanism comprises a plurality of spring loaded jaws (37) adapted to engage a complementary portion (12) of the other component, the jaws (37) being pivotable in an over-centre spring configuration between a first position in which they engage the complementary portion (12) to secure the first and second components one to the other, and a second position in which the first and second components are able to separate.Linvention concerne une fixation à sécurité intrinsèque pour laccouplement dune prothèse exosquelettique au membre dun patient comportant un montant fixé sur un os doté dune structure de fixation externe (1). La fixation à sécurité intrinsèque comprend un premier composant (2) conçu pour être connecté à la structure de fixation, et un deuxième composant (3) conçu pour être connecté à la prothèse. Un mécanisme de sécurité permet normalement de maintenir la prothèse dans une relation dinterconnexion rigide pratiquement sans mouvement avec la structure de fixation, ledit mécanisme de sécurité réagissant à une condition de contrainte excessive en permettant un mouvement relatif e
