An endosseous screw assembly (100) for an internal fixation system (SC； SP), whose connection to the rest of the system is unusually easy for the surgeon, comprising: a longitudinally extending rod (1) equipped with at least one threaded proximal portion (2)； a connection sleeve (3), within which a portion of the rod (1) is slidingly guided, said connection sleeve (3) being arranged to be inserted into a connection hole of an internal fixation member by snap-connecting within said connection hole up to reach a locking position； said rod (1) and said connection sleeve (3) comprising such mutual engagement means so as to form an axial constraint to the sliding of the rod (1) into the connection sleeve (3), so as to define, when the threaded proximal portion (2) advances into a bone site of the patient, a dragging of the connection sleeve (3) into the connection hole up to reach the locking position.
