The present invention refers to a jointed arm elbow with the tension element concealed, applicable to sun blind arms, with a configuration in which the tension element not only is not visible from the exterior, but also is detached from the inner surface of the core of the joint, thereby preventing damage to the surface and to the tension element itself. The tension element used is a chain to which is incorporated at least one semi-rigid outer or inner strip, or both of them, joined to each other in order to prevent relative movements. The invention comprises a set of particular solutions that permit the attachment of one semi-rigid strip to the other.