Abstract: A prosthesis or orthosis (orthotic brace) comprises at least two parts (1, 2) connected to each other by means of an artificial joint (K), and a control device for the joint, to brake or lock the joint. The prosthesis or orthosis comprises a sensor (5) which detects the position in relation to a fixed line (L) of a part connected to the joint (K) and which is connected to a control device (4) arranged to influence the joint (K) on the basis of position data given by the sensor (5). The prosthesis or orthosis is a lower limb prosthesis, such as a thigh prosthesis or a hip ex-articulation prosthesis, or a lower limb orthosis. The sensor (5) is arranged to detect the position of the thigh part (1) in relation to a vertical line (L). The control device (4) is arranged to influence the movement resistance properties of the joint (K) on the basis of data given by the sensor (5). The sensor (5) is based on detecting the direction of earth's gravity.