A knee orthosis and a method for controlling a knee orthosis including a thigh structure having a fastening structure to be fixed to a thigh, a lower leg structure which is pivotally coupled to the thigh rail using a joint mechanism and has a fastening structure to be fixed to a lower leg as well as a foot piece for supporting a foot, and an actuator device between the thigh structure and the lower leg structure. The fastening points of the actuator on the thigh structure and lower leg structure and the center of rotation of the joint mechanism form a triangle. The fastening points are arranged on the structures such that the connecting line between the fastening points extends perpendicular to a connecting line between a fastening point and the center of rotation in an angular position of the knee in which the lower leg is bent at an angle ranging from 0° to 90° relative to the thigh.
