A knee prosthesis, comprising: a shank link; a thigh link rotatably coupled to the shank link by a knee joint; at least one resistive control element configured to apply first, second, and third levels of resistance in resisting rotation of the thigh link relative to the shank link; at least one powered control element comprising an electric motor, distinct and separate from the resistive control element, configured to power rotation of the thigh link relative to the shank link; at least one sensor; and a controller, coupled to the at least one sensor, the controller configured to: receive sensor measurements from the at least one sensor and determine, based at least on the sensor measurements, a present state of a plurality of states comprising at least a swing state, a stance state, and a stair descent state; cause the at least one resistive control element to apply a first level of resistance if the present state is a swing state; cause the at least one resistive control element to apply a second level of resistance if the present state is a stance state; cause the at least one resistive control element to apply a third level of resistance if the present state is a stair descent state; and cause the at least one powered control element to power rotation if the present state is a swing state, wherein the at least one resistive control element further comprises a hydraulic actuator cylinder, the hydraulic actuator cylinder coupled to the knee joint and configured to provide the first, second, and third levels of resistance based on hydraulic fluid flow through a hydraulic valve, wherein the hydraulic fluid flow is generated by knee joint rotation, wherein the hydraulic valve comprising an orifice configured to couple to one of a first, second, and third orifice opening, wherein each orifice opening provides one of the first, second, and third levels of resistance, characterised in that the electric motor is (3 04) coupled to the thigh link and the shank link through a power screw transmission, the power screw transmission located within a rod of the hydraulic actuator cylinder. a shank link; a thigh link rotatably coupled to the shank link by a knee joint; at least one resistive control element configured to apply first, second, and third levels of resistance in resisting rotation of the thigh link relative to the shank link; at least one powered control element comprising an electric motor, distinct and separate from the resistive control element, configured to power rotation of the thigh link relative to the shank link; at least one sensor; and a controller, coupled to the at least one sensor, the controller configured to: receive sensor measurements from the at least one sensor and determine, based at least on the sensor measurements, a present state of a plurality of states comprising at least a swing state, a stance state, and a stair descent state; cause the at least one resistive control element to apply a first level of resistance if the present state is a swing state; cause the at least one resistive control element to apply a second level of resistance if the present state is a stance state; cause the at least one resistive control element to apply a third level of resistance if the present state is a stair descent state; and cause the at least one powered control element to power rotation if the present state is a swing state, receive sensor measurements from the at least one sensor and determine, based at least on the sensor measurements, a present state of a plurality of states comprising at least a swing state, a stance state, and a stair descent state; cause the at least one resistive control element to apply a first level of resistance if the present state is a swing state; cause the at least one resistive control element to apply a second level of resistance if the present state is a stance state; cause the at least one resistive control element to apply a third level of resistance if the present state is a stair descent state; and cause the at least one powered control element to power rotation if the present state is a swing state, wherein the at least one resistive control element further comprises a hydraulic actuator cylinder, the hydraulic actuator cylinder coupled to the knee joint and configured to provide the first, second, and third levels of resistance based on hydraulic fluid flow through a hydraulic valve, wherein the hydraulic fluid flow is generated by knee joint rotation, wherein the hydraulic valve comprising an orifice configured to couple to one of a first, second, and third orifice opening, wherein each orifice opening provides one of the first, second, and third levels of resistance, characterised in that the electric motor is (3 04) coupled to the thigh link and the shank link through a power screw transmission, the power screw transmission located within a rod of the hydraulic actuator cylinder.