A prosthetic device, especially a foot prosthesis or leg prosthesis, comprising: - a prosthesis shaft, which can be coupled to a leg of a patient to be attended to, - at least one treading body for contacting a ground, and - at least one joint device hingedly connecting the prosthesis shaft to the treading body, - wherein the joint device comprises an actuator which can be actively controlled by a controller in such a manner that the position of the treading body relative to the prosthesis shaft can be changed, - and wherein the prosthetic device further comprises at least one sensor element (26, 28, 30, 32, 34, 36, 41), which is configured for contact-free detection of the condition of the ground, wherein the actuator of the joint device can be controlled in accordance with the information regarding the condition of the ground detected in a contact-free manner by the sensor element (26, 28, 30, 32, 34, 36, 41), and at least one motion detection device configured for detecting motion parameters regarding the current movement of the prosthetic device, especially regarding rotation and translation of the prosthetic device, - characterized in that the controller is configured for evaluating the motion parameters detected by the motion detection device in combination with the information regarding the condition of the ground detected by the at least one sensor element (26, 28, 30, 32, 34, 36, 41) in order to determine a model of the ground, according to which the actuator of the prosthetic device can be adjusted, wherein the current position of the prosthetic device in space with respect to a global coordinate system is determined from the motion parameters, and the detected information regarding the ground and the condition thereof is then assigned to this global coordinate system. - a prosthesis shaft, which can be coupled to a leg of a patient to be attended to, - at least one treading body for contacting a ground, and - at least one joint device hingedly connecting the prosthesis shaft to the treading body, - wherein the joint device comprises an actuator which can be actively controlled by a controller in such a manner that the position of the treading body relative to the prosthesis shaft can be changed, - and wherein the prosthetic device further comprises at least one sensor element (26, 28, 30, 32, 34, 36, 41), which is configured for contact-free detection of the condition of the ground, wherein the actuator of the joint device can be controlled in accordance with the information regarding the condition of the ground detected in a contact-free manner by the sensor element (26, 28, 30, 32, 34, 36, 41), and at least one motion detection device configured for detecting motion parameters regarding the current movement of the prosthetic device, especially regarding rotation and translation of the prosthetic device, - characterized in that the controller is configured for evaluating the motion parameters detected by the motion detection device in combination with the information regarding the condition of the ground detected by the at least one sensor element (26, 28, 30, 32, 34, 36, 41) in order to determine a model of the ground, according to which the actuator of the prosthetic device can be adjusted, wherein the current position of the prosthetic device in space with respect to a global coordinate system is determined from the motion parameters, and the detected information regarding the ground and the condition thereof is then assigned to this global coordinate system.