Robotic leg-lengthening fixator using hybrid position/force control

The paper presents a unilateral external leg-lengthening fixator driven by 2 DoFs (Degrees-of-Freedom) planar mechanism and a hybrid position/force control scheme. In this paper, we show that the leg lengthening by the process of “distraction osteogenesis” is able to be achieved by using the proposed robotic fixator. In the operation process, the bone is supposed to be cut into two segments, the proposed external fixation mechanism periodically increases the gap between two segments of the bone, while new bone continues to grow between them. The frequency and magnitude of the gap generation is controlled using a neural oscillator proposed in the paper. Unlike the existing external fixators, the mechanism is proposed to be driven by electric motors. As the distance between two segments of the bone is increased, so the muscles and the tissues connected to the bone are also stretched. If the process of bone elongation is abruptly performed, it may cause a serious fatigue and damage to the muscles and other connected tissues. Also there may be misalignment or a small bend in newly formed bone which may result in knee joint axial deformity. As a remedy of these problems, the proposed leg lengthening mechanism is controlled by using a hybrid position/force control scheme. Finally, the effectiveness of the proposed scheme is suggested through several simulation studies.