## 4 Discussion
The fixator system can provide a larger force/moment with \(F_{\text{max}}=2.52\) KN to balance the corrective resistance from muscles and soft tissues during the correction. The lower output speed with 0.89 mm/s provided by the fixator system allows for very slow and continuous movement, which is effective for the safety of patients. Therefore, the external fixator system can not only achieve high deformity correction accuracy but also can be used as a teaching tool for clinicians to learn orthopedic deformity correction techniques in order to help them more intuitively and proficiently learn distraction osteogenesis (DO) and external fixation techniques. Meanwhile, combined with the development of computer-aided software, clinicians can perform preoperative simulation of the correction plan to ensure that the formulated correction strategy is safe and reliable, including frame configuration selection, preoperative trajectory simulation, preoperative limb-rodinterference detection, and three-dimensional simulation of the correction process. Therefore, the external fixator system has high clinical application and teaching value. During distraction osteogenesis, the soft tissue surrounding the bone will also be stretched to adapt to the growth of new bone tissue. The distraction osteogenesis is a very slow process (1 mm/day and four daily steps), which will reduce the damage of soft tissues and will not exceed the patient's tolerance of pain. When the electromotor-driven fixator is used for correction, multiple rounds of adjustment per day are also followed, and the correction amount per day is 1 mm to avoid the unbearable pain caused by the excessive correction amount. The working capability of the external fixator is not restricted by the musculoskeletal and soft tissues, the main source of resistance to the operation of the external fixator, which only causes a certain resistance to the operation of the external fixator. It should be noted here that the control strategy is position control based on PID (Proportion Integration Differentiation), not force control. Theoretically, the output force of each strut is not a constant value and the output force depends on the resistance from the musculoskeletal and soft tissues during the correction [29]. As long as the resistance is less than the maximum output force that the motor can achieve, the resistance from the musculoskeletal can be balanced by the external fixator. As we all know, the parallel external fixator has the advantage of strong rigidity and can provide sufficient strength. Each strut of the developed parallel external fixator can provide a maximum output force of 2.52 KN, which is enough to offset the resistance of the soft tissue and musculoskeletal system during the correction. In the future, a higher energy density battery and a more integrated control box will be used to reduce its volume and size, and the communication transmission between the PC and the control box will be changed from wired transmission to wireless transmission, which can allow the software to be used on more portable stand-alone devices (such as iPad) to reduce the difficulty of nursing during deformity correction. The force sensor will be installed at the end of the rod of the external fixator to monitor the force during the healing process. By studying the mechanism of dynamic correction force on the functional reconstruction of muscle and bone systems, dynamic correction trajectory planning based on quantitative monitoring and prediction of correction effect will also be carried out.