1. Analysis of clinically relevant factors affecting the efficacy of bone scab retraction surgery Patient’s own factors; lengthening speed and retraction time; osteotomy site; degree of preservation of blood supply at the osteotomy end; choice of limb lengthening device 2. Analysis of complications and their prevention (1) muscle contracture and joint stiffness: the most common complication in limb lengthening. Strengthening the active and passive flexion and extension activities of the joint is one of the most cost-effective measures; at the same time, the intermittent stress stimulation generated by the limb activity has a role in promoting bone healing. During the lengthening of the limb, especially the substantial lengthening, the mobility of the knee and ankle joints decreases, but the joint function can be improved or restored through timely active or passive exercises during and after the lengthening. (2) Axial deviation: imbalance of muscle force at the osteotomy, different osteotomy sites and bone types, and poor fixation of the external fixation frame are the main reasons for axial deviation. The proximal femur and distal tibia osteotomy tend to have inversion and anterior convexity offset, the middle femur osteotomy tends to have anterior convexity offset, and the proximal tibia osteotomy tends to have exostosis and anterior convexity offset. Preoperative detailed design, skilled anatomical knowledge and firm and stable external fixation after osteotomy are the basic conditions to maintain the axial direction to prevent angulation; in addition, when placing the external fixation frame during surgery, the pin can be tilted and fixed in the opposite direction where angulation may occur, and the axial deviation should be adjusted in time if it is found after surgery. (3) Early fusion: The main reasons are overemphasis on preserving the blood supply resulting in incomplete osteotomy, slow lengthening and failure of the external fixation frame to reach the standard of loosening and stretching. Therefore, intraoperative surgical operation should be standardized, a secure external fixation brace should be applied, and a lengthening plan should be made according to the individual; at the same time, regular postoperative review and timely radiographs should be taken to understand the progress of lengthening. In addition, studies have shown that if the waiting period for lengthening exceeds 2-3 weeks, early fusion is likely to occur, especially in smaller children with epiphyseal osteotomies. (4) Delayed healing, bone nonunion and re-fracture: To reduce the incidence of delayed healing and bone nonunion, we should avoid the vulnerable factors as much as possible, strictly review the system on a regular basis, close the contact between doctors and patients, and obtain the positive cooperation of patients. The method of promoting bone healing in bone lengthening is still being explored, and it has been proposed that axial compression and local micromotion immediately after lengthening can promote bone healing; at the same time, good nutrition and prevention of disuse osteoporosis during lengthening are also necessary to ensure. (5) Ankle dislocation: The upper tibial osteotomy lengthening in this group was complicated by one case of external ankle dislocation, because the lower tibiofibular joint was not fixed in the lengthening, and the external ankle was shortened and dislocated due to insufficient fibular lengthening, which was found to be a one-time lengthening of the distal fibula and external ankle repositioning. During surgery, we should ensure screw fixation of the distal tibiofibular joint, and review the film when necessary, so that the traction force is equivalent to the distal tibiofibular joint through the bone round pin, and the lengthening speed is synchronized. (6) Psychological barriers: preoperatively, patients and their families should be made fully aware of the problems that may be encountered during surgery and rehabilitation, and attention should be paid to regular communication with patients during lengthening to face and deal with various unfavorable situations together in a timely manner, and psychotherapy can be used when necessary. While eliminating psychological barriers, it will also get the positive cooperation of patients, which is conducive to early functional exercise and satisfactory results.