The normal human ankle flexion-internal rotation muscle group is significantly larger than the dorsal extension-external rotation muscle group, the gastrocnemius muscle in the calf triceps is the long muscle across the knee and ankle joint, the calf lengthening within 3cm, the tension on the muscle soft tissue, initially through elastic extension to adapt, lengthening greater than 3cm or 15% of the tibial length, in the continuous tension-stress Under continuous tension-stress, soft tissues such as blood vessels, nerves and muscles will follow the law of tension-stress (CTS) to regenerate simultaneously with bone lengthening, but the gastrocnemius muscles (including the peroneus longus and posterior tibial muscles across the ankle joint) are difficult to be subjected to continuous and constant tension, and the basic conditions that make these tissues regenerate will not arise, thus occurring muscle tendon relative Shortened foot drop, or foot drop inversion, valgus deformity (combined with peroneus longus or tibialis posterior muscle shortening), adults who lengthen the calf > 4cm, if not fixed ankle joint, often inevitably occur to varying degrees of foot drop deformity. Animal experiments have demonstrated that the number of bone and muscle lengthening during limb lengthening is not proportional. In the periosteal muscles recorded with a scorekeeper, the part of the periosteum close to the osteotomy break site that was lengthened was as wide as the gap between the osteotomy ends, so the bone ends were actually moving under the periosteum, while the muscle in the traction area that was lengthened was only 20% of the osteotomy gap [ ], indicating that the whole muscle from the starting point to the end point was involved in the lengthening process. In order to prevent the occurrence of foot drop deformity, scholars have used strengthening stretch walking exercises to solve this complication. 1960s, some scholars also used forefoot strengthening elastic rubber band plate and lengthening device fixed together to prevent the occurrence of foot drop, which can also produce some effect. In the 1980s, Ilizarov [ ] invented the use of a 1.6 mm diameter steel pin crossed over the heel bone, which was fixed to the steel ring of the hindfoot 3/4 and connected to the distal ring of the tibial lengthener with a screw rod, thus fixing the ankle joint in the “0” position. After surgery, the hindfoot is stabilized in neutral position while the tibia is lengthened and the Achilles tendon can be advanced in the same manner. If the patient has a mild contracture of the Achilles tendon before surgery, the threaded rod attached to the Achilles bone can be gradually rotated after surgery so that the Achilles tendon can be retracted, preventing foot drop during significant tibial lengthening. However, because the threaded rod connects the hind foot to the tibia, the ankle joint and the heel joint cannot move, and the ankle joint surface is prone to degeneration after long-term braking, and the ankle joint is prone to pain and limitation of movement after lengthening, and the tibia is not conducive to walking with weight during lengthening. The spring-loaded movable linkage rod, so that the postoperative rotating nut and spring pressure will gradually release the retraction force to the heel bone, producing a continuous tension suitable for physiology, which is a continuous dynamic force. When the affected foot walks on the ground, the ankle joint can also do the right amount of dorsiflexion and plantarflexion to prevent the degeneration of the joint surface of the ankle joint after the compression, so that the lengthening process of the lower leg is also conducive to blood and lymphatic circulation. When the tibia is lengthened, the Achilles tendon and the long muscles on the back side of the ankle joint will be regenerated by simultaneous stretching, and the substantial lengthening of the tibia will not be accompanied by deformities such as foot drop or inversion or valgus. The design of this synchronous lengthening device solves the long-standing problem of foot drop caused by lower limb lengthening.