Following an acute injury, approximately 20-40% of patients will experience prolonged and recurrent ankle weakness and sprain, especially when walking on uneven ground, and patients often feel a loss of control of the ankle joint and inversion occurs. The sprain may or may not be accompanied by painful swelling. Some patients may feel stiffness in the ankle joint. At this point, the patient enters the chronic instability phase. The patient may have either mechanical instability or functional instability. In the former case, the patient has symptoms of instability and the ankle joint mobility exceeds the normal physiological range; in the latter case, the ankle joint mobility does not exceed the normal physiological range, but for a long time after the injury, the ankle joint often becomes tender and is prone to repeated sprains when walking on uneven roads. In functional ankle instability, the patient’s subjective control over the ankle joint is reduced, but the ankle mobility does not exceed the normal physiological range. In chronic lateral instability, that is, the instability may be mechanical or functional. Lateral ankle ligament rupture and laxity is the main cause of mechanical instability. Functional instability, on the other hand, is related to many factors. For example, damage to the receptor nerve fibers in the joint capsule and ligaments leads to proprioceptive impairment, resulting in decreased motor and reflex control and weakness of the ankle joint. Other factors such as peroneal muscle weakness and instability of the subtalar joint are also common causes. Treatment 1. Non-surgical treatment The treatment of functional instability mainly consists of rehabilitation exercises such as peroneal muscle strength training, Achilles tendon pulling, ankle balance board and balance plate exercises. The duration of training should be no less than 10 weeks. In addition, external fixation with bandages and braces can reduce ankle hypermobility and increase the sense of ankle stability. However, Rarick reported that the use of adhesive tape fixation reduced the strength by 50% after 10 minutes of activity, and Freman reported that after functional rehabilitation training, 70-85% of functional instability could obtain good results. 2.Surgical treatment For patients with mechanical instability, functional rehabilitation should be carried out first, and if non-surgical treatment fails, surgical treatment can be considered. Surgical methods can be divided into two categories: (1) anatomical repair methods. Dr. Lennart Brostrom first reported anatomic repair in 1966. In 1980, Nathaniel Gould modified Brostrom’s surgical approach by suturing the lateral portion of the extensor support band to the distal fibula in a dorsal direction to further strengthen the ligament repair. This procedure was later often referred to as the modified Brostrom-Gould procedure. The advantage of anatomic repair of the lateral ligament is that it does not sacrifice its own tissues, and because there is no tendon fixation effect, there is little impact on the biomechanics of the ankle and subtalar joint and no stiffness of the subtalar joint occurs. Therefore, whether the injury is acute or chronic instability, anatomic repair methods can be used first, and when direct repair is difficult, non-anatomic reconstruction methods are used. Modified Brostrom-Gould postoperative rehabilitation program Phase 1 (1 week postoperatively) 1. Fix the ankle in neutral position with a calf cast brace 2. apply cold compresses for 3 days 3. relieve pain Phase 2 (2-6 weeks postoperatively) 1. replace the cast brace or fix it with a splint. 2. Prohibit ankle inversion and inversion 3. Start gentle ankle extension and flexion activities after 3 weeks 4. Start gentle peroneal tendon strength exercises after 3 weeks Phase 3 (6 weeks after surgery) 1. Start balance exercises 2. Peroneal muscle strength exercises 3. Joint mobility exercises Phase 4 (8-12 weeks) Gradually resume various activities and sports (2) Non-anatomical reconstruction methods. More than 50 types of surgery and their modifications have been reported in the literature. According to the different reconstruction materials used, they are further divided into 3 categories: 1.Use of peroneal tendon. 2) Use of metatarsal tendon, partial Achilles tendon or autologous free material graft. 3.The use of alternative materials such as carbon fiber, bovine collagen, etc. The most commonly used reconstructive material is still the peroneal tendon, and the commonly used procedure is the Chrisman-Snook procedure: 1/2 of the short peroneal tendon is cut from the proximal end, first through the talar neck bone foramen, then through the distal fibular bone foramen, down through the lateral wall bone foramen of the heel bone, and finally sutured to the short peroneal tendon. If the tendon is too short, it can be fixed directly to the lateral aspect of the heel. This procedure uses only half of the short peroneal tendon to reduce the effect on ankle valgus forces. The reconstructed tendon follows the anatomical direction of the original ligament, i.e. the anterior talofibular ligament is reconstructed and the heel-fibular ligament is reconstructed, which is an ideal non-anatomical reconstruction method.