Anterior talofibular ligament is the most injured ligament in ankle sprain. Investigators will include ankle sprain patients who have ankle pain or instability more than 3 months. Ultrasonography will be done for confirm ligament injury. Participants will be randomized into two groups. Participants in dextrose injection group will accept dextrose 15% injection to tendon and enthesis. In the other hand, subcutaneous sham injection to control group. Pain condition, stability test and function test, will be evaluated in 1 week, 4 weeks and 12 weeks after injection.

Background: Sprains constitute most of ankle injury and 85% ankle sprain is inversion injury. The conventional treatment includes medication, physical therapy, bracing and steroid injection. Anterior talofibular ligament is the most injured ligament in ankle sprain. Although the response of acute ligament sprain is usually quickly, treatment of chronic ligament sprain is difficult. Chronic pain and ankle instability is the most common symptom in chronic ankle sprain. Dextrose prolotherapies been used for treating soft tissue injury such as osteoarthritis, tendinopathy and ligament sprain. However, there is not randomized control trial for hypertonic dextrose injection to chronic ankle sprain.

Methods: Investigators will include 40 ankle sprain patients who have ankle pain or instability sensation more than 3 months. Ultrasonography will be done for confirm ligament injury. Participants will be randomized into two groups. Dextrose injection group will accept dextrose 15% injection to tendon and enthesis. Otherwise, investigators will do subcutaneous sham injection to control group. Investigators will measure pain threshold and peak pressure by algometer, the degree of ankle instability by ultrasound, the proprioception by single leg standing, and foot and ankle questionnaire. The examination will be done before injection, immediately after injection, 1 week, 4 weeks and 12 weeks after injection.To our hypothesis, investigators suggest dextrose prolotherapy injection could decrease pain and improved proprioception.

Inclusion Criteria:

1. 20-70 age
2. Chronic ankle sprain more than 3months with chronic ankle pain or instability sensation
3. Ultrasound diagnosed anterior talofibular ligament sprain

Exclusion Criteria:

1. Acute ankle sprain less than 3 months
2. Lower limb fracture history
3. Cognitive impairment
4. Other neurological or muscular disorders
5. Sever pain could not tolerate examination