Looped leg is often called knee inversion in the clinic, the common causes are mainly caused by physiological factors, such as physiological lower limb curvature in early childhood, but also may be caused by certain diseases, such as muscle group imbalance, rickets, systemic diseases and trauma and bone tumors and so on. 1. Physiological factors: physiological lower limb curvature usually occurs between 0 and 2 years of age, usually both lower limbs are symmetrical curvature, the figure is normal. Lower limb curvature will be spontaneously corrected with the development of children’s bones, until about 1.5 years old, children’s lower limbs will gradually become straight. This is a physiologic developmental process, so there is no need to worry too much. 2. Imbalance of muscle groups: Long-term poor posture, incorrect exertion posture or excessive participation in antagonistic sports can lead to an imbalance in the development of the muscle groups that govern the knee joint, resulting in the formation of knee inversion. 3. Systemic diseases: nutritional rickets and other metabolic bone diseases, due to calcium and phosphorus ratio imbalance, calcium deficiency, affecting the development of lower limb bones, affecting the normal knee posture and structure. 4. Bone tumors, trauma to the knee joint and its surrounding tissues or bone tumors can also damage the normal structure of the muscles or bones, which may also lead to the appearance of rotator cuffs. There are many possible causes of rotator cuff and the patient’s condition should be closely monitored. If there is further aggravation, the patient should go to the doctor in time and receive treatment as soon as possible, which will help the normal development of the lower limbs.