Children’s knees bending inward (commonly known as O-shaped legs) or turning outward (commonly known as X-shaped legs) are quite common and annoying to parents, as are inward and outward-facing feet. When they see that their child’s legs are bent and different from other children’s, parents are most worried: Is this normal? Will it get better in the future? If not, how ugly it will be! Should we correct it in time so that we don’t miss the opportunity to treat it? Most infants’ calves are inwardly curved. To distinguish normal from abnormal, we should first understand the normal process of lower limb development in children. Before birth, the fetus is flexed in a narrow space in the womb, and the lower limbs, especially the lower legs, are quite inwardly curved. Therefore, nine out of ten newborn babies have inwardly curved and internally rotated calves. First-time parents are often puzzled by this, mistaking it for something abnormal and asking for treatment, which is unnecessary. The inward bending of the knee becomes more apparent when the child begins to walk. When children land on their feet, most of them have a combination of inwardly curved feet that look as if a ball could pass through the middle of their legs. In fact, when the child is lying down for examination, both lower extremities still look bent, and the “O” leg is especially obvious when walking. This is also the time when parents often bring their children to the clinic. In fact, inward curvature is a normal physiological phenomenon around 1.5 years old. At the age of 2, the lower extremities gradually straighten out, and then the knees begin to turn outward and the bones on the inside of the knee appear to bulge, especially in tall, thin children. at the age of 3, this “X” shaped leg reaches its most severe level, and when standing, if the knees are leaning, the feet are spread apart and cannot close. It is very difficult to see when running, and the knees will touch each other internally and trip over themselves. At this stage, it is not uncommon for children to be brought to an orthopedic surgeon. Parents are worried that if they don’t look good in the future, they will have problems in the military because they may not even be able to stand upright! Fortunately, this situation will improve after the age of 4-5 years old, and as they grow, they will show a slight outward bend like adults. Therefore, physiologically a child’s knee will go through the normal process of inversion, straightness, valgus and slightly valgus. Ligamentous laxity in bent legs will improve as they grow Why do some children have more bent legs than others? Most of it can be said to be normal differences, just like people’s height and weight, not everyone is the same. The second is laxity of the ligaments. We know that the ligaments are very loose in children just after birth, so they can very gently put their toes in their mouths, bend their bunions to touch their forearms or fold their fingers back to be parallel to their forearms. When lying down, the feet appear to be fairly straight and have arches, but when standing, the knees are bent inward or backward and the phenomenon of flat feet is present, and the phenomenon of “O”-shaped legs is more obvious when walking. A detailed examination of children with “X” shaped legs around the age of 3 also reveals that their ligaments are slightly looser than those of people with straight legs. The phenomenon of ligament laxity is generally a physical factor that improves with growth, and only about 4-7% of people still have ligament laxity in adulthood, as we can see from the simple tests mentioned above. Also, some ligament laxity is hereditary, and it is less likely to improve in this group of people. Some people blame diapering or early learning to walk for their children’s bent legs, but we don’t think diapering has anything to do with it. Calcium or vitamin D deficiency can also bend the legs. A small number of inversions of the knee (X-shaped legs) are caused by disease. We should be suspicious if: 1) the bend in the leg does not correspond to the age. For example, if the leg turns outward after the age of 1 year, or if the leg still turns inward after the age of 2 years. (2) The leg is bent very much. Although the direction of the leg bend is consistent with age, if the bend is excessive, it is suspicious. ③ Asymmetry, that is, only unilateral bending or the degree and direction of bending of the two legs are different, there must be a big problem. Disease causing leg curvature. The most common is rickets caused by calcium or vitamin D deficiency. This type of child often only eats mother’s milk until about 1 year old, and rarely eats side dishes, cow’s milk or supplements, so they also look unhealthy in appearance. In addition to the strong inward bending of the legs, the ends of the bones also appear to be extraordinarily elevated. There are even multiple bulges at the junction of the rib cartilage in the chest. In addition, congenital skeletal abnormalities such as dwarfism are often combined with bending deformities of the lower extremities, which are not a problem to identify because the height, upper body, and extremities are abnormal. Rickets can also be caused by congenital abnormalities in calcium and phosphorus metabolism (e.g., hereditary hypophosphatemia) or by acquired kidney disease. The former often has a family history, while the latter is a chronic kidney disease and should not be difficult to diagnose. Acquired factors also include fractures and sequelae of inflammation, osteomas, or bone abnormalities. There is also a disease called “Blount’s” disease, both knees inversion than the average child is serious, is a tibia (calf bone) on the inside of the bone growth disorder, the cause is still not understood, generally thought to be related to the child is too fat or too early walking. The differential diagnosis between normal and abnormal leg curvature is not difficult, as already mentioned above, with age, family history, and detailed physical examination, more than 90% of people are normal. It is only when pathological factors are suspected that we ask the patient to take x-rays or blood and urine tests. Patients with rickets can see the widening of epiphysis and poor calcification on X-ray, and other diseases also have their special X-ray and blood changes. However, from a biomechanical point of view, a bent knee that persists into adulthood can lead to knee osteoarthritis due to uneven forces. Generally speaking, we do not encourage children to learn to walk too early, nor should they eat too much, because if they have already learned to walk, it is impossible to prohibit it. For most children who are still within the normal range, we can simply explain the developmental evolution. For those with lax ligaments, it is best to encourage more sun exposure, more outdoor activities and a normal diet, as long as the muscles and ligaments are strong, the legs will naturally straighten. Some parents are overly worried and insist on ordering braces or orthopedic shoes, because it often takes more than a year for the treatment to show results, not only children and adults suffer, but also children cannot enjoy a happy childhood. In fact, are braces or orthopedic shoes really responsible for the straightening of the legs? God knows! Many children also refuse to wear the bulky braces, and their parents’ money is wasted. As to whether these children need calcium supplements or other nutritional supplements, because the cause of this disease is not calcium deficiency, so there is no special effect, but we do not object to giving these things to children, at least it is beneficial, just do not hope too high. If a child’s legs are found to be caused by rickets, blood and urine tests must be performed to determine whether the problem is calcium or vitamin D deficiency, hereditary hypophosphatemia or renal rickets, so that appropriate treatment can be given for the individual disease. If it is a calcium deficiency or vitamin D deficiency, calcium tablets and large amounts of vitamin D should be supplemented to treat the condition. At the same time, dietary habits must be changed, such as supplementing dairy products, meat, milk and other calcium-containing foods and other side dishes, getting more sunlight and doing more outdoor activities. In particular, mothers who have been vegetarian for a long time should have more calcium in their mother’s milk and should supplement it. In case of hereditary hypophosphatemia or nephrogenic rickets, they can be treated with new vitamin D3, the latter of course while treating or controlling their kidney disease. Of course, regardless of the above-mentioned causes, if the legs are bent too much, they should be supplemented with brace treatment to avoid worsening the bent legs. Some rickets are cured but the leg is still bent, so surgery can be considered to correct it. The important thing to remember is that the disease must be cured or controlled before surgery, otherwise the leg curvature may still recur after surgery. Bronte’s disease can be corrected by bracing in the early stage, but in the late stage, it needs to be treated by open surgery. If the leg curvature is due to fracture, inflammation or osteoma affecting the epiphysis, their treatment is different and has to be decided on a case-by-case basis, with many options. All in all, most of the leg curvature is a physiological phenomenon within the “normal range” during the development process, and no special treatment is necessary. Ligamentous laxity, some people still have some degree of bending, but there is no big problem. The important thing is to distinguish between normal and pathological conditions, to find out the underlying disease of the leg bend, and to treat the individual disease in a timely manner so as not to affect its appearance in the future, or to lead to knee arthritis.