“Is an asymmetrical hip pattern a disease?” Asymmetrical hip pattern is one of the early signs of abnormal hip development in infants and children, and similar signs include “tightly divided legs” and “legs that are not the same length”. These signs are often indicative of early abnormal hip development and require further examination by a specialist to determine the presence of this condition. The medical name for this condition is developmental dysplasia of the hip (DDH), which is a generic term for congenital or developmental structural abnormalities of the hip joint in infancy and childhood, including hip dysplasia, hip subluxation and even total hip dislocation. “Developmental dysplasia of the hip (DDH), is this a common problem? How serious is it?” DDH is the most common known disease of the skeletal muscular system (pediatric orthopedics) in infancy, and the incidence of the disease is usually considered to be around 0.1% to 0.3%, and there is a lack of comprehensive and authoritative statistics in China, which seems to be small in isolation, but do you know the incidence of breast cancer, which is a serious threat to women’s health? In 1992, the incidence rate of female breast cancer in Shanghai was only about 25.6 cases per 100,000 people, which is a difference of more than a thousand times! In some cases of severe hip dislocation, even if treated with orthopedic surgery for correction, it is always difficult to avoid pain such as unequal lower limb length, limp, limited hip movement and early onset of traumatic joint. It has been suggested that about half of the degenerative arthritis in adult women comes from DDH that was undetected in infancy or treated unsatisfactorily. “How does DDH happen?” Our pediatric orthopedic surgeons have been searching for the mechanism by which DDH occurs, and several research institutions have now successfully obtained animal models of DDH in rats and rabbits through series of animal experiments. Although there are many hypotheses and some of them sound perfect, no single doctrine has yet been able to fully explain our clinical findings. Usually, we can say that DDH may be related or associated with certain factors, but it is difficult to specify the specific causative factors in each baby. Although the etiology is not clear, the following phenomena are currently considered by medical science as possibly suggesting a higher likelihood of a child with DDH, such as: female infancy, breech delivery, joint laxity, family history, history of first birth, etc. Some definite problems can also increase the incidence of DDH, such as: myotonic plagiocephaly, forefoot inversion (clubfoot), and low amniotic fluid, etc. If any of these phenomena or conditions are found, it is best to come to the pediatric orthopedic department for further examination for clarification as well. Other early symptoms that parents should pay attention to include: asymmetrical hip lines, asymmetrical thigh lines, difficulty in separating the thighs, frequent “thumping” when urinating or moving the lower limbs, and other lower limb asymmetries, parents are advised to bring their children to a pediatric orthopedic specialist for early examination. A certain percentage of suspected DDH cases are usually detected during the physical examination of newborns, but a certain percentage of these children will recover spontaneously during their later development. Clinical epidemiology has shown that DDH is more prevalent in regions or ethnic groups where newborns are wrapped in “candle wraps” or have their calves tied up, such as the Indian tribes of North America and parts of northern China. On the contrary, the incidence of DDH is significantly lower in Africa or in the southern part of China, where parents hold their children’s lower limbs separately due to the hot weather. These phenomena are difficult to explain by congenital, so the term “developmental hip dysplasia” is now used instead of “congenital hip dysplasia”. With regard to genetic problems, we have found interesting phenomena in our research and clinical practice. It has been suggested that the HOX family of genes, which dominate the development of the lower limbs, may be involved in the development of DDH, but the exact mechanism of development needs to be further investigated. Clinically, in Europe and the United States, it has been made a routine practice to have the child formally examined by a specialist during the neonatal period if DDH occurs in the immediate family. We in Shanghai, as one of the first cities to introduce DDH screening in child health screening, have achieved impressive results, thanks to the doctors who work in child health in Shanghai. Of the large number of children with DDH seen in our pediatric hospitals each year, almost all of the cases detected in the early stages are referred from the city’s child health care section, while the number of advanced, severe cases that must undergo orthopedic surgery decreases significantly each year. “Is DDH congenital? Is it hereditary?” Usually, our pediatric orthopedic specialty examination consists of three main components: history taking, physical examination, and imaging judgment. History taking often includes pregnancy, delivery, and family history to look for high risk factors for DDH. The physical examination includes comprehensive observation and examination of both lower limbs, usually we need to conduct a test – “abduction test”, some parents jokingly called “frog drill”. It is to straighten the baby’s legs together, then bend the knees together, and then separate the two knees to press the baby’s legs apart like frog legs, under normal circumstances at least 80 degrees down, if not or there are high-risk factors, we will recommend the baby to do an imaging test. The current impact study includes 2 common modalities: an ultrasound of the hip joint and an x-ray of the pelvis. “How do parents choose between ultrasound or x-ray radiographs?” The advantages of ultrasound are that the child is not damaged by ionizing radiation, it is easy and fast; however, the disadvantages are: the ultrasound picture is usually not fine enough and the measurements are often subject to technical errors. Usually we can distinguish serious hip dislocations or hips without problems by ultrasound. For those cases that are not normal hips but do not reach hip subluxation or total dislocation, more experienced ultrasound physicians are usually needed to operate and measure them correctly, otherwise the reference value is not much. X-rays are commonly used in pediatric orthopedics, but their disadvantages are, firstly, the well-known problem of ionizing radiation, secondly, the fact that they usually do not show the cartilaginous part of the child’s structure, and that they require the correct posture of the child and special angles during the shooting. Before and after comparison. Usually an orthopantomogram of the pelvis in a standard position and under standard conditions is the gold standard for clinical diagnosis of DDH. Of course the age of the child is usually a very important factor: if the child is very young (under 4.5 months) we recommend the parents to do an ultrasound, and if the child is older than 6 months, we usually recommend the parents to take an X-ray. If the child has normal early ultrasound results, but there are clear risk factors for DDH, we usually recommend, based on European and American research experience, that the child be followed up in an outpatient clinic around 6 to 7 months of age, with follow-up radiographs if necessary, until the child is able to walk normally with a good gait and normal radiographs. In summary, our pediatric orthopedic surgeons need to take a history and examine the child to initially assess the likelihood of DDH and recommend ultrasound or x-ray based on their experience. Usually, although there is a certain amount of ionizing radiation damage from X-ray, it is relatively safe for children as long as the necessary protection is taken care of. If the child must be X-rayed, it is recommended that the parents go to a specialist hospital to minimize the need for a second X-ray due to misplacement of the child or problems with the angle of exposure. “How should a child with DDH be treated?” DDH is usually divided into three degrees according to the severity of the disease: total hip dislocation, subluxation, hip dysplasia, etc. According to the current principles of clinical treatment, the methods usually used are: early baby sling (RB belt, Pavlik sling), double-layer hip diaper method + split-leg frog hold position, abductor frog cast fixation (not removable), abductor frog fixation brace (removable), advanced cases require admission to the hospital for surgical treatment. The specialist will recommend the best treatment based on the child’s condition and his or her experience. Of course, severe cases, as well as cases found at a late stage require surgery for skeletal correction. “When is the best time to start treatment for a child with DDH?” In clinical treatment, usually once DDH is detected, it should be treated early, when the child’s bones and joints are relatively young and malleable, and the effectiveness of early treatment is widely recognized in clinical practice. However, parents often find it psychologically difficult to accept this period, and specialists usually need to explain patiently to the family. Some parents take the attitude of avoiding or not accepting the reality, which is not desirable. A lot of clinical data confirm that the earlier the problem is detected, the shorter the treatment period, the less pain the child suffers, the more certain the treatment effect is, and the less financial burden the parents have to bear. It is a common phenomenon that parents do not think their child has a big problem at the time of the visit, but the doctor is very nervous because he knows the seriousness of the problem. Conversely if no treatment is given, until the parents find out that the child has a problem with walking, then the parents start to get nervous, unfortunately by this time the best opportunity for treatment has been missed and orthopedic surgery may be needed …… “How is early treatment defined?” Usually early treatment refers mainly to the stage before the child learns to walk and we usually use 18 months as a watershed in clinical treatment. before 18 months, conservative treatment with closed-replacement cast fixation is the main treatment. after 18 months, the child may face the trauma of skeletal orthopedic surgery. In the conservative treatment stage, the treatment effect is most certain before 6 months of age, as this stage is simple, less painful for the child, shorter treatment period, and more certain. Of course, if the problem can be detected in the neonatal stage, the treatment effect is even more certain. “After the child is 18 months old, is the only way to correct the problem is to operate?” The age of the child is only one of the important reference indicators for treatment, and this indicator is not absolute. Usually, cases of severe hip dislocation, above 18 months of age, often require skeletal orthopedic surgery (open correction). However, some of these cases may face post-operative femoral head necrosis and joint stiffness and immobility, so we take a relatively cautious approach to open surgery. After all, the child is the one who bears the risk, and many of the post-operative problems often need to be solved by a second surgery, so parents should consider carefully and repeatedly before deciding on surgery.