In the clinic, we often meet parents who are anxious to find a doctor because the two sides of their child’s thighs have different patterns, and many parents and friends send messages to consult. Q: My 4-month-old baby girl found out this morning that the two legs are different, the left leg is slightly longer and the right leg is shorter. I’m sure I’m not mistaken. I noticed that she often bends her legs and doesn’t want to straighten them, as if she has no strength. Do I need to treat this before it’s too late? Doctor: Hello, from the inquiry you sent, there are two problems, one is that the legs are not the same length and the other is that the legs move differently. I hope my answers will help you and your baby. First of all, let’s see what kind of problem can occur from the described symptoms, we must first rule out the possibility of abnormal hip development. Developmental Dysplasia of the Hip (DDH, Developmental Dysplasia of the Hip), formerly known as Congenital Dislocation of the Hip (CDH, Congenital Dislocation of the Hip), is a more common disease among pediatric limb deformities, with the continuous research, after the 90s of last century It was renamed as Developmental Dysplasia of the Hip (DDH) after the 1990s. DDH is a developmental abnormality of the hip joint that is underdeveloped at birth and continues to progress during later growth and development. It is characterized by the loss of normal alignment of the femoral head with the acetabulum at birth, with most of the head partially prolapsing from the acetabulum and a few completely prolapsing from the acetabulum; the lesion often involves the acetabulum, femoral head, joint capsule, and the ligaments and muscles surrounding the hip joint. Because the early clinical manifestations are not obvious, especially in the neonatal period, the diagnosis is easily missed and treatment is delayed. Some data show that DDH is not diagnosed and treated effectively in infancy and early childhood, which can lead to lameness and pain, and is a major factor in degenerative hip arthritis and joint replacement surgery in adults. So, how do we detect abnormalities in our children early? Since DDH may have an impact on later life, early detection and treatment is especially important. 1, first need to understand the child’s medical history, including prenatal intrauterine conditions and delivery, the way of swaddling after birth, whether there is a family history, etc. Physical examination of the child’s appearance, including whether the limbs are equal in length, whether the hip and thigh skin lines are symmetrical, whether the knee joints are in the same plane bilaterally, the joint movement of the hip joints, and whether there are abduction restrictions, and routine Barlow and Ortolani examinations and abduction tests to determine whether there are abnormal signs. In addition, ultrasound can clearly show the soft tissues such as glenoid lip and joint capsule, as well as the morphology of acetabulum and femoral cartilage; there is no radiological damage; it is highly sensitive and can observe lesions that are difficult to be detected by clinical and X-ray examinations at an early stage; and it can be repeated for continuous observation. Therefore, ultrasound examination has now become the main tool for early diagnosis and early screening of DDH. For infants over 6 months of age, because the ossification center of the femoral head has become larger and the bony occlusion of sound waves has increased greatly, it is generally advocated to perform x-ray examination to discern whether there is any abnormality in the hip joint