Pediatric lower extremity pain can be a mild symptom that appears momentarily, or it can be a more serious disease, but it should not be ignored. The lower extremities of growing children are responsible for movement and weight, and once abnormalities occur, they are easier to detect than other parts of the body, whether it is subjective pain or objective gait abnormalities that can be detected early by parents. Children’s sensory abnormalities are often not accurately described due to the limitation of small language vocabulary, such as crying, crying “pain” and not walking, etc. for fatigue, discomfort or pain. Therefore, although symptoms appear early, they need to be diagnosed early and treated appropriately. Pediatric lower extremity pain is a large group of diseases encountered in outpatient clinics. One of the ways to coordinate the diagnosis in a short time in the clinic is to pay attention to the gait of the child for limping and fast pounding steps. Also note whether the complaint of lower extremity pain is unilateral or bilateral. Which side is the limp on? Lower limb pain with claudication that is fixed unilaterally should be taken more seriously. The duration of lower extremity pain in children varies from a few days or weeks to months or years. It is also helpful to diagnose whether the onset is occasional intermittent pain or persistent pain. Persistent pain with a short onset time is a clue to the diagnosis of serious disease. Pain may be confined to any part of the lower extremity, and hip pain may radiate to the knee. The lesion may extend from the hip down through the thigh, calf, and into the foot. When the length of the limb, the range of motion of the joint, the presence of muscle atrophy, local swelling, and pressure pain are examined thoroughly, the diagnosis will not be missed. Of course, regular follow-up is indispensable for a definite diagnosis, as it allows for a period of observation. Diseases that often need to be identified: 1. Acute transient synovitis of the hip joint: this is a kind of aseptic synovial inflammation and joint effusion of unknown origin. The clinical manifestations are characterized by heavy symptoms and relatively light signs, the so-called heavy symptoms are caused by the anxiety of parents because the child refuses to walk on the ground. The hip joint activity is firstly light, and there is often a dispersive pain to the ipsilateral knee joint (Hilton’s law), which often misleads doctors to take X-ray pictures of the knee joint and ignore the hip joint lesion, resulting in untimely diagnosis. It can heal after a few days of non-weight bearing bed rest. It is worth noting that the early manifestations of ischemic necrosis of the femoral head in children are similar to this disease. Some scholars claim that about 4% of children with acute transient synovitis of the hip joint are actually in the early stages of Legg-Perthes disease, which should be confirmed by follow-up. 2, ischemic necrosis of the femoral head (Legg-Perthes disease): the disease occurs in boys, the ratio of male to female is 5:1. the cause is unknown, mainly vascular theory, such as venous return obstruction; Gershuni’s theory of femoral head oversize, that is, the head socket joint does not anastomosis to the articular cartilage surface nutritional defects and uneven weight bearing; Bleck’s theory of blood viscosity, referring to the increase in blood viscosity caused by The theory of blood viscosity, which refers to the impaired circulation caused by increased blood viscosity; and the theory of growth arrest, which means that some scholars have found that children with this disease are associated with short stature and lighter weight than normal children of the same age, and endocrine disorders are suspected. In conclusion, the ischemic factor prevails, but how it is caused is not known. The main clinical manifestations are hip pain, lameness and limited movement of the hip joint in multiple directions, highlighted by limited internal rotation. x-ray can make a clear diagnosis. 3, knee valgus: before the age of 3 years old, it is often found to have knee valgus, that is, O-leg. After the age of 3, the knee is gradually turned out, i.e. X-leg, which is the most common cause of lower limb pain in children. Some of them complain of inward pointing of the toes and easy falling. The severity of symptoms is related to the severity of the deformity. The ankle spacing within 5 cm is mostly developmental, that is, the development of thigh muscles is not enough to maintain the stability of the knee and the normal anatomical relationship, and it will correct itself with growth; the ankle spacing between 5 and 10 cm is caused by rickets, sometimes it is necessary to treat rickets at the same time supplemented with braces to correct; the ankle spacing between 10 and 15 cm or more should pay attention to the presence of systemic diseases such as anti-D rickets rickets, etc., it is advisable to cure It is advisable to perform osteotomy orthopaedic surgery on the basis of curing the disease. 4, tibial tubercle osteochondritis (Osgood’s disease): the average age of onset in 10 to 12 years old, often with a history of kicking, high jump, long jump sports, local elevation with pressure pain. It is now believed that this disease is no longer osteochondritis but ectopic bone due to cumulative injury of the patellar tendon at the tibial tuberosity junction. The pain is limited and can be unilateral or bilateral. The pain can be unilateral or bilateral. Suspension of sports, wearing “knee pads” and local braking can mostly heal spontaneously and rarely requires surgical treatment. 5. Fatigue fracture of the tibia (“stress fracture”): This disease can be caused by a sudden prolonged over-exercise after a lack of exercise. The elasticity of the bone is normal, and the repeated muscle pulling and stepping action is the cause. The lesion is a limited cortical discontinuity with subtle fracture lines and new bone formation visible on x-ray. The tibia and metatarsus are the preferred sites. The main manifestation is also localized pain in the lower limbs. 6, foot navicular bone ischemia (Kohler’s disease): local pain, pain-avoidance claudication, limited pressure pain, and typical local bone density increase and deformation on X-ray can make the diagnosis. Walking plaster protection for 6 weeks can heal spontaneously. Second metatarsal head embolism (Freberg embolism) pain and claudication with increased bone density of the navicular foot, nodal fracture or even free body. Walking cast conservative treatment can be more self-healing, occasionally need to stretch osteotomy. 7, subxiphoid warts: mostly caused by trauma to the toes. The appearance of abnormal, local pain and avoidance of painful limp. x-ray photographs of the end metatarsal dorsal elevation, protruding beyond the soft tissue can help clarify the diagnosis. Surgery to remove the muscle warts and preserve the nail bed can be cured. 8, pain behind the heel bone (heel bone synostosis epiphysitis): the epiphysis seen on X-ray has a high density, which is a normal manifestation. The disease is an accumulative injury to the Achilles tendon at the heel attachment or maladjustment to the heel shoes and flat shoes after the transfer. Heel padding 2 to 4 weeks more self-healing. 9.Osteoid osteoma: The tumor is characterized by small size and heavy pain, often requiring painkillers. tumor cavities are often visible on radiographs, and hot spots are visible on flash imaging. The symptoms disappear immediately after surgical excision. 10.Growing pain：Common in girls aged 4-8 years old, symptoms appear mostly in the evening and disappear during the day, complaining of pain in both lower limbs, without aggravation of symptoms or limping. It should be noted that in addition to the above-mentioned history, physical examination, follow-up examination and other methods, the diagnosis of “growing pain” should focus on systemic diseases, such as bone pain caused by leukemia; local diseases such as osteoid osteoma and common pediatric intermuscular hemangioma (localized mass with unclear border and pressure pain, angiography can be localized to understand the extent of the lesion) for differential diagnosis. (localized mass and pressure pain, angiography can be localized to understand the extent of the lesion) for differential diagnosis. 11, various types of joint inflammation: redness, swelling, pain, elevated temperature, joint deformity, fixed pain site (rheumatic and rheumatoid arthritis often involves multiple joints of the upper and lower extremities). Abnormalities in ancillary tests such as white blood cells, blood sedimentation, anti-chain “O”, C-reactive protein, rheumatoid factor, etc. It is very common to see pediatric patients with lower extremity pain in daily orthopedic clinics, and most of them can be relieved of their pain with conservative treatment. We believe that those who meet the following three points are mostly functional and can heal themselves: 1. the location of pain is not fixed, mostly both lower limbs are involved; 2. the pain occurs after strenuous activities, mainly in the afternoon and at night, and disappears after rest (morning rise); 3. there is no local swelling and pain, and there is no generalized fever.