Parents often see their children for joint rattling when they move, but after examination, they cannot find the cause. Most of the joint ringing is due to the sound of the tendons sliding around the joint activity, the knee joint is the most common, such as the sound of the outer N muscle sliding, generally known as “popping knee”. The next most common cause is the hip joint, which can be caused by the tendon sliding over the greater trochanter, and is often referred to as a “popping hip”. Simple rattling of the joint is not painful, does not require treatment, and does not have a significant impact on the body. However, when the knee rattling is accompanied by pain, swelling, tenderness, interlocking and other symptoms, active medical consultation is required to rule out the following diseases: disc meniscus (the thicker the meniscus, the more pronounced the rattling), congenital knee dislocation (rattling occurs when the knee is actively or passively flexed by 30-40), meniscal injury, meniscal calcification, meniscal ossification, exfoliative osteochondritis, synovial chondromatosis, synovial crease syndrome. In pediatric patients with abnormalities such as unequal limbs and asymmetrical thigh or hip skin pattern, it is necessary to consult a doctor to rule out developmental hip dislocation; and when there is a significant outward gait or pseudo-unequal gait of both lower limbs, it may also be caused by hip muscle contracture, and it is necessary to consult a doctor to rule it out.