The weakness of the back and knees can be seen in many diseases, mainly in the following areas: 1. The most common type of disease is due to urological diseases, such as chronic pyelonephritis, as this disease will appear persistent proteinuria, which can cause hypothermia, polyuria, weakness, and even symptoms of weakness of the back and knees. The clinical manifestations are also diverse, including proteinuria, hematuria, hypertension, edema of the lower extremities or face, and varying degrees of renal hypofunction, as well as symptoms of lumbar and knee weakness. 2. Orthopedic diseases, such as cervical spondylosis and lumbar disc herniation, can also lead to radiating pain in the lower extremities or weakness in both lower extremities. or weakness of both lower limbs. Another disease is osteoporosis, common in middle-aged and elderly people, due to bone loss resulting in the loss of strength of joints or muscles throughout the body, in the process of bone loss patients often feel weakness, as well as muscle fatigue easily, soreness, and joint pain is the main, the whole body of large joints will have different degrees of soreness. Of course, when the symptoms of back and knee weakness and weakness appear, the first step is to clear the diagnosis through examination, as well as through medical history, imaging, and laboratory tests, and to treat the symptoms, and to treat the cause in order to cure the symptoms and the root cause.