There are many clinical causes of weakness in one leg. The first and most common is the compression of nerves by a lumbar disc herniation, resulting in pain or numbness and weakness in the muscles of the innervated area. Generally the herniated disc compression over a longer period of time will lead to ischemia, degeneration and necrosis of the nerve, which in turn leads to numbness or weakness of the muscles in the innervated area. Secondly, cervical spondylosis or cervical disc herniation causes compression of the cervical spinal cord, resulting in weakness of the lower limbs, difficulty walking, and sometimes a feeling of stepping on cotton. The third type is craniocerebral lesions, such as cerebral hemorrhage, cerebral infarction, and brain tumors that compress brain tissue, resulting in weakness and difficulty walking on one side of the lower extremity, and intracranial lesions are usually combined with pathological changes in the central nervous system, such as distorted eyes and mouth or weakness in the upper extremity.