The clinical appearance of numbness in the back of the left foot should be considered for the following reasons: First, lumbar disc herniation: when the herniated disc tissue compresses the spinal nerve roots, radiating pain in the lower extremities and numbness in the foot will occur, especially when the lumbar 4-5 disc herniation compresses the lumbar 5 nerve roots. Second, peripheral nerve compression: in the dorsum of the foot is mainly innervated by the superficial peroneal nerve, when the superficial peroneal nerve is compressed, there will be numbness and discomfort of the skin of the dorsum of the foot. Third, some chronic diseases cause peripheral neuropathy: advanced diabetes can cause peripheral neuropathy, manifested as numbness of the skin of the hands and feet.