Knee skin numbness one month after lumbar disc herniation with steel nail may be caused by nerve root edema, intraoperative injury, and heavier nerve injury itself. 1. Nerve root edema: due to postoperative nerve ischemia and edema, in the absorption of the local hematoma enhancement, scar formation and other reasons can also cause patients to appear one month after the operation still exists in the knee joint skin numbness. 2. Intraoperative injury: due to intraoperative injury to the nerve root or excessive stretching of the nerve, resulting in injury to the nerve innervating the knee joint, the patient may still have numbness of the knee joint one month after the operation. 3. Heavy nerve damage: it is mostly seen in preoperative nerve compression for a long time, nerve root degeneration and other pathological changes, leg numbness exists in the preoperative period, and after surgical decompression of the nerve, the patient may still continue to suffer from leg numbness one month after the operation. If the knee numbness is not relieved one month after the lumbar intervertebral disc herniation surgery, or accompanied by other symptoms, you should go to the hospital in a timely manner to consult the doctor, and give targeted treatment after clarifying the cause.