Leg numbness after a little sitting may be caused by lumbar disc herniation, lumbar spinal stenosis, sciatica, pyriformis syndrome and so on. 1. Herniated lumbar intervertebral disc: under the action of external factors, the fibrous ring of the intervertebral disc ruptures, and the nucleus pulposus protrudes from the rupture place to the back or the spinal canal, which results in the adjacent spinal nerve roots being compressed or stimulated, thus generating pain and leading to numbness when the patient sits down for a little while. 2. Lumbar spinal stenosis: when affected by trauma, medical injury, degenerative changes, congenital development and other factors, resulting in compression of the spinal cord and nerve roots, resulting in numbness of the legs after sitting for a while, accompanied by lumbar pain, weakness and other symptoms. 3. Sciatica: If the nerve roots of the patient are compressed, the nerve roots are transmitted along the sciatic nerve pathway, radiating down from the buttocks, resulting in numbness of the legs after sitting for a while. 4. Piriformis syndrome: if the patient is affected by indirect violence, chronic strain injury and other factors, so that the piriformis muscle is pulled, resulting in local edema, congestion and other symptoms, which in turn causes a little sitting on the leg numbness of the situation. It is recommended to go to the hospital in time, under the guidance of the doctor, actively cooperate with the treatment.