The possible reasons for the sinking of the right leg after 40 days of lumbar disc herniation surgery are nerve compression degeneration, local adhesion scar compression of the nerve, incomplete removal of lumbar discs, and so on. 1. Nerve compression and degeneration: It may be due to the long time of nerve root compression caused by lumbar disc herniation, resulting in nerve ischemia and degeneration. Although the lumbar disc herniation surgery is done, the nerve recovery after the surgery is slow, and the symptom of sinking of the right leg after 40 days of the surgery may occur. 2. Localized adhesion and scarring compressing the nerves: After the lumbar disc herniation surgery, scarring is formed in the tissues around the nerve root, localized adhesion occurs, and scarring and adhesion compresses the nerve root, which may also lead to the symptom of the right leg sinking 40 days after the surgery. 3. Incomplete removal of lumbar intervertebral discs: the surgery may not remove the herniated lumbar intervertebral discs completely, resulting in the leftover part of the lumbar intervertebral disc tissues compressing the nerve root, which may cause the right leg to sink 40 days after the surgery. There may be other reasons why your right leg is heavy after 40 days of lumbar disc herniation surgery, so it is recommended that you go to the hospital in time, complete the examination to clarify the cause of the disease, and then give targeted treatment under the guidance of the doctor.