The possible causes of blood and water not falling from the drain after lumbar spine surgery include incision infection, fat liquefaction, cerebrospinal fluid leakage, and so on. 1. Incision infection: it may be due to poor suturing technique after lumbar spine surgery, resulting in wound residual dead space, incomplete hemostasis, formation of hematoma, resulting in incision infection, and the phenomenon of blood and water not falling from the drainage tube. 2. Fat liquefaction: it may be fat liquefaction caused by lumbar spine surgery which is too long and the tissue pulling is long and heavy. 3. Cerebrospinal fluid leakage: it may be caused by the formation of cerebrospinal fluid leakage due to the damage to the dura mater during the surgery. There may be other reasons why the blood and water in the drainage tube does not drop after lumbar spine surgery. It is recommended to consult the doctor in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or therapy under the guidance of the doctor.