Lumbar pain four months after lumbar fusion surgery may be caused by slow recovery, postoperative infection, displacement of internal fixation, recurrence of lumbar spine disease and other reasons. 1. Slow recovery: the presence of obesity, advanced age, osteoporosis, lack of exercise and other reasons may lead to slower recovery. 2. Post-operative infection: a few patients will be irritated by the internal fixation in the body to the muscles to produce inflammation, the typical symptoms of lumbar pain, redness, swelling, increased body temperature, and so on. 3. Displacement of internal fixation: it refers to the displacement caused by the loosening of internal fixation or insufficient fixation time, and the pain caused by the compression to the nerves or soft tissues. 4. Recurrence of lumbar spine disease: Lumbar spine fusion surgery is generally used for the treatment of lumbar disc herniation and lumbar spondylolisthesis, and if the disease recurs, there will be lumbar pain, pain in the lower limbs, and activity limitation. Lumbar spine fusion surgery four months back pain may also have other reasons, it is recommended that timely medical treatment, improve the relevant examination, under the guidance of the doctor for formal treatment.