Lumbar fusion is an accepted and effective technique for the treatment of lumbar degenerative disease. As the population ages, disability associated with spinal pathology and spinal surgery is rapidly increasing and there is a concomitant increase in prevalence of osteoporosis which is a detrimental factor for Lumbar fusion and instrumentation. Osteoporosis-related bone fragility is a primary reason for spinal fusion failure, implant fixation failure, and vertebral compression fractures above or below the fusion sites.

Denosumab is a human monoclonal antibody against RANKL, it inhibits osteoclast mediated bone destruction and has been found to be effective in treating osteoporosis, including reducing bone turnover markers, increasing bone mineral density (BMD), and reducing fractures. But few studies focus on the effects of Denosumab on lumbar fusion. In this study, we include osteoporotic patients with lumbar degenerative disease who have had lumbar interbody fusion surgery. The patients were randomized to either treatment of Denosumab or no treatment. All these patients are followed at 3, 6, 9, 12 months postoperation. During these periods, we detect bone metabolism and bone fusion of these patients. Finally, we would report whether Denosumab can improve bone metabolism and promote bone fusion or not.

Inclusion Criteria:

1. Diagnosis of degenerative lumbar diseases with symptoms of low-back pain and/or leg pain for at least 3 months, which was not be adequately controlled by nonoperative treatments.
2. Diagnosis of osteoporosis, defined as a bone mineral density (BMD) at lumbar or femoral neck with 2.5 standard deviations or more below the mean peak bone mass (T scores <-2.5 SD) measured by dual-energy X-ray absorptiometry (DXA).
3. Patients will be underwent single-level or two-level lumbar interbody fusion.

Exclusion Criteria:

1. Paget disease of bone,
2. Low laboratory tests for calcium,
3. Previous radiation treatment or fusion surgery to lumbar spine,
4. Bone tumors,
5. Bone infection,
6. Acute vertebral fractures
7. Severe spinal deformities such as degenerative scoliosis,
8. Other metabolic bone disease,
9. History of a anti-osteoporosis medication
10. Combined with severe morbidities,
11. Uncorrected bleeding diatheses
12. Application of steroids.