BACKGROUND Due to its rarity, surgical treatments for a complete fifth lumbar osteoporotic vertebral burst fracture (L5 OVBF) have yet to be well documented as compared to that for osteoporotic vertebral fractures of the thoracolumbar spine. The current case report discusses details of the surgical outcomes following posterior decompression and fusion for a complete L5 OVBF. METHODS Three women, ranging in age from 69 years to 82 years, were surgically treated for a complete L5 OVBF. Two of these patients were being treated for rheumatoid arthritis. Surgery was performed using the L5 shortening osteotomy or vertebroplasty, with one- or two-level posterior lumbar interbody fusion, and posterior spinal fixation for the L2 or L3 to the pelvis. Although the spinal alignment parameters, which included lumbar lordosis (LL), pelvic incidence-lumbar lordosis, T1 pelvic angle, and sagittal vertical axis, were better as compared to that observed before the surgery, these worsened at the final follow-up due to clinical fractures that occurred at the adjacent vertebral body and proximal junctional kyphosis. Compared to preoperative Japanese Orthopaedic Association (JOA) scores, postoperative JOA scores were improved and maintained at the final follow-up. CONCLUSIONS Posterior surgery of a complete L5 OVBF led to improvement of both the JOA score and spinal alignment after the surgery. Despite a worsening of the spinal alignment parameters, the JOA score was maintained at the final follow-up.