This is a prospective,observational single-center study. The osteoporotic patients requiring posterior lumbar interbody fusion(PLIF) with cages at the lowest fusion segment are prospectively enrolled and followed up. The patients undergoing PLIF with the 3D-printed porous titanium alloy cages are compared with those using PEEK cages. The hypothesis is that the use of 3D-printed porous titanium alloy cages can reduce the rate of pedicle screw loosening and increase the rate of lumbar fusion in osteoporotic patients.

Pedicle screw fixation is a widely used technique for the surgical treatment of degenerative lumbar diseases, which can stabilize the spine before solid fusion and restore spinal balance. However, because of population aging and the high rate of osteoporosis in the elderly with lumbar degenerative diseases, the pedicle screw loosening has become a frequently reported complication. The bone-screw interface in osteoporotic spine is unstable, leading to reduced pull-out force and cut-out force. Most of the previous studies only focused on the methods used to directly strengthen the pedicle screws, few of them explored the feasibility of reducing the loosening rate by accelerating the lumbar fusion precess.

The 3D-printed porous titanium alloy cages have been proved to have advantages in speeding up and enhancing the lumbar fusion over conventional PEEK cages. Therefore, we hypothesize that patients undergoing PLIF with 3D-printed cages can achieve lumbar fusion earlier than those using PEEK cages, thus the 3D-printed cages can reduce the load on pedicle screws sooner than PEEK cages. Finally, the 3D-printed cages can reduce the loosening rate and increase the fusion rate.

The osteoporotic patients requiring posterior lumbar interbody fusion(PLIF) with cages at the lowest fusion segment are prospectively enrolled and followed up. The researchers will invite appropriate patients to participate in the study after their surgical plans are determined. General patients data are collected after informed consent, such as age, gender, weight, height, bone mineral density measured in T-scores and Hounsfield units, detailed surgical plans, and etc. They are followed up at 3, 6, 12, and 24 months according to our clinical routine, including lumbar x-ray and certain questions about the clinical outcomes. In addition, this study requires the patients to have lumbar CT scans when the fusion status is unclear in x-ray, especially for the 6 months follow-up.

The patients undergoing PLIF with the 3D-printed porous titanium alloy cages are compared with those using conventional PEEK cages. The primary endpoints are the loosening rate and fusion rate at 6 months follow-up. The secondary endpoints are the loosening rate and fusion rate at other time point of follow-up , and the clinical outcomes(ODI and VAS) at every follow-up.

Inclusion Criteria:

• aged≥ 50 years old
• lumbar degenerative diseases requiring lumbar fusion with pedicle screw fixation, such as degenerative lumbar spinal stenosis, degenerative lumbar spondylolisthesis.
• no response to nonoperative treatment of at least 3 months
• osteoporosis diagnosed by any method for bone mineral density evaluation, such as DXA, QCT，or vertebral Hounsfield units
• the lowest instrumented vertebrae were at L5 or S1
• the surgical plan includes lumbar interbody fusion with cages at the lowest fusion level
• informed consent

Exclusion Criteria:

• the surgical plan includes any techniques used to strengthen the fixation,such as augmentation of the pedicle screw with bone cement
• no lumbar CT scans within 3 months before the surgery
• no dual energy x-ray absorptiometry within 6 months before the surgery
• spondylolysis
• allergic to metal
• history of lumbar fusion surgery
• cervical myelopathy，thoracic spinal stenosis, motor neuron disease,tuberculosis of spine,spinal tumor

In the orthopaedic department of the Peking University Third Hospital, the osteoporotic in-patients requiring lumbar fusion with pedicle screw for lumbar degenerative diseases are invited to participate in the study.

We will make the clinical study report available for half a year after the publication of the results of the study.

The IPD will become available for half a year after the publication of the results of the study.

The IPD is available to the readers of the journal in which our research is published. The corresponding author of the published papers will review the requests.