Subsidence of Screw-based Expandable Cages in Transforaminal Lumbar Interbody Fusion: A Retrospective Study

Introduction: Transforaminal lumbar interbody fusion (TLIF) is a surgical procedure indicated in the treatment of degenerative disc disease, spinal stenosis, spondylolisthesis, and other lumbar spinal pathologies. Interbody cages used within TLIF provide structural support, but cage subsidence, or the sinking of the cage into adjacent vertebral bodies, remains a significant concern. Understanding the progression of cage subsidence over time is critical for optimizing long-term outcomes in spinal fusion surgeries. This study aims to assess the rate and progression of subsidence of screw-based expandable cages used in TLIF procedures.

Methods: A retrospective chart review was conducted on patients who underwent TLIF at a single academic institution between January 2021 and January 2024. The study focused exclusively on cases utilizing screw-based cages. Radiographic measurements were taken from intraoperative and postoperative lumbar spine x-rays, both from the anteroposterior (AP) and lateral views. ImageJ software was used to calculate cage area and perimeter. The data was categorized into six time groups (1-100, 101-200, 201-300, 301-400, 401-500, and 501-600 days) to track subsidence progression.

Results: The study included a total of 79 patients, with an average subsidence rate of 1.27 mm²/day from the AP view and 0.17 mm²/day from the lateral view. Subsidence was highest in the early postoperative period (1-100 days) and decreased in the following time groups, indicating that subsidence slowed as the fusion construct stabilized.

Conclusion : The findings suggest that screw-based expandable cages experience the most significant subsidence early in the postoperative period, with a reduction in subsidence rate following the first 100 days. This emphasizes the need for careful postoperative monitoring and highlights the potential for improving cage design to promote long-term stability in TLIF procedures and minimizing early cage subsidence.