Radiographic Changes and Cage Subsidence following Vertically Expandable Interbody Cage Use in Single-level Lumbar Fusion for Nonosteoporotic Patients: A Retrospective Study

Abstract Background: Vertically expandable interbody cages are designed to restore disc height and reduce neural traction during lumbar fusion surgery. However, their effectiveness in correcting spinal alignment and their risk of subsidence, particularly in nonosteoporotic patients, remain unclear. Objectives: To evaluate the radiographic changes and the incidence, timing, and risk factors of cage subsidence following single-level lumbar fusion using vertically expandable cages in patients without osteoporosis. Materials and Methods: We retrospectively reviewed 34 patients who underwent single-level transforaminal lumbar interbody fusion with vertically uniplanar expandable cages between March 2023 and March 2024. Patients with osteoporosis, trauma, tumors, infections, or multi-level surgeries were excluded. Serial radiographs were obtained postoperatively at 1, 3, 6, and 12 months. Changes in disc height, foraminal dimensions, sagittal and coronal alignment, and cage subsidence were measured. Results: Significant increases were observed in disc height, foraminal height, and area postoperatively ( P < 0.01). No significant changes were found in lumbar or segmental lordosis ( P = 0.53, P = 0.47) or Cobb angle ( P = 0.71). Cage subsidence occurred in 16 patients (47%), all within the 1 st month. Subsidence was significantly associated with older age ( P = 0.04) but not correlated with cage position or degree of disc height increase. No neurological complications or revision surgeries were reported. Conclusions: Despite the exclusion of osteoporotic patients, the rate of early cage subsidence remained high. Alignment correction was minimal, and the theoretical benefits of sagittal or coronal correction were not evident. Vertically expandable cages may be most valuable in reducing neural traction in cases with large disc space, rather than alignment restoration.