MI-TLIF with Expandable Cages Results in Maintained Segmental Cobb Angle and Improved Foraminal Height

Introduction: Expandable cage use in minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) has become a more common approach in the treatment of lumbar degenerative disease as it affords safer insertion and interbody height adjustment after expansion. Expansion, however, may compromise the vertebral endplates, resulting in cage subsidence and subsequent loss of disc height. Cage stability relates directly to interbody height and segmental cobb angle, which in turn affects foraminal height. While prior studies have explored the ability of expandable cages to provide increased foraminal height and optimize segmental cobb angle, there is still a paucity of evidence regarding their use within minimally invasive spine surgery.

Methods: A maintained surgical registry at our institution was used to obtain a list of patients who underwent primary MI-TLIF with GLOBUS™ Altera expandable cages at L4-L5 for lumbar degenerative disease (including lumbar degenerative spondylolisthesis) from 2017 to 2023. Included patients had radiographic imaging available at at least two of the following timepoints: 6 weeks, 6 months, and 1 year. Paired t-tests between each of the three timepoints were performed for foraminal height (recorded in mm) and segmental Cobb angle. Significance was determined using the Bonferroni correction, and set at a p value of ≤0.0167.

Results: 64 patients met inclusion criteria. 8 patients were removed due to inadequate imaging. Segmental cobb angle was unchanged between pre-operative and all three postoperative timepoints. Foraminal height significantly increased between pre-operative (17.39 ± 3.50) and 6 weeks (21.08 ± 3.67), pre-operative (17.28 ± 3.48) and 6 months (20.71 ± 3.51), and pre-operative (17.47 ± 3.51 and 1 year (20.96 ± 3.58) (P = < 0.001 for all comparisons).

Conclusion : Expandable interbody cages inserted via MI-TLIF at L4-L5 result in increased foraminal height that is sustained at 1 year postoperatively, with no adverse effect on segmental cobb angle.