Minimally Invasive Transforaminal Lumbar Interbody Fusion (MIS-TLIF) with Expandable Cages that Expand Both Height and Lordosis: A Comparison of the One-Year Postoperative Outcomes of Two Cage Designs

Introduction: Minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) often fails to achieve lordotic alignment, even with expandable cages. This study compares two types of expandable cages in MIS-TLIF: one increasing only disc height (Group H) and another expanding both height and lordosis (Group HL). Over one year, we evaluated postoperative sagittal alignment, clinical outcomes, fusion rates, subsidence, and sagittal alignment maintenance.

Methods: Seventy-five MIS-TLIF patients were reviewed (35 in Group H, 40 in Group HL). Numeric rating scale of back pain (NRS-B), leg pain (NRS-L), and Oswestry Disability Index (ODI), and radiographic parameters of disc height, segmental, and lumbar lordosis were evaluated. Statistical analysis was conducted using SPSS 28.0. Chi-square or Fisher's tests were used for categorical variables, while T-tests or Mann-Whitney U tests were applied to continuous variables. A p-value < 0.05 was considered statistically significant.

Results: Both groups showed significant improvements in NRS-B, NRS-L, and ODI, with no inter-group differences at 1-year follow-up. Disc and foraminal height increased significantly postoperatively in both groups. Group HL demonstrated greater positive changes in segmental lordosis (4.0±3.3° vs 1.9±5.4°, p=0.018) and disc angle (5.8±4.1° vs 1.9±4.2°, p< 0.001) compared to Group H at one-year follow-up. The overall fusion rate was 92%, with a 32% incidence of subsidence (reduced to 20% after the learning phase). No difference was observed between the two groups regarding overall complications, including revision surgeries and neurological deterioration.

Conclusion : MIS-TLIF with lordosis-increasing expandable cages achieves favorable clinical and radiographic outcomes, high fusion rates, and greater segmental lordosis increases compared to conventional height-only expandable cages at one-year follow-up. Careful utilization is crucial to prevent excessive force leading to cage subsidence, pseudarthrosis, and failure to maintain lordotic alignment.