Foraminal Height Decreases in the Postoperative Period Following the use of Expandable TLIF Cages

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 disc disease as they may reduce the risk of neurological injury via ease of insertion through the Kambin triangle and allow for intraoperative interbody height adjustment. This process of expansion, however, may cause endplate damage, resulting in subsidence and loss of disc height. Stability in interbody height relates directly to maintenance of foraminal height and segmental Cobb angle. Although previous studies have explored the ability of expandable cages to provide increased foraminal height and optimized segmental Cobb angle when compared to preoperative imaging, there is still a lack of knowledge regarding the long-term conservation of these factors from a postoperative standpoint.

Methods: A maintained surgical registry at our institution was used to obtain a list of patients who underwent primary MI-TLIF with Altera expandable cages at L4L5 or L5S1 for degenerative disc disease from 2017 to 2023 with radiographic imaging postoperatively in 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 to be at P value ≤0.0167.

Results: 84 patients who met our criteria were identified. 20 patients were removed due to inadequate imaging. Segmental Cobb angle was unchanged across all three timepoints (Figure 1c/d). Overall postoperative foraminal height was significantly decreased between 6 weeks (20.80 ± 4.25) and 1 year (20.48 ± 4.13) (Figure 1a). L4L5 postoperative foraminal height was significantly decreased between 6 weeks (21.36 ± 3.72) and 1 year (20.95 ± 3.67) and between 6 months (21.08 ± 3.62) and 1 year (20.86 ± 3.57). There was no significant change in L5S1 postoperative foraminal height.

Conclusion : When analyzing postoperative changes in foraminal height and segmental cobb angle, expandable interbody cages inserted via MI-TLIF result in maintained segmental cobb angle but a statistically significant minor loss of foraminal height when placed at L4L5 by 1 year postoperatively.