Clinical and Radiographic Outcomes After Indirect Decompression with Minimally Invasive Transforaminal Lumbar Interbody Fusion

Introduction: With the availability of large-footprint expandable interbody cages for minimally invasive transforaminal lumbar interbody fusion (MI-TLIF), many surgeons have increasingly begun to rely on indirect decompression alone. However, the degree of indirect decompression achieved has not yet been fully determined. The objective of the present study was to assess the extent of indirect decompression achieved with MI-TLIF and the impact on patient-reported outcome measures (PROMs).

Methods: Adult patients who underwent primary one- or two-level MI-TLIF without direct decompression between March 2017-2021 with ≥1-year clinical follow-up were included. CT scans were used to measure disc height (DH), cross-sectional foraminal area (CSFA), and central canal area (CCA) at the operative levels. Sagittal radiographs were implemented for assessment of pelvic incidence (PI), lumbar lordosis (LL), and segmental lordosis. The most recent preoperative and postoperative patient-reported outcomes (Oswestry Disability Index, Patient-Reported Outcomes Measurement Information System, Visual Analog Scale Back/Leg, Short Form-12 (SF-12)) ≥1-year after surgery were evaluated. Paired t-tests were performed to compare preoperative and postoperative radiographic measurements and PROMs. Bivariate analysis was used to identify correlations between changes in radiographic measures and PROMs.

Results: 40 patients were included (single level: 80%; L5-S1: 52.1%). Average clinical and radiographic follow-up were 17.9 months and 14.6 months, respectively. Indirect decompression resulted in significant increases in DH (4.2 to 6.3mm, p< 0.001), operative side CSFA (140.8 to 180.8mm2, p< 0.001), contralateral side CSFA (146.9 to 170.7mm2, p< 0.001), and CCA (228.6 to 266mm2, p< 0.001) (Table 1). Sagittal alignment measures did not differ significantly between pre- and postoperative radiographs (p>0.05). Likewise, all PROMs except SF-12 MCS (p=0.439) showed a significant improvement postoperatively. Percentage change in DH was correlated with change in SF-12 Physical Component Score (r= -0.379, p=0.03).

Conclusion : Overall, MI-TLIF yielded a significant degree of indirect decompression and notable improvements in patient-reported outcomes at ≥1-year postoperative follow-up. Therefore, MI-TLIF may provide good clinical outcomes with indirect decompression alone.