INTRODUCTION
The aim of this study is to investigate the incidence of adjacent segment disease (ASD) and adjacent (cranial and caudal) disc height changes in patients undergoing minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) at our institution, with a 5-year postoperative follow-up. We also compare outcomes between 1-level and 2-level fusions.
METHODS
We reviewed 164 patients who underwent MIS-TLIF at our institution between April 2014 and August 2019. Of these, 98 patients (1-level: 83, 2-level: 15) who completed at least 5 years of follow-up were included in this study. We assessed the incidence of radiological ASD, symptomatic ASD, and changes in adjacent disc height. Radiological ASD was defined as slippage progression of ≥3 mm, posterior opening of ≥5°, or a narrowing of disc height of >3 mm on standing lateral radiographs compared to preoperative images. Symptomatic ASD was defined by the presence of leg symptoms or neurogenic claudication with confirmatory adjacent segment pathology on MRI. Disc height changes were measured using standing lateral radiographs preoperatively and at the 5-year follow-up.
RESULTS
At 5 years postoperatively, radiological ASD was observed in 31 patients (31.6%), and symptomatic ASD in 20 patients (20.4%), of whom 5 underwent revision surgery. In the 1-level fusion group, radiological ASD occurred in 25 patients (30.1%) and symptomatic ASD in 17 patients (20.5%), with 4 requiring revision surgery. In the 2-level fusion group, radiological ASD was seen in 6 patients (40.0%) and symptomatic ASD in 3 patients (20.0%), with 1 requiring revision surgery. No statistically significant differences were found in the incidence of radiological or symptomatic ASD, or the need for revision surgery, between the 1-level and 2-level fusion groups.
Changes in disc height at the adjacent cranial and caudal segments from preoperative to 5 years postoperatively were also analyzed. In the 1-level fusion group, the mean cranial anterior/posterior disc height changes were -0.75 mm/-0.96 mm, and caudal anterior/posterior disc height changes were -0.08 mm/-0.65 mm. In the 2-level fusion group, cranial changes were -0.70 mm/-0.81 mm, and caudal changes were -0.31 mm/+0.30 mm. No significant differences were observed between the two groups for any of the disc height changes from preoperative to 5 years postoperatively.
DISCUSSION
At the 5-year follow-up after the MIS-TLIF at our institution, no significant differences were observed between 1-level and 2-level fusion with respect to the incidence of ASD or reduction in disc height in adjacent segments. These findings suggest that the number of fusion levels (1 or 2) does not appear to affect the development of ASD or the progression of adjacent disc degeneration up to 5 years.