The aim of this study is to investigate the incidence of adjacent segment disease (ASD) at L3-4 and L5-S and the change in intervertebral disc height at L3-4 and L5-S at five years after L4-5 minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF).
We reviewed 164 patients who underwent MIS-TLIF at our institution between April 2014 and August 2019. Of these, 61 patients (122 intervertebral segments) who underwent single-level L4-5 fusion and 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 low back pain, 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.
At 5 years postoperatively, radiological ASD occurred in 20 segments (16.4%). Among these, radiological ASD was observed in the cranial L3-4 in 14 segments (23.0%) and in the caudal segment L5-S in 6 segments (9.8%). There was a non-significant trend toward higher incidence of radiological ASD at the L3-4 segment than at the L5-S segment (p=0.085). Symptomatic ASD occurred in 12 segments (9.8%). Among these, symptomatic ASD was observed in the L3-4 in 6 segments (9.8%) and in the L5-S in 6 segments (9.8%), with no significant difference between the two levels. There were two cases requiring reoperation, both at the L5-S level. With regard to changes in adjacent disc height at 5 years postoperatively, the mean changes in anterior/posterior disc height at the L3-4 and L5-S levels were 1.18 mm/1.13 mm and 0.03 mm/0.84 mm, respectively. A significant difference in anterior disc height changes was found between the L3-4 and the L5-S levels (p=0.022), while no significant difference was observed in posterior disc height changes (p=0.30).
After L4-5 MIS-TLIF, radiological ASD had a tendency for a higher incidence at the L3-4 compared to the L5-S and a reduction in disc height was observed particularly anteriorly at the L3-4 compared to the L5-S. However, there was no significant difference in the incidence of symptomatic ASD, and cases requiring reoperation were only found at the L5-S level, involving one case of foraminal stenosis and one case of lumbar disc herniation. These findings suggest that after single-level intervertebral MIS-TLIF L4-5 level, we should observe radiological changes in the cranial adjacent segment, while symptom development in both cranial and caudal segments.