What Affects Segmental Lordosis of the Surgical Site after Minimally Invasive Transforaminal Lumbar Interbody Fusion?

PURPOSE: This study was undertaken to identify factors that affect segmental lordosis (SL) after minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) by comparing patients whose postoperative SL increased with those whose decreased. MATERIALS AND METHODS: Fifty-five patients underwent MIS-TLIF at our institute from January 2018 to September 2019. Demographic, pre- and postoperative radiologic, and cage-related factors were included. Statistical analyses were designed to compare patients whose SL increased with decreased after surgery. RESULTS: After surgery, SL increased in 34 patients (group I) and decreased in 21 patients (group D). The index level, disc lordosis, SL, lumbar lordosis, proximal lordosis (PL), and Y-axis position of the cage (Yc) differed significantly between groups I and D. The cage in group I was more anterior than that in group D (Yc: 55.84% vs. 51.24%). Multivariate analysis showed that SL decreased more significantly after MIS-TLIF when the index level was L3/4 rather than L4/5 [odds ratio (OR): 0.46, p=0.019], as preoperative SL (OR: 0.82, p=0.037) or PL (OR: 0.68, p=0.028) increased, and as the cage became more posterior (OR: 1.10, p=0.032). CONCLUSION: Changes in SL after MIS-TLIF appear to be associated with preoperative SL and PL, index level, and Yc. An index level at L4/5 instead of L3/4, smaller preoperative SL or PL, and an anterior position of the cage are likely to result in increased SL after MIS-TLIF.