Differences in the interbody bone graft area and fusion rate between minimally invasive and traditional open transforaminal lumbar interbody fusion: a retrospective short-term image analysis.

PURPOSE: We aimed to quantify the interbody bone graft area following transforaminal lumbar interbody fusion (TLIF) using traditional open and minimally invasive surgeries (MIS) and investigate their correlations with rates of fusion, complications, and clinical outcomes.
METHODS: Patients undergoing TLIF of 1 or 2 levels between October 2015 and December 2016 were retrospectively included. Fusion and bone graft areas were assessed with computed tomography (CT) at 6 months postoperatively. The bone graft area ratio was defined as the bone graft area divided by the average endplate area. The distributions of bone graft area within the discs were also recorded. Clinical outcomes were assessed using the visual analog scale (VAS) and Oswestry Disability Index (ODI) questionnaires.
RESULTS: In total, 77 disc levels in 57 patients were analyzed. The fusion rate was 79.1% in the open group and 82.4% in the MIS group (p = 0.718). Clinical outcomes of both groups improved significantly. Changes in VAS and ODI scores at 12 months postoperatively were comparable between groups. Bone graft area ratio was not significantly different between the two groups (open, 38 ± 10.8%; MIS, 38.1 ± 9.0%, p = 0.977). Analysis of bone graft distribution revealed that the contralateral-dorsal part of the disc had the lowest bone graft area. The bone graft area ratio was significantly higher in the solid union group (39.2 ± 10.4%) than in the non-solid union group (33.5 ± 6.4%, p = 0.048).
CONCLUSIONS: The fusion rates, bone graft area ratios, clinical outcomes, and complications were similar between MIS and open TLIF. These slides can be retrieved under Electronic Supplementary Material.