Crenel lumbar interbody fusion is anatomically feasible at L5/S1 in most patients on MRI, more adaptable from the right side

Lateral lumbar interbody fusion (LLIF) at L5/S1 is challenging due to complex iliac vascular anatomy, especially the common iliac vein (CIV). Crenel lumbar interbody fusion (CLIF), a modified LLIF under direct visualization, has not been established at L5/S1. This MRI-based study assessed its anatomical feasibility at L5/S1. We retrospectively reviewed the MRI scans of the patients who had visited our outpatient clinic due to lumbar disc herniation from November 2022 to January 2023. Three axial T2-weighted MRI planes parallel to the L5/S1 intervertebral disc space were selected: the lower endplate of L5, the mid-disc space, and the upper endplate of S1. The evaluation of vascular position included assessing the distance between the CIV and the S1 nerve root (DVN), as well as determining whether the ascending lumbar vein (ALV) crossed the L5/S1 intervertebral space on three scanning planes. Perivascular adipose tissue (PVAT) was used to evaluate the morphology of iliac vessels and PVAT was categorized. The proportion of patients suitable for left-sided and right-sided approaches was compared. This study included a total of 116 patients (60 males and 56 females). The DVN on the right side was 16.2 ± 5.8 mm, while 14.7 ± 5.7 mm on the left side ( t = 3.48, P <0.001). There were 2 patients with ALV on the right side and 5 patients on the left side. 38 patients (32.8%) had PVAT on the left side, while 80 patients (69.0%) had PVAT on the right side ( χ 2 = 30.4, P <0.001). After excluding patients with ALV on the left and right sides, 61.2% and 36.2% of patients had an anatomical corridor for CLIF on the right and left sides respectively. 88.7% of patients had at least one feasible corridor for CLIF. The CLIF technique appears anatomically feasible at the L5/S1 segment in a substantial proportion of patients. Most of the patients have an operative corridor for L5/S1 CLIF, with a higher anatomical feasibility rate on the right side compared to the left. It is advisable to avoid L5/S1 CLIF when the ALV crosses the L5/S1 intervertebral space.