Impact of Psoas Morphology and Great Vessel Proximity on L4-L5 Lateral Lumbar Interbody Fusion (LLIF) Surgery Approach and Outcomes

Introduction: Lateral Lumbar Interbody Fusion (LLIF) is an effective technique for treating degenerative lumbar spine conditions, yet transitional anatomy, anterior psoas morphology, and proximity of great vessels at the L4-L5 level present concerns due to risks of lumbar plexus and vascular injuries. This study categorizes anatomical variations in psoas and vessel positioning and analyzes their impact on L4-L5 LLIF outcomes.

Methods: This retrospective study included 41 patients who underwent L4-L5 LLIF from January 2016 to December 2023. Preoperative CT and MRI assessed psoas muscle cross-sectional area (CSA), vessel positioning relative to the vertebral body, and transitional psoas anatomy presence. Clinical outcomes were evaluated using preoperative and postoperative VAS scores for back and leg pain and the Oswestry Disability Index (ODI). Fusion rates and radiographic outcomes, including scoliosis films and Bridwell grading after one-year follow-up, were analyzed, alongside complication rates.

Results: The cohort had a mean age of 64.3 years and a mean BMI of 29.7 kg/m², with 19 females and 22 males. Average CSA for the right and left psoas was 104.2 mm² and 111.5 mm², respectively, with vessel CSA averaging 387 mm². Vessel proximity to the vertebral body averaged 3.12 mm, and transitional anatomy was noted in 10.25% of cases. Risk analysis indicated 75.6% of patients were moderate risk, 14.6% high risk, 7.3% low risk, and 2.4% mild risk based on vessel-psoas relationships. No major neurological or vascular complications were reported. Significant postoperative improvements were seen, with VAS back pain scores decreasing from 5.2 to 2.4, VAS leg pain scores from 4.6 to 1.9 (p < 0.05 for both), and ODI scores improving from 2.1 to 1.2. Average pelvic tilt was 19.7°, lumbar lordosis was 49.8°, and fusion rates were high: 58% achieved Bridwell grade A, 26% grade B, and 16% grade C.

Conclusion : LLIF at L4-L5 is a safe, effective option for complex lumbar pathology, even with high-risk anatomy. It significantly reduces pain and improves function, though alternative approaches like ALIF and TLIF may be suitable in cases of challenging anatomy and surgeon expertise.