Magnetic Resonance Imaging Morphometric Analysis of the Lumbar Spine and Its Vascular and Muscular Relations: Anatomical Variability and Surgical Planning

BACKGROUND: Lumbar region anatomical variability significantly affects the safety of minimally invasive spine (MIS) approaches, yet quantitative patient-specific data remain limited. OBJECTIVE: The primary goal was to characterize vascular, muscular, and skeletal variability in Portuguese patients with lumbar disc disease and assess implications for MIS surgical corridors. A secondary objective was to explore associations between muscle area and disability. STUDY DESIGN: Cross-sectional observational study. METHODS: Lumbar magnetic resonance images from 46 adults were analyzed for vertebral and disc morphometry (L1-S1), psoas and intrinsic back muscles area (at the level of L4-L5 intervertebral disc), psoas-intervertebral disc overlap, psoas-vessel distances (abdominal aorta or the left common iliac artery), and iliac vessel spacing at L5 to S1 (distance between the left common iliac vein and the right common iliac artery). Sex and age were analyzed as comparative and correlational variables. The ante-psoas corridor narrowed caudally, with L4 to L5 being the most unfavorable level for oblique lateral interbody fusion (32.6% negative overlap). Psoas-vessel distances decreased from L1 to L5 and correlated positively with age. The aortic bifurcation was most frequently located at mid-L4 (50%). CONCLUSION: Marked anatomical variability influences MIS feasibility, particularly at the L4 to L5 level. Individualized preoperative imaging assessment is essential to ensure safe surgical planning and technique selection. CLINICAL RELEVANCE: Preoperative MRI assessment of patient-specific lumbar vascular and muscular anatomy may help identify anatomical constraints relevant to minimally invasive lumbar fusion and support individualized surgical approach selection, particularly at the L4-L5 level.