L5/S1 anterior lumbar interbody fusion: anatomical and technical considerations

Anterior lumbar interbody fusion (ALIF) at the L5/S1 level is a well-established surgical technique used in the management of degenerative, deformity, and instability-related pathologies of the lumbosacral junction. This region represents a biomechanically significant transition between the mobile lumbar spine and the pelvis, contributing substantially to overall lumbar lordosis while being subjected to considerable shear forces. Successful execution of L5/S1 ALIF requires a comprehensive understanding of both spinal and retroperitoneal vascular anatomy, including the relationship of the iliac vessels, median sacral vessels, and the superior hypogastric plexus. Careful patient selection and pre-operative planning are essential, particularly in the context of anatomical variation such as steep sacral slope or altered vascular positioning. This review outlines the key anatomical features, surgical approaches, and technical considerations involved in performing ALIF at L5/S1. The stages of the procedure-including exposure, discectomy, and reconstruction-are described, with emphasis on strategies to optimise access, maintain safety, and achieve stable fusion. Potential complications, including vascular injury and autonomic dysfunction, are also discussed. A thorough and methodical approach to L5/S1 ALIF can enhance surgical outcomes while minimising risk, reinforcing its role as a valuable technique in contemporary spine surgery.