About one in ten Australian patients with lumbar radiographs has a lumbosacral transitional vertebra. Radiologists report fewer than a third of them. In a minority of these patients the transitional segment causes persistent low back, buttock or hip pain, often beginning in the twenties, that flares to a severity that brings the patient to an emergency department. The condition is absent from the Low Back Pain Clinical Care Standard and from Australian primary-care journals, and the patient is commonly discharged with a diagnosis of non-specific low back pain.

This guide sets out what an emergency clinician needs in the few hours the patient is in the department. It covers the screening for serious pathology that comes first, the features of the Bertolotti presentation that distinguish it from non-specific low back pain, and the hip and sacroiliac differentials that coexist with a transitional segment. It explains what imaging is and is not useful in the flare, how to read imaging the patient already has when the report calls the finding incidental or uses variable vertebral numbering, and the radiology pitfalls specific to the lumbosacral junction. It covers analgesia in the acute flare, the criteria for admission, and what a discharge should contain so that the patient leaves with a direction rather than a label.

Every clinical figure is drawn from the published evidence.