Septic Arthritis: A Very Uncommon but Remarkable Complication Revealing Bertolotti Syndrome in a Child

Background Bertolotti syndrome is an uncommon cause of low back pain, particularly in children and adolescents. It is characterized by a lumbosacral transitional vertebra that may form a pseudoarticulation with the sacrum or ilium, potentially leading to mechanical and inflammatory complications. Septic arthritis involving this pseudoarticulation is exceptionally rare. Case Presentation A 13‐year‐old girl was admitted to our institution with fever and disabling low back pain. MRI revealed a neoarticulation between the enlarged transverse process of L5 and the sacrum, associated with imaging findings consistent with septic arthritis and a contiguous iliac abscess caused by Staphylococcus aureus . Clinical Outcomes The patient was successfully treated with targeted intravenous antibiotic therapy, and surgical drainage of the abscess was ultimately not required. To our knowledge, this represents one of the youngest reported patients with a severe infectious complication of Bertolotti syndrome. Conclusion This case highlights a rare but serious complication of Bertolotti syndrome in the pediatric population. Early diagnosis and appropriate management are essential to prevent complications and long‐term sequelae.