Sacral fatigue fracture in a young girl with no history of trauma or reported athletic activity: a case report.

Sacral fatigue fractures in the young population usually occur due to repetitious physical strain from vigorous athletic activity; they are extremely rare in those younger than 13 years without intense physical activity. We report a case of sacral fatigue fracture in a healthy elementary school girl without any history of trauma or excessive athletic activity. A healthy 11-year-old girl experienced sudden low back pain upon standing after a short break in a normal running exercise for physical education at school. At her first orthopaedic visit, she was unable to walk independently and was limping on her left leg. Neurological examination revealed that the left straight leg raising test was positive at 80 degrees with associated left buttock pain but without motor and sensory deterioration. Radiological examination showed no obvious fractures in the lumbar vertebrae or pelvis. Magnetic resonance imaging demonstrated high intensity signal changes on the short tau inversion recovery image of the left ala, and sacral fatigue fracture in the left ala was diagnosed. She was instructed to rest at home and allowed minimal walking with a crutch under endurable pain for 4 weeks. Within 3 weeks, her low back pain gradually reduced, and after 4 weeks, she could walk independently without gait pain. Sacral fatigue fractures should be considered in the diagnosis of young patients who present with unexplained low back pain.