Sacral fractures after lumbosacral fusion: a characteristic fracture pattern.

OBJECTIVE The purpose of this study was to describe the radiologic pattern of sacral fractures after lumbosacral fusion and to identify clinical characteristics relevant to the radiologic diagnosis. MATERIALS AND METHODS A search of CT, nuclear medicine, and MRI radiology reports over a 5-year period at our institution revealed a total of 23 patients with sacral fractures after lumbosacral fusion. Two radiologists reviewed all of the images to determine the sacral fracture pattern. The clinical records of these patients were reviewed for interval after surgery, fusion length, hardware, approach, preoperative diagnosis, symptoms, treatment, and risk factors. RESULTS All 23 sacral fractures were horizontal through the sacral body, involved the screw holes, and exited through the posterosuperior sacral alae. The fractures occurred within 3 months of fusion in 19 of 23 patients. All 23 patients had symptoms at the time of fracture. Seventeen of 23 fusions were long (more than four vertebrae). Four of 23 patients had osteoporosis. Eleven of 23 fractures healed without surgery, and 12 were managed with transiliac fixation. CONCLUSION Sacral fractures after lumbosacral fusion have a characteristic transverse pattern through the sacral screw holes that differs from the configuration of more common sacral insufficiency fractures. Most of these fractures occur within 3 months after surgery, and many of the patients need additional surgical fixation. Because few of the patients had osteoporosis and most underwent long fusion, the fractures might have been caused by hardware-related stress raisers in the sacrum.