Nonunion of an occult fracture in zone III of the sacrum

Summary Fractures in the midline of the sacrum are rare, a pseudarthrosis has not been described previously. We report about a 53-year-old woman with a midline fracture of the sacrum which has not been recognized, although there were indirect fracture signs on the native x-rays and a CT was performed. The surgical treatment with sacral compression bars was successful and pseudarthrosis healing resulted but the patient continued to have mild low back pain. The case reported here confirms that low back pain may caused by pathologic changes of the posterior part of the pelvis. The unusual fracture location could be caused by a bifid spinous process.