Nonunion of an occult fracture in zone III of the sacrum

Fractures in the midline of the sacrum are rare, a pseudarthrosis has not b een described previously. We report about a 53-year-old woman with a midlin e 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 s urgical treatment with sacral compression bars was successful and pseudarth rosis healing resulted but the patient continued to have mild low back pain . The case reported here confirms that low back pain may caused by patholog ic changes of the posterior part of the pelvis. The unusual fracture locati on could be caused by a bifid spinous process.