Fusion of the sacrum and spine. Frontal, three dimensional, coloured computed tomography (CT) scan of the sacrum of a patient with partial sacrilization of the lumbar-sacral region. The lowest lumbar vertebra (orange block, upper centre) is partially fused with the sacrum (below vertebra), a bone that joins to the coccyx (tail bone, lower centre) and the pelvis. This fusion, although abnormal, is not harmful and does not need to be repaired.