This elderly lady presented with very low back pain. Upright positional MRI was performed in a seated neutral position, flexion and extension. The selected T2 images show the fact that there is mobile subluxation of the coccyx at the sacro-coccygeal junction, with posterior movement of the coccygeal segments in both neutral (Fig1) and extension views. Normal alignment returns in flexion (Fig 2 ).
The issue causing her coccydynia is quite likely due to a previous fall or injury.
Visualisation of the exact nature of this problem and its variable manifestation was only due to attaining scans in variable patient positions. This is not possible with conventional supine MRI scanning. Additionally, this abnormaility would have been missed in many exams, as the lowest part of the spine would not have been included. Medserena includes the entire lumbo-sacral spine including the coccyx in cases of very low back pain