Abstract
OBJECTIVE: Imaging of the painful coccyx currently relies on standard and dynamic radiography. There are no literature data on MRI of the coccyx. This examination could provide information on the cause of pain. METHODS: 172 patients with severe chronic coccydynia underwent MRI and dynamic radiography of the coccyx. RESULTS: Disc abnormalities (seen in 70 patients) were related to either the presence of intradiscal liquid effusion (17/70), or abnormality of the endplates similar to Modic 1 changes (38/70), or uncertain abnormalities (15/70). Abnormalities of the tip of the coccyx (seen in 41 patients) were located in the surrounding soft tissues: venous dilatations (18/41), soft tissue inflammation (13/41) and ambiguous images (9/41). Vertebral bone oedema was observed in five cases and a benign tumour was observed once. The type of imaging feature depend broadly on the mobility of the coccyx: the 105 cases with a mobile coccyx mainly presented abnormal features mainly in a disc (63 cases vs. 4 cases for the tip), whereas the 67 patients with a rigid coccyx mainly showed abnormal features at the tip (37 cases vs. 7 for the joints, p < 0.001). CONCLUSIONS: We recommend MRI of the painful coccyx when dynamic radiography fails to reveal clearly a pathological lesion (i.e., normal or slightly increased mobility of the coccyx or a rigid coccyx lacking a spicule).