An Anatomical and Morphometric Study of the Coccyx Using Three-Dimensional Reconstruction.

To provide anatomical and morphological data regarding the coccyx using three-dimensional images, with a view to aiding the diagnosis of idiopathic coccydynia, one hundred and thirty-six normal adult pelvises were investigated. Three-dimensional models of the pelvis were reconstructed using software from computed tomography images of whole specimens. The following six coccyx parameters were measured: (1) width, (2) straight length, (3) thickness, (4) sacrococcygeal angle, (5) intercoccygeal angle, and (6) angle of lateral deviation of the coccyx. The presence of fusion between the sacral and coccygeal cornua, and between the sacrum and the transverse process of the coccyx was also investigated, and lateral deviations of the coccyx were classified and analyzed. Most of the measured coccyx parameters were larger in males than in females, with the exception of the sacrococcygeal and intercoccygeal angles. Unilateral or bilateral fusion of the sacral cornu and the coccygeal cornu was not a rare finding. With respect to the sacrum and the transverse process of coccyx, the separated type was more common than the fused type. The incidence and angle of lateral deviation of the coccyx varied widely between individuals. The present detailed description of the gross anatomy of the coccyx obtained using three-dimensional modeling will help toward understanding the mechanism underlying the development of idiopathic coccydynia. Fusion of the sacrum and coccyx or lateral deviation of the coccyx may cause coccydynia by compressing the coccygeal nerves.