Concurrent lumbosacral and sacrococcygeal fusion: a rare aetiology of low back pain and coccygodynia?

Sacrum is a triangular bone placed in the base of the spine and formed by the synostosis of five sacral vertebrae (S1–S5). Its upper part is connected with the inferior surface of the body of L5 vertebra forming the lumbosacral joint, while its lower part is connected with the base of the coccyx forming the sacrococcygeal symphysis, an amphiarthrodial joint. The existence of four pairs of sacral fora­mina in both anterior and posterior surface of the sacrum is the most common anatomy. Nevertheless, supernumerary sacral foramina are possible to be created by the synostosis of lumbosacral joint or sacrococcygeal symphysis. We present a case of an osseous cadaveric specimen of the sacrum belonging to a 79-year-old Caucasian woman. A rare variation of the anatomy of the sacrum is reported; in which, the simultaneous fusion of the sacrum with both the L5 vertebra and the coccyx has created six pairs of sacral foramina. This variation should be taken into serious consideration, especially in the domain of radiology, neurosurgery, orthopaedics and spine surgery, because low back pain, coccygodynia and other neurological symptoms may emerge due to mechanical compression. (Folia Morphol 2018; 77, 2: 397–399