When I was thirteen I was told I had a birth defect that only 5% of the population at the time had where I have an extra bone or hook on my tailbone that can hitch into my lower vertebrae, causing extreme pain and causes me to become immobile for a few days when it acts up. Can you tell me what it is?
There is a phenomenon which is congenital and benign referred to as SACRALIZATION or SUMMARIZATION where either the L5 vertebra fuses with the sacrum or the S1 vertebra fuses with the lumbar portion of the spine (L5).  Typically, this is not a painful condition. If you would like to discuss this further then, upload a PDF of a radiographic report which demonstrates the defect to