Although it is relatively rare to have an extra bone, such as a sixth lumbar vertebra (known as a transitional vertebra), it is not actually that extraordinary. It is estimated that about 10% of adults have some form of spinal abnormality, which can include an extra vertebra.
While having an extra bone typically does not serve any function, it also typically results in no symptoms for most people. However, if a bone should fuse with another bone, it can cause back pain or lead to bulging or herniated discs. For individuals with spinal cord injuries, it is particularly important to let your doctor know if you have an extra vertebra to ensure there is no miscounting during assessments and treatments.
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