An occasional variant in the anatomy of the lower spine is the failure to fuze of the 1st sacral vertebra with its neighbor below.
This results in an additional vertebra inferior to L5, where normally the sacrum is one bone consisting of several fuzed, no longer separate, vertebrae.
In some patients with this anatomical variant, it presents no problems, whereas in others the anomaly creates a vulnerability to low back stresses.
These patients may need more frequent intermittent spinal balancing to maintain comfort and normal function.
