Block vertebra (MRI)
Chronic low back pain
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There is a fusion of the L5 and S1 vertebral bodies with loss of intervening disc. The posterior elements are also fused.
This anatomical variant is an incidental finding.
Block vertebra is a congenital failure of segmentation of somites. May be partial or complete involving anterior and/or posterior elements.
Usually, the height combined vertebrae equal the sum of the heights of the involved bodies and the intervertebral discs between them.
In acquired vertebral fusion, this dimension is less than in the case of congenital fusion.