What is a midline disk bulge?

Disk. Dont mention which part spine. A disc is an hydraulic unit to distribute pressure. Many people have bulges which is not a ruptured disk. They are a common finding on x-ray in hard workers, overweight or with age. Generally no symptoms. Mid line is center of body so bulge in low back midline would aim towards front of vertebra or spinal cord.. Symptoms if present would affect nerve to leg, not back.
This may be normal.. Mri or ct scans of the spine frequently show discs that protrude beyond the edge of the vertebral bodies. This may be associated with degenerative disc disease and arthritis, but it is such a very common finding, some experts would consider this a normal variant.