Not very specific.
see Winking owl sign
Plain x-rays are quite good at evaluating bony metastases, but not good at evaluating the spinal cord and surrounding soft tissues. Metastatic epidural spinal cord compression most commonly occurs at the site of vertebral involvement on plain x-ray, especially where there is evidence of vertebral collapse. Most common findings on x-rays include pedicle erosion, paravertebral soft shadow, vertebral collapse, and pathologic fracture or dislocation 2).
In 1990, x-rays were found to have a 10% to 17% false negative rate 5).
The rate of missed metastatic epidural spinal cord compression is unacceptable.