MRI is limited in patients (post operative) with fixation hardware due to metallic suspectibility artifacts produced by metallic devices. Metallic substances produces local magnetic field inhomogenity resulting in spatial mismapping and production of image distrotion which compromises intrepretabiltiy.
small sclerotic lesion in the vertebrae which is uncghanged on serial xrays is probably with out any significance and may indicate something which is called a bone island. (benign finding) However, to be on a safer side serial follow up has been advised. Sclerosis in common english means increased density.