- Degenerative changes in the intervertebral disc in one or both of the two lowest levels of the lumbar spine (L4/L5 and/or L5/S1). (Degenerative changes are classified based on MR findings according to the following criteria: At least 40% reduction of disc height, Modic changes type I and/or II, "High intensity zone" in the disc, Morphological changes classified as changes in signal intensity in the disc. To classify the disc as degenerative the first criteria alone or at least two of the other criteria must be present. The MR series are evaluated by two independent observers.)