No correlation between patient outcome and abnormal lumbar MRI findings 21 years after posterior or posterolateral fusion for isthmic spondylolisthesis in children and adolescents

Between 1977 and 1987, posterior (n=29) or posterolateral (n=73) fusion was performed for mild to moderate (slip <50%) isthmic spondylolisthesis on 102 patients (46 females, 56 males). The patients’ average age at the time of operation was 15.9 (range, 8.1–19.8) years. Clinical (physical examination and Oswestry disability index (ODI)) and radiological (MRI and plain radiographs) examinations were performed on these patients after an average follow-up time of 21.0 (range, 26.2–15.1) years. In the radiographs, the mean slip preoperatively was 27% (range, 5–50%) and at the last follow-up visit 26% (range, 5–78%). Inside the fusion, there were a total of 148 intervertebral discs, 121 (82%) of them had decreased signal intensity in T2-weighted MR images and 113 (76%) were narrowed. Above the fusion level, 27 (27%) discs were speckled and 27 (27%) were black; 21 (21%) intervertebral disc spaces were narrowed. Two levels above the fusion level the numbers were 8 (8%), 16 (16%) and 16 (16%), respectively. Six (6%) patients had a prolapse. Degenerative facet joint hypertrophy above fusion was seen at 80 (79%) of the levels studied. When compared to healthy subjects higher frequency of disc and facet joint degeneration was found. In MR images, none of the patients had lumbar spinal stenosis inside or above the fusion. Narrowing of one or both of the neural foramina at the level of the L5–S1 interververtebral disc was noted in 32 (31%) patients. Seventeen (17%) of the patients had, usually mild, muscular atrophy of the psoas and 33 (32%) of the paraspinal muscles. There was no difference in frequency of abnormal MRI findings between patients (n=93) with ODI 20 or less compared with patients (n=9) with ODI more than 20. In situ fusion due to isthmic spondylolsthesis at adolescence is associated with moderate degenerative changes in the lumbar spine during a 20-year follow-up. Changes were most commonly found at the level of the spondylolisthesis and above fusion level. Neural foramina stenosis seems to be associated with spondylolisthesis and its severity to severity of the slip. Muscle atrophy tended to be mild. However, there was no correlation between patient outcome (ODI) and abnormal lumbar MRI findings.