Long-term outcome after posterolateral, anterior, and circumferential fusion for high-grade isthmic spondylolisthesis in children and adolescents: magnetic resonance imaging findings after average of 17-year follow-up.

STUDY
DESIGN: A cross-sectional study to evaluate the long-term result of posterolateral (PLF), anterior (AF), and circumferential fusion (CF) for isthmic spondylolisthesis.
OBJECTIVES: To assess the long-term effects of PLF, AF, or CF for high-grade isthmic spondylolisthesis on lumbar spine in children and adolescents by using MRI. SUMMARY OF BACKGROUND DATA: Short- and mid-term clinical and plain radiographic results of isthmic spondylolisthesis and of PLF, AF, and CF in severe slip are well documented. The long-term effect of the fusion on soft tissues, on the intervertebral discs inside and above fusion in particular, is, however, unclear.
METHODS: Between 1977 and 1991, PLF (n = 21), AF (n = 22), or CF (n = 24) was performed on 67 patients (42 females, 25 males) with high-grade (slip > or =50%) isthmic spondylolisthesis. The average age of patients at the time of operation was 14.4 (range, 8.9-19.6) years. Clinical, spinal mobility and trunk strength in addition to MRI and plain radiograph examinations were performed on these patients after an average follow-up time of 17.3 years (range, 10.7-26.0 years).
RESULTS: Three (14%) patients in the PLF and AF groups, but none in the CF group, reported back pain often or very often at rest. The mean Oswestry Disability Index (ODI) was 9.7 (range, 0-62) in the PLF, 8.1 (0-32) in the AF, and 2.3 (0-14) in the CF group (P < 0.05). The mean slip before surgery was 66% (range, 50%-100%) and at the last follow-up visit 66% (range, 26%-106%). Disc degeneration was most common in the PLF group (P = 0.0014) and inside the fusion and in the lowest moving intervertebral disc spaces in all subgroups. Only 1 patient had an asymptomatic prolapse. In MR images, none of the patients had lumbar central canal stenosis inside or above the fusion. In contrast, the spinal canal was wide at the spondylolysis and spondylolisthesis level in 23 (34%) patients. Of the patients, 19 (28%) patients (32 neural foramens) had severe narrowing of the neural foramen with impingement of the nerve root. No patients had clinically confirmed L5 nerve root symptoms. Muscle degeneration was found in 29 (43%) of patients. Longer fusion and muscle degeneration, but not disc degeneration, were associated with lower performance in spinal mobility and trunk-strength measurement tests.
CONCLUSIONS: The clinical outcome was best in the CF group as measured by ODI. Degenerative changes were most commonly found at the level of the slip and above the fusion level. The prevalence of disc prolapses was low. Spinal fusion for isthmic spondylolysis is not associated with central canal stenosis above the fusion. Radiologic nerve root stenosis was common but asymptomatic. Mild muscle atrophy was common.