In contrast, spondylolisthesis presenting after a spinal fusion for scoliosis, trauma, or other diagnoses may require special consideration because of the altered biomechanical forces at work on the spine, rather than because of causation. Koptan and colleagues have presented ten pediatric patients with spondylolysis and low-grade spondylolisthesis after a posterior fusion for scoliosis and recommended direct repair of the spondylolysis in these cases to preserve motion segments in these patients with already decreased spinal motion [10]. However, this strategy is only feasible for young patients without degenerative disease and with very minimal spondylolisthesis. For other patients, fusion is generally required if surgical treatment is to be pursued.

When fusion below a long construct is considered, a number of factors must be taken into account: whether to connect to the previous fusion, caudal extent, anterior support, and overall sagittal balance. Connection to the previous fusion should be considered if the spondylolisthesis is adjacent to the previous fusion or within one or two spinal levels of it; if there is additional degenerative changes between the previous fusion and the new spondylolisthesis; or if there is curve progression inferior to the previous construct. If connection to the previous construct is elected, an assessment of the bony fusion should be made so that the decision to remove or replace hardware or explore the existing fusion can be acted upon at the same surgery. If the fusion is found to be solid, fewer points of fixation within the fusion levels will be required. If a non-union is detected, this area should be repaired and included among the instrumented levels.

The caudal extent of the fusion may be a straightforward-decision if the spondylolisthesis levels are not being connected to the previous fusion. However, if a long construct is planned, consideration should be given to pelvic fixation. Additionally, interbody support at L5-S1 might be required for purposes of encouraging fusion at this critical point of the construct. An anterior approach for lumbar interbody fusion works well both for this purpose and also for spondylolisthesis reduction and lordosis preservation and is the approach of choice for the senior author. The overall sagittal balance should be assessed because of the importance of preserving lordosis and preventing “flat back syndrome” which may necessitate extensive osteotomy correction in the future if this critical component is neglected, especially when long constructs are planned.