Lumbopelvic parameters and the extent of lumbar fusion

BACKGROUND Following lumbar fusion, sacroiliac (SI) joint pain has been regarded as a form of adjacent segment disease. Prior studies suggest increased stress to the SI joint and pelvis with lumbar fusion. Limited studies have evaluated the relationship between the extent of lumbar fusion and its potential influence on lumbopelvic parameters, which may provide the insights to persistent back pain. METHODS Three hundred fifty-five patients underwent lumbar fusions at our institution between fall 2010 and winter 2012; 80 patients met criteria for the study. Inclusion criteria included appropriate imaging available (preoperative and postoperative lateral films), follow-up >1-year, fusion where the rostral extent was up to L1 and the caudal extent was at most S1. Exclusion criteria included prior lumbar fusion, history of SI joint syndrome, follow-up <1-year, fusion involving thoracic levels, and inadequate films (inability to visualize appropriate anatomy). The patients were divided into groups based on the extent of fusion. The patients were evaluated based on age, sex, diagnosis, lumbar lordosis, pelvic incidence, pelvic tilt, and sacral slope. The preoperative values were compared among the groups, the postoperative values were compared among the groups, and the pre- and post-operative values were compared within each group. RESULTS There were no statistically significant differences between pre- and post-operative lumbopelvic parameters within each fusion group. CONCLUSION The results imply that the extent of instrumentation, including the involvement of the sacrum, may not alter lumbopelvic parameters. This appears to argue against the idea that longer fusion constructs induce more stress on the pelvis and SI joint.