Introduction: The SI joint and the pelvis are adjacent to a fused segment after lumbar fusion surgery. SI joint pain has been regarded as a form of adjacent segment disease. Prior studies suggest increase stress to the SI joint and pelvis with lumbar fusion. The goal of the study is to evaluate whether the extent of lumbar instrumentation induces changes to lumbopelvic parameters.

Methods: Among 355 patients underwent lumbar fusions at our institution between fall 2010 to winter 2012, 80 patients met criteria for the study. Inclusion criteria included age > 18, appropriate imaging available (pre operative and post operative lateral films), fusion where the rostal extent is up to L1 and the caudal extent at most S1. Exclusion criteria included prior lumbar fusion, history of SI joint syndrome, inappropriate follow up (<1 year), fusion involving thoracic levels, and inadequate films (unable to visual appropriate anatomy). The patients were subdivided into groups based on extent of lumbar instrumentation. The patients were evaluated based on age, sex, diagnosis, lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS). The values were compared preoperatively among the groups, postoperatively among the groups, and preoperative vs postoperatively with the same group.

Results: There were no statistically significant differences between preoperative and postoperative lumbopelvic parameters among each fusion group.

Conclusions: 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.

Patient Care: This research adds to the literature regarding the extent of lumbar fusion and its influence on lumbopelvic parameters. Prior studies suggest that post operative SI joint pain may be related to lumbar fusion. Surgical strategies for lumbar fusion may reduce the incidence of post operative SI joint pain. This study supports the idea that the extent of the fusion construct does not change lumbopelvic parameters. Since the lumbopelvic parameters do not change, the stress towards the SI joint may not be significant. Knowledge of factors that may induce post operative SI joint pain will help contribute to better patient outcome after lumbar fusion.

Learning Objectives: Participants should be able to 1) Describe various lumbopelvic parameters, 2) Possess background knowledge of the recent literature regarding sacroiliac joint pain after lumbar fusion as a possible manifestation of adjacent level disease, 3) Entertain the possibility that the extent of lumbar fusion constructs may not induce significant stress to the pelvis and SI joint to alter lumbopelvic parameters.

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