INTRODUCTION: The pelvic incidence is the key anatomical factor to regulate sagittal spinopelvic balance. The objective of this study was to evaluate changes of spinopelvic balance following long spinal fusion with and without iliac fixation for degenerative lumbar scoliosis (DLS).
METHODS: Twenty‐seven (65.9±7.2 yrs) and thirty‐three (68.5±6.9 yrs) patients of DLS who underwent long fusion including sacrum with and without iliac fixation were retrospectively selected for groups of iliac fixation (ILF) and non‐iliac fixation (Non‐ILF), respectively. Whole‐spine radiographs were taken at pre‐operative and 3, 12 and 24‐month post‐operative time‐points. Pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), lumbar lordosis (LL), T9 offset (T9O) and thoracic kyphosis (THK) were measured on sagittal X‐Ray at each time‐point. Each dependent variable was compared with 4 time‐points in each group (ILF, Non‐ILF).
RESULTS: In the pelvic parameters, the PI of both groups and the SS of ILF significantly increased post‐operatively and did not change at the later time‐points. The PT of both groups and the SS of Non‐ILF did not change over times. The PI of Non‐ILF (48.2±7.5°) and ILF (52.5±13°) increased to 50.5±8.8° (P=0.015) and 55.0±12.4° (P=0.012), respectively. In the spinal parameters, the LL and T9O of both groups and the THK of ILF significantly increased post‐operatively and did not change at the later time‐points.
DISCUSSION: Long spinal fusion increased PI with restoring LL and T9O and without changing PT in patients with DLS when performing spinal fusion with or without iliac fixation. The use of iliac fixation may have better controls of sacral orientation when comparing with spinal fusion without iliac fixation. This study suggests that the pelvic incidence is not the constant but the variable that is changed by the long spinal fusion. The clinical effect on changes in pelvic incidence is not yet known and will require further study.