Pelvic incidence changes with adult deformity correction: is intraoperative measurement needed?

BACKGROUND CONTEXT: Pelvic incidence (PI) is a measurement used to evaluate patient specific spinal alignment. PI was thought to be fixed. Recent studies suggest that PI does change after lumbopelvic fixation in adult spinal deformity (ASD) surgery, likely through positionally-dependent motion across the sacroiliac joints (SIJ) while prone. Normal SIJ flexion/extension is 1.1 – 2.2°. PURPOSE: Because lumbar lordosis correction goals are formulated based on PI, the purpose of this study was 1) to evaluate the change in PI on preoperative; intraoperative; and postoperative measurements and 2) determine if intra-operative measurement of PI following prone lumbopelvic fixation alters patient specific alignment goals. STUDY DESIGN/SETTING: Retrospective Cohort study. PATIENT SAMPLE: N/A OUTCOME MEASURES: N/A METHODS: Retrospective single-center review with inclusion criteria of: age >18 years old who underwent surgical correction for ASD with lumbopelvic fixation. PI was measured by two fellowship-trained spine surgeons on preoperative and 6-week postoperative full-body (EOS) standing Xray, and intra-operatively on prone lateral radiographs (O-arm 2D long film) following instrumentation. Paired t-tests were used to determine the differences between the pre-, intra-, and postoperative PI measurements, with intra-class correlation coefficient (ICC) to evaluate inter-rater reliability. RESULTS: A total of 114 consecutive patients (51M:63F) with a mean age of 63.5(±9.9) years were included. PI ICC average measures for pre- and postop measurements was “good” (ICC=0.84, ICC=0.87 respectively), and “moderate” for intra-op measurements (ICC=0.74). ICC single measures for intra-op measurements was “fair” (ICC=.0.58). Mean difference between preoperative and intra-operative PI was 6.3° (p=0.06), preoperative and postoperative 5.7° (p=0.08), and intra-operative and postoperative -0.6° (p=0.16). PI values changed (4.5°) in 108/114 subjects (95%) from preop standing to 6-week standing radiographs. 34/114 subjects (30%) achieved an absolute change of ³6°. CONCLUSIONS: 30% of the cohort demonstrated an absolute change in PI of ³6° (300% of normal SIJ motion). The average absolute change of 4.5° represents a 200% change. This change in PI can alter lumbar lordosis realignment targets intraoperatively. However, inter-rater reliability was only “fair” for intra-operative PI measurements, indicating improvement in reproducibility of intra-operative PI radiographic measurements is needed. FDA Device/Drug Status: This abstract does not discuss or include any applicable devices or drugs.

Duke Scholars

Author Kristen Jones Neurosurgery