1. Does vertebral level of Pedicle Subtraction Osteotomy correlate with degree of spino- pelvic parameter correction? Schwab Frank; Lafage Virginie; Patel Ashish; Hart Robert ; Burton Douglas; Boachie-Adjei Oheneba; Shelokov Alexis; Hostin Richard; Shaffrey Christopher; Gupta Munish; Akbarnia Behrooz; Bess Shay

2. Context Pedicle subtraction osteotomy – –Correction of sagittal spinal malalignment Impact of PSO level ? – –Caudal lumbar PSO results in greater correction of SVA ? Effect of PSO level on immediate post-operative spino-pelvic alignment?

3. Purpose Evaluate radiographic changes of spinal and pelvic parameters induced by PSO surgeryEvaluate radiographic changes of spinal and pelvic parameters induced by PSO surgery Define differences regarding spinal and pelvic parameters related to level and degree of osteotomy performed.Define differences regarding spinal and pelvic parameters related to level and degree of osteotomy performed.

4. Clinical group Multi-center retrospective study – –70 patients – –54 female, 16 male – –Lumbar PSO Full length x-rays – –Pre-op – –Post-op – –Spineview Analysis SpineView®

5. X-ray Analysis Regional Parameters Lumbar Lordosis Lumbar Lordosis Thoracic Kyphosis Thoracic Kyphosis Thoraco-Lumbar Thoraco-Lumbar Global Alignment SVA SVA T1 & T9 sagittal tilt T1 & T9 sagittal tilt Global Inclination Global Inclination Pelvic Parameters Sacral Slope Sacral Slope Pelvic Tilt Pelvic Tilt Pelvic Incidence Pelvic Incidence SpineView® software …. >300 parameters

6. Analysis 2. PSO parameters Vertebral level Degree of resection 3. Correlation ? 1. Radiographic Changes Pre-op versus Post-op t-test

7. PSO level vs focal correction No significant difference in focal correction by level PSO Level # of subjects Focal correction L1624° L21524° L32925° L42022°

8. Change in Regional Curvatures Mean ± 1SD Lumbar Lordosis Thoracic Kyphosis Thoraco Lumbar Pre 22 ± 20-30 ± 21-10 ± 16 Post 47 ± 15-38 ± 18-6 ± 10 ∆26 ± 17-8 ± 124 ± 12 p0.0000.0010.026 Significant increase of sagittal curvatures Significant reduction of TL kyphosis

9. Change in Global Balance SVA T1 sagittal Tilt T9 sagittal Tilt Pre 116 ± 823 ± 8-8 ± 9 Post 31 ± 57-4 ± 5-11 ± 6 ∆-85 ± 57-7 ± 6-3 ± 6 p0.000 Mean ± 1SD Significant SVA decrease T1 Sagittal tilt “normalized” SVA

10. Change in Pelvic Parameters Pelvic Incidence Pelvic Tilt Sacral Slope Pre55 ± 1331 ± 1224 ± 12 Post56 ± 1323 ± 1032 ± 10 ∆0 ± 2-8 ± 108 ± 10 p0.5170.000 Mean ± 1SD No Change in PI Significant decrease of PT

11. PSO vs Change in Spinal parameters SVA (global sagittal balance)SVA (global sagittal balance) – –No correlation with PSO parameters Lumbar LordosisLumbar Lordosis – –increases when PSO degree increases – –Not with PSO vertebral level Thoracic KyphosisThoracic Kyphosis – –increases when PSO degree increases +12°short fusion ( compensatory mechanism + 5°long fusion (>T10) Correlations Correlation with PSO degree Correlation with PSO level ∆ SVA+0.217- ∆ L1-S1+0.655 **- ∆ T4-T12- 0.424 **-

12. PSO vs Change in Pelvic parameters PT correctionPT correction increases when – –PSO located on lower levels – –PSO degree increases Correlations Correlation with PSO degree Correlation with PSO level ∆ Sacral Slope+0.471 **+0.32 ** ∆ Pelvic Tilt-0.436 **-0.410 ** When selecting PSO level, desired PT correction is an important consideration.

13. Conclusion PSO degree – –Affects regional curvatures Directly (Lumbar) Indirectly (Compensation) PSO level – –Impacts post-operative pelvic tilt correction but not SVA