1. The Effect of the Fixed Sagittal Plane caused by Spinal Instrumentation at an Early Age on the Natural Evolution of Pelvic Incidence During Growth
Bekmez S, Demirkiran G, Dede O, Kruyt MC, Atici Y, Balioglu B, Yazici M

2. Introduction
Sagittal pelvic alignment has profound impact on outcomes after spinal surgery
In normal children, there is a natural evolution of Pelvic incidence during growth
Increase of approx. 0.6 deg/year

3. Purpose
“Determine the effect of stabilizing the sagittal spinal alignment on the natural progression of pelvic orientation in children.”

4. Patients and Methods Four separate Institutions Between 2004-2013
36 patients with idiopathic or idiopathic-like EOS
Lower instrumented vertebra L3 or upper
>2 years f/u

5. Radiographic Analyzes
Sagittal balance (SB)
Pelvic Incidence (PI)
Sacral slope (SS)
Pelvic tilt (PT)
Thoracic kyphosis (TK: T2-T12)
Lumbar lordosis (LL: L1-L5)

6. Results Average age at the index surgery 7.7 years (range 4 to 10)
Average f/u time 72 months (range 27 to 132)
Average L1-S1 50.1° (preop.) ° (index sur.)  46.8 (last f/u)

7. Results The difference is statistically significant
Average PI of the study group
44.8° (preop.) 44° (index sur.) 45.9° (last f/u)
If sagittal alignment have not been stabilized in these children, the average PI would progress to 48.7°
The difference is statistically significant

8. Results
No significant difference in TK and L1-S1 angle during follow-up
No correlation between L1-S1 angles and PI

9. Conclusion
The natural evolution of pelvic incidence was not observed after stabilizing the lumbar sagittal alignment
The consequences of this arrest in adult period are not known
These patients should therefore be monitored carefully during follow-up