Impact of sagittal plane spinal deformity on the spino-pelvic relationship and gravity line position in adults

1. Impact of sagittal plane spinal deformity on the spino-pelvic relationship and gravity line position in adults Virginie Lafage, Frank Schwab, Francisco Rubio, Jean-Pierre Farcy Maimonides Medical Center - NYU HJD, New York

2. Context Loss of global alignment (Plumbline shift anteriorly) Adult Sagittal Imbalance Remains poorly understood and challenging • => Increasing disability • SF-12, SRS-29, ODI (p<0.001) => Lumbar kyphosis marked disability SRS-29, ODI (p<0.05) • Degenerative, Pathology, Iatrogenic

3. Force Plate and X-ray Analysis • X-rays • Global alignment • Spinal parameters (SVA, kyphosis, lordosis, …) • Pelvic Parameters (incidence, tilt, sacral slope) • Forceplate technology • Location of anatomical components Gravity Line (GL) and Feet • Compensatory mechanisms • Pelvis (rotation / translation) • Lower extremities • feet

4. Purpose Investigate differences between asymptomatic adults and patients with sagittal plane spinal deformity Are there changes* in the relationship between GL and spino-pelvic parameters? *Group differences were evaluated by independent sample t-tests.

5. Clinical Group Prospective IRB Inclusion criteria Age > 18 y.o. No Previous spine surgery Cobb angle < 20 C7 Frontal Imbalance < 5cm Group S Sagittal pane spinal deformity SVA > 5 cm OR pelvic tilt > 20° 40 subjects Mean age = 65y.o. Group N No sagittal plane deformity 44 volunteer subjects Mean age = 57y.o.

6. Simultaneous assessment of X-Rays and load distribution Frontal & Sagittal XRays Free standing position Gravity Line (GL) and heel line projected on X-rays pressure distribution feet Force Plate Method • Offsets between: GL, Heel line and anatomical landmarks

7. X-rays parameters Differences over the 2 groups Significant differences Pelvic Incidence increases Pelvis Tilt increases* Lordosis Decreases Forward Trunk Flexion SVA increases* * Inclusion criteria

8. Sagittal plane Forceplate & x-ray Group S Group N GL vs. Heels = constant Pelvis shifts posteriorly Heels Line Gravity Line

9. Sagittal plane Forceplate & x-ray Increasing C7 plumbline and pelvic retroversion Pelvic Parameters: Pelvic Incidence increases Pelvic Tilt increases* GL Heels Line Trunk tilts forward Spinal Parameters: Lordosis decreases SVA increases * Group N GL - Heels offset does not change Pelvis shifts backward GL Parameters: Group S * Inclusion criteria

10. Conclusions Key points • Gravity line varies little vs. heel position • Pelvis translates vs. GL • Posteriorly with age and some pathologies • Global inclination more anterior with age/pathology • Pelvis rotates around femoral heads • Retroversion with age (?) and pathology Force Plate and Balance assessment

11. Sagittal Balance Gravity Line vs. Heel = Constant Required to keep standing position Age and pathologies do not affect this constraint By definition, the whole body mass is equally distributed around the gravity line What do we know ? Pelvis moves backward Pelvic tilt increases Feet do not move How to maintain balance if the trunk inclines or shifts forward ? Only possible if lower extremities are involved Hip flexion ? Knee flexion ? Ankle regulation ? Young Adult Schematic Representation !!!!

12. Conclusion • Wide variation of SVA / pelvic tilt can be tolerated • compensatory mechanisms to maintain standing balance • Evaluation requires foot position • Balance formula ? • regional spinal and pelvic parameters • global parameters • foot position • all adding up to a rather fixed GL-heel offset (GHO)