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

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

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

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

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

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

SRS X-rays parameters Differences over the 2 groups GroupIncidence Sacral slope Pelvic Tilt LordosisKyphosis Global inclination SVA N S Significant differences Pelvic Incidence increases Pelvis Tilt increases* Lordosis Decreases Forward Trunk Flexion SVA increases* * Inclusion criteria

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

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

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

SRS Sagittal Balance Schematic Representation !!!! Young Adult How to maintain balance if the trunk inclines or shifts forward ? 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 Only possible if lower extremities are involved Hip flexion ? Knee flexion ? Ankle regulation ?

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