Impact of sagittal plane spinal deformity on the

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 SDSG, Chicago 2005

Context Adult Sagittal Imbalance Remains poorly understood and challenging Loss of global alignment (Plumbline shift anteriorly) => Increasing disability SF-12, SRS-29, ODI (p<0. 001) => Lumbar kyphosis marked disability SRS-29, ODI (p<0. 05) Degenerative, Pathology, Iatrogenic SRS - 2006

Force Plate and X-ray Analysis n X-rays § Global alignment § Spinal parameters (SVA, kyphosis, lordosis, …) § Pelvic Parameters (incidence, tilt, sacral slope) n Forceplate technology § Location of anatomical components Gravity Line (GL) and Feet § Compensatory mechanisms – – – Pelvis (rotation / translation) Lower extremities feet SRS - 2006

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. SRS - 2006

Clinical Group Prospective IRB Inclusion criteria Age > 18 y. o. No Previous spine surgery Cobb angle < 20 C 7 Frontal Imbalance < 5 cm Group N No sagittal plane deformity 44 volunteer subjects Mean age = 57 y. o. Group S Sagittal pane spinal deformity SVA > 5 cm OR pelvic tilt > 20° 40 subjects Mean age = 65 y. o. SRS - 2006

Method 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 Þ Offsets between: GL, Heel line and anatomical landmarks SRS - 2006

X-rays parameters Differences over the 2 groups Group Incidence Sacral slope Pelvic Tilt Lordosis Kyphosis Global inclination SVA N S 51 38 13 58 -43 -12 0 60 34 27 46 -51 -3 8 Significant differences Pelvic Incidence increases Pelvis Tilt increases* Lordosis Decreases Forward Trunk Flexion SVA increases* * Inclusion criteria SRS - 2006

Sagittal plane Group N Forceplate & x-ray Group S GL vs. Heels = constant Pelvis shifts posteriorly Heels Line Gravity Line SRS - 2006

Sagittal plane Group N GL Increasing C 7 plumbline and pelvic retroversion Heels Line Forceplate & x-ray Pelvic Incidence increases Parameters: Pelvic Tilt increases* Spinal Parameters: GL Parameters: Trunk tilts forward Lordosis decreases SVA increases * GL - Heels offset does not change Pelvis shifts backward Group S * Inclusion criteria SRS - 2006

Conclusions Key points Force Plate and Balance assessment n Gravity line varies little vs. heel position n Pelvis translates vs. GL – Posteriorly with age and some pathologies – Global inclination more anterior with age/pathology n Pelvis rotates around femoral heads – Retroversion with age (? ) and pathology SRS - 2006

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 How to maintain balance if the trunk inclines or shifts forward ? Young Adult Schematic Representation !!!! 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 - 2006

Conclusion n Wide variation of SVA / pelvic tilt can be tolerated – compensatory mechanisms to maintain standing balance – Evaluation requires foot position n Balance formula ? – regional spinal and pelvic parameters – global parameters – foot position § all adding up to a rather fixed GL-heel offset (GHO) SRS - 2006