616 - Understanding Variability in Pelvic Tilt (PT) Response to Spinal Defor...

Oral Posters: Adult Spinal Deformity

Presented by: R. Lafage - View Audio/Video Presentation (Members Only)


R. Lafage(1), T. Pannu(1), B. Liabaud(1), F. Schwab(1), J. Smith(2), C. Ames(3), R. Hostin(4), C. Shaffrey(2), G. Mundis(5), D. Burton(6), H.J. Kim(1), C. Jalai(7), E. Klineberg(8), V. Lafage(1), International Spine Study Group (ISSG)

(1) Hospital for Special Surgery, Spine Service, New York, NY, United States
(2) University of Virginia Medical Center, Department of Neurosurgery, Charlottesville, VA, United States
(3) San Francisco Medical Center, University of California, Department of Neurosurgery, San Francisco, CA, United States
(4) Baylor Scoliosis Center, Plano, TX, United States
(5) Scripps Clinic Torrey Pines, La Jolla, CA, United States
(6) University of Kansas Medical Center, Department of Orthopaedic Surgery, Kansas City, KS, United States
(7) NYU Langone Medical Center, Spine Division, Department of Orthopaedics, New York, NY, United States
(8) University of California, Davis, Department of Orthopedic Surgery, Sacramento, CA, United States


Introduction and Purpose: Despite an extensive research in ASD, the impact of regional lumbar correction on pelvic response remains poorly understood. Traditionally, pelvic relaxation following lumbar correction was disregarded as part of pure global spinal correction. The purpose of this investigation was to examine this theory based on a virtual model that isolates the change in global alignment from the impact of pelvic compensation.

Methods: Surgical patients with 1 year follow-up were included and stratified based on PT correction into: dPT (deterioration of PT >2°), mPT (maintenance of pre-op PT) and cPT (correction of PT >2°). To isolate the change in sagittal vertical axis, SVA from its induced pelvic compensation, a simulated alignment (Figure 1) was created by combining the post-op alignment of the spine with the pre-op pelvic orientation. The SVA of this virtual alignment (SVAsim) was computed and all radiographic parameters were compared across the 3 groups. A stepwise regression was carried out to establish the amount of change in SVAsim required to reach a given change in SVA and PT simultaneously. The regression was computed on 75% of patients and validated on the remaining 25% of patients.

Results: 384 patients were included (57.4 years old (y/o), 83 % female) in the analysis: 91 dPT, 80 mPT, and 213 cPT. dPT pts were younger (52.1 vs. 56.9 vs. 59.9 y/o), had a lower PT at baseline (BL) (15.6 vs. 22.7 vs. 28˚), and a smaller SVA (25.6 vs. 57.9 vs. 87.7mm), p< 0.05 for all. Post-op, dPT had an increased PT (6.2˚ vs. 0 vs. -8.6˚, p=0.001) and the least SVA correction (-4.3 vs. -22.4 vs. -67 mm, p< 0.001). Virtual simulation showed increase of SVA in dPT (SVAsim: +51.8 vs. -22.6 vs. -142.9 mm, p=0.001). Regression analysis lead to the equation: ΔSVAsim = ΔSVA + 0.8*ΔPT (r2 = 0.99) with a mean error of -0.02mm±7.9mm, RMSE: 8 mm.

Conclusion: One complexity in planning surgical realignment for ASD relates to the indirect corrections that occur in SVA and PT following regional spinal alignment changes. The formulated predictive model permits the calculation of the truncal correction needed based on desired change in SVA and PT. Patients who experienced an increase in PT sustained an increase in truncal inclination in respect to their pelvis.

Decomposition PT correction and SVA correction