General Session: Adult Spinal Deformity - Hall F

Presented by: V. Lafage


G. Beyer(1), M. Khalifé(2), R. Lafage(3), J. Moon(4), P. Zhou(4), J. Tishelman(4), D. Vasquez-Montes(4), T. Errico(4), A. Buckland(4), F. Schwab(3), V. Lafage(3)

(1) SUNY Downstate Medical Center, New York, NY, United States
(2) Hôpital Européen Georges-Pompidou, Paris, France
(3) Hospital for Special Surgery, New York, NY, United States
(4) New York University Langone Orthopedic Hospital, New York, NY, United States


Introduction: Despite the direct anatomic and physiologic relationship between pelvic incidence and the compensatory retroversion of the pelvis in sagittal malialignment, there is little work that explores the available range of compensation that a patient may employ given their static pelvic incidence. The question stays whether large degree of retroversion represents exhaustion of the compensatory reserve, or simply a relatively normal degree of retroversion given a large PI. Given the clear clinical impact of PI and PT, the relationship of PT to various possible PI values must be explored.

Purpose: To elucidate the relationship between sagittal malalignment and PT at varying magnitudes of pelvic incidence in order to determine whether anatomic variation portends varying degrees of physiologic compensation in response to sagittal malalignment.

Methods: This is a retrospective review of a prospectively collected database. From our analysis, we included only the initial visit of patients with a T1 pelvic angle (TPA) greater than 10 degree to include a wide range of patients with varying sagittal malalignment with a focus on anterior malalignment. Radiographic assessment of pts included PI, PT and TPA. Analysis involved stratification of PI into Very Low PI (≤ Mean PI - 1.5 SD), Low PI (Mean PI - 1.5SD < Low PI ≤ Mean PI - 0.5 SD), High PI (Mean PI + 0.5SD ≤ High PI < Mean PI + 1.5 SD) and Very High PI (Mean PI + 1.5 SD ≤). Radiographic parameters were compared between these groups and linear relationship between PI and PT was explored. Finally, in order to capture how much PT varied at different levels of sagittal malalignment, a chart was constructed for each PI group showing one and two standard deviations of PT for different levels of sagittal malalignment as quantified by TPA.

Results: A total of 2077 patients met inclusion criteria (mean age: 62.2 yrs). PT varied between PI groups: mean PT was 32.4° for Very High PI pts, 27.9° for High PI group, 24.1° for Average PI pts, 20.7° when the PI was Low and 18.6° for Very Low PI, but linear regression analysis revealed no significant linear relationship of PT to PI within any of the PI sub-groups. With respect to the full cohort, the relationship between TPA and PT was highly variable between PI groups. On multivariate linear regression, as compared to pts with an average PI, pts with Very Low PI had 3.4° lower PT while holding TPA constant (p < 0.001). Further, patients with Very High PI displayed a PT of 1.9° higher than patients with an Average PI while holding TPA constant (p = 0.01). A similar difference of -1.8°, and 1.2° with respect to the Average PI group was observed in the Low and High PI groups, respectively (p < 0.001).

Conclusion: Previous research has demonstrated a clear link between both PT and PI to demographic data. However this is the first study showing that pelvic incidence is associated with varied use of pelvic retroversion when holding sagittal malalignment constant. The results reported herein are intended to allow surgeons to assess a patient's magnitude of compensatory retroversion given a patient's anatomic determinants.