• Renaud Lafage, Priya Duvvuri, Jonathan Elysee, Bassel Diebo, Shay Bess, Douglas Burton, Alan Daniels, Munish Gupta, Richard Hostin, Khaled Kebaish, Michael Kelly, Han Jo Kim, Eric Klineberg, Lawrence Lenke, Stephen Lewis, Christopher Ames, Peter Passias, Themistocles Protopsaltis, Christopher Shaffrey, Justin S Smith, Frank Schwab, Virginie Lafage, and International Spine Study Group.
• Department of Orthopaedic Surgery, Northwell Health, Lenox Hill Hospital, New York, NY.
• Spine. 2023 Aug 1; 48 (15): 108210881082-1088.

Study DesignThis is a multicenter, prospective cohort study.ObjectiveThis study tests the hypothesis that the elimination of lower limb compensation in patients with adult spinal deformity (ASD) will significantly increase the magnitude of sagittal malalignment.Summary Of Background DataASD affects a significant proportion of the elderly population, impairing functional sagittal alignment and inhibiting the overall quality of life. To counteract these effects, patients with ASD use their spine, pelvis, and lower limbs to create a compensatory posture that allows for standing and mobility. However, the degree to which each of the hips, knees, and ankles contributes to these compensatory mechanisms has yet to be determined.MethodsPatients undergoing corrective surgery for ASD were included if they met at least one of the following criteria: complex surgical procedure, geriatric deformity surgery, or severe radiographic deformity. Preoperative full-body x-rays were evaluated, and age and pelvic incidence -adjusted normative values were used to model spine alignment based upon three positions: compensated (all lower extremity compensatory mechanisms maintained), partially compensated (removal of ankle dorsiflexion and knee flexion, with maintained hip extension), and uncompensated (ankle, knee, and hip compensation set to the age and pelvic incidence norms).ResultsA total of 288 patients were included (mean age 60 yr, 70.5% females). As the model transitioned from the compensated to uncompensated position, the initial posterior translation of the pelvis decreased significantly to an anterior translation versus the ankle (P.Shift: 30 to -7.6 mm). This was associated with a decrease in pelvic retroversion (pelvic tilt: 24.1-16.1), hip extension (SFA: 203-200), knee flexion (knee angle: 5.5-0.4), and ankle dorsiflexion (ankle angle: 5.3-3.7). As a result, the anterior malalignment of the trunk significantly increased: sagittal vertical axis (65-120 mm) and G-SVA (C7-ankle from 36 to 127 mm).ConclusionsRemoval of lower limbs compensation revealed an unsustainable truncal malalignment with two-fold greater SVA.Copyright © 2023 Wolters Kluwer Health, Inc. All rights reserved.

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