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Predictors of Poor Global Alignment and Proportion Score After Surgery for Adult Spinal Deformity

Ohba, Tetsuro MD, PhD; Ebata, Shigeto MD, PhD; Oba, Hiroki MD∗,†; Koyama, Kensuke MD, PhD; Yokomichi, Hiroshi MD, PhD, MPH, DrPH; Haro, Hirotaka MD, PhD

doi: 10.1097/BRS.0000000000003086
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Study Design. Retrospective observational study of a cohort of consecutive patients.

Objective. To determine 1) the correlation between clinical and radiographic outcomes and Global Alignment and Proportion (GAP) score, and 2) which preoperative parameters predominantly influence the risk for poor GAP scores.

Summary of Background Data. Although numerous investigators have indicated their criteria for sagittal correction, it is still not unusual to observe poor outcome or complications even after ideal correction. The recently developed GAP score indicates spinopelvic alignment and setting surgical goals according to the score might decrease the prevalence of mechanical complications. However, there is no clear evidence of correlation between the GAP score and clinical outcomes, or which patient factors are preoperative predictors of poor postoperative GAP score.

Methods. We included 128 consecutive patients treated with spinal correction surgery who had a minimum 2-year follow-up. The correlations between clinical outcomes, increased proximal junctional angle, and GAP score were determined. Univariate and multivariate logistic regression analyses were conducted to clarify potential preoperative risk factors for poor GAP score.

Results. Based on total GAP score, 32 (25%) patients were grouped into proportioned, 50 (39.1%) into moderately disproportioned, and 44 (34.3%) into severely disproportioned spinopelvic alignment. Our present study showed a significantly positive correlation between Oswestry Disability Index, increased proximal junctional angle 2 years after surgery, and total GAP score. Uni and multivariate regression analysis showed a large global tilt was a risk factor for a poor GAP score and that the risk for a poor GAP score increased with ageing.

Conclusions. Because GAP score correlated with Oswestry Disability Index and increased proximal junctional angle 2 years after surgery, GAP score might define targets for sagittal spinopelvic alignment for favorable outcomes of corrective spinal surgery. A large preoperative global tilt is a potential predictor of poor postoperative GAP score.

Level of Evidence: 3

GAP score might define targets for sagittal spinopelvic alignment for favorable outcomes of corrective surgery for adult spinal deformity, including “amplitude of lumbar lordosis,” the proportion of lumbar lordosis or pelvic parameters, or both. A large preoperative global tilt is a potential predictor of poor postoperative GAP score.

Department of Orthopaedic Surgery, University of Yamanashi, Chuo, Yamanashi, Japan

Department of Orthopaedic Surgery, School of Medicine, Shinshu University, Matsumoto, Nagano, Japan

Department of Health Sciences, University of Yamanashi, Chuo, Yamanashi, Japan.

Address correspondence and reprint requests to Tetsuro Ohba, MD, PhD, Department of Orthopaedics, University of Yamanashi, 1110, Shimokato, Chuo, Yamanashi 409-3898, Japan; E-mail: tooba@yamanashi.ac.jp)

Received 6 November, 2018

Revised 28 February, 2019

Accepted 5 April, 2019

The manuscript submitted does not contain information about medical device (s)/drug (s).

No funds were received in support of this work.

No relevant financial activities outside the submitted work.

Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.