The impact of obesity on compensatory mechanisms in response to progressive sagittal malalignment

Cyrus M. Jalai, Bassel G. Diebo, Dana L. Cruz, Gregory W. Poorman, Shaleen Vira, Aaron J. Buckland, Renaud Lafage, Shay Bess, Thomas J. Errico, Virginie Lafage, Peter G. Passias

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


Background Context Obesity's impact on standing sagittal alignment remains poorly understood, especially with respect to the role of the lower limbs. Given energetic expenditure in standing, a complete understanding of compensation in obese patients with sagittal malalignment remains relevant. Purpose This study compares obese and non-obese patients with progressive sagittal malalignment for differences in recruitment of pelvic and lower-limb mechanisms. Study Design/Setting Single-center retrospective review. Patient Sample A total of 554 patients (277 obese, 277 non-obese) were identified for analysis. Outcome Measures Upper body alignment parameters: sagittal vertical axis (SVA) and T1 spinopelvic inclination (T1SPi). Compensatory lower-limb mechanisms: pelvic translation (pelvic shift [PS]), knee (KA) and ankle (AA) flexion, hip extension (sacrofemoral angle [SFA]), and global sagittal angle (GSA). Methods Inclusion criteria were patients ≥18 years who underwent full-body stereographic x-rays. Included patients were categorized as non-obese (N-Ob: body mass index [BMI]<30 kg/m2) or obese (Ob: BMI≥30 kg/m2). To control for potential confounders, groups were propensity score matched by age, gender, and baseline pelvic incidence (PI), and subsequently categorized by increasing spinopelvic (pelvic incidence minus lumbar lordosis [PI−LL]) mismatch: <10°, 10°–20°, >20°. Independent t tests and linear regression models compared sagittal (SVA, T1SPi) and lower limb (PS, KA, AA, SFA, GSA) parameters between obesity cohorts. Results A total of 554 patients (277 Ob, 277 N-Ob) were included for analysis and were stratified to the following mismatch categories: <10°: n=367; 10°–20°: n=91; >20°: n=96. Obese patients had higher SVA, KA, PS, and GSA than N-Ob patients (p<.001 all). Low PI−LL mismatch Ob patients had greater SVA with lower SFA (142.22° vs. 156.66°, p=.032), higher KA (5.22° vs. 2.93°, p=.004), and higher PS (4.91 vs. −5.20 mm, p<.001) than N-Ob patients. With moderate PI−LL mismatch, Ob patients similarly demonstrated greater SVA, KA, and PS, combined with significantly lower PT (23.69° vs. 27.14°, p=.012). Obese patients of highest (>20°) PI−LL mismatch showed greatest forward malalignment (SVA, T1SPi) with significantly greater PS, and a concomitantly high GSA (12.86° vs. 9.67°, p=.005). Regression analysis for lower-limb compensation revealed that increasing BMI and PI−LL predicted KA (r2=0.234) and GSA (r2=0.563). Conclusions With progressive sagittal malalignment, obese patients differentially recruit lower extremity compensatory mechanisms, whereas non-obese patients preferentially recruit pelvic mechanisms. The ability to compensate for progressive sagittal malalignment with the pelvic retroversion is limited by obesity.

Original languageEnglish (US)
Pages (from-to)681-688
Number of pages8
JournalSpine Journal
Issue number5
StatePublished - May 2017
Externally publishedYes


  • Compensatory mechanisms
  • Full-body imaging
  • Lower extremities
  • Obesity
  • Sagittal malalignment
  • Spinopelvic mismatch

ASJC Scopus subject areas

  • Surgery
  • Orthopedics and Sports Medicine
  • Clinical Neurology


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