title: The impact of obesity on compensatory mechanisms in response to progressive sagittal malalignment.
abstract: 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.
  
  
  
  This study compares obese and non-obese patients with progressive sagittal malalignment for differences in recruitment of pelvic and lower-limb mechanisms.
  
  
  
  Single-center retrospective review.
  
  
  
  A total of 554 patients (277 obese, 277 non-obese) were identified for analysis.
  
  
  
  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).
  
  
  
  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.
  
  
  
  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).
  
  
  
  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.
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Joint Diseases, NYU Langone Medical Center, 301 East 17th St, New York, NY 10003, USA.
authors.forename: Cyrus M
authors.initials: CM
authors.lastname: Jalai
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 E 70th St, New York, NY 10021, USA.
authors.forename: Bassel G
authors.initials: BG
authors.lastname: Diebo
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Joint Diseases, NYU Langone Medical Center, 301 East 17th St, New York, NY 10003, USA.
authors.forename: Dana L
authors.initials: DL
authors.lastname: Cruz
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 E 70th St, New York, NY 10021, USA.
authors.forename: Gregory W
authors.initials: GW
authors.lastname: Poorman
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Joint Diseases, NYU Langone Medical Center, 301 East 17th St, New York, NY 10003, USA.
authors.forename: Shaleen
authors.initials: S
authors.lastname: Vira
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Joint Diseases, NYU Langone Medical Center, 301 East 17th St, New York, NY 10003, USA.
authors.forename: Aaron J
authors.initials: AJ
authors.lastname: Buckland
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 E 70th St, New York, NY 10021, USA.
authors.forename: Renaud
authors.initials: R
authors.lastname: Lafage
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Joint Diseases, NYU Langone Medical Center, 301 East 17th St, New York, NY 10003, USA.
authors.forename: Shay
authors.initials: S
authors.lastname: Bess
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Joint Diseases, NYU Langone Medical Center, 301 East 17th St, New York, NY 10003, USA.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Errico
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 E 70th St, New York, NY 10021, USA.
authors.forename: Virginie
authors.initials: V
authors.lastname: Lafage
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Joint Diseases, NYU Langone Medical Center, 301 East 17th St, New York, NY 10003, USA. Electronic address: peter.passias@nyumc.org.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Passias
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008141:Lordosis / Q000150:complications / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications*; D011187:Posture; D011859:Radiography
keywords: Compensatory mechanisms; Full-body imaging; Lower extremities; Obesity; Sagittal malalignment; Spinopelvic mismatch