title: Global sagittal axis: a step toward full-body assessment of sagittal plane deformity in the human body.
abstract: OBJECTIVE Sagittal malalignment requires higher energy expenditure to maintain an erect posture. Because the clinical impact of sagittal alignment is affected by both the severity of the deformity and recruitment of compensatory mechanisms, it is important to investigate new parameters that reflect both disability level and compensatory mechanisms for all patients. This study investigated the clinical relevance of the global sagittal axis (GSA), a novel measure to evaluate the standing axis of the human body. METHODS This is a retrospective review of patients who underwent full-body radiographs and completed health-related quality of life (HRQOL) questionnaires: Oswestry Disability Index (ODI), Scoliosis Research Society-22, EuroQol-5D (EQ-5D), and the visual analog scale for back and leg pain. The GSA was defined as the angle formed by a line from the midpoint of the femoral condyles to the center of C-7, and a line from the midpoint between the femoral condyles to the posterior superior corner of the S-1 sacral endplate. After evaluating the correlation of GSA/HRQOL with sagittal parameters, linear regression models were generated to investigate how ODI and GSA related to radiographic parameters (T-1 pelvic angle, pelvic retroversion, knee flexion, and pelvic posterior translation). RESULTS One hundred forty-three patients (mean age 44 years) were included. The GSA correlated significantly with all HRQOL (up to r = 0.6 with EQ-5D) and radiographic parameters (up to r = 0.962 with sagittal vertical axis). Regression between ODI and sagittal radiographic parameters identified the GSA as an independent predictor (r = 0.517, r2= 0.267; p < 0.001). Analysis of standardized coefficients revealed that when controlling for deformity, the GSA increased with a concurrent decrease in pelvic retroversion (-0.837) and increases in knee flexion (+0.287) and pelvic posterior translation (+0.193). CONCLUSIONS The GSA is a simple, novel measure to assess the standing axis of the human body in the sagittal plane. The GSA correlated highly with spinopelvic and lower-extremities sagittal parameters and exhibited remarkable correlations with HRQOL, which exceeded other commonly used parameters.
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, New York, New York.
authors.forename: Bassel G
authors.initials: BG
authors.lastname: Diebo
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, New York, New York.
authors.forename: Jonathan H
authors.initials: JH
authors.lastname: Oren
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, New York, New York.
authors.forename: Vincent
authors.initials: V
authors.lastname: Challier
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, New York, New York.
authors.forename: Renaud
authors.initials: R
authors.lastname: Lafage
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, New York, New York.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Ferrero
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, New York, New York.
authors.forename: Shian
authors.initials: S
authors.lastname: Liu
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, New York, New York.
authors.forename: Shaleen
authors.initials: S
authors.lastname: Vira
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, New York, New York.
authors.forename: Matthew Adam
authors.initials: MA
authors.lastname: Spiegel
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, New York, New York.
authors.forename: Bradley Yates
authors.initials: BY
authors.lastname: Harris
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, New York, New York.
authors.forename: Barthelemy
authors.initials: B
authors.lastname: Liabaud
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, New York, New York.
authors.forename: Jensen K
authors.initials: JK
authors.lastname: Henry
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, New York, New York.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Errico
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, New York, New York.
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Schwab
authors.affiliation: Department of Orthopaedic Surgery, New York University Langone Medical Center, New York, New York.
authors.forename: Virginie
authors.initials: V
authors.lastname: Lafage
mesh_terms: D000328:Adult; D000368:Aged; D001416:Back Pain / Q000000981:diagnostic imaging / Q000209:etiology; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D011788:Quality of Life; D012044:Regression Analysis; D012189:Retrospective Studies; D012720:Severity of Illness Index; D013121:Spinal Curvatures / Q000150:complications / Q000000981:diagnostic imaging*; D051598:Whole Body Imaging / Q000379:methods*
keywords: CBVA = chin-brow vertical angle; EQ-5D = EuroQol-5D; GSA; GSA = global sagittal axis; HRQOL = health-related quality of life; KA = knee flexion angle; LL = lumbar lordosis; ODI = Oswestry Disability Index; PI = pelvic incidence; PT = pelvic tilt; SRS22r = Scoliosis Research Society–22, refined; SVA = sagittal vertical axis; TPA = T-1 pelvic angle; VAS = visual analog scale; deformity; full-body sagittal alignment; global sagittal axis