Global sagittal axis: a step toward full-body assessment of sagittal plane deformity in the human body.
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.
['Diebo|Bassel G|BG|', 'Oren|Jonathan H|JH|', 'Challier|Vincent|V|', 'Lafage|Renaud|R|', 'Ferrero|Emmanuelle|E|', 'Liu|Shian|S|', 'Vira|Shaleen|S|', 'Spiegel|Matthew Adam|MA|', 'Harris|Bradley Yates|BY|', 'Liabaud|Barthelemy|B|', 'Henry|Jensen K|JK|', 'Errico|Thomas J|TJ|', 'Schwab|Frank J|FJ|', 'Lafage|Virginie|V|']
D000328:Adult D000368:Aged D001416:Back Pain 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 D051598:Whole Body Imaging
global sagittal axis deformity GSA CBVA = chin-brow vertical angle EQ-5D = EuroQol-5D 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 full-body sagittal alignment