Sagittal vertical axis/alignment (SVA) is one of the simplest and most widely used methods to assess sagittal balance 1-3.
Measurement
This measurement is performed on lateral standing full-length spine x-rays. A plumb line is drawn vertically from the middle of the C7 vertebral body 1,2 or the midpoint of the C7 inferior endplate 3 to S1, and the distance is measured between the plumb line and the posterosuperior corner of S1 1-3.
Interpretation
The position of this line can be positive, neutral or negative:
positive balance: the plumb line passes >2 cm in front of the posterosuperior corner of the S1 vertebral body
neutral balance: C7 plumb line intersects the posterosuperior corner of S1 (mean SVA in asymptomatic adults is 0.5 cm +/- 2.5 cm) 1
negative balance: the plumb line passes more than 2 cm behind the posterosuperior corner of the S1 vertebral body
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