From the Spinopelvic Parameters to Global Alignment and Proportion Scores in Adult Spinal Deformity

Abstract

In the last 20 years, sagittal alignment and balance of the spine have become one of the most important issues in the field of spine surgery. Recent studies emphasize that sagittal balance and alignment are more important for health-related quality of life. The understanding of normal and abnormal sagittal alignment of the spine is necessary for the diagnosis and appropriate treatment of adult spinal deformity (ASD), and we will discuss the currently used classification of ASD, the parameters of sagittal alignment that are essential for the diagnosis of spinal deformity, compensatory actions to maintain sagittal balance, and the relationship between sagittal alignment and clinical symptoms. Furthermore, we will also discuss the recently introduced Global Alignment and Proportion scores. The Korean Spinal Deformity Society is publishing a series of review articles on spinal deformities to help spine surgeons better understand spinal deformities.

Keywords: Adult spinal deformity; Lumbar kyphosis; Spinal deformity.

Fig. 1.

SRS-Schwab adult spinal deformity classification. A coronal curve pattern is categorized and each of 3 sagittal modifiers (PI-LL, SVA, and PT) is classified as ‘nonpathological (0),’ ‘moderate deformity (+),’ or ‘marked deformity (++).’ SRS, Scoliosis Research Society; PI, pelvic incidence; LL, lumbar lordosis; SVA, sagittal vertical axis; PT, pelvic tilt.

Fig. 2.

Spinopelvic parameters. C7PL, C7 plumb line; TK, thoracic kyphosis; LL, lumbar lordosis; SSA, spinosacral angle; SVA, sagittal vertical axis; SS, sacral slope; PT, pelvic tilt; PI, pelvic incidence.

Fig. 3.

Schematic representation of pelvic retroversion which increase PT and decrease SS by bringing back the sacrum closer to the axis of the femoral heads. This mechanism compensates for the anterior shift in the center of gravity. SS, sacral slope; PT, pelvic tilt.

Fig. 4.

The correlation of spinopelvic parameters such as PI, PT, SS, and LL. PI, pelvic incidence; LL, lumbar lordosis; SS, sacral slope; PT, pelvic tilt.

Fig. 5.

Parameters of the sagittal balance of the spine and pelvis. The spinal balance is defined as the horizontal offset between the midsacral point and C7 plumb line (C7PL); spinopelvic balance, between hip axis and C7PL; and sacropelvic balance, between hip axis and midsacral point. SVA, sagittal vertical axis; HA, hip axis.

Fig. 6.

Measurement of global spinal balance. Spinosacral angle, spinal tilt, spinopelvic angle, T1 pelvic angle (TPA), and C7 translation ratio. C7PL, C7 plumb line.