Does vertebral level of pedicle subtraction osteotomy correlate with degree of spinopelvic parameter correction?

Clinical article

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Pedicle subtraction osteotomy (PSO) is a spinal realignment technique that may be used to correct sagittal spinal imbalance. Theoretically, the level and degree of resection via a PSO should impact the degree of sagittal plane correction in the setting of deformity. However, the quantitative effect of PSO level and focal angular change on postoperative spinopelvic parameters has not been well described. The purpose of this study is to analyze the relationship between the level/degree of PSO and changes in global sagittal balance and spinopelvic parameters.


In this multicenter retrospective study, 70 patients (54 women and 16 men) underwent lumbar PSO surgery for spinal imbalance. Preoperative and postoperative free-standing sagittal radiographs were obtained and analyzed by regional curves (lumbar, thoracic, and thoracolumbar), pelvic parameters (pelvic incidence and pelvic tilt [PT]) and global balance (sagittal vertical axis [SVA] and T-1 spinopelvic inclination). Correlations between PSO parameters (level and degree of change in angle between the 2 adjacent vertebrae) and spinopelvic measurements were analyzed.


Pedicle subtraction osteotomy distribution by level and degree of correction was as follows: L-1 (6 patients, 24°), L-2 (15 patients, 24°), L-3 (29 patients, 25°), and L-4 (20 patients, 22°). There was no significant difference in the focal correction achieved by PSO by level. All patients demonstrated changes in preoperative to postoperative parameters including increased lumbar lordosis (from 20° to 49°, p < 0.001), increased thoracic kyphosis (from 30° to 38°, p < 0.001), decreased SVA and T-1 spinopelvic inclination (from 122 to 34 mm, p < 0.001 and from +3° to −4°, p < 0.001, respectively), and decreased PT (from 31° to 23°, p < 0.001). More caudal PSO was correlated with greater PT reduction (r = −0.410, p < 0.05). No correlation was found between SVA correction and PSO location. The PSO degree was correlated with change in thoracic kyphosis (r = −0.474, p < 0.001), lumbar lordosis (r = 0.667, p < 0.001), sacral slope (r = 0.426, p < 0.001), and PT (r = −0.358, p < 0.005).


The degree of PSO resection correlates more with spinopelvic parameters (lumbar lordosis, thoracic kyphosis, PT, and sacral slope) than PSO level. More importantly, PSO level impacts postoperative PT correction but not SVA.

Abbreviations used in this paper: PI = pelvic incidence; PSO = pedicle subtraction osteotomy; PT = pelvic tilt; SPI = spinopelvic inclination; SVA = sagittal vertical axis.

Article Information

Current affiliation for Dr. Bess: Presbyterian/St. Luke's, Rocky Mountain Scoliosis and Spine, Denver, Colorado.

Address correspondence to: Virginie Lafage, Ph.D., Research Scientist, Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, 380 2nd Avenue, Suite 1001, New York, New York 10010. email:

Please include this information when citing this paper: published online December 24, 2010; DOI: 10.3171/2010.9.SPINE10129.

© AANS, except where prohibited by US copyright law.



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    Measures of sagittal spinal radiological parameters. The SVA is the horizontal distance between a C-7 plumb line dropped vertically from the center of the C-7 vertebral body and the posterior superior aspect of S-1. Positive and negative values of SVA reflect the C-7 plumb line anterior and posterior to the posterior superior aspect of S-1, respectively. Thoracic kyphosis was measured as the Cobb angle from T-4 to T-12, and lumbar lordosis was measured as the Cobb angle from L-1 to S-1. The T-1 SPI and T-9 SPI are the angles between the vertical plumb line and the line drawn from the vertebral bodies of T-1 or T-9, respectively, to the center of the bicoxofemoral axis.

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    Pelvic parameters. Sacral slope is defined as the angle subtended by a horizontal reference line and a line drawn parallel to the sacral endplate. Pelvic incidence is the angle subtended by a line dropped perpendicular to the sacral endplate and a line drawn from the center of the sacral endplate to the center of the bicoxofemoral axis. Pelvic tilt is defined as the angle subtended by a horizontal reference line and a line drawn from the center of the sacral endplate to the center of the bicoxofemoral axis. Note that PI = sacral slope + PT.

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    Measurement of the pedicle subtraction angle, which is the variation of the angle formed by the lower vertebral endplate of the adjacent cephalic vertebra and the upper vertebral endplate of the adjacent caudal vertebra.

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    Chain of correlation among the entire set of measured parameters. Correlation coefficients reflect the degree of correlation between the indicated parameters. Values between 0 and 0.3 (0 and −0.3) reflect a weak positive (negative) linear relationship. Values between 0.3 and 0.7 (−0.3 and −0.7) reflect a moderate positive (negative) linear relationship. Values between 0.7 and 1.0 (−0.7 and −1.0) reflect a strong positive (negative) linear relationship. *p < 0.05; **p < 0.001.


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