Sagittal realignment failures following pedicle subtraction osteotomy surgery: are we doing enough?

Clinical article

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Pedicle subtraction osteotomy (PSO) is a surgical procedure that is frequently performed on patients with sagittal spinopelvic malalignment. Although it allows for substantial spinopelvic realignment, suboptimal realignment outcomes have been reported in up to 33% of patients. The authors' objective in the present study was to identify differences in radiographic profiles and surgical procedures between patients achieving successful versus failed spinopelvic realignment following PSO.


This study is a multicenter retrospective consecutive PSO case series. The authors evaluated 99 cases involving patients who underwent PSO for sagittal spinopelvic malalignment. Because precise cutoffs of acceptable residual postoperative sagittal vertical axis (SVA) values have not been well defined, comparisons were focused between patient groups with a postoperative SVA that could be clearly considered either a success or a failure. Only cases in which the patients had a postoperative SVA of less than 50 mm (successful PSO realignment) or more than 100 mm (failed PSO realignment) were included in the analysis. Radiographic measures and PSO parameters were compared between successful and failed PSO realignments.


Seventy-nine patients met the inclusion criteria. Successful realignment was achieved in 61 patients (77%), while realignment failed in 18 (23%). Patients with failed realignment had larger preoperative SVA (mean 217.9 vs 106.7 mm, p < 0.01), larger pelvic tilt (mean 36.9° vs 30.7°, p < 0.01), larger pelvic incidence (mean 64.2° vs 53.7°, p < 0.01), and greater lumbar lordosis–pelvic incidence mismatch (−47.1° vs −30.9°, p < 0.01) compared with those in whom realignment was successful. Failed and successful realignments were similar regarding the vertebral level of the PSO, the median size of wedge resection 22.0° (interquartile range 16.5°−28.5°), and the numerical changes in pre- and postoperative spinopelvic parameters (p > 0.05).


Patients with failed PSO realignments had significantly larger preoperative spinopelvic deformity than patients in whom realignment was successful. Despite their apparent need for greater correction, the patients in the failed realignment group only received the same amount of correction as those in the successfully realigned patients. A single-level standard PSO may not achieve optimal outcome in patients with high preoperative spinopelvic sagittal malalignment. Patients with large spinopelvic deformities should receive larger osteotomies or additional corrective procedures beyond PSOs to avoid undercorrection.

Abbreviations used in this paper:ASD = adult spinal deformity; BMI = body mass index; IQR = interquartile range; LL = lumbar lordosis; PI = pelvic incidence; PSO = pedicle subtraction osteotomy; PT = pelvic tilt; SS = sacral slope; SVA = sagittal vertical axis; TK = thoracic kyphosis; TL-Kypho = thoracolumbar kyphosis.

Article Information

Address correspondence to: Virginie Lafage, Ph.D., 380 2nd Avenue, Suite 1001, New York, New York 10010. email:

Please include this information when citing this paper: published online March 30, 2012; DOI: 10.3171/2012.2.SPINE11120.

© AANS, except where prohibited by US copyright law.



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    Radiographic parameters included in the analysis.

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    Differences in age (left) and BMI (right) between the successful and failed realignment groups (white and dark gray boxes, respectively). The boxplots show the IQR (25%–75%), with whiskers indicating the 5%–95% range. The horizontal bars indicate median values.

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    Pedicle subtraction osteotomy degree of wedge resection by vertebral level. No significant association was found between the vertebral level at which the PSO was performed and the angle of PSO wedge resection.

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    Sagittal vertical axis. Preoperative (Pre) and postoperative (Post) SVA differences between the successful and failed realignment groups. White zone indicates optimal SVA, light gray zone intermediate SVA (neither optimal nor poor), dark gray zone poor SVA.

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    Pelvic tilt. Preoperative and postoperative PT differences between the successful and failed realignment groups. White zone indicates optimal PT, light gray zone intermediate PT (neither optimal nor poor), dark gray zone poor PT. Degs = degrees.

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    Lumbar lordosis. Preoperative and postoperative LL differences between the successful and failed realignment groups.

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    Pelvic incidence. Preoperative PI differences between the successful and failed realignment groups.

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    Lumbar lordosis–pelvic incidence relationship. Preoperative and postoperative LL-PI differences between the successful and failed realignment groups. The white zone indicates optimal LL-PI, the light gray zone intermediate LL-PI (neither optimal nor poor), the dark gray zone poor LL-PI.


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