Elsevier

World Neurosurgery

Volume 104, August 2017, Pages 904-908.e1
World Neurosurgery

Original Article
A Novel Tool for Deformity Surgery Planning: Determining the Magnitude of Lordotic Correction Required to Achieve a Desired Sagittal Vertical Axis

https://doi.org/10.1016/j.wneu.2017.05.086Get rights and content

Objective

We sought to create a model capable of predicting the magnitude of pelvic incidence–lumbar lordosis (PI-LL) correction necessary to achieve a desired change in sagittal vertical axis (SVA).

Methods

A retrospective review was conducted of a prospectively maintained multicenter adult spinal deformity database collected by the International Spine Study Group between 2009 and 2014. The independent variable of interest was the degree of correction achieved in the PI-LL mismatch 6 weeks after surgery. Primary outcome was the change in global sagittal alignment 6 weeks and 1 year after surgery. We used a linear mixed-effects model to determine the extent to which corrections in the PI-LL relationship affected postoperative changes in SVA.

Results

A total of 1053 adult patients were identified. Of these patients, 590 were managed surgically. Eighty-seven surgically managed patients were excluded because of incomplete or missing PI-LL measurements on follow-up; the remaining 503 patients were selected for inclusion. For each degree of improvement in the PI-LL mismatch at 6 weeks, the SVA decreased by 2.18 mm (95% confidence interval, −2.56, −1.79; P < 0.01) and 1.67 mm (95% confidence interval, −2.07, −1.27; P < 0.01) at 6 weeks and 12 months, respectively. A high SVA measurement (>50 mm) 1 year after surgery was negatively associated with health-related quality of life as measured by the Scoliosis Research Society 22 outcomes assessment.

Conclusions

We describe a novel model that shows how surgical correction of the PI-LL relationship affects postoperative changes in SVA. This model may enable surgeons to determine preoperatively the amount of LL necessary to achieve a desired change in SVA.

Introduction

The spinal column, an essential component of the overall structural support necessary to maintain an upright posture, functions optimally when the head, shoulders, pelvis, and feet are aligned: an equilibrium termed sagittal alignment.1 Sagittal malalignment may occur because of spinal deformity: a common problem that often requires surgical intervention to improve quality of life and prevent disability.2 Postoperative measurements of the sagittal vertical axis (SVA) represent one way to assess the efficacy of deformity surgery; the typical benchmark of an effective deformity surgery is a postoperative SVA of <50 mm.3 However, SVA alone may underestimate global sagittal malalignment and should therefore be used in conjunction with measurements of pelvic tilt (PT), pelvic incidence (PI), and lumbar lordosis (LL) to determine the true extent of postoperative sagittal malalignment.4

Restoration of a normal SVA is the single most important factor in deformity surgery and positively correlates with major clinical outcomes.5 In most surgical cases, the relationship between PI and LL (PI-LL) is the primary parameter modified intraoperatively to achieve postoperative restoration of a proper SVA.6 For instance, patients with very large PIs require concomitantly large LLs to achieve optimal SVAs. Conversely, patients with low PIs have optimal SVAs with smaller LLs. Previous literature has described a goal PI-LL relationship of 10° to achieve an ideal SVA.7 Despite knowledge of this relationship, no model has been able to quantify the degree to which surgical modification of the PI-LL relationship affects subsequent SVA correction. Establishing such a model (one with the ability to predict the number of millimeters that the SVA changes for each degree of surgical correction of the PI-LL) may help surgeons plan the degree of PI-LL correction necessary to achieve a desired postoperative SVA.

Herein, we analyze a large, prospectively maintained database of adult patients with spinal deformity to create a model capable of estimating the magnitude of PI-LL correction needed to achieve a desired change in SVA.

Section snippets

Study Design and Population

A retrospective review was conducted in 2016 of a prospectively maintained multicenter adult spinal deformity database collected between 2009 and 2014. The database is composed of consecutively enrolled patients with adult spinal deformity (defined by age >18 years and at least 1 of the following: coronal Cobb angle >20°, SVA >50 mm, PT >25°, or thoracic kyphosis ≥60°) collected through the International Spine Study Group. This study was conducted in accordance with the amended Declaration of

Results

A total of 1053 adult patients were identified in the database (Figure 1). Of these patients, 463 did not undergo a surgical procedure and 87 had incomplete information on PI-LL measurement and were thus excluded. The remaining 503 patients are the focus of the present analysis.

The mean age of included patients was 57.0 years (SD, ± 15.4 years); 79.2% of these patients were male. The most common comorbidities at baseline were arthritis and major depression (Table 1). The mean SVA at baseline

Discussion

Even although depression, obesity, age, and smoking have all been identified as potential factors affecting clinically relevant outcomes after deformity surgery, the correction of the SVA remains the single most important determinant of HRQOL in these circumstances.5, 7, 8 However, outcomes after deformity surgery are highly variable, meaning that not all patients benefit from a full correction to a normal SVA of <5 cm. Therefore, surgeons must evaluate additional parameters such as PI-LL and

Conclusions

We report on a simple model that shows how changes in the PI-LL relation affect the SVA. Our model may allow surgeons to determine preoperatively how much LL is needed to achieve a desired SVA change after surgery. Further validation of our results, in the form of a prospective trial with a longer follow-up period and a patient population that includes patients with baseline spine deformity, remains warranted.

Acknowledgments

E.G. and F.A. were involved in the design and conception of the manuscript. E.G. and N.A. performed the literature search. E.G., F.A., and N.A. composed the primary manuscript. F.A. and N.A. compiled the tables and figures. B.F., P.C.G., A.S.K., D.O.O., P.P., J.S., T.P., V.L., R.L., F.S., S.B., C.A., and D.K.H. critically revised the manuscript. All authors have approved the manuscript as it is written.

References (13)

  • B.G. Diebo et al.

    Sagittal alignment of the spine: What do you need to know?

    Clin Neurol Neurosurg

    (2015)
  • K. Endo et al.

    Sagittal spinal alignment in patients with lumbar disc herniation

    Eur Spine J

    (2010)
  • F.J. Schwab et al.

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

    J Neurosurg Spine

    (2012)
  • B.J. Van Royen et al.

    Accuracy of the sagittal vertical axis in a standing lateral radiograph as a measurement of balance in spinal deformities

    Eur Spine J

    (1998)
  • Y.J. Kim et al.

    Results of lumbar pedicle subtraction osteotomies for fixed sagittal imbalance

    Spine (Phila Pa 1976)

    (2007)
  • J.S. Smith et al.

    Change in classification grade by the SRS-Schwab Adult Spinal Deformity Classification predicts impact on health-related quality of life measures: prospective analysis of operative and nonoperative treatment

    Spine (Phila Pa 1976)

    (2013)
There are more references available in the full text version of this article.

Cited by (3)

  • Adult spinal deformity

    2019, The Lancet
    Citation Excerpt :

    Several radiographical indices have been identified as pragmatic in determining patient-specific alignment targets for surgical planning.126 Work in risk stratification has augmented surgical planning to permit surgeons to identify surgically modifiable parameters to predict outcomes.127 However, other factors, such as age, should also be incorporated into planning, since Lafage and colleagues78 showed that older patients (mean age 53·7 years SD 16·4) might require less aggressive alignment goals than would younger patients.

Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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