Incidence and risk factors of iatrogenic coronal malalignment after adult spinal deformity surgery: a single-center experience

Scott L. Zuckerman Department of Orthopaedic Surgery, Columbia University Medical Center, The Och Spine Hospital at NewYork-Presbyterian, New York, New York; and
Department of Neurosurgery, Vanderbilt University Medical Center, Nashville, Tennessee

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Christopher S. Lai Department of Orthopaedic Surgery, Columbia University Medical Center, The Och Spine Hospital at NewYork-Presbyterian, New York, New York; and

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Yong Shen Department of Orthopaedic Surgery, Columbia University Medical Center, The Och Spine Hospital at NewYork-Presbyterian, New York, New York; and

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Nathan J. Lee Department of Orthopaedic Surgery, Columbia University Medical Center, The Och Spine Hospital at NewYork-Presbyterian, New York, New York; and

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Mena G. Kerolus Department of Orthopaedic Surgery, Columbia University Medical Center, The Och Spine Hospital at NewYork-Presbyterian, New York, New York; and

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Alex S. Ha Department of Orthopaedic Surgery, Columbia University Medical Center, The Och Spine Hospital at NewYork-Presbyterian, New York, New York; and

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Ian A. Buchanan Department of Orthopaedic Surgery, Columbia University Medical Center, The Och Spine Hospital at NewYork-Presbyterian, New York, New York; and

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Eric Leung Department of Orthopaedic Surgery, Columbia University Medical Center, The Och Spine Hospital at NewYork-Presbyterian, New York, New York; and

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Meghan Cerpa Department of Orthopaedic Surgery, Columbia University Medical Center, The Och Spine Hospital at NewYork-Presbyterian, New York, New York; and

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Ronald A. Lehman Department of Orthopaedic Surgery, Columbia University Medical Center, The Och Spine Hospital at NewYork-Presbyterian, New York, New York; and

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Lawrence G. Lenke Department of Orthopaedic Surgery, Columbia University Medical Center, The Och Spine Hospital at NewYork-Presbyterian, New York, New York; and

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OBJECTIVE

The authors’ objectives were: 1) to evaluate the incidence and risk factors of iatrogenic coronal malalignment (CM), and 2) to assess the outcomes of patients with all three types of postoperative CM (iatrogenic vs unchanged/worsened vs improved but persistent).

METHODS

A single-institution, retrospective cohort study was performed on adult spinal deformity (ASD) patients who underwent > 6-level fusion from 2015 to 2019. Iatrogenic CM was defined as immediate postoperative C7 coronal vertical axis (CVA) ≥ 3 cm in patients with preoperative CVA < 3 cm. Additional subcategories of postoperative CM were unchanged/worsened CM, which was defined as immediate postoperative CVA within 0.5 cm of or worse than preoperative CVA, and improved but persistent CM, which was defined as immediate postoperative CVA that was at least 0.5 cm better than preoperative CVA but still ≥ 3 cm; both groups included only patients with preoperative CM. Immediate postoperative radiographs were obtained when the patient was discharged from the hospital after surgery. Demographic, radiographic, and operative variables were collected. Outcomes included major complications, readmissions, reoperations, and patient-reported outcomes (PROs). The t-test, Kruskal-Wallis test, and univariate logistic regression were performed for statistical analysis.

RESULTS

In this study, 243 patients were included, and the mean ± SD age was 49.3 ± 18.3 years and the mean number of instrumented levels was 13.5 ± 3.9. The mean preoperative CVA was 2.9 ± 2.7 cm. Of 153/243 patients without preoperative CM (CVA < 3 cm), 13/153 (8.5%) had postoperative iatrogenic CM. In total, 43/243 patients (17.7%) had postoperative CM: iatrogenic CM (13/43 [30.2%]), unchanged/worsened CM (19/43 [44.2%]), and improved but persistent CM (11/43 [25.6%]). Significant risk factors associated with iatrogenic CM were anxiety/depression (OR 3.54, p = 0.04), greater preoperative sagittal vertical axis (SVA) (OR 1.13, p = 0.007), greater preoperative pelvic obliquity (OR 1.41, p = 0.019), lumbosacral fractional (LSF) curve concavity to the same side of the CVA (OR 11.67, p = 0.020), maximum Cobb concavity opposite the CVA (OR 3.85, p = 0.048), and three-column osteotomy (OR 4.34, p = 0.028). In total, 12/13 (92%) iatrogenic CM patients had an LSF curve concavity to the same side as the CVA. Among iatrogenic CM patients, mean pelvic obliquity was 3.1°, 4 (31%) patients had pelvic obliquity > 3°, mean preoperative absolute SVA was 8.0 cm, and 7 (54%) patients had preoperative sagittal malalignment. Patients with iatrogenic CM were more likely to sustain a major complication during the 2-year postoperative period than patients without iatrogenic CM (12% vs 33%, p = 0.046), yet readmission, reoperation, and PROs were similar.

CONCLUSIONS

Postoperative iatrogenic CM occurred in 9% of ASD patients with preoperative normal coronal alignment (CVA < 3 cm). ASD patients who were most at risk for iatrogenic CM included those with preoperative sagittal malalignment, increased pelvic obliquity, LSF curve concavity to the same side as the CVA, and maximum Cobb angle concavity opposite the CVA, as well as those who underwent a three-column osteotomy. Despite sustaining more major complications, iatrogenic CM patients did not have increased risk of readmission, reoperation, or worse PROs.

ABBREVIATIONS

ASD = adult spinal deformity; BMI = body mass index; C7PL = C7 plumb line; CM = coronal malalignment; CVA = coronal vertical axis; EBL = estimated blood loss; LSF = lumbosacral fractional; ODI = Oswestry Disability Index; PRO = patient-reported outcome; SM = sagittal malalignment; SRS-22r = Scoliosis Research Society–22r; SVA = sagittal vertical axis.

OBJECTIVE

The authors’ objectives were: 1) to evaluate the incidence and risk factors of iatrogenic coronal malalignment (CM), and 2) to assess the outcomes of patients with all three types of postoperative CM (iatrogenic vs unchanged/worsened vs improved but persistent).

METHODS

A single-institution, retrospective cohort study was performed on adult spinal deformity (ASD) patients who underwent > 6-level fusion from 2015 to 2019. Iatrogenic CM was defined as immediate postoperative C7 coronal vertical axis (CVA) ≥ 3 cm in patients with preoperative CVA < 3 cm. Additional subcategories of postoperative CM were unchanged/worsened CM, which was defined as immediate postoperative CVA within 0.5 cm of or worse than preoperative CVA, and improved but persistent CM, which was defined as immediate postoperative CVA that was at least 0.5 cm better than preoperative CVA but still ≥ 3 cm; both groups included only patients with preoperative CM. Immediate postoperative radiographs were obtained when the patient was discharged from the hospital after surgery. Demographic, radiographic, and operative variables were collected. Outcomes included major complications, readmissions, reoperations, and patient-reported outcomes (PROs). The t-test, Kruskal-Wallis test, and univariate logistic regression were performed for statistical analysis.

RESULTS

In this study, 243 patients were included, and the mean ± SD age was 49.3 ± 18.3 years and the mean number of instrumented levels was 13.5 ± 3.9. The mean preoperative CVA was 2.9 ± 2.7 cm. Of 153/243 patients without preoperative CM (CVA < 3 cm), 13/153 (8.5%) had postoperative iatrogenic CM. In total, 43/243 patients (17.7%) had postoperative CM: iatrogenic CM (13/43 [30.2%]), unchanged/worsened CM (19/43 [44.2%]), and improved but persistent CM (11/43 [25.6%]). Significant risk factors associated with iatrogenic CM were anxiety/depression (OR 3.54, p = 0.04), greater preoperative sagittal vertical axis (SVA) (OR 1.13, p = 0.007), greater preoperative pelvic obliquity (OR 1.41, p = 0.019), lumbosacral fractional (LSF) curve concavity to the same side of the CVA (OR 11.67, p = 0.020), maximum Cobb concavity opposite the CVA (OR 3.85, p = 0.048), and three-column osteotomy (OR 4.34, p = 0.028). In total, 12/13 (92%) iatrogenic CM patients had an LSF curve concavity to the same side as the CVA. Among iatrogenic CM patients, mean pelvic obliquity was 3.1°, 4 (31%) patients had pelvic obliquity > 3°, mean preoperative absolute SVA was 8.0 cm, and 7 (54%) patients had preoperative sagittal malalignment. Patients with iatrogenic CM were more likely to sustain a major complication during the 2-year postoperative period than patients without iatrogenic CM (12% vs 33%, p = 0.046), yet readmission, reoperation, and PROs were similar.

CONCLUSIONS

Postoperative iatrogenic CM occurred in 9% of ASD patients with preoperative normal coronal alignment (CVA < 3 cm). ASD patients who were most at risk for iatrogenic CM included those with preoperative sagittal malalignment, increased pelvic obliquity, LSF curve concavity to the same side as the CVA, and maximum Cobb angle concavity opposite the CVA, as well as those who underwent a three-column osteotomy. Despite sustaining more major complications, iatrogenic CM patients did not have increased risk of readmission, reoperation, or worse PROs.

In Brief

The objectives of this study were to 1) evaluate the incidence and risk factors of iatrogenic coronal malalignment (CM) and the outcomes of patients with CM, and 2) to assess the outcomes of patients with all three types of postoperative CM. Postoperative iatrogenic CM occurred in 9% of ASD patients with preoperative normal coronal alignment (coronal vertical axis < 3 cm). Clinicians can use these findings to predict which patients are likely to see continued improvements in alignment, as evidenced by radiologic correction, and to help manage patient's expectations of postoperative recovery.

Postoperative coronal malalignment (CM) after surgery for adult spinal deformity (ASD) has gained attention in recent years and has been associated with unsatisfactory patient-reported outcomes (PROs) and increased rates of revision surgery.1–4 Previous thresholds to define CM include coronal vertical axis (CVA) measurements of 2 cm,2,4 3 cm,1,5,6 4 cm,3,7–9 and even 5 cm,10 yet most prior studies use a threshold value of 3 cm.3,11,12 Rates of postoperative CM can be as high as 40%,1,3 and some studies report higher rates of postoperative CM than preoperative CM.13 Risk factors for postoperative CM include preoperative CM,1 osteoporosis,3 anterior approach surgery,3 L4–5 tilt,4 and maximum Cobb angle to the opposite side of global balance.1 Postoperative CM most commonly occurs when coronal alignment is undercorrected or worsens for various reasons, including a rigid lumbosacral fractional (LSF) curve, prior fused spinal segments, or concomitant sagittal malalignment (SM). However, it is possible to induce CM in patients with normal preoperative coronal alignment.

Iatrogenic CM is defined as postoperative CM (CVA ≥ 3 cm) in patients with normal preoperative coronal alignment (CVA < 3 cm). Rates of iatrogenic CM are sparsely reported but have been described to be 0%,14 21%,3 and 24%.1 Several studies do not report rates of iatrogenic CM,2,4,13 though in fairness, this may be due in part to not dichotomizing the continuous variable of CVA. Iatrogenic CM is not often specifically studied, likely owing to small sample sizes.1,15 The few previous studies that report rates of iatrogenic CM often limit any analysis to a small portion of the Results section, without significant discussion.1,3,5 Moreover, several other types of postoperative CM exist, such as improved but persistent CM and worsened CM in the setting of known preoperative CM.

Due to the potential for reoperation and creation of a new deformity, we believe that the topic of iatrogenic CM and worsened coronal alignment after ASD surgery warrants in-depth study. In a cohort of ASD patients who underwent corrective surgery, we sought to address the following objectives: 1) to evaluate the incidence and risk factors of iatrogenic CM, and 2) to assess the outcomes of patients with all three types of postoperative CM (iatrogenic vs unchanged/worsened vs improved but persistent).

Methods

Study Design

This retrospective cohort study was based on data that were prospectively collected by a single institution from patients treated by two spine deformity surgeons (L.G.L. and R.A.L.). After institutional review board approval, data were collected on all ASD patients who underwent posterior ASD surgery between June 1, 2015, and December 31, 2019.

Patient Population

Preoperative enrollment criteria were similar to those of prior studies of ASD patients.16,17 The inclusion criteria were age > 18 years when instrumented fusion with ≥ 6 levels was performed and at least one of the following radiographic criteria: Cobb angle > 30°, sagittal vertical axis (SVA) > 5 cm, CVA > 3 cm, pelvic tilt > 25°, or thoracic kyphosis > 60°. Importantly, to calculate the true incidence of iatrogenic CM, only patients with preoperative CVA < 3 cm and no preoperative CM were included in the analysis of iatrogenic CM. All patients underwent standing, full-body or full-spine, low-dose stereoradiography (EOS imaging) at the following time points: before surgery, immediately after surgery when the patient was discharged from the hospital, 1 year after surgery, and 2 years after surgery.

Independent Variables

Demographic and perioperative variables were collected, including age, sex, body mass index (BMI), diagnosis, primary versus revision surgery, preoperative alignment status, total instrumented levels, three-column osteotomy, operative time, estimated blood loss (EBL), length of stay, fusion to sacrum with pelvic instrumentation, major complications, and reoperations.

Several preoperative radiographic variables were collected to determine their importance to predicting postoperative CM. To measure global alignment, both CVA and SVA were measured in centimeters. CVA was measured by determining the distance between the coronal C7 plumb line (C7PL) (a vertical line dropped from the middle of the C7 vertebral body) and the central sacral vertical line (a vertical line that passes through the center of the sacrum).18 Similarly, SVA is the distance from the sagittal C7PL (a vertical line drawn from the middle of the C7 body) and the posterior superior aspect of the S1 vertebral body.18 Although CVA to the left is considered negative and CVA to the right is positive, absolute values were used given the lack of clinical difference between left- and right-sided CVA. In accordance with prior studies, CM was defined as CVA ≥ 3 cm.3,11,12 Additional radiographic variables included pelvic obliquity (the angle between the line from the superior iliac crest and the horizontal reference line) and leg-length discrepancy (difference in the lengths from the femoral head to tibial plafond between the right and left legs).

Directionality of Coronal Measurements

Directionality of the maximum Cobb angle, LSF curve, and CVA were also recorded. The maximum Cobb angle was the maximum coronal curve of the following four curves: LSF curve, thoracolumbar curve, main thoracic curve, and proximal thoracic curve. LSF curve was defined as the angle between the sacrum and distal lumbar spine, which was L3, L4, or L5 depending on alignment. The previously published Qiu classification was used to assess directionality,1 which categorized CM into three groups on the basis of CVA as follows: type A, CVA ≤ 3 cm; type B, CVA > 3 cm and C7PL shifted to the concave side of the major curve; and type C, CVA > 3 cm and C7PL shifted to the convex side of the major curve.1 In addition, because the Qiu classification does not differentiate curves with CVA < 3 cm or differentiate between LSF curve and maximum Cobb angle, the directionality of both curves in relation to each other and to the CVA was taken into account for two binary variables: LSF curve concavity to the same side as CVA (yes or no) and maximum Cobb angle concavity opposite the CVA (yes or no).

Definitions of Different Types of Postoperative CM

Three groups were defined a priori to capture all forms of postoperative CM. All radiographs were obtained on the day of discharge from index hospitalization, which was mean postoperative day 8. 1) Iatrogenic CM required an immediate postoperative CVA ≥ 3 cm in patients with preoperative normal alignment (CVA < 3 cm). This group was drawn from only patients with no evidence of preoperative CM; by definition, it is impossible to create new iatrogenic CM if CM had already existed preoperatively. 2) Unchanged or worsened CM required an immediate postoperative CVA that was within 0.5 cm of or worse than preoperative CVA. This group consisted of only patients with preoperative CM. 3) Improved but persistent CM required an immediate postoperative CVA that was at least 0.5 cm better than preoperative CVA but still ≥ 3 cm. This group consisted of only patients with preoperative CM. Of note, the patients with unchanged or worsened CVA were combined into a single group owing to small sample size. Only 6 patients with CM had unchanged CVA, whereas the remaining 13 patients had CVA that worsened.

Primary and Secondary Outcomes

For the first analysis, the primary outcome of interest was iatrogenic CM, as defined above. Secondary outcomes included medical/surgical complications and PROs. The three medical/surgical complications were 1) presence of a major complication through 2 years postoperation, in accordance with a prior study;19 2) hospital readmission within 2 years or more after surgery; and 3) reoperation for revision spine surgery within 2 years or more after surgery. Revision spine surgery was performed owing to a major complication that included deep surgical site infection, pseudarthrosis, rod fracture, or worsening alignment. The two PRO variables used were scores on the 1) Oswestry Disability Index (ODI) version 2.1a20,21 and 2) Scoliosis Research Society–22r (SRS-22r) instrument.22 ODI gives a single score, with higher values corresponding to worse function. SRS-22r gives a total score and several subdomains that are rated 1–5, with lower values corresponding to worse function. Determined a priori on the basis of clinical relevance, the included SRS-22r subdomains were function, appearance, and pain. PROs were analyzed according to group values.

Statistical Analysis

Descriptive statistics were used to summarize patient demographic characteristics and radiographic data. Categorical data were presented as frequencies and percentages, whereas continuous data were presented as mean ± SD. Univariate logistic regression was used to determine the factors associated with the primary outcome of interest, i.e., iatrogenic CM. To determine differences between PROs, the Wilcoxon rank-sum test was used for continuous data (mean PRO values) and the chi-square proportion test was used for count data. Statistical significance was set at an alpha level < 0.05. All statistical analyses were performed with Stata version 14 (StataCorp LP).23

Results

Demographic Characteristics

A total of 243 patients underwent ASD surgery, and 153 (63%) patients had normal preoperative coronal alignment (CVA < 3 cm). The demographic and perioperative variables of all 153 patients are summarized in Table 1. The mean ± SD age was 49.3 ± 18.3 years, and mean number of instrumented levels was 13.5 ± 3.9. The mean preoperative CVA was 2.9 ± 2.7 cm. Preoperative alignment was neutral (CVA < 3 cm and SVA < 5 cm) in 115 (47%) patients, CM only (CVA ≥ 3 cm and SVA < 5 cm) in 48 (20%), SM only (CVA < 3 cm and SVA ≥ 5 cm) in 38 (16%), and combined CM/SM (both CVA ≥ 3 cm and SVA ≥ 5 cm) in 42 (17%). A total of 90 patients (37%) had preoperative CM.

TABLE 1.

Demographic, radiographic, and perioperative data of all 243 ASD patients who underwent spinal reconstruction, and bivariate analysis of patients with normal preoperative coronal alignment (CVA < 3 cm) and iatrogenic CM versus those without CM

VariableEntire Cohort (n = 243)Iatrogenic CMp Value
No (n = 140)Yes (n = 13)
Age, yrs49.3 ± 18.348.5 ± 18.752.8 ± 21.70.436
Female163 (67)92 (66)8 (62)0.762
ASA
 I25 (10)18 (13)1 (8)
 II150 (62)86 (61)6 (46)
 III68 (28)37 (26)6 (46)
BMI, kg/m225.5 ± 5.725.3 ± 6.124.1 ± 3.90.492
Depression48 (20)21 (15)5 (38)0.031*
Scoliosis diagnosis0.608
 Adult idiopathic121 (50)75 (54)6 (46)
 Degenerative122 (50)65 (46)7 (54)
Qiu classification0.011*
 Type A153 (63)31 (22)7 (54)
 Type B53 (22)
 Type C37 (15)
Revision surgery150 (62)91 (65)8 (62)0.803
Preop CVA, cm2.9 ± 2.7 (0.1 to 19.7)1.3 ± 0.7 (0.1 to 2.9)1.6 ± 0.9 (0.6 to 2.9)0.182
Preop SVA, cm3.7 ± 6.8 (−8.8 to 26.1)1.7 ± 5.5 (−8.8 to 18.6)6.3 ± 9.1 (−4.5 to 24.8)0.003*
Max Cobb angle, °43.0 ± 26.5 (0.0 to 134.3)40.3 ± 25.7 (0.0 to 131.7)38.3 ± 27.0 (5.2 to 88.3)0.790
LSF curve, °12.1 ± 9.9 (0.2–62.3)11.0 ± 9.610.4 ± 9.20.829
Pelvic obliquity, °2.3 ± 2.4 (0–22.1)1.9 ± 1.53.2 ± 2.70.012*
Total instrumented levels13.5 ± 3.913.2 ± 3.911.3 ± 3.50.112
Pelvic instrumentation172 (71)13 (9)4 (31)0.018*
3-column osteotomy35 (14)89 (63.6)7 (53.9)0.488
Op time, min471.0 ± 133.9439.9 ± 115.4435.8 ± 143.30.907
EBL, ml1315.8 ± 786.61124.5 ± 602.21080.8 ± 644.70.804
Length of stay, days8.0 ± 7.97.5 ± 8.28.5 ± 5.70.692
Major complication41 (17)37 (26)4 (31)0.721
Readmission38 (16)35 (25)3 (23)0.917
Reop34 (14)31 (22)3 (23)0.905

ASA = American Society of Anesthesiologists Physical Status Classification.

Values are shown as number (percent), mean ± SD, or mean ± SD (range) unless indicated otherwise.

Statistically significant (p < 0.05).

Regarding preoperative Qiu classification, type A was noted in 63% of patients, type B in 22%, and type C in 15%. With respect to the LSF curve and maximum Cobb angle, 42 (17%) patients had LSF curve concavity and maximum Cobb angle concavity to the same side. With respect to overall CVA and global coronal alignment, 130 (54%) patients had their LSF curve concavity to the same side as the CVA, and 121 (50%) patients had the maximum Cobb angle concavity to the same side as the CVA.

Operatively, all but 2 patients underwent a posterior-only approach, and both of these patients underwent an oblique prepsoas approach for lumbar interbody cage placement. Moreover, for each patient, intraoperative long-cassette films were obtained and coronal alignment was adjusted accordingly. Radiographs were used to image the spine from the skull to the femoral heads, and if CM persisted, compression/distraction maneuvers were performed or a kickstand rod was placed. The mean ± SD (range) number of posterior-column osteotomies per patient was 4.8 ± 3.1 (0–14). Transforaminal lumbar interbody fusion was performed on 111 (46%) patients.

Classification of Postoperative CM

A total of 43 patients (18%) had postoperative CM. Of these 43 patients, the types of postoperative CM were iatrogenic (13 patients [30%]), unchanged or worsened CM (19 [44%]), and improved but persistent CM (11 [26%]). Figure 1 summarizes all three types of postoperative CM.

FIG. 1.
FIG. 1.

Three types of postoperative CM. Figure is available in color online only.

Iatrogenic CM

Among the 153 patients with no preoperative CM and CVA < 3 cm, 13 (9%) patients had iatrogenic CM. Preoperatively, patients with iatrogenic CM were more likely to have depression (p = 0.031), SM (p = 0.011), increased preoperative SVA (p = 0.003), and increased pelvic obliquity (p = 0.012), and they were more likely to undergo three-column osteotomy (p = 0.018) (Table 1). In terms of medical/surgical complications and PROs, patients with iatrogenic CM were more likely to sustain a major complication during the 2-year postoperative period than patients without iatrogenic CM (12% vs 33%, p = 0.046), yet the readmission and reoperation rates were similar (Table 2). The mean 1-year and 2-year PROs were similar between groups (Table 2).

TABLE 2.

Medical/surgical outcomes and PROs at 1 and 2 years in patients with normal preoperative coronal alignment (CVA < 3 cm) and iatrogenic CM versus those without CM

OutcomePostop Iatrogenic CMp Value*
No (n = 140)Yes (n = 13)
Medical/surgical
 Complication (n = 174)17 (12)4 (33)0.046
 Readmission (n = 174)18 (13)3 (23)0.261
 Reoperation (n = 174)15 (11)3 (23)0.154
PRO
 1 yr949
  ODI16.7 ± 17.918.2 ± 15.00.550
  SRS-22r
   Total89.7 ± 13.086.0 ± 13.80.506
   Appearance4.3 ± 0.74.2 ± 0.60.514
   Function4.1 ± 0.83.7 ± 0.80.189
   Pain3.9 ± 0.93.8 ± 0.70.154
 2 yrs506
  ODI14.2 ± 16.817 ± 13.50.696
  SRS-22r
   Total87.9 ± 14.985.4 ± 16.50.735
   Appearance4.0 ± 0.83.4 ± 0.60.143
   Function4.1 ± 0.73.7 ± 0.70.302
   Pain3.7 ± 0.93.9 ± 0.90.706

Values are shown as number, number (percent), or mean ± SD unless indicated otherwise.

The Wilcoxon rank-sum test was used to evaluate continuous data, and the chi-square test was used to evaluate count data.

The assessment of risk factors for iatrogenic CM revealed 6 significant risk factors (Table 3). These risk factors were anxiety/depression (OR 3.54, 95% CI 1.06–11.87, p = 0.040), greater preoperative SVA (OR 1.13, 95% CI 1.03–1.23, p = 0.007), greater preoperative pelvic obliquity (OR 1.41, 95% CI 1.06–1.87, p = 0.019), LSF curve concavity to the same side as CVA (OR 11.67, 95% CI 1.48–92.12, p = 0.020), maximum Cobb concavity opposite the CVA (OR 3.85, 95% CI 1.01–14.58, p = 0.048), and three-column osteotomy (OR 4.34, 95% CI 1.17–16.07, p = 0.028). A representative case that captures all relevant risk factors for iatrogenic CM is presented in Fig. 2. Given the importance of preoperative SM in predicting iatrogenic CM, we performed a subsequent analysis to determine whether amount of sagittal correction was associated with iatrogenic CM. Somewhat counterintuitively, sagittal correction was not associated with iatrogenic CM (OR 1.11, 95% CI 0.99–1.40, p = 0.375).

TABLE 3.

Univariate logistic regression analysis of risk factors of iatrogenic CM in patients with only normal preoperative coronal alignment (CVA < 3 cm)

FactorOR (95% CI)p Value
Demographic
 Age1.01 (0.98 to 1.05)0.436
 BMI0.96 (0.85 to 1.08)0.487
 Revision0.86 (0.27 to 2.88)0.803
 Anxiety/depression3.54 (1.06 to 11.87)0.040*
Preop radiographic
 CVA1.66 (0.78 to 3.50)0.186
 SVA1.13 (1.03 to 1.23)0.007*
 Max Cobb angle1.00 (0.97 to 1.02)0.789
 LSF curve0.99 (0.93 to 1.06)0.827
 L4 tilt0.98 (0.91 to 1.07)0.662
 L5 tilt0.95 (0.83 to 1.09)0.471
 Pelvic obliquity1.41 (1.06 to 1.87)0.019*
 Leg-length discrepancy1.03 (0.22 to 4.92)0.969
Preop directionality
 LSF curve concavity to same side as CVA11.67 (1.48 to 92.12)0.020*
 Max Cobb concavity opposite of CVA3.85 (1.01 to 14.58)0.048*
Op
 Total instrumented levels0.88 (−0.75 to 1.03)0.115
 3-column osteotomy4.34 (1.17 to 16.07)0.028*
 Transforaminal lumbar interbody fusion0.95 (0.43 to 2.06)0.886
 Durotomy0.50 (0.06 to 4.06)0.517
 EBL0.99 (0.89 to 1.09)0.802
 Op time0.98 (0.74 to 1.32)0.906
 Fusion to sacrum0.67 (0.21 to 2.1)0.490

Statistically significant (p < 0.05).

FIG. 2.
FIG. 2.

Radiographs obtained from a patient with all significant risk factors for iatrogenic CM, including pelvic obliquity, large preoperative SVA, LSF curve concavity to the same side as the CVA, and maximum Cobb concavity opposite the CVA (A and B); all these risk factors were present in the setting of normal preoperative coronal alignment. Postoperative iatrogenic CM was seen at 3.2° with a corrected SVA of 0.9 cm (C and D). Figure is available in color online only.

We summarized our in-depth review of all 13 patients with postoperative iatrogenic CM (Table 4). Twelve of these 13 patients (92%) had an LSF curve that was to the same side as the CVA despite normal CVA. Mean pelvic obliquity was 3.2° among patients with iatrogenic CM, and 4 (31%) of these patients had a pelvic obliquity greater than 3°. Furthermore, the mean preoperative absolute SVA was 8.0 cm, and 7 (54%) patients had preoperative SM. Additional representative cases of iatrogenic CM and their curve characteristics are summarized in Fig. 3. Importantly, of the 13 patients with iatrogenic CM in the immediate postoperative period, several (7/13 [54%]) had improved CVA during the postoperative follow-up period of 2 years. Thus, immediate postoperative imaging may not reflect long-term alignment, and correction may occur as alignment and muscles settle. Importantly, of all patients with iatrogenic CM, 3 (23%) underwent revision surgery, but this was not performed specifically to correct their iatrogenic CM. One patient had pseudarthrosis in the middle of their construct, 1 had perioperative quadriceps weakness requiring decompression shortly after surgery, and 1 had proximal junctional failure requiring extension to C5.

TABLE 4.

Patients with iatrogenic CM

Patient No.Age/SexDiagnosisQiu TypeCVA (cm)Max Cobb Angle (°)LSF Curve (°)SVA (cm)Curve Type
PreopPostopPreopPostopPreopPostopPreopPostop
158/FAdISA−1.5−5.877.233.932.910.7−2.03.4LSF curve to lt, TL curve to rt, & CVA to lt
229/FDLSA−1.0−3.242.511.918.713.7−2.6−0.9LSF curve to lt, TL curve to rt, & CVA slightly to lt
363/FDLSA−0.8−3.277.834.916.57.99.50.9LSF curve to lt, TL curve to rt, MT curve to lt, & CVA to lt
418/MAdISA2.75.827.35.59.13.45.56.2LSF curve to rt, small TL curve to lt, & CVA to rt
558/FAdISA−2.2−4.588.330.38.54.20.7−1.2Small LSF curve to lt, large TL curve to rt, large MT curve to lt, & CVA to lt
679/FDLSA−0.6−3.821.35.86.25.73.57.3Small LSF curve to lt, TL curve to lt, & CVA to lt
726/FAdISA−2.9−3.916.611.55.81.77.3−1.1Small LSF curve to lt, MT curve to lt, & CVA to lt
876/MAdISA−0.63.230.914.61.11.1−4.5−0.5No LSF curve, PT curve to rt, & CVA slightly to lt
964/MDLSA1.03.85.27.60.00.06.83.4No LSF curve, long & small MT curve to rt, & CVA to rt
1066/FAdISA2.74.915.92.70.42.124.810.6Small LSF curve to lt, small MT curve to rt, & CVA to rt
1167/FDLSA2.04.947.49.04.11.7−1.71.1LSF curve to rt, TL curve to lt, & CVA to rt
1257/MDLSA0.64.031.713.316.33.714.014.7LSF curve to rt, TL curve to lt, & CVA to rt
1319/FAdISA2.64.315.820.05.68.920.80.9No LSF curve, PT curve to rt, & CVA to rt

AdIS = adult idiopathic scoliosis; DLS = degenerative lumbar scoliosis; MT = main thoracic; PT = proximal thoracic; TL = thoracolumbar.

FIG. 3.
FIG. 3.

Radiographs obtained from a patient with several risk factors for iatrogenic CM, including LSF curve concavity to the same side of the CVA and maximum Cobb angle concavity to the opposite side of the CVA (A and B). Iatrogenic CM was seen with worsened CVA to −5.8 cm (C and D). Figure is available in color online only.

Comparison of Outcomes Among Patients With All Types of Postoperative CM

The outcomes of all patients with postoperative CM were compared in Table 5. No significant differences were seen in the rates of major complications, readmission, or reoperation. Moreover, PROs at 1 year and 2 years were similar among all three groups (Table 5). However, due to loss to follow-up and the subdivision of an already small cohort, the sample sizes were admittedly small for PROs.

TABLE 5.

Medical/surgical outcomes and PROs at 1 and 2 years for patients with all three types of postoperative CM

OutcomeIatrogenic CM (n = 13)Unchanged or Worsened CM (n = 19)Improved but Persistent CM (n = 11)p Value*
Medical/surgical131911
 Major complication (n = 174)4 (31)7 (37)2 (19)0.554
 Readmission (n = 174)3 (23)2 (11)1 (9)0.452
 Reoperation (n = 174)3 (23)2 (11)1 (9)0.452
PROs
 1 yr997
  ODI18 ± 1516 ± 1723 ± 200.615
  SRS-22r
   Total86 ± 1489 ± 1877 ± 130.227
   Appearance4.2 ± 0.64.0 ± 0.63.4 ± 0.60.170
   Function3.7 ± 0.83.9 ± 0.83.1 ± 0.70.211
   Pain3.8 ± 0.73.9 ± 1.43.1 ± 1.20.435
 2 yrs654
  ODI17 ± 1415 ± 1722 ± 210.832
  SRS-22r
   Total85 ± 1792 ± 1779 ± 320.575
   Appearance3.4 ± 0.63.9 ± 0.63.5 ± 0.30.417
   Function3.7 ± 0.74.2 ± 0.62.7 ± 1.80.202
   Pain3.7 ± 0.93.8 ± 1.42.7 ± 1.80.448

Values are shown as number, number (percent), or mean ± SD unless indicated otherwise.

Determined with the Kruskal-Wallis test.

Discussion

In a population of ASD patients who underwent spinal reconstruction, we sought to further study iatrogenic CM and compare outcomes between patients with three different types of postoperative CM. Among those with normal preoperative alignment, iatrogenic CM occurred in 9% of patients. Significant risk factors for iatrogenic CM were increased preoperative SVA, increased pelvic obliquity, LSF curve concavity to the same side as the CVA, maximum Cobb angle concavity opposite the CVA, and three-column osteotomy. Patients with iatrogenic CM were also more likely to sustain a major complication, although no difference was seen in the rates of readmission, reoperation, or PROs. In the comparison to patients with all three types of postoperative CM, no difference was seen in medical/surgical outcomes or PROs. Taken together, these results put forth a clear phenotype of ASD patients who are most at risk for iatrogenic CM: patients with normal coronal alignment, increased pelvic obliquity, severe SM, LSF curve concavity to the same side of the CVA, and maximum Cobb angle concavity opposite the CVA who have undergone three-column osteotomy.

The incidence of iatrogenic CM in our cohort was 9% among patients with normal preoperative coronal alignment (CVA < 3 cm), which appears to be on the lower end of reported values (range 0%–24%).1,3,14 In a study by Bao et al.,1 10 of 42 (24%) patients with type A curve had iatrogenic CM. Interestingly, the average number of fused levels was 9.7 and pelvic fixation was performed on 26% of patients; these values are lower than our mean total number of instrumented levels of 13.5 and 71% of patients who underwent pelvic fixation. Ploumis et al.3 reported that 9 of 43 (21%) patients with type A curve had iatrogenic CM. In 42 patients who underwent circumferential minimally invasive surgery, Walker and colleagues14 reported that 0% of 26 patients with type A curve had postoperative CM. However, given the minimally invasive nature of the intervention, the surgical population was not surprisingly different, with a mean number of fused segments of 4.9 and a prior fusion surgery rate of 14%, compared with our number of fused segments of 13.5 and revision surgery rate of 62%. Unfortunately, other studies have not reported rates of iatrogenic CM,2,4,13 which may in part be due to not dichotomizing the continuous CVA variable and small cohort sizes.24

Regarding directionality, our results build on prior studies while also offering new insights into the previous finding that patients with type C curve are most at risk for postoperative CM. Specifically, our findings indicate that 1) type A patients (with normal CVA < 3 cm) with similar curve characteristics to those of type C patients may be at risk for iatrogenic CM, and 2) evaluation of the directionality of LSF and major curve concavities in tandem may portend risk of iatrogenic CM. Previous studies have shown that type C patients are the most at risk for postoperative CM;1,14 however, type C patients do not have normal preoperative alignment (CVA < 3 cm). Our results showed that even type A patients with similar curve characteristics to those of type C patients had increased risk of iatrogenic CM. Even in patients with CVA < 3 cm (and < 1 cm in many patients), large LSF curve concavity to the same side of the CVA and maximum Cobb angle concavity opposite the CVA were both risk factors of iatrogenic CM. Furthermore, greater preoperative pelvic obliquity was also a risk factor for iatrogenic CM, which further indicates the presence of coronal plane abnormalities despite normal CVA. Taken together, directionality of LSF curve concavity and major curve concavity with respect to the CVA—even when CVA is small—may lead to increased risk of postoperative CM.

The novel risk factor associated with iatrogenic CM was increased preoperative SVA causing SM, which often necessitated three-column osteotomy. Sagittal plane correction is rarely mentioned, and almost never the focus of the analysis, in the recent wave of research focused on postoperative CM.2,3,5,13,15,25–27 Bao et al.1 found that patients with postoperative CM also had greater postoperative SVA than those without postoperative CM (4.3 cm vs 15.2 cm, p = 0.027), yet preoperative SVA was not mentioned. Lewis et al.4 found slightly decreased SVA in 14 patients with postoperative CM compared with that of 32 patients without postoperative CM (7.4 vs 8.6 cm, p = 0.54), though it is unknown if these 14 patients had iatrogenic or persistent CM. In a comparison between 9 patients with postoperative CM and 45 patients without, Ploumis et al.3 found slightly greater SVA among those with postoperative CM (9.2 cm vs 8.3 cm); however, this was not in an exclusively iatrogenic CM population either. Additional studies do not mention preoperative sagittal alignment based on postoperative or iatrogenic CM.2,13 To our knowledge, the additional new finding of preoperative SM as a risk factor for iatrogenic CM has not previously been reported. In patients with only preoperative SM and without CM, it is understandable why less attention may be paid to the coronal plane, especially when performing three-column osteotomy for sagittal correction. These results suggest that, in patients with only SM, close attention should be paid to the LSF curve concavity and how any three-column osteotomies are performed, even if the only objective is sagittal plane correction. It appears that, even when coronal alignment is normal, powerful osteotomies meant for sagittal correction may cause three-dimensional alignment changes in the wrong direction.

Whether or not iatrogenic CM—or any type of CM—had an impact on postoperative outcomes appears to be less clear. The one significant finding of iatrogenic CM was its association with the rate of major complications, yet no differences were seen in the rates of readmission, reoperation, or PROs. The studies included in the existing literature report mixed results, and importantly, these studies considered all types of postoperative CM and did not specifically evaluate iatrogenic CM. Tanaka and colleagues2 showed that postoperative CM had no impact on ODI or Roland-Morris Disability Questionnaire scores, despite its association with rod factures. Bao et al.1 reported no difference in ODI scores between patients with and without postoperative CM, yet CM patients had decreased SF-12 and visual analog scale scores. Walker et al.14 recently showed that type C patients with CM had worse visual analog scale scores for back pain at 1 year compared with those of patients without CM (5 vs 1, p = 0.01). Our study showed no differences in PROs between iatrogenic CM patients and those with the three types of postoperative CM. In a similar study by Daubs et al. of 85 ASD patients with CVA > 4 cm,7 sagittal alignment improvement was the strongest predictor of improved PROs, even in patients with caudal cervical spondylomyelopathy. Moreover, in patients with only CM, the authors reported a nonsignificant trend of improvement in PROs (p = 0.092). The impact of postoperative CM, and especially iatrogenic CM, remains an active area of study. Lastly, our results showed that many iatrogenic CM patients achieved correction at 2 years, which further complicates the study and questions the significance of postoperative CM. However, these findings may be useful during postoperative counseling at discharge for patients with iatrogenic CM. We can use these findings to predict which patients are likely to see continued improvements in alignment, as evidenced by radiological correction, and help manage patients’ expectations of postoperative recovery.

The current retrospective cohort study has limitations. First, although all patients underwent standard full-length radiography at each time point, data collection was subject to the limitations of retrospective data extraction from electronic medical records, and interobserver validity of the radiographic measurements was not evaluated. Second, follow-up was incomplete, especially for some PROs. Although our 2-year follow-up rate was 71.6% (174/243 patients), PRO data collection was sparse, and this was mostly due to some patients not reaching the 2-year follow-up. PRO comparisons were very limited, which was a major shortcoming of our study and inhibited our ability to show statistically significant differences. Larger studies may reveal differences between improved but persistent CM and unchanged or worsened CM. Third, some patients with immediate postoperative iatrogenic CM showed improved coronal alignment with longer follow-up. Although the a priori primary objective of the current study was to evaluate iatrogenic CM immediately after surgery, significant and spontaneous correction that may ensue with long-term follow-up should continue to be studied in order to better understand the clinical importance of iatrogenic CM immediately after surgery. Fourth, only univariate logistic regression was performed, rather than multivariate. This was done owing to the small number of patients with the primary outcome (n = 13), as well as to avoid a potentially spurious, unstable regression model. Although a more powerful multivariate regression analysis was not performed, our intention was to provide thoughtful insight regarding why rare iatrogenic CM may occur. Lastly, we used the 3-cm cutoff to be consistent with the Qiu classification that utilizes 3 cm, but admittedly this was the low end of the previously defined CVA threshold and may have been too low. It is possible that using 4 cm may have been more useful and more clinically relevant.

Conclusions

Postoperative iatrogenic CM occurred in 9% of ASD patients with preoperative normal coronal alignment (CVA < 3 cm). A phenotype of ASD patients who are most at risk for iatrogenic CM emerged: specifically, patients with preoperative SM, increased pelvic obliquity, LSF curve concavity to the same side as the CVA, and maximum Cobb angle concavity opposite the CVA who have undergone three-column osteotomy. Despite an increased risk of major complication, iatrogenic CM portended no increased risks of readmission, reoperation, or worsened PROs. The clinical impact of postoperative iatrogenic CM remains unclear.

Disclosures

Dr. Lehman receives royalties from Medtronic; is a consultant for Medtronic; and receives non–study-related clinical or research effort from the Department of Defense. Dr. Lenke is a consultant for Medtronic, DePuy-Synthes Spine, K2M, Abryx, EOS Technologies, and Acuity Surgical; has other financial relationships with Broadwater, Seattle Science Foundation, Scoliosis Research Society, Stryker Spine, The Spinal Research Foundation, EOS, Setting Scoliosis Straight Foundation, Fox Rothschild LLC, Evans Family Donation, Fox Family Foundation, and AO Spine; and receives royalties from Quality Medical Publishing.

Author Contributions

Conception and design: Cerpa, Zuckerman, Kerolus, Ha, Buchanan, Lehman, Lenke. Acquisition of data: Cerpa, Zuckerman, Lai, Shen, Lee, Leung. Analysis and interpretation of data: Cerpa, Zuckerman, Kerolus, Lenke. Drafting the article: Zuckerman, Lai, Shen. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Cerpa. Statistical analysis: Zuckerman. Administrative/technical/material support: Cerpa, Leung. Study supervision: Lehman, Lenke.

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  • Collapse
  • Expand
Illustration from Levi and Schwab (pp 653–659). Copyright Roberto Suazo. Published with permission.
  • FIG. 1.

    Three types of postoperative CM. Figure is available in color online only.

  • FIG. 2.

    Radiographs obtained from a patient with all significant risk factors for iatrogenic CM, including pelvic obliquity, large preoperative SVA, LSF curve concavity to the same side as the CVA, and maximum Cobb concavity opposite the CVA (A and B); all these risk factors were present in the setting of normal preoperative coronal alignment. Postoperative iatrogenic CM was seen at 3.2° with a corrected SVA of 0.9 cm (C and D). Figure is available in color online only.

  • FIG. 3.

    Radiographs obtained from a patient with several risk factors for iatrogenic CM, including LSF curve concavity to the same side of the CVA and maximum Cobb angle concavity to the opposite side of the CVA (A and B). Iatrogenic CM was seen with worsened CVA to −5.8 cm (C and D). Figure is available in color online only.

  • 1

    Bao H, Yan P, Qiu Y, Liu Z, Zhu F. Coronal imbalance in degenerative lumbar scoliosis: Prevalence and influence on surgical decision-making for spinal osteotomy. Bone Joint J. 2016;98-B(9):1227-1233.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 2

    Tanaka N, Ebata S, Oda K, Oba H, Haro H, Ohba T. Predictors and clinical importance of postoperative coronal malalignment after surgery to correct adult spinal deformity. Clin Spine Surg. 2020;33(7):E337E341.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 3

    Ploumis A, Simpson AK, Cha TD, Herzog JP, Wood KB. Coronal spinal balance in adult spine deformity patients with long spinal fusions: a minimum 2- to 5-year follow-up study. J Spinal Disord Tech. 2015;28(9):341347.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 4

    Lewis SJ, Keshen SG, Kato S, Dear TE, Gazendam AM. Risk factors for postoperative coronal balance in adult spinal deformity surgery. Global Spine J. 2018;8(7):690697.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 5

    Bao H, Liu Z, Zhang Y, Sun X, Jiang J, Qian B, et al. Sequential correction technique to avoid postoperative global coronal decompensation in rigid adult spinal deformity: a technical note and preliminary results. Eur Spine J. 2019;28(9):21792186.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 6

    Plais N, Bao H, Lafage R, Gupta M, Smith JS, Shaffrey C, et al. The clinical impact of global coronal malalignment is underestimated in adult patients with thoracolumbar scoliosis. Spine Deform. 2020;8(1):105113.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 7

    Daubs MD, Lenke LG, Bridwell KH, Kim YJ, Hung M, Cheh G, et al. Does correction of preoperative coronal imbalance make a difference in outcomes of adult patients with deformity?. Spine (Phila Pa 1976). 2013;38(6):476483.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 8

    Negrini A, Vanossi M, Donzelli S, Zaina F, Romano M, Negrini S. Spinal coronal and sagittal balance in 584 healthy individuals during growth: normal plumb line values and their correlation with radiographic measurements. Phys Ther. 2019;99(12):17121718.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 9

    Lau D, Haddad AF, Deviren V, Ames CP. Asymmetrical pedicle subtraction osteotomy for correction of concurrent sagittal-coronal imbalance in adult spinal deformity: a comparative analysis. J Neurosurg Spine. Published online August 7, 2020.doi:10.3171/2020.5.SPINE20445

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 10

    Chan AK, Lau D, Osorio JA, Yue JK, Berven SH, Burch S, et al. Asymmetric pedicle subtraction osteotomy for adult spinal deformity with coronal imbalance: complications, radiographic and surgical outcomes. Oper Neurosurg (Hagerstown). 2020;18(2):209216.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 11

    Berjano P, Lamartina C. Classification of degenerative segment disease in adults with deformity of the lumbar or thoracolumbar spine. Eur Spine J. 2014;23(9):18151824.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 12

    Glassman SD, Berven S, Bridwell K, Horton W, Dimar JR. Correlation of radiographic parameters and clinical symptoms in adult scoliosis. Spine (Phila Pa 1976). 2005;30(6):682688.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 13

    Zhang J, Wang Z, Chi P. Risk factors for immediate postoperative coronal imbalance in degenerative lumbar scoliosis patients fused to pelvis. Global Spine J. 2021;11(5):649655.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 14

    Walker CT, Godzik J, Angel S, Giraldo JP, Turner JD, Uribe JS. Coronal balance with circumferential minimally invasive spinal deformity surgery for the treatment of degenerative scoliosis: are we leaning in the right direction?. J Neurosurg Spine. Published March 12, 2021.doi:10.3171/2020.8.SPINE201147

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 15

    Theologis AA, Lertudomphonwanit T, Lenke LG, Bridwell KH, Gupta MC. The role of the fractional lumbosacral curve in persistent coronal malalignment following adult thoracolumbar deformity surgery: a radiographic analysis. Spine Deform. 2021;9(3):721731.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 16

    Yilgor C, Sogunmez N, Boissiere L, Yavuz Y, Obeid I, Kleinstück F, et al. Global alignment and proportion (GAP) score: development and validation of a new method of analyzing spinopelvic alignment to predict mechanical complications after adult spinal deformity surgery. J Bone Joint Surg Am. 2017;99(19):16611672.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 17

    Baum GR, Ha AS, Cerpa M, Zuckerman SL, Lin JD, Menger RP, et al. Does the Global Alignment and Proportion score overestimate mechanical complications after adult spinal deformity correction?. J Neurosurg Spine. 2020;34(1):96102.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 18

    Ames CP, Smith JS, Scheer JK, Bess S, Bederman SS, Deviren V, et al. Impact of spinopelvic alignment on decision making in deformity surgery in adults: a review. J Neurosurg Spine. 2012;16(6):547564.

    • Crossref
    • PubMed
    • Search Google Scholar
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  • 19

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