Changes in peri-apical vertebral body and intervertebral disc shape in both the sagittal and coronal planes correlate with scoliosis severity: a 3D study of 397 patients.

PURPOSE: To evaluate associations between vertebrae and disc shape asymmetry and adolescent idiopathic scoliosis (AIS) curve severity. METHODS: Analysis included normal screening referrals and patients with right, main thoracic AIS who underwent upright, biplanar radiographs with 3D reconstruction at a single institution from 2010 to 2015. Peri-apical anterior, posterior, right, and left vertebral body heights (aVBH, pVBH, rVBH, lVBH) and intervertebral disc heights (DH) were measured, and ratios of these measurements were calculated in sagittal and coronal planes. Correlations were performed between curve severity and height measurements. Sagittal and coronal plane components of these measurements were compared between normal controls with coronal curve measurements < 11° and patients with moderate (11°-49°) and severe curves (≥ 50°), with tolerance intervals established for the normal controls. RESULTS: The analysis included a total of 397 patients. Patients with AIS had coronal curve measurements ranging from 11° to 101°. Greater coronal curve severity strongly correlated with smaller pVBH relative to aVBH and moderately correlated with smaller pDH relative to aDH (r = - 0.643, r = - 0.305, respectively). aVBH was greater for larger curves; pVBH remained stable. Scoliosis severity strongly correlated with right relative to left VBH and DH ratios (r = 0.919, r = 0.865 respectively). In comparison of normal controls to severe curves, severe curves had significantly greater aVBH and aDH, while pVBH was not significantly different and pDH was significantly less. Nearly half (46.9%) of the severe curves were below the range of normal for PA vertebral height ratio. CONCLUSION: In right, main thoracic AIS, greater main thoracic curve severity is associated with greater sagittal and coronal plane asymmetry of both the vertebral bodies and the discs. Severity more strongly correlates with vertebral changes in symmetry than with disc changes, though both are present.

Obesity Is Associated With Increased Thoracic Kyphosis in Adolescent Idiopathic Scoliosis Patients and Nonscoliotic Adolescents.

STUDY DESIGN: Retrospective comparative cohort study. OBJECTIVE: To compare radiographic parameters between adolescents with a greater body mass index (BMI) percentile to underweight individuals. SUMMARY OF BACKGROUND DATA: Increased BMI percentile has been associated with increased complications after surgical correction of adolescent idiopathic scoliosis (AIS). However, association between BMI percentile and preoperative sagittal plane alignment has not been evaluated. The purpose of this study was to evaluate the effect of BMI percentile on sagittal alignment in AIS patients compared with nonscoliotic adolescents. METHODS: Posterior-anterior and lateral spinal radiographs of 1,551 AIS patients with a thoracic major curve (Lenke 1-4) and 70 nonscoliotic adolescent patients were compared. BMI percentile was determined based on age and sex, and patients were divided into four categories: underweight (<5th percentile), normal-weight (5th-85th percentile), overweight (85th-95th percentile), and obese (≥95th percentile). RESULTS: Coronal plane deformity magnitude was not significantly different between the 4 categories of AIS patients (p = .51). Increased BMI percentile was associated with increased thoracic kyphosis globally (T2-T12: p < .005) as well as segmentally (T2-T5: p < .001; T5-T12: p < .001) in patients with AIS. This was also true in obese adolescents without spinal deformity (p < .04). Lumbar lordosis, pelvic incidence, and pelvic tilt were not significantly different between AIS patients in the four BMI percentile categories (p > .07). Pelvic incidence was significantly greater in AIS patients compared with nonscoliotic adolescents (54 ± 13 vs. 46 ± 11; p = .01). CONCLUSION: Increased BMI percentile is associated with increased thoracic kyphosis in AIS patients and nonscoliotic adolescents. Excess weight may reduce anterior vertebral growth. AIS patients have an increased pelvic incidence compared with nonscoliotic adolescents; however, this variable is not influenced by body mass. These relationships should be taken into account when planning sagittal plane deformity correction or considering neuro axis disorders (also associated with increased kyphosis) in patients with scoliosis. LEVEL OF EVIDENCE: Level II.

A three-dimensional analysis of scoliosis progression in non-idiopathic scoliosis: is it similar to adolescent idiopathic scoliosis?

PURPOSE: To evaluate the three-dimensional (3D) characteristics of spine deformity in patients with non-idiopathic scoliosis compared with those observed in patients with adolescent idiopathic scoliosis (AIS). METHODS: A retrospective chart review was conducted to identify patients with non-idiopathic scoliosis. Twenty-eight patients with neural axis (NA) abnormalities (Chiari 1, syrinx) and 20 patients with connective tissue disorder (CTD) (Marfan's, Beal's, Ehlers-Danlos syndrome, mixed) were identified. The 3D parameters of the coronal, sagittal, and axial plane were compared with 284 AIS patients with a similar range of coronal deformity. RESULTS: The average coronal curve was similar between all three groups (AIS 48 ± 15°, CTD 43 ± 22°, and NA 49 ± 18°; p = 0.4). The NA patients had significantly greater 3D thoracic kyphosis (20 ± 18° vs 10 ± 15°, p = 0.001) and less thoracic apical vertebral rotation (- 5 ± 18° vs - 12 ± 10°, p = 0.003) when compared with AIS. The CTD group's 3D thoracic kyphosis (p = 0.7) and apical vertebral rotation (p = 0.09) did not significantly differ from AIS. Significant negative correlations were found in all three groups between thoracic kyphosis and coronal curve magnitude (AIS r = - 0.49, CTD r = - 0.772, NA r = -0.677, all p < 0.001). CONCLUSIONS: Scoliotic patients with NA abnormalities have a more kyphotic, less-rotated 3D profile than patients with AIS, while scoliosis patients with CTD have 3D features similar to AIS. Irrespective of the underlying diagnosis, however, greater scoliotic curves were associated with a greater loss of intersegmental kyphosis, suggesting a similar biomechanical pathophysiology for curve progression.

The 3D Sagittal Profile of Thoracic Versus Lumbar Major Curves in Adolescent Idiopathic Scoliosis.

STUDY DESIGN: Retrospective. OBJECTIVE: To compare the 3D sagittal profile of patients with main thoracic or thoracolumbar/lumbar adolescent idiopathic scoliosis (AIS) to a normal cohort. SUMMARY OF BACKGROUND INFORMATION: Thoracic AIS is often associated with a loss of kyphosis. Classically, this measure has been made in 2D, which may underestimate the true sagittal deformity. METHODS: Biplanar upright radiographs were obtained on 152 primary thoracic (TH: Lenke 1-4), 50 primary thoracolumbar/lumbar (TL/L: Lenke 5-6) curves, and 89 normal controls (NC). 3D spinal reconstructions were created using sterEOS software. MATLAB code was used to create segmental measurements of kyphosis/lordosis for each vertebral and disc segment from T1 to S1 in the local coordinate system of each motion segment. Comparisons were made between groups for the 3D summed segmental measures (T1-T5, T5-T12, T12-S1), pelvic incidence, sacral slope, and pelvic tilt. RESULTS: Mean 2D Cobb was 57°±12° (range 40°-115°) for TH curves and 52°±9° (range 37°-75°) for TL/L curves. Significant differences in 3D sagittal measures were found between the 3 groups. Post hoc tests revealed significant differences at T1-T5, TH

Three-Dimensional Radiographic Analysis of Two Distinct Lenke 1A Curve Patterns.

STUDY DESIGN: Retrospective review of three-dimensional (3D) imaging from a multicenter database of surgically treated adolescent idiopathic scoliosis (AIS) patients. OBJECTIVE: To use 3D analysis software to compare Lenke 1AR and 1AL curves in the coronal, sagittal, and axial planes. BACKGROUND DATA: The Lenke 1AR and AL curve patterns have been shown to be two distinct curve types, with 1AL curves being more likely to add on after fusion. Analysis in 3D may help define some of the intricacies of these two curves. METHODS: Ninety-four AIS patients with Lenke 1A curves and upright biplanar scanned radiographs were reviewed. Analysis was performed using 3D reconstruction software to evaluate the 3D coronal, sagittal and axial plane deformities. Coronal L4 tilt was used to distinguish between the two curve patterns. RESULTS: The main thoracic Cobb was not significantly different between the AR (n = 43) and AL (n = 51) curves (52° ± 8° vs. 50° ± 5°; p = .25). The thoracolumbar/lumbar Cobb was significantly smaller in the AR curves (28° ± 8° vs. 32° ± 7°; p = .02). In the sagittal plane, T5-T12 kyphosis and T12-S1 lordosis were not significantly different (p >.2); however, the T10-L2 alignment was significantly more lordotic in the AR curves (11° ± 8° vs. 4° ± 10° lordosis; p <.001). In the axial plane, thoracic apical rotation was significantly greater in AR curves (21° ± 6° vs. 14° ± 6°; p <.001) and lumbar apical rotation was significantly smaller in AR curves (1° ± 5° vs. 6° ± 5°; p <.001). CONCLUSION: 3D spinal analysis demonstrates that 1AR and AL curves are distinctly different in all three planes. Although the treatment-based Lenke classification system combines these two curve patterns into one curve type, the 3D assessment suggests there are clear features that differentiate these curve patterns. The differing features of the nonstructural lumbar curves may help define the variance in fusion level selection and risk of adding-on for these two curve patterns. LEVEL OF EVIDENCE: Level II, prognostic.

Relationship Between Lumbar Lordosis and Pelvic Incidence in the Adolescent Patient: Normal Cohort Analysis and Literature Comparison.

STUDY DESIGN: Retrospective review; literature comparison. OBJECTIVES: To review the literature on the relationship between lumbar lordosis (LL) and pelvic incidence (PI) and evaluate this relationship in asymptomatic adolescents while testing the validity of previously reported adult correlation models between LL and PI in an adolescent population. SUMMARY OF BACKGROUND DATA: Accurate understanding of the normal spinopelvic relationship is critical when considering surgical fusion of the lumbar spine. Many studies have reported relationships between pelvic measurements and LL in adult populations, but data in pediatric populations is lacking. METHODS: A literature search was performed to identify previously reported relationships between pelvic parameters and LL in adults and pediatric patients. A cohort of 125 asymptomatic adolescent patients evaluated at our institution was evenly split into two cohorts for model development and validation. Linear regression between LL and PI was performed. The resultant regression model was tested in the validation cohort along with previously reported formulae with LL as a function of PI. Mean absolute error (MAE) was calculated and compared between prior models and the newly developed adolescent model using analysis of variance and post-hoc testing. RESULTS: In our adolescent cohort (mean age: 13 ± 2), there was a strong correlation between PI and LL (r = 0.53). Regression analysis in the development cohort produced the following predictive model: LL = 0.66(PI) + 24.2. Testing in the validation cohort revealed a good correlation between predicted and actual LL (r = 0.51) and an MAE of 8.3. All but three previously reported models functioned with similar accuracy in the adolescent population, with only two methods having an MAE over 10. CONCLUSIONS: The majority of previously published formulae for predicting LL as a function of PI developed in adults can be extrapolated to adolescent populations. These relationships are important in understanding how to surgically restore the sagittal alignment in adolescents with spinal deformity. LEVEL OF EVIDENCE: Level IV.

A Novel Method for Estimating Three-Dimensional Apical Vertebral Rotation Using Two-Dimensional Coronal Cobb Angle and Thoracic Kyphosis.

STUDY DESIGN: Retrospective cohort analysis. OBJECTIVES: To use a large cohort of three-dimensional (3D) spinal reconstructions to create a simple mathematical formula capable of estimating 3D apical vertebral rotation (AVR) based on the correlation with routinely obtained two-dimensional (2D) measurements of scoliosis. SUMMARY OF BACKGROUND DATA: Quantification of vertebral rotation in AIS using 2-dimensional (2D) imaging is inherently challenging as the axial plane cannot be directly visualized. METHODS: A database of 279 3D spinal reconstructions was queried for patients with thoracic major adolescent idiopathic scoliosis (AIS). 2D thoracic Cobb angle, T5-T12 thoracic kyphosis, pelvic incidence, sacral slope, and pelvic tilt were recorded. 3D AVR was calculated for each patient from 3D reconstructions. Patients were divided into development (n = 186) and validation (n = 93) cohorts. Within the development cohort, univariate analysis was performed between 2D measurements and 3D AVR with significance set at p < .05 for inclusion in multivariate analysis. In multivariate analysis, significance was set at p < .01 for inclusion in the final model. Model performance was tested in development and validation cohorts. RESULTS: Only 2D thoracic Cobb and T5-T12 thoracic kyphosis had significance in univariate (p < .05) and multivariate analyses (p < .01), meriting inclusion in the final model. 3D AVR (°) = 0.26*(T5-T12 kyphosis) + 0.34*(coronal Cobb) - 5.38. In the development cohort, the model performed well (R = 0.739, r2 = 0.54). In testing with the validation cohort, the model proved generalizability (R = 0.703) and had a mean absolute error <5°. CONCLUSIONS: This model is capable of estimating 3D AVR given 2D thoracic Cobb and T5-T12 kyphosis. The accuracy of this method is comparable to previously reported methods of 2D axial rotation measurement. However, this model provides 3D axial rotation and requires no physical instruments, non-standard measurements, or software programs. Such a model is valuable for both routine evaluation of AIS and operative preparation. LEVEL OF EVIDENCE: Level II, diagnostic.

Thoracic Idiopathic Scoliosis Severity Is Highly Correlated with 3D Measures of Thoracic Kyphosis.

BACKGROUND: Loss of thoracic kyphosis has been associated with thoracic idiopathic scoliosis. Modern 3-dimensional (3D) imaging systems allow more accurate characterization of the scoliotic deformity than traditional radiographs. In this study, we utilized 3D calculations to characterize the association between increasing scoliosis severity and changes in the sagittal and axial planes. METHODS: Patients evaluated in a scoliosis clinic and determined to have either a normal spine or idiopathic scoliosis were included in the analysis. All underwent upright, biplanar radiography with 3D reconstructions. Two-dimensional (2D) measurements of the magnitude of the thoracic major curve and the thoracic kyphosis were recorded. Image processing and MATLAB analysis were utilized to produce a 3D calculation of thoracic kyphosis and apical vertebral axial rotation. Regression analysis was performed to determine the correlation of 2D kyphosis, 3D kyphosis, and apical axial rotation with the magnitude of the thoracic major curve. RESULTS: The 442 patients for whom 2D and 3D data were collected had a main thoracic curve magnitude ranging from 1° to 118°. Linear regression analysis of the 2D and 3D T5-T12 kyphosis versus main thoracic curve magnitude yielded significant models (p < 0.05). The 2D model had a minimally negative slope (-0.07), a small R value (0.02), and a poor correlation coefficient (-0.14). In contrast, the 3D model had a strongly negative slope (-0.54), a high R value (0.56), and a strong correlation coefficient (-0.75). Curve magnitude also had a strong correlation with loss of 3D T1-T12 kyphosis and increasing apical axial rotation. CONCLUSIONS: Segmentally calculated 3D thoracic kyphosis had a strongly negative correlation with the magnitude of the main thoracic curve. With near uniformity, 3D thoracic kyphosis progressively decreased as scoliosis magnitude increased, at a rate of more than half the increase in the main thoracic curve magnitude. Analysis confirmed a surprisingly strong correlation between scoliosis severity and loss of 3D kyphosis that was absent in the 2D analysis. A similarly strong correlation between curve magnitude and apical axial rotation was evident. These findings lend further credence to the concept that scoliosis progresses in the coronal, sagittal, and axial planes simultaneously. CLINICAL RELEVANCE: The findings of this study suggest that 3D assessment is critical for adequate characterization of the multiplanar deformity of idiopathic scoliosis and deformity in the sagittal plane is linked to deformity in the coronal plane. Increasing severity of coronal plane curvature is associated with a progressive loss of thoracic kyphosis that should be anticipated so that the appropriate intraoperative techniques for correction of idiopathic scoliosis can be applied in all 3 planes.

Predicting 3D Thoracic Kyphosis Using Traditional 2D Radiographic Measurements in Adolescent Idiopathic Scoliosis.

STUDY DESIGN: Retrospective. OBJECTIVE: To develop and validate a prediction formula to estimate three-dimensional (3D) T5-T12 kyphosis in adolescent idiopathic scoliosis (AIS) from standard two-dimensional (2D) radiographic measurements. SUMMARY OF BACKGROUND DATA: 2D measurements of thoracic kyphosis in AIS patients overestimate 3D kyphosis; however, there is a lack of widespread availability of 3D imaging technology. METHODS: Retrospective review was performed for AIS patients with right thoracic curves evaluated with EOS Imaging from January 2010 to June 2014. Standard 2D posteroanterior and lateral radiographic measurements, pelvic incidence, Nash-Moe grade, Perdriolle rotation, and "3D T5-T12" sagittal measures (reconstructed with sterEOS, analyzed with custom MatLab code) were input into a multivariate logistic analysis to create a prediction model for 3D T5-T12 sagittal alignment. An initial cohort of 66 patients (curves 14°-85°) was used to create a predictive model, and a separate cohort of 129 patients (curves 16°-84°) was used to validate the formula. RESULTS: 2D thoracic coronal Cobb and 2D T5-T12 kyphosis were the only significant predictors in the model. The prediction formula for estimating 3D T5-T12 sagittal measurement from standard 2D measurements, in degrees, was 18.1 + (0.81*2D T5-T12 sagittal Cobb) - (0.54*2D coronal Cobb), r2 = 0.84. The average model error between predicted and measured 3D T5-T12 kyphosis was ±7°. The predicted 3D T5-T12 kyphosis (8.6° ± 12.1°) and measured 3D T5-T12 kyphosis (8.5° ± 13.0°) were not significantly different (p = .8). 3D kyphosis was less than standard measures of 2D kyphosis (8.5° ± 13.0° vs. 20.2° ± 12.6°, p < .001). CONCLUSION: This simple validated formula to predict 3D T5-T12 sagittal alignment using routine 2D thoracic Cobb and T5-T12 kyphosis for thoracic AIS patients has great potential value in assessing historical data collected prior to the development of 3D imaging methods as well as understanding/planning surgical hypokyphosis correction in patients without access to 3D imaging.

Paper #10: 3D Assessment of Spine Growth in Early Onset Scoliosis during Growing Rod Lengthening.

Measuring the true spine growth during growing rod (GR) lengthening is limited with 2D radiographs. With 3D imaging, this study demonstrates that during GR lengthening the spine lengthens and vertebra increase in size suggesting spinal growth that matches the relative increase in rod length during the distraction period.

New EOS Imaging Protocol Allows a Substantial Reduction in Radiation Exposure for Scoliosis Patients.

STUDY DESIGN: Prospective. OBJECTIVE: To evaluate the reliability of three-dimensional (3D) spinal models from Micro Dose EOS x-rays compared to standard, Low Dose EOS x-rays utilized for evaluating patients with adolescent idiopathic scoliosis (AIS). SUMMARY OF BACKGROUND DATA: There is a strong suggestion that radiation exposure to scoliosis patients can be further reduced. METHODS: Sixty AIS patients who received biplanar, posteroanterior, and lateral standard Low Dose spine x-rays in our EOS imaging unit (∼0.33 mGy) as part of routine care also underwent an additional set of new reduced "Micro Dose" EOS x-rays (∼0.05 mGy) using a recently developed protocol. Two measurers created 3D models of the images using sterEOS software (Low Dose x2, Micro Dose x2). From this 3D modeling software, coronal Cobb angles, sagittal (T1-T12, T4-T12, L1-L5, L1-S1), and apical axial rotation measurements were obtained. Intraclass correlations (ICCs) and standard error of measurement (upper bound of 95% confidence interval) for the differences between Low Dose and Micro Dose measurements were compared. Interrater reliability was assessed on standard two-dimensional (2D) radiographic measurements. RESULTS: The ICCs were rated as "substantial" to "almost perfect" for Low Dose 3D, Micro Dose 3D, and 2D measures (range 0.78-0.99). The calculated measurement error was not significantly different between groups except for intrarater error on 3D L1-L5 lordosis (2.9° Micro Dose vs. 2.2°, p = .04), interrater 3D rotation of the lumbar apex (2.6° Micro Dose vs. 1.7°, p = .03), and 2D T12-sacrum lordosis (4.6° Micro Dose vs. 3.4°, p = .04). CONCLUSIONS: Although statistically significant differences in average measurement error were observed in lordosis and lumbar apex rotation, these differences are not believed to be clinically significant. The Micro Dose images have slightly less clarity qualitatively, yet the critical 2D and 3D measures of the curvature were reliably measured with error of measurement comparable to standard radiologic techniques. LEVEL OF EVIDENCE: Level I, Diagnostic.

Defining the "Three-Dimensional Sagittal Plane" in Thoracic Adolescent Idiopathic Scoliosis.

BACKGROUND: Obtaining accurate measurements of scoliosis from two-dimensional (2-D) radiographs can be challenging because of the three-dimensional (3-D) nature of the deformity. Previous studies have shown that the sagittal plane, in particular, is misrepresented on 2-D radiographs because of the influence of axial plane rotation. The purpose of the current study was to define a methodology for measuring the 3-D segmental sagittal alignment of the spine in patients with adolescent idiopathic scoliosis (AIS) and to assess the effect of axial plane rotation on differences between 3-D and 2-D measures of deformity. METHODS: Preoperative and postoperative EOS images of 120 consecutive patients with AIS (primary thoracic curves) treated with segmental thoracic pedicle-screw instrumentation were analyzed in the "3-D sagittal plane." The technique measured 3-D kyphosis or lordosis in the specific plane of sagittal motion for each spinal motion segment. The kyphosis (+) and lordosis (-) values of the segments from T5 to T12 were summed to give the 3-D measurement of T5-T12 kyphosis. These values were compared with the standard 2-D measurements of T5-T12 kyphosis on lateral radiographs, and a correlation analysis with regard to axial plane rotation of the apex was performed. RESULTS: The average age (and standard deviation) of the patients was 14 ± 2 years. The mean preoperative Cobb angle on the standard 2-D view was 55° ± 10° and on the 3-D view was 52° ± 9° (p ≤ 0.001). On the 3-D view, the mean preoperative T5-T12 kyphosis was 6° ± 14°, and the kyphosis significantly increased to 26° ± 6° postoperatively (p < 0.001). The T5-T12 kyphosis on the standard 2-D view measured 18° ± 13° preoperatively and 27° ± 6° postoperatively (p < 0.001). The difference between the 2-D and 3-D measurements of T5-T12 kyphosis strongly correlated with apical vertebral rotation (r = 0.85; p < 0.01). CONCLUSIONS: Routine 2-D measurements of thoracic kyphosis erroneously underestimate the preoperative loss of kyphosis in AIS because of errors associated with axial plane rotation, an inherent component of thoracic scoliosis.