Surgical treatment of double thoracic adolescent idiopathic scoliosis with a rigid proximal thoracic curve

Techniques of Deformity Correction in Adolescent Idiopathic Scoliosis-A Narrative Review of the Existing Literature

Surgical management of adolescent idiopathic scoliosis [AIS] is a complex undertaking with the primary goals to correct the deformity, maintain sagittal balance, preserve pulmonary function, maximize postoperative function, and improve or at least not harm the function of the lumbar spine. The evolution of surgical techniques for AIS has been remarkable, transitioning from rudimentary methods of spinal correction to highly refined, biomechanically sound procedures. Modern techniques incorporate advanced three-dimensional correction strategies, often leveraging pedicle screw constructs, which provide superior rotational control of the vertebral column. A number of surgical techniques have been described in the literature, each having its own pros and cons. This narrative review provides a detailed analysis of the contemporary surgical techniques used in the treatment of patients with AIS.

Influence of Lateral Translation of Lowest Instrumented Vertebra on L4 Tilt and Coronal Balance for Thoracolumbar and Lumbar Curves in Adolescent Idiopathic Scoliosis

This study aimed to evaluate the lowest instrumented vertebra translation (LIV-T) in the surgical treatment of thoracolumbar/lumbar adolescent idiopathic scoliosis and to analyze the radiographic parameters in relation to LIV-T and L4 tilt and global coronal balance. A total of 62 patients underwent posterior spinal fusion (PSF, n = 32) or anterior spinal fusion (ASF, n = 30) and were followed up for a minimum of 2 years. The mean preoperative LIV-T was significantly larger in the ASF group than the PSF (p < 0.01), while the final LIV-T was equivalent. LIV-T at the final follow-up was significantly correlated with L4 tilt and the global coronal balance (r = 0.69, p < 0.01, r = 0.38, p < 0.01, respectively). Receiver-operating characteristic analysis for good outcomes, with L4 tilt <8° and coronal balance <15 mm at the final follow-up, calculated the cutoff value of the final LIV-T as 12 mm. The cutoff value of preoperative LIV-T that would result in the LIV-T of ≤12 mm at the final follow-up was 32 mm in PSF, although no significant cutoff value was calculated in ASF. ASF can centralize the LIV better than PSF with a shorter segment fusion, and could be useful in obtaining a good curve correction and global balance without fixation to L4 in cases with large preoperative LIV-T.

Systematic review and meta-analysis for the impact of rod materials and sizes in the surgical treatment of adolescent idiopathic scoliosis

PURPOSE

To assess surgical and safety outcomes associated with different rod materials and diameters in adolescent idiopathic scoliosis (AIS) surgery.

METHODS

A systematic literature review and meta-analysis evaluated the surgical management of AIS patients using pedicle screw fixation systems (i.e., posterior rods and pedicle screws) with rods of different materials and sizes. Postoperative surgical outcomes (e.g., kyphosis and coronal correction) and complications (i.e., hyper/hypo-lumbar lordosis, proximal junctional kyphosis, revisions, reoperations, and infections) were assessed. Random-effects models (REMs) pooled data for outcomes reported in ≥ 2 studies.

RESULTS

Among 75 studies evaluating AIS surgery using pedicle screw fixation systems, 46 described rod materials and/or diameters. Two studies directly comparing titanium (Ti) and cobalt-chromium (CoCr) rods found that CoCr rods provided significantly better postoperative kyphosis angle correction vs. Ti rods during a shorter follow-up (0-3 months, MD = - 2.98°, 95% CI - 5.79 to - 0.17°, p = 0.04), and longer follow-up (≥ 24 months, MD = - 3.99°, 95% CI - 6.98 to - 1.00, p = 0.009). Surgical infection varied from 2% (95% CI 1.0-3.0%) for 5.5 mm rods to 4% (95% CI 2.0-7.0%) for 6 mm rods. Reoperation rates were lower with 5.5 mm rods 1% (95% CI 0.0-3.0%) vs. 6 mm rods [6% (95% CI 2.0-9.0%); p = 0.04]. Differences in coronal angle, lumbar lordosis, proximal junctional kyphosis, revisions, and infections did not differ significantly (p > 0.05) among rods of different materials or diameters.

CONCLUSION

For AIS, CoCr rods provided better correction of thoracic kyphosis compared to Ti rods. Patients with 5.5 mm rods had fewer reoperations vs. 6.0 and 6.35 mm diameter rods.

LEVEL OF EVIDENCE

III.

Four-Dimensional Anatomical Spinal Reconstruction in Thoracic Adolescent Idiopathic Scoliosis

Recent surgical techniques involve 3-dimensional (3D) deformity correction of adolescent idiopathic scoliosis (AIS)^1-4. However, next-generation surgical strategies should ensure that the final corrected spine is not only “non-scoliotic,” but has an anatomically correct shape. We developed a 4D anatomical spinal reconstruction technique that involves the use of spatiotemporal deformity prediction to preoperatively calculate the postoperative apex of thoracic kyphosis in order to achieve an anatomically correct spinal curvature^5-7.

Is the Combination of Convex Compression for the Proximal Thoracic Curve and Concave Distraction for the Main Thoracic Curve Using Separate-rod Derotation Effective for Correcting Shoulder Balance and Thoracic Kyphosis?

BACKGROUND

Posterior correction of the proximal thoracic curve in patients with adolescent idiopathic scoliosis has been recommended to achieve shoulder balance. However, finding a good surgical method is challenging because of the small pedicle diameters on the concave side of the proximal thoracic curve. If the shoulder height can be corrected using screws on the convex side, this would appear to be a more feasible approach.

QUESTIONS/PURPOSES

In patients with adolescent idiopathic scoliosis, we asked: (1) Is convex compression with separate-rod derotation effective for correcting the proximal thoracic curve, shoulder balance, and thoracic kyphosis? (2) Which vertebrum is most appropriate to serve as the uppermost-instrumented vertebra? (3) Is correction of the proximal thoracic curve related to the postoperative shoulder balance?

METHODS

Between 2015 and 2017, we treated 672 patients with scoliosis. Of those, we considered patients with elevated left shoulder, Lenke Type 2 or 4, or King Type V idiopathic scoliosis as potentially eligible. Based on that, 17% (111 of 672) were eligible; 5% (6 of 111) were excluded because of other previous operations and left-side main thoracic curve, 22% (24 of 111) were excluded because they did not undergo surgery for the proximal thoracic curve with only pedicle screws, 21% (23 of 111) were excluded because the proximal thoracic curve was not corrected by convex compression and separate rod derotation, and another 3% (3 of 111) were lost before the minimum study follow-up of 2 years, leaving 50% (55 of 111) for analysis. During the study period, we generally chose T2 as the uppermost level instrumented when the apex was above T4, or T3 when the apex was T5. Apart from the uppermost-instrumented level, the groups did not differ in measurable ways such as age, sex, Cobb angles of proximal and main thoracic curves, and T1 tilt. However, shoulder balance was better in the T3 group preoperatively. The median (range) age at the time of surgery was 15 years (12 to 19 years). The median follow-up duration was 26 months (24 to 52 months). Whole-spine standing posteroanterior and lateral views were used to evaluate the improvement of radiologic parameters at the most recent follow-up and to compare the radiologic parameters between the uppermost-instrumented T2 (37 patients) and T3 (18 patients) vertebra groups. Finally, we analyzed radiologic factors related to shoulder balance, defined as the difference between the horizontal lines passing both superolateral tips of the clavicles (right-shoulder-up was positive), at the most recent follow-up.

RESULTS

Convex compression with separate-rod derotation effectively corrected the proximal thoracic curve (41° ± 11° versus 17° ± 10°, mean difference 25° [95% CI 22° to 27°]; p < 0.001), and the most recent shoulder balance changed to right-shoulder-down compared with preoperative right-shoulder-up (8 ± 11 mm versus -8 ± 10 mm, mean difference 16 mm [95% CI 12 to 19]; p < 0.001). Proximal thoracic kyphosis decreased (13° ± 7° versus 11° ± 6°, mean difference 2° [95% CI 0° to 3°]; p = 0.02), while mid-thoracic kyphosis increased (12° ± 8° versus 18° ± 6°, mean difference -7° [95% CI -9° to -4°]; p < 0.001). Preoperative radiographic parameters did not differ between the groups, except for shoulder balance, which tended to be more right-shoulder-up in the T2 group (11 ± 10 mm versus 1 ± 11 mm, mean difference 10 mm [95% CI 4 to 16]; p = 0.002). At the most recent follow-up, the correction proportion of the proximal thoracic curve was better in the T2 group than the T3 group (67% ± 10% versus 49% ± 22%, mean difference 19% [95% CI 8% to 30%]; p < 0.001). In the T2 group, T1 tilt (6° ± 4° versus 6° ± 4°, mean difference 1° [95% CI 0° to 2°]; p = 0.045) and shoulder balance (-14 ± 11 mm versus -7 ± 9 mm, mean difference -7 mm [95% CI -11 to -3]; p = 0.002) at the most recent follow-up improved compared with those at the first erect radiograph. The most recent shoulder balance was correlated with the correction proportion of the proximal thoracic curve (r = 0.29 [95% CI 0.02 to 0.34]; p = 0.03) and change in T1 tilt (r = 0.35 [95% CI 0.20 to 1.31]; p = 0.009).

CONCLUSION

Using the combination of convex compression and concave distraction with separate-rod derotation is an effective method to correct proximal and main thoracic curves, with reliable achievement of postoperative thoracic kyphosis and shoulder balance. T2 was a more appropriate uppermost-instrumented vertebra than T3, providing better correction of the proximal thoracic curve and T1 tilt. Additionally, spontaneous improvement in T1 tilt and shoulder balance is expected with upper-instrumented T2 vertebrae. Preoperatively, surgeons should evaluate shoulder balance because right-shoulder-down can occur after surgery in patients with a proximal thoracic curve.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Impact of multilevel facetectomy on segmental spinal flexibility in patients with thoracic adolescent idiopathic scoliosis

BACKGROUND

The aim of this study was to intraoperatively assess the effects of multilevel facetectomy on segmental spinal flexibility in patients with thoracic adolescent idiopathic scoliosis.

METHODS

Twenty patients who underwent posterior thoracic adolescent idiopathic scoliosis curve correction were evaluated. Compressive or distractive loaded force of 50N was applied on the handle of a compressor or distractor connected to the necks of pedicle screws inserted at T7 to T11. Segmental spinal flexibility rates were calculated based on the distance between screw heads under the loaded and unloaded conditions. In addition, the flexibility rates were obtained before and after multilevel facetectomy.

FINDINGS

Absolute flexibility rates of all segments significantly increased after multilevel facetectomy under both compressive and distractive forces (P < 0.01). The absolute change in the flexibility rate was significantly higher at the concave side than at the convex side under both compressive (P < 0.01) and distractive loaded forces (P = 0.046). No significant correlation was found between change in the flexibility rates and preoperative Cobb angle or preoperative curve flexibility.

INTERPRETATION

From a biomechanical point of view, multilevel facetectomy provides proper spinal flexibility to improve the correction rate of posterior adolescent idiopathic scoliosis surgery. The effects are higher at the concave side than at the convex side.

Impact of lowest instrumented vertebra tilt and rotation on uninstrumented lumbar curve and L4 tilt in thoracic adolescent idiopathic scoliosis

OBJECTIVE

Controversy exists regarding the effects of lowest instrumented vertebra (LIV) tilt and rotation on uninstrumented lumbar segments in adolescent idiopathic scoliosis (AIS) surgery. Because the intraoperative LIV tilt from the inferior endplate of the LIV to the superior sacral endplate is not stable after surgery, the authors measured the LIV angle of the instrumented thoracic spine as the LIV angle of the construct. This study aimed to evaluate the effects of the LIV angle of the construct and the effects of LIV rotation on the postoperative uninstrumented lumbar curve and L4 tilt in patients with thoracic AIS.

METHODS

A retrospective correlation and multivariate analysis of a prospectively collected, consecutive, nonrandomized series of patients at a single institution was undertaken. Eighty consecutive patients with Lenke type 1 or type 2 AIS treated with posterior correction and fusion were included. Preoperative and 2-year postoperative radiographic measurements were the outcome measures for this study. Outcome variables were postoperative uninstrumented lumbar segments (LIV tilt, LIV translation, uninstrumented lumbar curve, thoracolumbar/lumbar [TL/L] apical vertebral translation [AVT], and L4 tilt). The LIV angle of the construct was measured from the orthogonal line drawn from the upper instrumented vertebra to the LIV. Multiple stepwise linear regression analysis was conducted between outcome variables and patient demographics/radiographic measurements. There were no study-specific biases related to conflicts of interest.

RESULTS

Predictor variables for postoperative uninstrumented lumbar curve were the postoperative LIV angle of the construct, number of uninstrumented lumbar segments, and flexibility of TL/L curve. Specifically, a lower postoperative uninstrumented lumbar curve was predicted by a lower absolute value of the postoperative LIV angle of the construct (p < 0.0001). Predictor variables for postoperative L4 tilt were postoperative LIV rotation, preoperative L4 tilt, and preoperative uninstrumented lumbar curve. Specifically, a lower postoperative L4 tilt was predicted by a lower absolute value of postoperative LIV rotation (p < 0.0001).

CONCLUSIONS

The LIV angle of the construct significantly affected the LIV tilt, uninstrumented lumbar curve, and TL/L AVT. LIV rotation significantly affected the LIV translation and L4 tilt.

Posterior Correction Techniques for Adolescent Idiopathic Scoliosis

Adolescent idiopathic scoliosis represents a complex, three-dimensional deformity of the spine. Posterior spinal fusion is commonly performed in severe cases to avoid the long-term adverse sequelae associated with progressive spinal deformity. The goals of spinal fusion include halting the progression of deformity, optimizing spinal balance, and minimizing complications. Recent advances in short-segment spinal fixation have allowed for improved three-dimensional deformity correction. Preoperative planning and assessment of spinal flexibility is essential for successful deformity correction and optimization of long-term outcomes. Judicious use of releases and/or spinal osteotomies may allow for increased mobility of the spine but are associated with increased surgical time, blood loss, and risk of complications. Appreciation of implant design and material properties is critical for safe application of correction techniques. Although multiple reduction techniques have been described, no single technique is optimal for every patient.

Does image guidance decrease pedicle screw-related complications in surgical treatment of adolescent idiopathic scoliosis: a systematic review update and meta-analysis

PURPOSE

Surgical treatment of severe adolescent idiopathic scoliosis (AIS) with posterior spinal instrumentation and fusion with pedicle screws is common, requiring careful screw insertion to prevent pedicle breaches and neurologic complications. Image guidance has been suggested to improve breach rates, though the radiation risk for AIS precludes its common usage. The purpose of this systematic review and meta-analysis was to compare the breach rates and screw-related complications for AIS patients undergoing spine surgery with pedicle screws between freehand screw insertion and image guidance methods.

METHODS

A comprehensive search of MEDLINE, EMBASE, CINAHL, CENTRAL and Web of Science databases was conducted. Two reviewers independently screened abstracts, full-texts, extracted data and performed risk of bias assessment using the QUIPS quality appraisal tool. Level of evidence summary statements were formulated based on consistency and quality of reporting.

RESULTS

Ninety-four studies were found, with 18 studies of moderate risk of bias or better. Moderate evidence from two head-to-head studies shows CT guidance has lower breach rates than freehand methods (OR 0.28 [0.20-0.40, I2 = 1%]), with no complications in either study. From individual studies, moderate evidence showed lower breach rates for image guidance versus freehand methods (13%, I2 = 98% vs. 20%, I2 = 95%). Complication rates were conflicting (0-1.6% for image guidance, 0-1.7% for freehand). Moderate evidence showed increased surgical time for image guidance versus freehand (257.7 min vs. 226.8 min).

CONCLUSIONS

Meta-analyzed breach rates show moderate evidence of decreased breaches with CT navigation compared with freehand methods. Complication rates remain unknown due to the low complication rates from small sample sizes. These slides can be retrieved under Electronic Supplementary Material.

Effect of thoracic kyphosis formation and rotational correction by direct vertebral rotation after the simultaneous double rod rotation technique for idiopathic scoliosis

OBJECTIVE

The objective of the present study was to evaluate the effect of thoracic kyphosis formation and rotational correction by direct vertebral rotation (DVR) after the simultaneous double-rod rotation technique (SDRRT) for idiopathic scoliosis (IS).

PATIENTS AND METHODS

The present study included twelve patients with IS who received SDRRT (SDRRT group) and twelve patients with IS who received DVR after SDRRT (SDRRT + DVR group). We investigated the following parameters preoperatively, postoperatively, and at postoperative 2 years: Cobb angle (PT, MT, T/L, C7-CSVL, AVT, TK (T5-12), LL(L1-S1) RSH, the angle of rotation (RAsag), percent change of RAsag and SRS22 (at postoperative 2 years only).

RESULTS

Preoperatively, the mean main thoracic curve was 58.9 ± 12.4° for the SDRRT group and 59.9 ± 16.0° for the SDRRT + DVR group, which was corrected to 14.6 ± 6.7° and 13.4 ± 4.9° postoperatively. and 14.9 ± 7.1° and 14.3 ± 4.1° at postoperative 2-year follow-up, respectively. Correction rates were 75.4 ± 10.4% and 77.2 ± 8.0 % postoperatively. Thoracic kyphosis increased postoperatively and at postoperative 2-year follow-up in both the SDRRT group and the SDRRT + DVR group. The mean preoperative TK was 11.4 ± 7.3° in the SDRRT group, and 12.8 ± 11.5° in the SDRRT + DVR group, which improved significantly to 24.8 ± 5.2° and 23.6 ± 3.5° postoperatively and 23.3 ± 3.9° and 24.2 ± 6.0° at postoperative 2-year follow-up, respectively. Correction of vertebral rotation as RAsag was significantly better in the SDRRT + DVR group than in the SDRRT group. The mean preoperative RAsag was 19.1 ± 6.7° in the SDRRT group, and 18.3 ± 7.5° in the SDRRT + DVR group, which improved to 13.3 ± 4.3° and 10.1 ± 2.9° postoperatively (P = 0.04) and 13.9 ± 4.0° and 10.6 ± 2.8° at postoperative 2-year follow-up (P = 0.02), respectively.

CONCLUSION

DVR after SDRRT for idiopathic scoliosis allowed for rotation correction without compromising kyphosis formation.

Identification of optimized rod shapes to guide anatomical spinal reconstruction for adolescent thoracic idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS), the most common pediatric musculoskeletal disorder, causes a three-dimensional deformity of the spine. Although rod curvature could play an important role in anatomical spinal reconstruction in patients with thoracic AIS, intraoperative contouring of the straight rod induces notches into the rod, leading to decreased fatigue strength. Here, we analyzed pre-bent rod geometries from 46 intraoperative tracings of the rod geometry, which can provide anatomical spinal reconstruction in patients with thoracic AIS. The center point clouds of the rod shapes were extracted and approximated as arcs and straight lines. The difference between the center point clouds were evaluated using the iterative closest point methods. When the rod shapes were divided into six groups based on length followed by hierarchical cluster analysis, 10 representative rod shapes were obtained with a difference value of 5 mm. Thus, we identified optimized rod shapes to guide anatomical spinal reconstruction for thoracic AIS, which will reduce not only the risk of rod breakage but also operation time, leading to decreased patient burden. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3219-3224, 2018.

Radiographic methods to estimate surgical outcomes based on spinal flexibility assessment in patients who have adolescent idiopathic scoliosis: A systematic review

BACKGROUND CONTEXT

Adolescent idiopathic scoliosis (AIS) is a three-dimensional deformity recognized with lateral curvature of the spine as well as axial vertebral rotation. Surgical interventions are recommended when patients with AIS have severe curvature (Cobb angle >45^o). Spinal flexibility is one of important parameters for surgeons to plan surgical treatment. Few radiographic methods have been developed to assess spinal flexibility.

PURPOSE

A systematic review was performed to evaluate which preoperative radiographic methods should be used to estimate spinal flexibility based on the postoperative outcomes.

STUDY DESIGN

Studies which included any of the five radiographic methods: (1) supine side-bending (SBR), (2) fulcrum-bending (FBR), (3) traction, (4) push-prone, and (5) suspension were reviewed and compared to determine which method provided the most accurate estimation of the postoperative outcomes.

PATIENT SAMPLE

Seven case series, one case control, and multiple cohort studies reported the flexibility assessment methods with the estimations of postoperative outcomes on patients with AIS.

OUTCOME MEASURES

The flexibility index defined as a correction rate relative to flexibility rate was used to estimate the immediate and final follow-up postoperative outcomes.

METHODS

Seven databases searched included MEDLINE, CENTRAL, EMBASE, CINAHL, Web of Science, LILACS, and Google Scholar. Three independent reviewers were involved for abstracts and full-texts screening as well as data extraction. The Quality in Prognostic Studies quality appraisal tool was used to assess the risk of bias within the studies. Also, the GRADE system rate was used to assess the evidence level across the studies.

RESULTS

Forty-six articles were included. The distribution of the five flexibility methods in these 46 studies were SBR 38/46 (83%), fulcrum bending radiograph (FBR) 16/46 (35%), traction radiograph 5/46 (11%), push-prone 1/46 (2%), and suspension 1/46 (2%). Based on the overall assessment of flexibility indices, FBR had the best estimation of postoperative correction among the five methods. FBR method provided the best estimations of immediate and final follow-up postoperative outcomes for moderate (25°-45°) and severe (>45°) curves, respectively. For main thoracic and thoracolumbar/lumbar curves, the best estimations were traction, and FBR. However, in the reviewed articles, the risk of bias was rated moderate and the quality of evidence was rated very low to low so that a strong conclusive statement cannot be made.

CONCLUSIONS

SBR method was the most commonly used method to assess the spinal flexibility. The FBR method was the most accurate method to estimate the postoperative outcomes based on the limited evidence of the 46 articles.

Impact of Multilevel Facetectomy and Rod Curvature on Anatomical Spinal Reconstruction in Thoracic Adolescent Idiopathic Scoliosis

STUDY DESIGN

A prospective, nonrandomized study.

OBJECTIVE

The aim of this study was to assess surgical outcomes of multilevel facetectomy and rod curvature with simultaneous double-rod rotation technique for anatomical spinal reconstruction in thoracic adolescent idiopathic scoliosis (AIS).

SUMMARY OF BACKGROUND DATA

Although some surgical techniques maintain or restore thoracic kyphosis (TK), next-generation strategies for thoracic AIS should include corrections in three anatomical planes.

METHODS

The study included 39 consecutive patients with Lenke 1 or Lenke 2 thoracic AIS treated at our institution. After all-level facetectomy at instrumentation level, except for the lowest intervertebral segment, two rods were identically bent to guide postoperative anatomical TK without reference to the intraoperative coronal alignment of the AIS deformity. Outcome measures included patient demographics, radiographic measurements, and Scoliosis Research Society (SRS) questionnaire scores.

RESULTS

After 2 years of follow-up, the average main thoracic Cobb angle correction rate was 83.5%, and the final correction loss was 2.2°. The average preoperative TK (T5-T12) significantly increased from 13.2° to 24.6° (P < 0.001) at final follow-up. The percentage of patients with a T6-T8 location of the TK apex significantly increased from 51.3% preoperatively to 87.2% at final follow-up. The average preoperative vertebral rotation angle significantly decreased from 18.7° to 12.8° postoperatively (P < 0.001). The average preoperative total SRS questionnaire score significantly increased from 3.5 to 4.5 (P < 0.001) at final follow-up. There was no implant breakage and vascular and neurologic complications, with all patients demonstrating solid fusion at final follow-up.

CONCLUSION

Multilevel facetectomy and rod curvature play an important role in anatomical spinal reconstruction in patients with thoracic AIS. From the spatiotemporal point of view, four-dimensional correction could be actively performed by rod curvature under multilevel facetectomy and is expected to obtain an anatomical thoracic spine postoperatively, indicating that an anatomically designed rod could be supplied as a pre-bent rod.

LEVEL OF EVIDENCE

3.

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.

Correlation analysis between change in thoracic kyphosis and multilevel facetectomy and screw density in main thoracic adolescent idiopathic scoliosis surgery

BACKGROUND CONTEXT

Controversy exists regarding the effects of multilevel facetectomy and screw density on deformity correction, especially thoracic kyphosis (TK) restoration in adolescent idiopathic scoliosis (AIS) surgery.

PURPOSE

This study aimed to evaluate the effects of multilevel facetectomy and screw density on sagittal plane correction in patients with main thoracic (MT) AIS curve.

STUDY DESIGN

A retrospective correlation and comparative analysis of prospectively collected, consecutive, non-randomized series of patients at a single institution was undertaken.

PATIENT SAMPLE

Sixty-four consecutive patients with Lenke type 1 AIS treated with posterior correction and fusion surgery using simultaneous double-rod rotation technique were included.

OUTCOME MEASURES

Patient demographics and preoperative and 2-year postoperative radiographic measurements were the outcome measures for this study.

METHODS

Multiple stepwise linear regression analysis was conducted between change in TK (T5-T12) and the following factors: age at surgery, Risser sign, number of facetectomy level, screw density, preoperative main thoracic curve, flexibility in main thoracic curve, coronal correction rate, preoperative TK, and preoperative lumbar lordosis. Patients were classified into two groups: TK<15° group defined by preoperative TK below the mean degree of TK for the entire cohort (<15°) and the TK≥15° group, defined by preoperative TK above the mean degree of kyphosis (≥15°). Independent sample t tests were used to compare demographic data as well as radiographic outcomes between the two groups. There were no study-specific biases related to conflicts of interest.

RESULTS

The average preoperative TK was 14.0°, which improved significantly to 23.1° (p<.0001) at the 2-year final follow-up. Greater change in TK was predicted by a low preoperative TK (p<.0001). The TK <15° group showed significant correlation between change in TK and number of facetectomy level (r=0.492, p=.002). Similarly, significant correlation was found between change in TK and screw density (r=0.333, p=.047). Conversely, in the TK ≥15° group, correlation was found neither between change in TK and number of facetectomy level (r=0.047, p=.812), nor with screw density (r=0.030, p=.880). Furthermore, in patients with preoperative TK<15°, change in TK was significantly correlated with screw density at the concave side (r=0.351, p=.036) but not at the convex side (r=0.144, p=.402).

CONCLUSIONS

In patients with hypokyphotic thoracic spine, significant positive correlation was found between change in TK and multilevel facetectomy or screw density at the concave side. This indicates that in patients with AIS who have thoracic hypokyphosis as part of their deformity, the abovementioned factors must be considered in preoperative planning to correct hypokyphosis.

Effects of Multilevel Facetectomy and Screw Density on Postoperative Changes in Spinal Rod Contour in Thoracic Adolescent Idiopathic Scoliosis Surgery

Flattening of the preimplantation rod contour in the sagittal plane influences thoracic kyphosis (TK) restoration in adolescent idiopathic scoliosis (AIS) surgery. The effects of multilevel facetectomy and screw density on postoperative changes in spinal rod contour have not been documented. This study aimed to evaluate the effects of multilevel facetectomy and screw density on changes in spinal rod contour from before implantation to after surgical correction of thoracic curves in patients with AIS prospectively. The concave and convex rod shapes from patients with thoracic AIS (n = 49) were traced prior to insertion. Postoperative sagittal rod shape was determined by computed tomography. The angle of intersection of the tangents to the rod end points was measured. Multiple stepwise linear regression analysis was used to identify variables independently predictive of change in rod contour (Δθ). Average Δθ at the concave and convex side were 13.6° ± 7.5° and 4.3° ± 4.8°, respectively. The Δθ at the concave side was significantly greater than that of the convex side (P < 0.0001) and significantly correlated with Risser sign (P = 0.032), the preoperative main thoracic Cobb angle (P = 0.031), the preoperative TK angle (P = 0.012), and the number of facetectomy levels (P = 0.007). Furthermore, a Δθ at the concave side ≥14° significantly correlated with the postoperative TK angle (P = 0.003), the number of facetectomy levels (P = 0.021), and screw density at the concave side (P = 0.008). Rod deformation at the concave side suggests that corrective forces acting on that side are greater than on the convex side. Multilevel facetectomy and/or screw density at the concave side have positive effects on reducing the rod deformation that can lead to a loss of TK angle postoperatively.