Adolescent idiopathic scoliosis treated with posteromedial translation: radiologic evaluation with a 3D low-dose system

Maximal Axial Vertebral Rotation in Adolescent Idiopathic Scoliosis: Is the Apical Vertebra the Most Rotated?

STUDY DESIGN

Retrospective cross-sectional study.

OBJECTIVES

It is generally believed that the apical vertebra has the largest axial rotation in adolescent idiopathic scoliosis. We investigated the relationship between apical axial vertebral rotation (apicalAVR) and maximal axial vertebral rotation (maxAVR) in both major and minor curves using biplanar stereo-imaging.

METHODS

EOS 2D/3D biplanar radiograph images were collected from 332 patients with adolescent idiopathic scoliosis (Cobb angle range 10°-122°, mean age 14.7 years). Based on the X-ray images, with the help of 3D full spine reconstructions Cobb angle, curvature level, apicalAVR and maxAVR were determined. These parameters were also determined for minor curves in Lenke 2, 3, 4, 6 type patients. Maximal thoracic rotation and maximal thoracolumbar/lumbar rotation were calculated. Statistical analysis was performed with descriptive statistics, Shapiro-Wilk test, and Wilcoxon signed-rank test.

RESULTS

The apical vertebrae were the most rotated vertebra in only 40.4% of the major curves, and 31.7% in minor curves. MaxAVR significantly exceeded apicalAVR values in the major curves (P < .001) as well as in minor curves (P < .001). The 2 parameters differed significantly in each severity group and Lenke type.

CONCLUSIONS

The apical vertebrae were not the most rotated vertebra in more than half of cases investigated indicating that apicalAVR and maxAVR should be considered as 2 distinct parameters, of which maxAVR fully describes the axial dimension of scoliosis. Furthermore, the substitution of maxAVR for the apicalAVR should be especially avoided in double and triple curves, as the apical vertebra was even less commonly the most rotated in minor curves.

Proximal junctional kyphosis is a rebalancing spinal phenomenon due to insufficient postoperative thoracic kyphosis after adolescent idiopathic scoliosis surgery

PURPOSE

Many authors tried to explain proximal junctional kyphosis (PJK) after adolescent idiopathic scoliosis (AIS) surgery by looking for risk factors. Latest publications focus on sagittal alignment. Each healthy adolescent has a specific thoracic kyphosis (TK) depending on their pelvic parameters and lumbar lordosis (LL). The objective of this work is to determine if the difference between TK at follow-up (TKFU) and the patient-specific TK (PSTK) plays a role in PJK occurrence after AIS surgery. The secondary objective was to find other risk factors.

METHODS

We analyzed retrospectively 570 thoracic AIS who underwent a posterior thoracic fusion from nine centers. The series was separated in two groups: with and without PJK. PSTK was calculated with the formula PSTK = 2(PT + LL-PI). TK Gap was the difference between TKFU and PSTK. Logistic regression was utilized to test the impact of TK Gap and other known risk factors on PJK occurrence.

RESULTS

Univariate analysis showed 15 factors significantly different between the groups. In a multivariate analysis, three factors had a strong significant influence on PJK: TKFU, TK Gain and TK Gap. Four additional factors affected the rate of PJK: Posterior translation on two rods, preoperative TK, preoperative LL and number of instrumented vertebrae.

CONCLUSION

PJK is related to the insufficient TK at follow-up, compared to the specific TK that every patient should have according to their pelvic parameters. PJK incidence is significantly reduced by a strong gain in TK and a thoracic selective fusion which leaves the proximal lumbar vertebrae free.

LEVEL OF EVIDENCE I

Diagnostic: individual cross-sectional studies with consistently applied reference standard and blinding.

Three-dimensional analysis of spinal deformity correction in adolescent idiopathic scoliosis: comparison of two distinct techniques

PURPOSE

To compare 3D postoperative deformity correction using two distinct commonly utilized techniques for the treatment of adolescent idiopathic scoliosis (AIS).

METHODS

AIS patients with major thoracic (Lenke 1-2) curves at two sites who underwent deformity correction via posterior spinal instrumented fusion using one of two distinct techniques were retrospectively reviewed. Patients were matched 1:1 between sites for Lenke type (95% Lenke 1) and follow-up time. The "band site" performed posteromedial translation using thoracic sublaminar bands and 5.5-mm rods. The "screw site" performed spine derotation using differential rod contouring with pedicle screws and 5.5-mm rods. 3D measures of deformity from spinal reconstructions were compared between sites.

RESULTS

Preoperatively, the groups had similar thoracic curve magnitudes (band, 55 ± 12° vs. screw, 52 ± 10°; p > 0.05); the "screw site" had less T5-T12 kyphosis (2 ± 14° vs. 7 ± 12°, p = 0.05) and greater thoracic apical rotation (- 19 ± 7° vs. - 14 ± 8°, p = 0.007). Postoperatively, the "screw site" had greater percent correction (61% vs. 76%, p < 0.001) and kyphosis restoration (p = 0.002). The groups achieved a similar amount of apical derotation (p = 0.9). The "band site" used cobalt chromium rods exclusively; the "screw site" used cobalt chromium (3%) and stainless steel (97%; p < 0.001). The "band site" performed significantly longer fusions.

CONCLUSIONS

Significant variations were found between two commonly utilized techniques in AIS surgery, including rod material, correction mechanisms, and fusion levels. Significantly, a greater 3D deformity correction of the coronal and sagittal planes was observed at the "screw site" compared to the "band site", but with no difference in axial plane correction.

Axial plane characteristics of thoracic scoliosis and their usefulness for determining the fusion levels and the correction technique

PURPOSE

There is insufficient information regarding axial plane characteristics of scoliosis despite its 3D nature. The posterior-anterior vertebral vector (VV) has been proposed to characterize the axial plane appearances of the thoracic scoliosis. This study aimed to highlight the importance of knowledge of axial plane features when determining fusion levels and correction techniques of thoracic curves.

METHODS

Altogether, 233 thoracic curves were analyzed using the VV after proving its usability instead of 3D angles to determine axial plane parameters such as apical vertebral (APV) axial rotations, APV lateral displacement, and intervertebral rotations (IVR). K-means clustering and regression analysis were used to identify axial plane curve patterns and determine the relationship between the coronal angles and axial plane characteristics, respectively.

RESULTS

A close correlation was found between 3D angles and VV projected angles. Eight axial plane clusters were distinct, exhibiting different lateral APV displacement toward the interacetabular axis with relatively small axial rotations and a simultaneous decrease in sagittal curves. The regression analysis showed that the correlation of coronal curve magnitude was significantly stronger (r = 0.78) with APV lateral translation than with APV axial rotation (r = 0.65).

CONCLUSION

Based on these findings, the primary goal of scoliosis correction should focus on minimizing lateral translation rather than eliminating axial rotation. Knowing the IVR in the axial plane helps accurately determine the limits of the structural curves. VV-based axial views can facilitate the accurate determination of the end vertebrae and selection of the appropriate correction technique of the curve. These slides can be retrieved under Electronic Supplementary Material.

Bivertebral autostable claws for the proximal fixation in thoracic adolescent idiopathic scoliosis surgery

STUDY DESIGN

Retrospective monocentric study.

OBJECTIVES

To report radiologic outcomes of a consecutive series of AIS patients, operated with a bivertebral autostable claw for the upper instrumentation over a 5-year period. The upper fixation represents the weakest part of long constructs because of local anatomy and the high pull-out forces. Various implants have been proposed, but proximal junctional failures (PJF) and shoulder imbalance still occur with variable incidence. The autostable claw is a new implant, safe, and low profile, combining the mechanical strength of hooks with the initial stability of pedicle screws.

METHODS

All AIS patients operated between January 2010 and July 2015 for a Lenke 1 or 2 curve with the bivertebral autostable claw were included. A minimum 2-year follow-up was required. Full-spine biplanar stereoradiographs were performed preoperatively, within 8 weeks postoperative and at latest examination. Local and global sagittal and coronal parameters were analyzed and complications were reported.

RESULTS

237 patients (191 Lenke 1 and 46 Lenke 2) were included, with a mean follow-up of 4.1 ± 0.6 years. PJF occurred in 2 patients (0.8%), and radiologic PJKs were observed in 8.4% of the series. Shoulder balance was efficiently restored or maintained in 88.2%.

CONCLUSIONS

The bivertebral autostable claw is a safe and robust alternative to pedicle screws for proximal fixation in AIS long constructs. Compression and/or distraction can be applied to level shoulders, and mechanical failures remain rare at 4-year follow-up.

LEVEL OF EVIDENCE

IV.

Sublaminar polyester bands for the correction of idiopathic and neuromuscular scoliosis

Recent literature suggests that sublaminar bands (SB) can provide good coronal plane correction, comparable to pedicle screw constructs, as well as good correction in the sagittal plane, even in patients with preoperative hypokyphosis; comparable results have been reported in patients with adolescent idiopathic scoliosis (AIS) and in patients with neuromuscular scoliosis (NMS). Two types of SB constructs can be performed: the band-only construct, indicated for non-ambulatory patients with NMS, and the hybrid construct indicted for ambulatory patients with NMS and for patients with AIS. SB are made of polyester or acrylic material and do provide a safe alternative to sublaminar Luque-type wires (stainless steel) as well as an increased contact area between SB and bone allowing higher corrective forces and reduced laminar fracture risk; the use of SB is not associated with increased risk of neurological injury nor with an increased risk of deep postoperative infection. SB used in a hybrid or in a band-only construct in patients with AIS and NMS, appear to be safe in a trained surgeon hands and can achieve well-balanced spine in both coronal and sagittal planes. This article aimed to provide a review of how SB can restore normal frontal and sagittal spine alignment in patients with AIS and NMS.

Decreased Vertical Trunk Inclination Angle and Pelvic Inclination as the Result of Mid-High-Heeled Footwear on Static Posture Parameters in Asymptomatic Young Adult Women

The influence of high-heel footwear on the lumbar lordosis angle, anterior pelvic tilt, and sacral tilt are inconsistently described in the literature. This study aimed to investigate the impact of medium-height heeled footwear on the static posture parameters of homogeneous young adult standing women. Heel geometry, data acquisition process, as well as data analysis and parameter extraction stage, were controlled. Seventy-six healthy young adult women with experience in wearing high-heeled shoes were enrolled. Data of fifty-three subjects were used for analysis due to exclusion criteria (scoliotic posture or missing measurement data). A custom structured light surface topography measurement system was used for posture parameters assessment. Three barefoot measurements were taken as a reference and tested for the reliability of the posture parameters. Two 30-degree wedges were used to imitate high-heel shoes to achieve a repeatable foot position. Our study confirmed the significant (p < 0.001) reduced vertical balance angle and pelvis inclination angle with large and medium-to-large effects, respectively, due to high-heel shoes. No significant differences were found in the kyphosis or lordosis angles. High-heeled shoes of medium height in young asymptomatic women can lead to a straightening effect associated with a reduced vertical balance angle and decreased pelvic inclination.

Pulmonary Function After Convex Thoracoplasty in Adolescent Idiopathic Scoliosis Patients Treated by Posteromedial Translation

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

To analyze the morbidity of thoracoplasty, and more specifically its effect on pulmonary function, after surgery with hybrid constructs using sublaminar bands in adolescent idiopathic scoliosis (AIS).

BACKGROUND

Cosmetic concern is one of the main reasons to consider surgery in adolescent idiopathic scoliosis. Several studies have demonstrated significant improvement of self-image scores after thoracoplasty. However, consequences of thoracoplasty on pulmonary function (ie, pulmonary function tests [PFTs]) remain controversial.

METHODS

After institutional review board approval, 96 consecutive AIS patients with thoracic curves (Lenke 1 and 2) were included between January 2014 and November 2015. All patients underwent low-dose stereoradiography with 3D reconstructions. Surgical procedure was the same in all patients: posterior correction using posteromedial translation technique with hybrid constructs (thoracic sublaminar bands and lumbar pedicle screws). Pulmonary function was explored with PFTs (forced vital capacity, forced expiratory volume in 1 second, and total lung capacity). Radiographic parameters and PFT results were compared between patients with and without thoracoplasty preoperatively and at two years postoperation.

RESULTS

Mean age was 15 ± 2 years, and body mass index averaged 18.8 ± 2.6. Thirty-six patients (37.5%) underwent thoracoplasty. Both groups were comparable preoperatively regarding demographic data, radiographic parameters, and PFT results. No significant difference was found between groups regarding postoperative correction rates. At the two-year follow-up, PFT results were similar to the preoperative ones and no difference was observed between groups. However, pleural effusions were reported in 26 patients (72%) on chest radiographs. Only one pleural effusion due to thoracoplasty required drainage.

CONCLUSION

Results of the current study demonstrated that thoracoplasty associated with posteromedial translation technique did not alter PFT results at two years postoperation. The morbidity of the procedure is limited, and it can therefore be considered in patients with high cosmetic demand and significant residual rib hump after main curve correction. However, hump height and pain evaluation would be interesting data in a prospective study.

LEVEL OF EVIDENCE

Level IV.

Compensation of Respiratory-Related Postural Perturbation Is Achieved by Maintenance of Head-to-Pelvis Alignment in Healthy Humans

The maintenance of upright balance in healthy humans requires the preservation of a horizontal gaze, best achieved through dynamical adjustments of spinal curvatures and a pelvic tilt that keeps the head-to-pelvis alignment close to vertical. It is currently unknown whether the spinal and pelvic compensations of respiratory-related postural perturbations are associated with preservation of the head-to-pelvis vertical alignment. We tested this hypothesis by comparing postural alignment variables at extreme lung volume (total lung capacity, TLC; residual volume, RV) with their reference value at functional residual capacity (FRC). Forty-eight healthy subjects [22 women; median age of 34 (26; 48) years] were studied using low dose biplanar X-rays (BPXR; EOS^®system). Personalized three-dimensional models of the spine and pelvis were reconstructed at the three lung volumes. Extreme lung volumes were associated with changes of thoracic curvature bringing it outside the normal range. Maximal inspiration reduced thoracic kyphosis [T1–T12 angle = 47° (37; 56), -4° variation (-9; 1), p = 0.0007] while maximal expiration induced hyperkyphosis [T1–T12 angle = 63° (55; 68); +10° variation (5; 12), p = 9 × 10^-12]. Statistically significant (all p < 0.01) cervical and pelvic compensatory changes occurred [C3–C7 angle: +4° (-2; 11) and pelvic tilt +1° (0; 3) during maximal inspiration; C3–C7 angle: -7° (-18; -1) and pelvic tilt +5° (1; 8) during maximal expiration], resulting in preserved head-to-pelvis alignment (no change in the angle between the vertical plane and the line connecting the odontoid process and the midpoint of the line connecting the center of the two femoral heads ODHA). Lung volume related postural perturbations were more marked as a function of age, but age did not affect the head-to-pelvis alignment. These findings should help understand balance alterations in patients with chronic respiratory diseases that modify lung volume and rib cage geometry.

The third dimension of scoliosis: The forgotten axial plane

Idiopathic scoliosis is a three-dimensional (3D) deformity of the spine. In clinical practice, however, the diagnosis and treatment of scoliosis consider only two dimensions (2D) as they rely solely on postero-anterior (PA) and lateral radiographs. Thus, the projections of the deformity are evaluated in only the coronal and sagittal planes, whereas those in the axial plane are disregarded, precluding an accurate assessment of the 3D deformity. A universal dogma in engineering is that designing a 3D object requires drawing projections of the object in all three planes. Similarly, when dealing with a 3D deformity, knowledge of the abnormalities in all three planes is crucial, as each plane is as important as the other two planes. This article reviews the chronological development of axial plane imaging and spinal deformity measurement.

How to Optimize Axial Correction Without Altering Thoracic Sagittal Alignment in Hybrid Constructs With Sublaminar Bands: Description of the "Frame" Technique

STUDY DESIGN

Retrospective monocentric database study.

OBJECTIVES

To describe the "frame" reduction technique and report the 3D quantitative analysis of postoperative corrections in a consecutive series of thoracic adolescent idiopathic scoliosis (AIS) patients.

SUMMARY OF BACKGROUND DATA

Posteromedial translation technique using sublaminar bands have been proved to be efficient and safe for 3D correction of the deformity and overall cosmetic aspect of the trunk. However, the ability to correct the axial plane may tend to rotate the vertebra clockwise instead of counterclockwise, thus increasing apical vertebra axial rotation (AVR) and the rib hump. A technical improvement was developed to emphasize axial correction.

METHODS

60 thoracic AIS patients consecutively operated by posteromedial translation using the "frame" reduction technique were included with a minimum 2-year follow-up. Precontoured rods were connected with fixed transverse connectors according to a personalized preoperative planning. Rods were first inserted distally in the pedicle screws to achieve lumbar correction, and then in the upper anchors, and finally sublaminar bands were connected to their corresponding rods to progressively bring the concave lamina to the concave rod to correct the thoracic deformity. Sagittal and coronal 3D measures were performed preoperatively and at the latest follow-up using SterEOS (EOS Imaging, Paris, France) to assess the efficiency of the technique.

RESULTS

The distance from the center of the apical vertebra to the reference axis in the frontal plane was reduced from 4.7 to 1.1 cm, traducing the efficient medial translation of the spine during correction. T1-T12 kyphosis significantly increased after surgery (28°-35°). 3D location of the upper instrumented vertebra (UIV) was not affected. The apical rotation was significantly reduced after surgery (19°-11°), and the AVR correction rate averaged 42.2%.

CONCLUSION

The "frame" technique is an innovative way of using polyester bands, optimizing axial correction while respecting sagittal alignment.

LEVEL OF EVIDENCE

Level IV.

Coronal Balance vs. Sagittal Profile in Adolescent Idiopathic Scoliosis, Are They Correlated?

Background: Clinical evaluation of the postural balance in adolescent idiopathic scoliosis has been evaluated by coronal and sagittal parameters. The relationship between coronal and sagittal parameters has not been fully studied in adolescent idiopathic scoliosis. Objective: This study aimed to evaluate the relationship between coronal and sagittal parameters in idiopathic scoliosis. Methods: One hundred and three patients of Adolescent Idiopathic Scoliosis (AIS) were recruited. Radiographs were evaluated for the following spine and pelvic measurements. Coronal parameters including thoracic Cobb angle (TC), lumbar Cobb angle (LC), global coronal balance (GCB), apical translation of the major curve (AT), and coronal pelvic tilt (CPT) were analyzed. Sagittal parameters including thoracic kyphosis (TK), lumbar lordosis (LL), sagittal vertical axis (SVA), pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS) were analyzed. A canonical correlation analysis was performed between all of the coronal parameters and sagittal parameters. Results: One hundred and three patients were recruited (male 15, female 88; aged 12.5 ± 1.5 years). Compared with the published age-matched normal population, TK, PI, LL, and SS were not statistically different in the normal group. However, PT was significantly increased in patent groups (P = 0.003). Canonical correlation analysis showed strong correlation between coronal parameters and sagittal parameters, F _{(20, 313)} = 2.44, p = 0.001. SVA was not correlated with any coronal parameter. Conclusions: Children with AIS showed an increased pelvic tilt sign. In this study, TC, LC, GCB, AT, CPT, TK, LL, SVA, PI, PT, and SS contributed to the postural balance. In AIS, coronal balance is contributed to sagittal balance.

New sagittal classification of AIS: validation by 3D characterization

INTRODUCTION AND AIM

In order to improve surgical planning of sagittal correction in AIS, we proposed a new sagittal classification-Abelin-Genevois et al. Eur Spine J (27(9):2192-2202, 2018. https://doi.org/10.1007/s00586-018-5613-1 ). The main criticism is related to the fact that 2D lateral view results from the projection of the 3D deformity. The aim of this study is to show that the new sagittal classification system is a reliable system to describe the different sagittal scenarios that AIS could create both in 2D and 3D.

METHODS

We performed retrospective radiograph analysis of prospectively collected data from 93 consecutive AIS patients who underwent an examination of the whole spine using the EOS^® imaging system. 2D (Keops^®) and 3D analyses (sterEOS^®) provided frontal and sagittal spinal and spinopelvic parameters. In addition, 3D analysis provided apical vertebra rotation (AVR).

RESULTS

Comparing 2D and 3D measurements for the general cohort, excellent correlation can be found for all parameters, but only fairly good for T10L2 and L1S1 angles. The highest variability was observed for T10L2, differences between 2D and 3D measurements being greater when the Cobb angle increased. AVR did not influence concordance between 2D and 3D measurements. Eighty-two percent were similarly classified in 2D and 3D according to the new classification. Misclassified patients were all AIS sagittal type 3 in 3D analysis, thoracolumbar junction (TLJ) lordosis being underestimated on 2D view.

DISCUSSION

In conclusion, for the majority of cases (82%), 2D analysis may provide enough information for decision making when using a semi-automated 2D measurement system. However, in severe cases, especially when Cobb angle exceeds 55°, 3D analysis should be used to get a more accurate view on the thoracolumbar junction behavior. These slides can be retrieved under Electronic Supplementary Material.

Quasi-automatic 3D reconstruction of the full spine from low-dose biplanar X-rays based on statistical inferences and image analysis

PURPOSE

To design a quasi-automated three-dimensional reconstruction method of the spine from biplanar X-rays as the daily used method in clinical routine is based on manual adjustments of a trained operator and the reconstruction time is more than 10 min per patient.

METHODS

The proposed method of 3D reconstruction of the spine (C3-L5) relies first on a new manual input strategy designed to fit clinicians' skills. Then, a parametric model of the spine is computed using statistical inferences, image analysis techniques and fast manual rigid registration.

RESULTS

An agreement study with the clinically used method on a cohort of 57 adolescent scoliotic subjects has shown that both methods have similar performance on vertebral body position and axial rotation (null bias in both cases and standard deviation of signed differences of 1 mm and 3.5° around, respectively). In average, the solution could be computed in less than 5 min of operator time, even for severe scoliosis.

CONCLUSION

The proposed method allows fast and accurate 3D reconstruction of the spine for wide clinical applications and represents a significant step towards full automatization of 3D reconstruction of the spine. Moreover, it is to the best of our knowledge the first method including also the cervical spine. These slides can be retrieved under electronic supplementary material.

Spinal phantom comparability study of Cobb angle measurement of scoliosis using digital radiographic imaging

Background

Computed radiography (CR), digital radiography (DR) and biplanar radiography (EOS™ imaging system) are common imaging tools for radiographic evaluation of adolescent idiopathic scoliosis (AIS). The effect of imaging methods in relation to later-on Cobb angle measurements on radiographs is not yet quantified. The study aimed to examine the compatibility between CR, DR and EOS for scoliotic quantification by evaluating the reliability, agreement of different imaging methods, and assessing the prediction performance for EOS measurement from that of CR and DR.

Method

A flexible spine phantom was used to simulate 32 different scoliotic curves ranging from 10° to 60°. Each curvature was imaged using DR, CR and EOS systems accordingly. Each of the six observers independently measured Cobb angle twice on each image at a two-week interval. Intraclass correlation coefficient (model 2 and 3), Bland-Altman plot and linear regression analysis were completed to evaluate the reliability, agreement, and the prediction of Cobb angle measurement, respectively.

Results

Reliability analysis showed excellent intra-observer reliability (Intraclass correlation coefficient >0.9) for each observer and good inter-observer reliability (Intraclass correlation coefficient = 0.84 for EOS; 0.739 for CR; 0.877 for DR) for each method. Bland-Altman plots demonstrated good agreement between imaging methods without fixed or proportional bias. Excellent coefficient of determination was achieved, with 0.980 for CR versus EOS measurements, and 0.973 for DR versus EOS measurements.

Conclusions

Radiographs produced by all of the three methods can provide reliable and accurate Cobb angle measurements for scoliosis assessments. None of the methods systemically underestimates or overestimates the Cobb angle measurement. Additionally, all of the evaluated methods are satisfactory in obtaining images for Cobb angle measurement in AIS. However, the 3D post-processing techniques offered by EOS should also be taken into consideration as it takes a vital role in treatment and monitoring of 3D deformity in the case of scoliosis.

The translational potential of this article

In view of the limited availability of biplanar radiography (EOS™ imaging system), computed radiography and digital radiography are demonstrated to be reliable alternatives in scoliosis monitoring as evident in the reliability, agreement and prediction of Cobb angle measurement.

Factors influencing spinal curvature measurements on ultrasound images for children with adolescent idiopathic scoliosis (AIS)

The measurements of spinal curvatures using the ultrasound (US) imaging method on children with scoliosis have been comparable with radiography. However, factors influencing the reliability and accuracy of US measurement have not been studied. The purpose of this study is to investigate the effects of curve features and patients' demographics on US measurements and to determine which factors influence the reliability and accuracy. Two hundred children with scoliosis were recruited and scanned with US by one experienced operator and three trainees. One experienced rater measured the proxy Cobb angles from US images twice one week apart and compared the results with clinical radiographic records. The correlation and accuracy between the US and radiographic measurements were subdivided by different curve severities, curve types, subjects' weight status and US acquisition experiences. A total of 326 and 313 curves were recognized from radiographs and US images, respectively. The mean Cobb angles of the 13 missing curves were 17.4±7.4° and 11 at the thoracic region. Among the 16 curves showing large discrepancy (≥6°) between US and radiographic measurements, 7 were main thoracic and 6 were lumbar curves. Twelve had axial vertebral rotation (AVR) greater than 8°. The US scans performed by the experienced operator showed fewer large discrepancy curves, smaller difference and higher correlation than the scans from the trainees (3%, 1.7±1.5°, 0.95 vs 6%, 2.4±1.8°, 0.90). Only 4% missing and 5% large discrepancy curves were demonstrated for US measurements in comparison to radiography. The missing curves were mainly caused by small severity and in the upper spinal region. There was a higher chance of the large discrepancy curves in the main thoracic and lumbar regions with AVR>8°. A skilled operator acquired better US images and led to more accurate measurements especially for those subjects with larger curvatures, AVR and body mass index (BMI).

Preliminary experience with SpineEOS, a new software for 3D planning in AIS surgery

PURPOSE

Preoperative planning of scoliosis surgery is essential in the effective treatment of spine pathology. Thus, precontoured rods have been recently developed to avoid iatrogenic sagittal misalignment and rod breakage. Some specific issues exist in adolescent idiopathic scoliosis (AIS), such as a less distal lower instrumented level, a great variability in the location of inflection point (transition from lumbar lordosis to thoracic kyphosis), and sagittal correction is limited by both bone-implant interface. Since 2007, stereoradiographic imaging system is used and allows for 3D reconstructions. Therefore, a software was developed to perform preoperative 3D surgical planning and to provide rod's shape and length. The goal of this preliminary study was to assess the feasibility, reliability, and the clinical relevance of this new software.

METHODS

Retrospective study on 47 AIS patients operated with the same surgical technique: posteromedial translation through posterior approach with lumbar screws and thoracic sublaminar bands. Pre- and postoperatively, 3D reconstructions were performed on stereoradiographic images (EOS system, Paris, France) and compared. Then, the software was used to plan the surgical correction and determine rod's shape and length. Simulated spine and rods were compared to postoperative real 3D reconstructions. 3D reconstructions and planning were performed by an independent observer.

RESULTS

3D simulations were performed on the 47 patients. No difference was found between the simulated model and the postoperative 3D reconstructions in terms of sagittal parameters. Postoperatively, 21% of LL were not within reference values. Postoperative SVA was 20 mm anterior in 2/3 of the cases. Postoperative rods were significantly longer than precontoured rods planned with the software (mean 10 mm). Inflection points were different on the rods used and the planned rods (2.3 levels on average).

CONCLUSION

In this preliminary study, the software based on 3D stereoradiography low-dose system used to plan AIS surgery seems reliable for preoperative planning and precontoured rods. It is an interesting tool to improve surgeons' practice, since 3D planning is expected to reduce complications such as iatrogenic malalignment and to help for a better understanding of the complications, choosing the location of the transitional vertebra. However, further work is needed to improve thoracic kyphosis planning. These slides can be retrieved under Electronic Supplementary Material.

Reliability and Reproducibility of Subject Positioning with EOS Low-Dose Biplanar X-ray

BACKGROUND

EOS low-dose biplanar X-ray used with tantalum bead implantation is an appealing imaging modality to evaluate limb length and physeal growth due its relatively low radiation exposure, excellent inter- and intra-observer reliability, and minimal magnification/shrinkage error.

QUESTIONS/PURPOSES

The purpose of this study was to establish the error in total length and inter-bead distances using EOS and tantalum beads due to variable positioning in the EOS gantry, by assessing variation in measurements made on the same subject repeatedly positioning by one positioner (intra-positioner measurement error) and variation in measurements made on the same subject with positioning by multiple positioners (inter-positioner measurement error).

METHODS

Tantalum bead markers were placed about the distal femoral physis of a cadaveric lamb femur. Three investigators positioned the femur in the EOS gantry 10 times, totaling 30 EOS scans. Total limb length and inter-bead distances were measured on AP and lateral views; mean and standard error were calculated. A random effects analysis of variance for nested data was used to determine the proportion of variation due to differences between positioners and differences between positioning by the same positioner.

RESULTS

Intra-positioner measurement error ranged from 0.01 to 0.06 mm. Inter-positioner measurement error ranged from 0.00 to 0.09 mm.

CONCLUSIONS

EOS has relatively low radiation and allows standing assessment of limb length and alignment. In this study, length measurements and inter-bead distances demonstrated minimal error due to positioning in the EOS gantry, documenting that there is minimal error from positioning, minimal magnification/shrinkage error, and exceptional inter and intra-rater reliability. EOS is the preferred method for length and angular measurements, and with tantalum beads, is ideal for measuring growth about the physis.

Assessment of Curve Flexibility on Scoliotic Surgical Candidates Using Ultrasound Imaging Method

The ultrasound imaging method was implemented to assess the spinal curve flexibility of scoliotic surgical candidates, or how much correction it can achieve while patients are bending or lying down. Fifteen participants were recruited. Pre-operative radiographs and ultrasound images in both standing and bending positions were acquired. The post-operative standing radiographs were obtained 1 wk after surgery. Two raters (RZ, EL) measured the ultrasound images twice, 1 wk apart. A curve correction index (C_I) was developed to estimate the curve flexibility. The C_I from the pre-operative bending radiograph, ultrasound and post-operative radiograph were 0.51 ± 0.18; R1: 0.74 ± 0.08 vs R2: 0.72 ± 0.09 and 0.60 ± 0.10, respectively. The correlation of C_I between ultrasound and post-operative radiography was slightly higher than the pre-operative bending and post-operative radiography. This pilot study demonstrated the bending ultrasound method is a promising supplemental tool to assess curve flexibility before surgical intervention for scoliotic surgical candidates.

How Sublaminar Bands Affect Postoperative Sagittal Alignment in AIS Patients with Preoperative Hypokyphosis? Results of a Series of 34 Patients with 2-Year Follow-Up

Hypokyphosis is currently observed in thoracic idiopathic scoliosis. The use of sublaminar bands allows a good restoration of sagittal balance of the spine. The aim of the study was to provide a middle-term radiographic analysis of patients with adolescent idiopathic scoliosis with preoperative hypokyphosis treated by posterior arthrodesis with sublaminar bands. This retrospective study included 34 patients with Lenke 1 scoliosis associated with hypokyphosis (TK < 20°). A radiographic evaluation was performed with a 2-year follow-up. Cobb angle, cervical lordosis, thoracic kyphosis, lumbar lordosis, and pelvic parameters were measured preoperatively, postoperatively, and at 6-month and 2-year follow-up. The mean preoperative thoracic kyphosis was 10.5° versus 24.1° postoperatively (p < 0.001), representing a mean gain of 13°. Cobb angle ranged from 59.3° to 17.9° postoperatively (mean correction 69%, p < 0.001). Cobb angle increased between the immediate postoperative measurement and the 6-month follow-up (17.9 versus 19.9, p = 0.03). Cervical curvature changed from a 5.6° kyphosis to a 3.5° lordosis (p = 0.001). Concerning lumbar lordosis, preoperative measurement was 39.7° versus 41.3° postoperatively (p = 0.27). At 6-month follow-up, lumbar lordosis significantly increased to 43.6° (p = 0.03). All parameters were stable at final follow-up. Correction performed by sublaminar bands is efficient for both fontal and sagittal planes. Moreover, the restoration of normal thoracic kyphosis is followed by an adaptation of the adjacent curvatures with improved cervical lordosis and lumbar lordosis.

The effect of sublaminar wires on the rib hump deformity during scoliosis correction manoeuvres

INTRODUCTION

During thoracic curve correction, the tightening of the sublaminar wires through concavity creates a medial and a dorsal translation of the spine. However, little is known about the effect of the sublaminar wires on the axial plane.

METHODS

This is prospective case series analysis of 30 consecutive surgical patients with main thoracic adolescent idiopathic scoliosis. All of the patients were fused with hybrid instrumentation (apical concavity-sublaminar wires) and differential rod contouring (over-kyphosis concavity/under-kyphosis convexity). The degrees of the rib hump were measured with a scoliometer placed at the apex of the deformity at five different times: (1) preoperatively through the Adam's test, and during surgery (sterilised scoliometer), (2) with the patient lying prone, (3) after the Ponte osteotomies, (4) after the apical sublaminar tightening, and (5) after convexity apical derotation and compression manoeuvres.

RESULTS

(1) Preoperatively, the Adam's test was 16.3° ± 4.6. (2) Lying prone and under general anaesthesia, it decreased to 11.4° ± 3.9. (3) After exposure and Ponte osteotomies, it was 7.1° ± 4. (4) After the wire tightening, it was 10.8° ± 4.7. (5) After the convexity manoeuvres, it was 4.8° ± 3.7. The degrees of the rib hump final correction were 11.6° ± 4 (70 % correction). The tightening of the sublaminar wires increased the rib hump by 3.5°.

CONCLUSIONS

The sublaminar wire tightening towards the concave rod seemed to create an effect opposite of the desired effect, increasing the apical rotation and the thoracic rib hump deformity. Convexity manoeuvres (apical screw derotation and compression) are necessary and must be coupled with an under-bending of the convex rod to neutralise this effect.

Sagittal spino-pelvic adjustment in severe Lenke 1 hypokyphotic adolescent idiopathic scoliosis patients

PURPOSE

The human standing position requires permanent reciprocal spino-pelvic adjustments to obtain a dynamic and economic posture. This study focuses on a hypokyphotic Lenke 1 adolescent idiopathic scoliosis (AIS) patients cohort and points out their particular lumbo-pelvic adaptive mechanisms to maintain a neutral sagittal balance.

METHODS

Preoperative retrospective analysis of prospectively collected data on a monocentric cohort of 455 AIS patients planned for corrective surgery. Radiological low-dose system coupled with a validated clinical routine software allowed to obtain data from eighty-four hypokyphotic [thoracic kyphosis (TK) <20°] Lenke 1 patients and were separately analyzed. Bilateral Student and one-way ANOVAs were conducted for statistical analysis.

RESULTS

Mean Cobb angle was 46.3° (±7.2), TK was 11° (±7.1), sagittal vertical axis (SVA) was -10.1 mm (±30.9), pelvic incidence (PI) was 55.7° (±12.9). Fifty percents of patients were posteriorly imbalanced. Among them, patients with a low PI used an anteversion of their pelvis [indicated by a high pelvic tilt (PT) angle] but were not able to increase their lumbar lordosis (LL) to minimize the posterior spinal shift.

CONCLUSIONS

Hypokyphotic Lenke 1 AIS patients use lumbo-pelvic compensatory mechanisms to maintain their global balance with a poor effectiveness. Subjects with a low PI have a restricted range of LL adaptation. Attention should be paid during surgical planning not to overcorrect lordosis in the instrumented levels in case of non-selective fusion, that may induce posterior shift of the fusion mass and expose to junctional syndromes and poor functional outcomes in this particular patients.

Flexibility analysis in adolescent idiopathic scoliosis on side-bending images using the EOS imaging system

INTRODUCTION

Analysis of preoperative flexibility in adolescent idiopathic scoliosis (AIS) is essential to classify the curves, determine their structurality, and select the fusion levels during preoperative planning. Side-bending x-rays are the gold standard for the analysis of preoperative flexibility. The objective of this study was to examine the feasibility and performance of side-bending images taken in the standing position using the EOS imaging system.

MATERIAL AND METHODS

All patients who underwent preoperative assessment between April 2012 and January 2013 for AIS were prospectively included in the study. The work-up included standing AP and lateral EOS x-rays of the spine, standard side-bending x-rays in the supine position, and standing bending x-rays in the EOS booth. The irradiation dose was measured for each of the tests. Two-dimensional reducibility of the Cobb angle was measured on both types of bending x-rays.

RESULTS

The results were based on the 50 patients in the study. No significant difference was demonstrated for reducibility of the Cobb angle between the standing side-bending images with the EOS imaging system and those in the supine position for all types of Lenke deformation. The irradiation dose was five times lower during the EOS bending imaging.

CONCLUSION

The standing side-bending images in the EOS device contributed the same results as the supine images, with five times less irradiation. They should therefore be used in clinical routine.

LEVEL OF EVIDENCE

2.

Prevalence and Consequences of the Proximal Junctional Kyphosis After Spinal Deformity Surgery: A Meta-Analysis

The aim of this study was to estimate the prevalence and patient outcomes of proximal junctional kyphosis (PJK) in pediatric patients and adolescents who received surgical interventions for the treatment of a spinal deformity.Literature was searched in electronic databases, and studies were selected by following précised eligibility criteria. Percent prevalence values of the PJK in individual studies were pooled to achieve a weighted effect size under the random effects model. Subgroup and meta-regression analyses were performed to appraise the factors affecting PJK prevalence.Twenty-six studies (2024 patients) were included in this meta-analysis. Average age of the patients was 13.8 ± 2.75 years of which 32 ± 20 % were males. Average follow-up was 51.6 ± 38.8 (range 17 ± 13 to 218 ± 60) months. Overall, the percent prevalence of PJK (95% confidence interval) was 11.02 (10.5, 11.5) %; P < 0.00001 which was inversely associated with age (meta-regression coefficient: -1.607 [-2.86, -0.36]; 0.014). Revision surgery rate in the patients with PJK was 10%. The prevalence of PJK was positively associated with the proximal junctional angle at last follow-up (coefficient: 2.248; P = 0.012) and the change in the proximal junctional angle from surgery to last follow-up (coefficient: 2.139; P = 0.014) but not with preoperative proximal junctional angle.The prevalence of PJK in the children and adolescent patients is 11%. About 10% of those affected require revision surgery.

Role of Intraoperative Radiographs in the Surgical Treatment of Adolescent Idiopathic Scoliosis

BACKGROUND

One of the main goals of scoliosis surgery is to obtain a balanced fused spine. Although preoperative planning remains essential, intraoperative posteroanterior radiographs are the only available tool during the procedure to verify shoulder and coronal spinal balance and, if necessary, adjust the construct. The aim of this study was to quantify the direct influence of intraoperative radiographs on the surgical procedure itself during correction of adolescent idiopathic scoliosis.

METHODS

Retrospective analysis of prospectively collected data on a monocentric cohort of adolescent idiopathic scoliosis patients undergoing corrective surgery. A total 148 consecutive patients operated in the same department following the same validated preoperative planning method were included in this prospective radiologic study. The mean follow-up averaged 33 months. Frontal Cobb angles, T1 tilt, shoulder tilt, iliolumbar angle, and frontal balance were measured and compared on intraoperative, early postoperative, and latest follow-up radiographs. Any intraoperative modification of the correction performed after analysis of the intraoperative radiograph were recorded.

RESULTS

The analysis of all radiologic parameters was possible in 90.5% of the cases. In 9.5% of the cases, shoulders could not be properly distinguished. Significant modifications on the upper thoracic curve to correct T1 tilt or shoulder balance were performed in 29% of the patients, and changes at the distal levels were recorded in 19%, underlining planification imperfections. On postoperative standing radiographs, the average coronal parameters were neutral, without loss of correction at follow-up.

CONCLUSIONS

Intraoperative radiographs remain necessary to ensure compensation of the shortcomings of the modern preoperative planification method.

Pelvic Evaluation in Thoracolumbar Corrective Spine Surgery: How I Do It

Surgeons and radiologists have traditionally focused on frontal radiographs and the measurement of scoliosis curves as important tools in the management of spinal deformity. It has become evident, however, that the management of spinal deformity should use a multidimensional approach with an increased emphasis on standing lateral radiographs and the sagittal position of the spine. Furthermore, they have come to realize the critical role that the pelvis plays in the maintenance of posture. Failure to recognize pelvic compensation can lead to under-treatment and poor postoperative outcomes.

Evaluating Length: The Use of Low-dose Biplanar Radiography (EOS) and Tantalum Bead Implantation

BACKGROUND

Low-dose biplanar radiography (EOS) is an appealing imaging modality for use in children given its low radiation and ease of use. The goal of this study was to determine the accuracy and reliability of EOS compared with CT scanogram for measurement of leg length and to assess interrater and intrarater reliability of measured interbead distances for EOS and CT scanogram after insertion of tantalum beads into lamb femurs.

METHODS

Tantalum beads (0.8 mm) were inserted into the cortex on both the medial and lateral sides of 10 skeletally immature lamb femurs. CT scanogram and EOS imaging were obtained. Measurements of total length and distance between bead pairs were recorded on anteroposterior and lateral views by 2 orthopaedic surgeons on 2 separate occasions. Pearson correlations were performed for statistical comparisons.

RESULTS

EOS measurements showed near-perfect correlation to those of CT scanogram (r>0.96, P<0.001). Intrarater reliability was excellent for all measurements with EOS (r>0.98, P<0.001) and CT scanogram (r>0.99, P<0.001) as was interrater reliability for EOS (r>0.98, P<0.001) and CT scanogram (r>0.99, P<0.001).

CONCLUSIONS

EOS is comparable with CT scanogram in the assessment of limb length and the distance between 2 radiopaque markers. Reliability was excellent for all measurements. The combination of EOS imaging and tantalum bead implantation may be an effective way to evaluate physeal growth following procedures such as epiphysiodesis and physeal bar resection.

LEVEL OF EVIDENCE

Level II—diagnostic

EOS microdose protocol for the radiological follow-up of adolescent idiopathic scoliosis

PURPOSE

Imaging plays a key role in adolescent idiopathic scoliosis (AIS) to determine the prognosis and accordingly define the best therapeutic strategy to follow. Conventional radiographs with ionizing radiation have been associated with 1-2 % increased lifetime risk of developing cancer in children, and physicians, therefore, need a sensitive but harmless way to explore patients at risk, according to the "as low as reasonably achievable" concept. The EOS system (EOS imaging, Paris, France) is available in routine clinical use since 2007, and allows 3D reconstructions of the trunk in standing position with significant radiation reduction. With recent technical advances, further dose reduction can be obtained, but at the cost of image quality that might alter the reliability of 3D reconstructions. The aim of the present study was to analyze the reproducibility of a "microdose" protocol, and evaluate its use in clinical practice.

METHODS

32 consecutive patients followed for AIS were prospectively included. Biplanar radiographs were obtained with the EOS system according to the new microdose protocol. From the microdose images obtained, three experienced operators performed 3D reconstructions, two times for each subject in a random order (total, 192 reconstructions). The intraoperator repeatability and interoperator reproducibility were evaluated, as recommended by the International Organization for Standardization, for the most clinically relevant 3D radiological parameters.

RESULTS

The identification of the required anatomical landmarks for the "fast spine" reconstruction process was possible in all cases. None of the patients required a second acquisition for 3D analysis. Mean time for reconstruction was 5 ± 2 min. The intraoperator repeatability was better than interoperator reproducibility for all parameters, with values ranging between 3° and 8° for frontal and sagittal spinal parameters, and between 1° and 8° for pelvic measurements. The agreement was very good for all clinical measurements. No correlation was found between the BMI and the reliability of the measurements.

CONCLUSIONS

Because children are notably more sensitive to the carcinogenic effects of ionizing radiation, judicious use of imaging methods and a search for newer technologies remain necessary. Results of the current study show that the new microdose acquisition protocol can be used in clinical practice without altering the quality of the images. Relevant clinical measurements can be made manually, but the landmarks are also visible enough to allow accurate 3D reconstructions (ICC >0.91 for all parameters). The resulting radiation exposure was 5.5 times lower than that received with the prior protocol, corresponding now to a 45-fold reduction compared to conventional radiographs, and can, therefore, almost be considered negligible.

Cervical sagittal alignment in idiopathic scoliosis treated by posterior instrumentation and in situ bending

STUDY DESIGN

Retrospective radiographical analysis of cervical and thoracolumbar sagittal alignment in young adults with idiopathic scoliosis.

OBJECTIVE

To analyze cervical alignment types, the relationship between cervical and thoracolumbar alignment and the effect of posterior instrumentation.

SUMMARY OF BACKGROUND DATA

Thoracic scoliosis with hypokyphosis may decrease cervical lordosis. Additional adaptive positional changes of the mobile cervical segment may exist, because sigmoid cervical patterns are observed. Sagittal alignment of the instrumented thoracolumbar spine may influence cervical alignment.

METHODS

Pre- and postoperative full-spine radiographs of 52 patients were analyzed at 8-year average follow-up. Sagittal thoracolumbar measurements were T1 slope, T1-T4 kyphosis, T4-T12 kyphosis, L1-S1 lordosis, pelvic incidence, pelvic tilt, sacral slope, sagittal vertical axis (SVA) C7, and SVA C2. Cervical measurements were C0-C2, C2-C6, C2-C4, C4-C6, and C2-T1 lordosis, chin-brow vertical angle.

RESULTS

Five cervical alignment types were identified: lordotic, hypolordotic, kyphotic, sigmoid with cranial lordosis, and sigmoid with cranial kyphosis. Spinopelvic parameters and global thoracolumbar balance remained unchanged postoperatively. The average C2-C6 lordosis increased by 6.4° (P < 0.0001). Twenty-seven of the 52 patients changed cervical alignment postoperatively. SVA C2-C7 difference changed in this subgroup (P = 0.0159). In 21 of the 27 patients, SVA changed more than 5 mm at C2 (P = 0.0029), and in 25 of the 27 patients at C7 (P < 0.0001). A correlation existed between T4-T12 kyphosis and L1-S1 lordosis, C2-C4 and L1-S1 lordosis, L1-S1 lordosis, and pelvic tilt. T1-T4 kyphosis and T1 slope correlated with C2-T1 lordosis, but proximal junctional kyphosis was not linked to a specific cervical alignment type.

CONCLUSION

Postoperative adaptive changes occurred at C7 and C2 by shifting anteriorly or posteriorly, resulting in different radiographical cervical shapes. The amount of lumbar lordosis may influence cervical lordosis, which needs to be considered for surgical correction. Adaptive hip movements may influence thoracolumbar and cervical alignment. The amount of proximal thoracic kyphosis influenced cervical lordosis. Global thoracic hypokyphosis might influence cervical alignment, but it was not evidenced.

LEVEL OF EVIDENCE

4.