Thoracic Adolescent Idiopathic Scoliosis Research Articles

Spinal penetration index assessment in adolescent idiopathic scoliosis using EOS low-dose biplanar stereoradiography

The spinal penetration index (SPI) quantifies the portion of the rib cage occupied by vertebrae. When measured by computed tomography (CT) or magnetic resonance imaging, SPI can only be determined in the reclining position, which modifies spinal and thoracic morphology. CT results in high radiation exposure. The authors studied rib cage and spinal morphology using low-dose biplanar stereoradiography and their impact on respiratory function in adolescent idiopathic scoliosis (AIS). In eighty thoracic AIS patients, a slot-scanning radiologic device allowing simultaneous acquisition of orthogonal images and 3D reconstructions with low exposure to radiation (EOS) was used to determine thoracic volume, mean spinal penetration index (SPIm), apical spinal penetration index (SPIa), main thoracic (MT) curve Cobb angle, T4-T12 kyphosis, and apical vertebral rotation (AVR). Thoracic volume was correlated with thoracic kyphosis (r = 0.31, p = 0.006), but not with SPI, MT Cobb angle, or AVR. SPIm and SPIa were negatively correlated with thoracic kyphosis. Forced vital capacity and forced expiratory volume in 1 s were significantly lower in the hypokyphotic patients (p = 0.04, p = 0.03, respectively) and correlated with thoracic volume and T4-T12 kyphosis. No correlation was found between spinal penetration indices and pulmonary function tests, but SPIm was significantly greater in patients with obstructive syndrome (p = 0.01). With little radiation exposure, EOS biplanar stereoradiography permits routine imaging is a functional standing position. Hypokyphotic patients had significantly decreased FEV1 and FVC. SPIm was significantly higher in patients with obstructive syndrome.

Do Multilevel Ponte Osteotomies in Thoracic Idiopathic Scoliosis Surgery Improve Curve Correction and Restore Thoracic Kyphosis?

To compare the routine use of posterior-based (Ponte) osteotomies to complete inferior facetectomies in thoracic idiopathic scoliosis. Hypokyphosis is common in thoracic adolescent idiopathic scoliosis. The use of pedicle screw fixation in deformity correction can exacerbate this hypokyphosis. We hypothesized that by utilizing posterior-based Ponte osteotomies rather than facetectomies, we could improve coronal plane correction and decrease the loss of kyphosis during curve correction. The radiographs and clinical charts of patients with idiopathic scoliosis (Lenke types I, II) who underwent isolated thoracic posterior spinal fusion utilizing primarily pedicle screw constructs from January 2008 to August 2010 were reviewed. Maximum preoperative Cobb angle, thoracic kyphosis (T5-T12), levels instrumented, number of posterior-based osteotomies, operative time, estimated blood loss, and postoperative residual coronal Cobb angle and kyphosis were recorded. Operative time per level, blood loss per level, percent main curve correction, and change in thoracic kyphosis was calculated. Patients having undergone complete inferior facetectomies and those with multilevel Ponte osteotomies were then compared. Eighteen patients underwent posterior spinal fusion with osteotomies and 19 patients had complete inferior facetectomies during this time period. The osteotomy cohort had a larger preoperative Cobb angle [59±10 vs. 52±8 (mean±SD); P=0.03]. No difference was observed in the preoperative kyphosis (22±15 vs. 25±12) or in levels fused (9±1 vs. 8±1). Patients with routine osteotomies had them performed at 76% of the levels instrumented. No significant difference was found in terms of percentage of coronal plane correction (84% in both groups), average postoperative kyphosis 28±8 versus 25±7, or the change in kyphosis 6±14 versus 0±2 degrees, in the osteotomy and the facetectomy groups, respectively. Estimated blood loss per level was significantly higher in the osteotomy group (97±42 mL vs. 66±25 mL; P=0.01) as was time per level 31±5 versus 23±3 minutes/level (P<0.001). This study shows a significantly higher blood loss and operative time associated with the use of routine posterior osteotomies in the thoracic spine without a significant improvement in coronal or sagittal correction.

Relationship between thoracic hypokyphosis, lumbar lordosis and sagittal pelvic parameters in adolescent idiopathic scoliosis

Sagittal spine and pelvic alignment of adolescent idiopathic scoliosis (AIS) is poorly described in the literature. It generally reports the sagittal alignment with regard to the type of curve and never correlated to the thoracic kyphosis. The objective of this study is to investigate the relationship between thoracic kyphosis, lumbar lordosis and sagittal pelvic parameters in thoracic AIS. Spinal and pelvic sagittal parameters were evaluated on lateral radiographs of 86 patients with thoracic AIS; patients were separated into hypokyphosis group (n = 42) and normokyphosis group (n = 44). Results were statistically analyzed. The lumbar lordosis was lower in the hypokyphosis group, due to the low proximal lordosis. The thoracic kyphosis was not correlated with any pelvic parameters but with the proximal lordosis. The pelvic incidence was correlated with sacral slope, pelvic tilt, lumbar lordosis and highly correlated with distal lumbar lordosis in the two groups. There was a significant linear regression between thoracic kyphosis and proximal lordosis and between pelvic incidence and distal lordosis. We can consider that the proximal part of the lordosis depends on the thoracic kyphosis and the distal part depends on the pelvic incidence. The hypokyphosis in AIS is independent of the pelvic parameters and could be described as a structural parameter, characteristic of the scoliotic deformity.

Pedicle morphology using CT-based navigation system in adolescent idiopathic scoliosis

BackgroundPedicle diameter in AIS patients was narrower on theconcavesideofthescolioticcurve.Manyresearchershave measured pedicle diameter and length of AISpatients by using standard CT, or magnetic resonanceimaging (MRI), but only few have used three-dimensional(3D) imaging, especially CT-based navigation.AimThe purpose of this study was to use multidimensionalanalysis with a computed tomography (CT) based naviga-tion system to measure the outer cortical diameter, andthe maximum screw trajectory length, of the pedicle of thethoracic and lumbar regions of the spine in adolescentidiopathic scoliosis (AIS) patients. Another objective wasto identify pedicles that require cautious insertion ofscrews.MethodsFifteen patients with right-side thoracic AIS, who under-went pedicle screw fixation, were studied. CT-based naviga-tion system was used to measure the pedicle diameter,defined as the widest outer cortical diameter at the narrow-est part of the pedicle. Moreover, the maximum pediclescrew trajectory length was measured as the distancebetween the posterior cortical entry point of the pediclescrew, and the anterior vertebral cortex in line with the axisof the pedicle between T1 and L5. In addition, the values ofeach parameter taken using the CT navigation system, andthe standard axial CT, were compared.ResultsPedicles on the concave side of the main thoracic curveapex and proximal thoracic c urve tended to have thenarrowest diameters. The mean length, of the longestscrew that could be fixed, was longer on the right side,except for T8 and T9. Our data showed screw size feasibil-ity as follows: 25 mm or 30 mm screws were feasible fromT1 to T5; 30 mm or 35 mm screws, from T6 to T12; and35 mm or 40 mm screws, from L1 to L5. Pedicle diametermeasured by the CT navigation system was larger thanthat measured by standard a xial CT. Left-side pediclelength measured by the CT navigation system was lessthan that measured by standard axial CT.ConclusionPedicle diameter in patients with AIS is narrower on theconcave side of the scoliotic curve. Therefore, cautionshould be exercised during screw insertion on the con-cave side.

Long-term Outcomes of Anterior Spinal Fusion for Treating Thoracic Adolescent Idiopathic Scoliosis Curves

Retrospective review. To assess the long-term outcomes of anterior spinal fusion (ASF) for treating thoracic adolescent idiopathic scoliosis (AIS). Although ASF is reported to provide good coronal and sagittal correction of the main thoracic (MT) AIS curves, the long-term outcomes of ASF is unknown. A consecutive series of 25 patients with Lenke 1 MT AIS were included. Outcome measures comprised radiographical measurements, pulmonary function, and Scoliosis Research Society outcome instrument (SRS-30) scores (preoperative SRS-30 scores were not documented). Postoperative surgical revisions and complications were recorded. Twenty-five patients were followed-up for 12 to 18 years (average, 15.2 yr). The average MT Cobb angle correction rate and the correction loss at the final follow-up were 56.7% and 9.2°, respectively. The average preoperative instrumented level of kyphosis was 8.3°, which significantly improved to 18.6° (P = 0.0003) at the final follow-up. The average percent-predicted forced vital capacity and forced expiratory volume in 1 second were significantly decreased during long-term follow-up measurements (73% and 69%; P = 0.0004 and 0.0016, respectively). However, no patient had complaints related to pulmonary function. The average total SRS-30 score was 4.0. Implant breakage was not observed. All patients, except 1 who required revision surgery, demonstrated solid fusion. Late instrumentation-related bronchial problems were observed in 1 patient who required implant removal and bronchial tube repair, 13 years after the initial surgery. Overall radiographical findings and patient outcome measures of ASF for Lenke 1 MT AIS were satisfactory at an average follow-up of 15 years. ASF provides significant sagittal correction of the main thoracic curve with long-term maintenance of sagittal profiles. Percent-predicted values of forced vital capacity and forced expiratory volume in 1 second were decreased in this cohort; however, no patient had complaints related to pulmonary function.

Evaluation des sagittalen Profils nach operativer Therapie der thorakalen adoleszenten idiopathischen Skoliose Lenke Typ 1

The principle philosophy of posterior spinal instrumentation and fusion (PSIF) for the treatment of adolescent idiopathic scoliosis (AIS) has changed during recent decades. In the past the treatment of AIS mainly focused on correction of the major curve in the frontal plane while the sagittal profile and balancing were only of inferior interest in treatment planning. Various long-term outcome studies have demonstrated that many AIS patients developed a flatback syndrome (decrease of thoracic kyphosis and lumbar lordosis) associated with pain. It was concluded that treatment of AIS should consider the sagittal profile and balance; however, there are only few studies addressing additional procedures, which include the correction of the sagittal profile. The purpose of this study was to evaluate the effects of different posterior correction techniques on sagittal profile and balance. A total of 36 consecutive patients with thoracic AIS, who were treated with selective thoracic posterior correction were included in this retrospective study. The patients were further assigned to three different subgroups according to different surgical strategies: A: pedicle screws, B: long-head pedicle screws and C: additional Ponte osteotomy. Standardized radiographs in the standing position of the whole spine in two planes were evaluated before and at least 2 years after correction for all patients and a subgroup analysis was done to identify differences between the three groups. A significant correction of the major curve was achieved in all three groups (p < 0.001). There was a significant difference between the groups with groups B and C showing significantly higher levels of major curve correction in comparison to group A (p < 0.001). Concerning the sagittal profile, there was a significant difference in the development of thoracic kyphosis (TK) and lumbar lordosis (LL). While a significant reduction of TK and LL was found in groups A and B after surgery, a significant increase of TK and LL was noted in group C which was associated with a decrease of pelvic tilt and an increase of sacral slope. The 2-year follow-up showed the lowest ODI-% value only in group C which was positively correlated with reduction in pelvic tilt. The results of this study underline that the PSIF technique alone using pedicle screws leads to a satisfactory correction in the frontal plane but is associated with adverse effects on the sagittal profile (flat back syndrome), corroborating previous studies. It was further shown that significant improvements of sagittal parameters were achieved by adding techniques for the lengthening of the dorsal thoracic column. This approach can therefore be recommended for the treatment of AIS Lenke type 1.

Pedicle Morphology Using Computed Tomography-based Navigation System in Adolescent Idiopathic Scoliosis

Retrospective study. The purpose of this study was to use multidimensional analysis with a computed tomography (CT)-based navigation system to measure the outer cortical diameter and the maximum screw trajectory length of the pedicle of the thoracic and lumbar regions of the spine in adolescent idiopathic scoliosis (AIS) patients. Another objective was to identify pedicles that require cautious insertion of screws. Pedicle diameter in AIS patients was narrower on the concave side of the scoliotic curve. Many researchers have measured pedicle diameter and length of AIS patients by using standard CT or magnetic resonance imaging (MRI), but only few have used 3-dimensional imaging, especially CT-based navigation. Fifteen patients with right-side thoracic AIS who underwent pedicle screw fixation were studied. A CT-based navigation system was used to measure the pedicle diameter, defined as the widest outer cortical diameter at the narrowest part of the pedicle. Moreover, the maximum pedicle screw trajectory length was measured as the distance between the posterior cortical entry point of the pedicle screw and the anterior vertebral cortex in line with the axis of the pedicle between T1 and L5. In addition, the values of each parameter taken using the CT navigation system and the standard axial CT were compared. Pedicles on the concave side of the main thoracic curve apex and proximal thoracic curve tended to have the narrowest diameters. The mean length of the longest screw that could be fixed was longer on the right side, except for T8 and T9. Our data showed screw size feasibility as follows: 25 or 30 mm screws were feasible from T1 to T5; 30 or 35 mm screws, from T6 to T12; and 35 or 40 mm screws, from L1 to L5. Pedicle diameter measured by the CT navigation system was larger than that measured by standard axial CT. Left-side pedicle length measured by the CT navigation system was lesser than that measured by standard axial CT. Pedicle diameter in patients with AIS is narrower on the concave side of the scoliotic curve, and therefore, caution should be exercised during screw insertion on the concave side.

Maintenance of Thoracic Kyphosis in the 3D Correction of Thoracic Adolescent Idiopathic Scoliosis Using Direct Vertebral Derotation

ObjectivesThrough a review of prospectively collected data, we sought to analyze the outcomes related to 3-dimensional correction of adolescent idiopathic scoliosis (AIS) after posterior spinal fusion (PSF) and instrumentation using an aggressive combination of correction strategies. Background SummaryNew techniques have been used to address sagittal plane deformity while maximizing coronal and axial correction, including Ponte osteotomy, differential rod over-contouring, and direct vertebral rotation with uniplanar screws. MethodsThis is a consecutive single-center series of AIS patients with thoracic curves (Lenke 1 and 2) with 2-year follow-up who underwent PSF and instrumentation with the use of the following correction strategies: segmental uniplanar screws, ultra high-strength 5.5 mm steel rods, aggressive differential rod contouring, periapical Ponte osteotomies, and segmental direct vertebral derotation. Scoliosis Research Society (SRS)-22, radiographic and clinical parameters were evaluated at preoperative and 2-year time points. ResultsTwenty-six patients were included (mean age 13.6 ± 1.5 years). Preoperative thoracic Cobb measured 52 ± 9°, which improved to 17 ± 4° at 2-year follow-up, resulting in 68 ± 9% correction. The average thoracic kyphosis from T5-T12 did not significantly change (21 ± 10° to 22 ± 5° at 2 years); however, in patients with kyphosis less than 20° preoperatively (avg. 13 ± 5°) kyphosis increased significantly at 2-year follow-up (avg. 20 ± 4°, p<.05). Preoperatively, axial rotation was more than 13° in 21 of 26 cases. At 2-year follow-up, axial rotation remained more than 13° in 4 of 26 cases (p<.01). Rib hump prominence was 17 ± 5° preoperatively, which improved significantly to 10 ± 4° at 2-year follow-up (p<.05). Postoperative SRS domain scores significantly improved in pain (4.3 to 4.7), self-image (3.7 to 4.3), and satisfaction (3.3 to 4.6) (p<.05). ConclusionA high degree of coronal correction can be achieved in association with vertebral derotation without sacrificing sagittal plane alignment. High-strength rods aggressively bent to create kyphosis allow both restoration of kyphosis and axial plane derotation in thoracic idiopathic scoliosis.

Late Implant Removal After Posterior Correction of AIS With Pedicle Screw Instrumentation—A Matched Case Control Study With 10-Year Follow-up

Study DesignMatched case-control study. ObjectiveTo find the amount of progression of deformity and its clinical consequences in the long term after implant removal (IR) as a result of late infection in adolescent idiopathic scoliosis (AIS). Background SummaryLate IR is occasionally necessary after instrumented posterior correction of AIS because of late implant infection or implant-associated pain. The long-term outcome is not yet known because of the lack of studies with a comparable control group. MethodsWe observed 50 patients with AIS, who had pedicle screw instrumentation for posterior correction, for at least 10 years. Seven of these patients needed IR after 3.4 years (range, 1.1–7.9 years) years because of late implant-associated infection. We matched these patients with another 7 who had no complications (control), by curve type, Risser stage, age, and gender. We performed radiological measurements preoperatively, at 6 weeks, and 2, 5, and 10 years postoperatively. All patients completed the SRS-24 questionnaire at 2- and 10-year follow-up. ResultsAlthough the curve magnitude of the main thoracic curve was similar preoperatively (Cobb angle: IR, 57°±6°; control, 57°±10°) and corrected equally (IR, 18°±4°; control, 20°±7°) at 6 weeks, the deformity progressed in the IR group at 2 years (IR, 25°±11°; control, 17°±6°) and became statistically different at 10 years (IR, 31°±10°; control, 19°±6°; p<.05). There was no significant difference in total Scoliosis Research Society score between groups (IR, 99±13; control, 90±17; p>.05) at 10 years. ConclusionsLate implant removal after posterior correction of thoracic AIS with pedicle screw instrumentation results in a loss of Cobb angle correction of about one third in coronal plane at 10-year follow-up, but without clinical relevance, as measured by the Scoliosis Research Society-24 questionnaire.

Does Thoracic Hypokyphosis Matter in Lenke Type 1 Adolescent Idiopathic Scoliosis?

Study DesignWe analyzed a prospective cohort of Lenke 1ABC adolescent idiopathic scoliosis (AIS) patients based on differences in T5–T12 sagittal alignment. ObjectiveOur objective was to determine whether patients with hypokyphotic scoliosis demonstrate unique characteristics in terms of baseline health status and response to surgery. Background SummaryRight thoracic AIS often presents as a hypokyphotic scoliosis, with rotatory deformity resulting in a diminution of the normal thoracic kyphosis. The perceived importance is indicated by the inclusion of a sagittal plane modifier within Lenke’s classification system for AIS and studies examining reduction strategies to restore thoracic kyphosis. MethodsWe grouped patients based on thoracic kyphosis, measured from T5 to T12, as either less than 10° (hypokyphotic) or greater than or equal to 10° (normal/kyphotic). We used Student t test for independent samples to compare continuous variables between the hypokyphotic and normal/kyphotic groups. ResultsThere was a significant difference in age between groups (mean age, 14.9 years in the hypokyphotic group versus 13.4 years in the normal/kyphotic group; p = .007). Differences in baseline health status measures were statistically significant but small. Hypokyphotic patients reported less pain than normal/kyphotic patients, with a mean Scoliosis Research Society (SRS) Pain score of 4.15 versus 4.03 (p = .044), better SRS Mental Domain scores (4.06 vs. 3.92; p = .026), and better SRS Total scores (3.92 vs. 3.83, p = .027). The hypokyphotic group also had better SRS Appearance (3.36 vs. 3.30) and Activity scores (4.20 vs. 4.13), but these differences did not reach statistical significance. ConclusionsThere were no differences in baseline or 2-year postoperative outcome scores in Lenke 1 AIS patients with hypokyphosis compared with patients with normal sagittal alignment. Maintenance of or restoration to normal kyphosis in hypokyphotic patients with Lenke 1 AIS may not improve clinical outcome compared with patients who remain lordotic after surgical correction.

Voie antérieure versus voie postérieure dans la correction tridimensionnelle de la scoliose idiopathique de l’adolescent : une méta-analyse

Systematic review was conducted to compare effectiveness and safety of anterior and posterior surgical approach in three-dimensional correction of adolescent idiopathic thoracic scoliosis. Data sources were Medline and Scopus databases. We included studies on the use of either anterior or posterior instrumentation, or their combination, in surgical correction of adolescent idiopathic thoracic scoliosis, with at least 10 enrolled patients, aged less than 20 years at the time of surgery, and a follow-up of at least 24 months. A study was eligible if it reported the number of patients, mean estimate and dispersion of three key outcome measures (frontal and sagittal Cobb angle, apical vertebra rotation according to Perdriolle) at three measurement points (preoperatively, postoperatively, at follow-up). The quality of studies was assessed using the scale by Pilkington. Although 24 articles met the inclusion criteria, no randomized controlled trials (RCTs) was identified. None of the articles was of high quality. Both instrumentations provided a similar degree of reduction of frontal Cobb angle. Long-term effects of surgical correction on the sagittal Cobb angle seemed to be more stable in patients treated by posterior approach, while the anterior approach was more effective in the reduction of apical vertebral rotation. The surgery parameters were more favorable for anterior approach, particularly for the number of fused vertebrae. Although the available evidence favors neither of the two approaches, our study revealed several important issues: the reports are heterogeneous and provide incomplete relevant information. High-quality studies, particularly RCTs, are called for. Level II.

Posterior correction of thoracic adolescent idiopathic scoliosis with pedicle screw instrumentation: results of 48 patients with minimal 10-year follow-up

Since early 1990s pedicle screws in thoracic spine have been used in posterior correction of adolescent idiopathic scoliosis (AIS). Long-term results are scarce. We report clinical, radiological and pulmonary function results of 48 consecutive patients with 10-year minimal follow-up. Forty-eight consecutive patients (42 females, 6 males) with 41 Lenke 1 (lumbar modifier A = 19, B = 8, C = 14), 7 Lenke 2 (lumbar modifier A = 2, B = 4, C = 1) were operated for AIS from posterior with pedicle screw alone instrumentation. Risser stage at the time of operation was 0-3 in 24, more than 3 in 24 patients. Mean age was 15.3 years. The data were prospectively collected preoperatively, at 6 weeks, 2 years and 10 years postoperatively. Cobb angle, sagittal and coronal balance, distal adjacent disc angle and lowest fused vertebral tilt were documented at all time-points. Choice of fusion levels is described. Not every vertebra was instrumented with pedicle screws. The implant density was average one pedicle screw per vertebra or 50 %. Derotation and translation of apical vertebrae on the concave side were performed for correction. The overall outcome and the outcome of different curve types were analyzed statistically. Lowest instrumented vertebra (LIV) was distal end vertebra in two-thirds of the patients and was one below distal end vertebra in one-third of the patients. The main thoracic curve correction was 63 %, from 58° ± 12° preoperative to 21° ± 9° at 6 weeks. The Cobb angle was 23° ± 10° at 2 years and 26° ± 10° at 10 years. The apical vertebral rotation improved 35 %, the non-instrumented lumbar curves improved 47 %, the distal adjacent disc angle decreased from 6° ± 3° preoperatively to -2° ± 4° postoperatively and the last instrumented vertebral tilt decreased from 23° ± 8° preoperatively to 5° ± 5° postoperatively. All these parameters remained stable up to 10-year follow-up. The scoliosis correction was not associated with any change in the preoperative thoracic kyphosis and lumbar lordosis. The % FVC remained unchanged with 74 ± 21 % preoperatively to 74 ± 11 % at 2 years and 75 ± 10 % at 10 years. The SRS-24 score was 93 ± 18 points at 2 years and 95 ± 22 points at 10 years. There were no neurological complications, no pedicle screw-related complications. Posterior correction of thoracic AIS with pedicle screw instrumentation is safe and produces a long-term stable correction and high patient satisfaction. An implant density of 50 % is sufficient to achieve these results. LIV can be the distal end vertebra or one below the distal end vertebra depending on the position of the distal end vertebra to the centre sacral line. The preoperative pulmonary function does not change on long term.

Anterior versus posterior approach in 3D correction of adolescent idiopathic thoracic scoliosis: A meta-analysis

Systematic review was conducted to compare effectiveness and safety of anterior and posterior surgical approach in 3D correction of adolescent idiopathic thoracic scoliosis. Data sources were MEDLINE and SCOPUS databases. We included studies on the use of either anterior or posterior instrumentation, or their combination, in surgical correction of adolescent idiopathic thoracic scoliosis, with at least 10 enrolled patients, aged less than 20 years at the time of surgery, and a follow-up of at least 24 months. A study was eligible if it reported the number of patients, mean estimate and dispersion of three key outcome measures (frontal and sagittal Cobb angle, apical vertebra rotation according to Perdriolle) at three measurement points (preoperatively, postoperatively, at follow-up). The quality of studies was assessed using the scale by Pilkington. Although 24 articles met the inclusion criteria, no randomized controlled trials (RCT) was identified. None of the articles was of high quality. Both instrumentations provided a similar degree of reduction of frontal Cobb angle. Long-term effects of surgical correction on the sagittal Cobb angle seemed to be more stable in patients treated by posterior approach, while the anterior approach was more effective in the reduction of apical vertebral rotation. The surgery parameters were more favorable for anterior approach, particularly for the number of fused vertebrae. Although the available evidence favors neither of the two approaches, our study revealed several important issues: the reports are heterogeneous and provide incomplete relevant information. High quality studies, particularly RCT, are called for. Level II.

CT and radiographic analysis of sagittal profile changes following thoracoscopic anterior scoliosis surgery

BackgroundPrevious studies report an increase in thoracic kyphosis after anterior approaches and a flattening of sagittal contours following posterior approaches. Difficulties with measuring sagittal parameters on radiographs are avoided with reformatted sagittal CT reconstructions due to the superior endplate clarity afforded by this imaging modality.MethodsA prospective study of 30 Lenke 1 adolescent idiopathic scoliosis (AIS) patients receiving selective thoracoscopic anterior spinal fusion (TASF) was performed. Participants had ethically approved low dose CT scans at minimum 24 months after surgery in addition to their standard care following surgery. The change in sagittal contours on supine CT was compared to standing radiographic measurements of the same patients and with previous studies. Inter-observer variability was assessed as well as whether hypokyphotic and normokyphotic patient groups responded differently to the thoracoscopic anterior approach.ResultsMean T5-12 kyphosis Cobb angle increased by 11.8 degrees and lumbar lordosis increased by 5.9 degrees on standing radiographs two years after surgery. By comparison, CT measurements of kyphosis and lordosis increased by 12.3 degrees and 7.0 degrees respectively. 95% confidence intervals for inter-observer variability of sagittal contour measurements on supine CT ranged between 5-8 degrees. TASF had a slightly greater corrective effect on patients who were hypokyphotic before surgery compared with those who were normokyphotic.ConclusionsRestoration of sagittal profile is an important goal of scoliosis surgery, but reliable measurement with radiographs suffers from poor endplate clarity. TASF significantly improves thoracic kyphosis and lumbar lordosis while preserving proximal and distal junctional alignment in thoracic AIS patients. Supine CT allows greater endplate clarity for sagittal Cobb measurements and linear relationships were found between supine CT and standing radiographic measurements. In this study, improvements in sagittal kyphosis and lordosis following surgery were in agreement with prior anterior surgery studies, and add to the current evidence suggesting that anterior correction is more capable than posterior approaches of addressing the sagittal component of both the instrumented and adjacent non instrumented segments following surgical correction of progressive Lenke 1 idiopathic scoliosis.

Apical vertebral derotation in the posterior treatment of adolescent idiopathic scoliosis: myth or reality?

Direct apical vertebral rotation represents an important goal of posterior surgery for thoracic adolescent idiopathic scoliosis (AIS), so as to obtain a better cosmetic effect and to avoid posterior thoracoplasty. However, the real effectiveness in correction of vertebral rotation, using posterior only procedures, is still open to debate. The aim of the present study is to compare the correction of axial apical rotation obtained with direct rotation procedure versus simple concave rod rotation, in patients treated by posterior fusion for thoracic AIS using pedicle screw-only construct. A retrospective review was performed on a total of 62 consecutive patients (one single institution, three different surgeons) affected by AIS, who had undergone a posterior spinal fusion with pedicle screw-only instrumentation between January 2005 and April 2008 at the reference center. All cases presented a main thoracic curve (Lenke type 1 and 2). The angle of rotation (RAsag) of the apical vertebra was measured from the preoperative and last follow-up axial CT. According to the derotation procedure, two groups were identified: a direct vertebral rotation group (DR group; n = 32 patients) and a simple concave rod rotation group (No-DR group; n = 30 patients). There were no statistical differences between the two groups, in terms of age, Risser's sign, curve patterns, Cobb main thoracic (MT) curve magnitude and flexibility, extension of fusion, offset measurements on the coronal plane and sagittal preoperative contour. All 62 patients were reviewed at an average follow-up of 3.7 years (range 2.5-4.2 years). The DR group compared to the No-DR group showed a significantly better final correction of apical vertebral rotation (DR 63.4 % vs. No-DR 14.8 %; p < 0.05) and a greater final correction (61.3 vs. 52.4 %; p < 0.05) with better maintenance of the initial correction (-1.7° vs. -1.9°; ns) of the main thoracic curve. Concerning the coronal balance, there was the same aforementioned trend of better results in the DR group, with less final apical MT vertebra translation (DR 2.2 cm vs. No-DR 4.1 cm), greater overall change (preop-final) of lower instrumented vertebra (LIV) coronal tilt (-14.9° vs. -11.1°; p < 0.05); the final global coronal balance (C7-S1) resulted quite better in DR group, but without a significant difference. The T5-T12 kyphosis angle was quite similar in both group before surgery (DR 16.8° vs. No-DR 17.5°) and was little lower at final follow-up evaluation in direct vertebral rotation group (14.5° vs. 16.5°). The T10-L2 sagittal alignment angle was similar in each group before surgery (12.5° in DR vs. 11.8° in No-DR), and at the latest follow-up averaged 5.3° versus 8.2°, respectively. Lumbar lordosis was similar in each group before surgery (DR -42° vs. No-DR -44.1°) and at the final follow-up evaluation (-45.9° vs. -43.2°). At the latest follow-up, SRS-30 and SF-36 findings were similar between the two groups. The complication rate was higher in the simple concave rod rotation group (13.3 vs. 9.3 %), related in two cases to thoracoplasty, which was never utilized in direct rotation patients. The direct vertebral rotation obtained significantly better final results, when compared to simple concave rod rotation, both concerning correction of apical vertebral rotation and magnitude of MT curve. On the other hand, the DR group presented a little reduction in T5-T12 kyphosis at follow-up, in comparison with concave rod rotation procedure. Both procedures were found to be satisfying from patients' perspective. Nevertheless overall complication rate was higher in the simple concave rod rotation group, related mainly to thoracoplasty (2 cases), which was never necessary in direct rotation patients.

The Position of the Aorta Changes With Altered Body Position in Single Right Thoracic Adolescent Idiopathic Scoliosis

A prospective clinical magnetic resonance imaging study. To explore the differences in the position of the aorta relative to the spine in patients with single right thoracic adolescent idiopathic scoliosis (RT-AIS) in 2 different body positions (supine and prone). Pedicle screws are used widely in scoliosis surgery. With an increase in the incidence of vascular complications that result from misplaced pedicle screws, studies regarding the spatial relationship of the aorta and the vertebral body have also gradually increased and show that the aorta is positioned more posteriorly in patients with RT-AIS than in normal subjects. In these imaging studies, the patients received computed tomographic or magnetic resonance (MR) scans in the supine position. Recent studies of subjects without a spinal deformity found that the aorta moves from a posterolateral to an anteromedial position when the subject changes from a supine position to a prone position. However, no studies investigated aorta shifting with changing body position in patients with AIS. Twenty-six patients with single RT-AIS were recruited into this study. Each patient received an axial MR scan from T5 through L3 in both the supine and prone positions. In the Cartesian coordinate system, the left pedicle-aorta (LtP-Ao) angle, LtP-Ao distance, and vertebral rotation angle were measured from T5 through L3 in the axial plane MR images. We also simulated misplacement of the pedicle screw with commonly used length and 20° direction error, and the potential risk of aorta impingement was defined as the virtual pedicle screw crossing the aorta. The paired sample t test was used to compare these parameters between the 2 body positions. The mean LtP-Ao angle and mean LtP-Ao distance differed between the body positions at each level. At the T5-T10 levels, the patients in the prone position exhibited significantly smaller LtP-Ao angles (26.2° vs. 38.8°; P, 0.01) and distances (27.0 vs. 30.7 mm; P, 0.01) than those in the supine position. The vertebral rotation angle was larger in the prone position than in the supine position at periapical levels, although this difference did not reach statistical significance (P . 0.05). The percentage of potential risk of aorta impingement was significantly higher in the prone position than in the supine position at the T5-T10 levels (19.7% vs. 6.6%, respectively; P, 0.05). CONCLUSION.: The aorta shifts more anteromedially and more closely to the spine at the T5-T10 levels when patients with RT-AIS change from the supine to the prone position. Thus, in the prone position, the aorta is potentially at a higher risk for injury from anterior and lateral cortex penetration by the left pedicle screws. The spinal surgeon should be aware of these altered conditions to avoid injury to the aorta during pedicle screw insertion in patients with RT-AIS who are in the prone position.

Postoperative Changes in Spinal Rod Contour in Adolescent Idiopathic Scoliosis

Prospective case series. To evaluate the change in spinal rod contour from before implantation to after surgical correction of thoracic curves in patients with adolescent idiopathic scoliosis. With segmental pedicle screw spinal instrumentation and vertebral derotation, many authors have reported a loss of thoracic kyphosis postoperatively. Although surgeons anticipate some flattening of the preimplantation rod contour in the sagittal plane, the magnitude of this change in shape has not been documented. The concave and convex rod shapes of 5.5-mm ultrahigh-strength steel spinal rods (200 KSI) from patients with thoracic adolescent idiopathic scoliosis (n = 27), which were contoured with benders by the surgeon, were traced prior to insertion. Postoperative (average, 5 weeks) sagittal rod shape was determined from lateral 2-dimensional radiographs. Maximal rod deflection and angle of the tangents to rod end points (Cobb) were measured. Repeated measures analysis of variance assessed differences between pre- and postoperation. The scoliosis of 55° ±14° was corrected 72% to 15° ± 5°. The preinsertion rod shapes were more kyphotic for the concave (45.6°) than for the convex (31.4°) rods. Following correction, the concave rods flattened, with decrease in deflection of 13 mm and reduction in angle of 21° (both P < 0.001). The convex rods increased 1.5 mm in deflection and 2° in angle (P < 0.01, P = 0.18). The sagittal profile was maintained postoperatively as measured from T5-T12: 19° ±14° versus 22° ± 6° (pre vs. post, P > 0.1). We found a significant difference between pre- and postoperative rod contour, particularly for concave rods. Rod overcontouring (by ~20° for concave rod) resulted in high degrees of correction without loss of sagittal alignment. The resulting deformations are likely associated with substantial in vivo deforming forces.

Anatomic Deviation Between the Central Hip Vertical Axis and Central Sacral Vertical Line in Adolescent Idiopathic Scoliosis

A radiographic and clinical study. To compare the anatomic deviation between the central hip vertical axis (CHVA) and central sacral vertical line (CSVL) in 2 distinct adolescent idiopathic scoliosis (AIS) groups (right thoracic vs. left thoracolumbar/lumbar) and normal adolescents. The CSVL was traditionally used as a reference line to assess spinal deformity. Recently, the Scoliosis Research Society 3-dimensional (3D) committee proposed the CHVA as a reference line for the 3D evaluation of scoliosis. However, a previous study showed that the CHVA was on an average 3.2 mm to the right compared with the CSVL in right thoracic AIS patients, generating a shift in evaluation of the coronal plane measurements. Fifty-five AIS girls with right thoracic curves (TC) and 56 AIS girls with left thoracolumbar/lumbar curves (TLC) were recruited. AIS girls who had a Cobb angle >40 degrees were excluded from this study in consideration of the potential pelvic rotation in patients with large curves. Another 57 normal girls were set to be the control group. All girls were between 10 and 18 years old. The deviation between the CHVA and CSVL was measured on each posteroanterior radiograph and compared between the 3 groups. The shift of CHVA relative to CSVL was found to be significantly greater in the TC and TLC groups (2.2±3.3 mm vs. 2.3±4.0 mm, respectively) when compared with the control group (0.1±2.6 mm), but had no statistical difference between the 2 AIS groups. No significant correlations were found between age, Cobb angle, and the CHVA shift in the 3 groups. The CHVA was more commonly found to be at the right side of the CSVL in the TC (50.9%) and TLC (51.8%) groups, whereas superposition of the 2 lines was more commonly found in the control group (52.6%). Anatomic deviation between the CHVA and CSVL was significantly different in the TC and TLC groups when compared with the control group, but was similar between the 2 AIS groups. The CHVA was on an average approximately 2 mm to the right when compared with the CSVL in AIS girls. Adaption of the measures related to the CSVL is necessary to adopt the CHVA as a reference axis for the 3D evaluation of idiopathic scoliosis.

The Left Bending Stable Vertebra; A Method for Determining the Lower Instrumented Vertebra in Single Thoracic (Lenke IA and IB) Adolescent Idiopathic Scoliosis

Background Data: The selection of the lower instrumented vertebra (LIV) in single thoracic (Lenke1A and B) Adolescent Idiopathic Scoliosis (AIS) remains controversial. Purpose: To report a new method of selecting the LIV and report the results of surgery based upon this method. Study Design: Retrospective radiological analysis of Lenke 1A and B AIS patients. Patients and Methods: Fifty six patients met the inclusion criteria, 4 (7.1%) male and 52 (92.9%) females. Mean age at time of surgery was 14.7 years. The following data were recorded on preoperative, immediate postoperative andlatest follow up x-rays: the lower end vertebra (EV), the stable vertebra (SV), the neutral vertebra (NV), the vertebra most closely bisected by a central sacral perpendicular line that was designated the left bending stable vertebra (LBSV)and the lower instrumented vertebra (LIV). Patients were checked for coronal balance and the development of adding on the latest follow up X-rays. Results: Patients were followed up for a mean of 28.5 months. Mean thoraciccurve correction was 69%. Five patients (9%) developed adding on at their latest follow up. All patients instrumented at or distal to the LBSV were balanced without adding on. Five out of the six patients (83%) instrumented proximal tothe LBSV developed adding on at their latest follow up. Conclusion: The LBSV is a useful and reliable way of determining the LIV in Lenke 1A and B AIS. Both the LBSV and Suk et al method predicted adding on; however, the LBSV can allow a more proximal LIV and therefore a shorter fusion in up to 46% of this case series. (2012ESJ022)

Long-term Retrospective of the Kaneda Anterior Scoliosis System in Thoracic Adolescent Idiopathic Scoliosis

Currently, the Kaneda anterior scoliosis system (KASS) is reported to be acceptable for the treatment of adolescent idiopathic scoliosis (AIS), particularly thoracolumbar and lumbar deformities. Its use in thoracic AIS is not as established. Retrospective analysis of long-term results in patients treated with the KASS for thoracic AIS to determine specific factors associated with success or failure. We analyzed 16 consecutive patients who met the following criteria: thoracic AIS, anterior spinal fusion and KASS, and ≥24 months of follow-up or progression to failure, defined as the need for revision surgery or progression of the main thoracic curve (MTC) ≥50 degrees. Comparison of the MTC on the preoperative, postoperative, and final follow-up was the major evaluation criteria. On the basis of data analysis, patients were divided for comparison into 2 study groups: nonfailure group (n=11) and failure group (n=5). Statistical analysis was performed using paired and independent t tests. All curves were classified as Lenke 1 (n=14) and 2 (n=2). Mean age at surgery and levels fused were 14.6±2.7 years and 5±1 vertebrae, respectively. Mean follow-up was 4.2 years (range, 1.0 to 6.2 y). The failure group consisted of 5 patients that progressed to ≥50 degrees. In the nonfailure group, the mean MTC preoperative, postoperative, and at final follow-up were 52±8, 19±8, and 29±7 degrees, respectively. In the failure group, these measurements were 74±11, 35±8, and 56±12 degrees, respectively. This retrospective, long-term follow-up study found more KASS failures in thoracic AIS than previously reported. Even in the nonfailure group, 5 of the 11 patients progressed 10 degrees or more. Our results indicate an increased incidence of KASS failure with preoperative MTC curve ≥70 degrees. We consider an MTC≥70 degrees a likely contraindication for KASS instrumentation for thoracic AIS. Four of the 5 failures were fused short of the end vertebrae either proximally, distally, or both. Although short apical fusions were popular during the time these cases were done, fusion to the end vertebrae is an important principle for anterior fusions. Reaching the upper end vertebrae may be more difficult in these larger curves. We also recommend continued follow-up past 2 years as progression can occur after this time. Retrospective comparative study, level III.