Anterior dual rod instrumentation in idiopathic thoracic scoliosis: a computed tomography analysis of screw placement relative to the aorta and the spinal canal

Accuracy of thoracic pedicle screw placement using freehand technique and triggered EMG in adolescent idiopathic scoliosis: Is it different between concave and convex side?

PURPOSE

To evaluate and compare the accuracy of the placement of thoracic pedicle screws between concave and convex side curve using freehand technique and triggered electromyogram (EMG).

METHODS

Three-hundred sixty eight thoracic pedicle screws were included for the evaluation of accuracy from postoperative computed tomography (CT) scans in 24 patients with adolescent idiopathic scoliosis with a mean follow-up of 27 months (range 24-58 months). All screws had stimulation thresholds greater than 6 mA. We divided the screws into two groups: (1) group A: concave side curve-254 screws (2) group B: convex side curve-114 screws.

RESULTS

The mean age at surgery was 12.8 years (range 11-17 years). The preoperative Cobb angle was 57.5° (range 50-75°). There were 41 total breaches (medial = 21, lateral = 20, p = 0.66) with an overall incidence of 11.1%. The overall breach rate did not attain statistically significant difference (group A = 11.8%, group B = 9.6%, p = 0.59). The rate of medial breaches was also similar for both concave and convex side (group A = 6.1%, group B = 5.9%, p > 0.05). No postoperative neurological or vascular complications were noted in both groups.

CONCLUSION

Thoracic pedicle screw placement using both freehand technique and triggered EMG for adolescent idiopathic scoliosis surgery is safe and reliable. The overall accuracy rate is 88.9% with similar breaches on the concave and convex side on postoperative CT scans.

Mid-length Pedicle Screws in Posterior Instrumentation of Scoliosis

Study Design

Prospective analysis of collected data.

Purpose

We determine the need for the use of mid-length pedicle screws (screws with 2.5-mm long increments) during posterior spinal instrumentation.

Overview of Literature

Many biomechanical studies have been performed showing that increasing the pedicle screw insertion depth provides an improved resistance to pullout, cyclic loading, and derotational forces, but no intermediate length screws were used.

Methods

We prospectively evaluated 120 patients who received posterior segmental instrumentation for structural scoliosis. Preoperatively, 91.44-cm long cassette anteroposterior (AP), lateral, and AP bending radiographs and multiplanar computed tomography were performed in all patients routinely. We measured chord length to determine the maximum probable screw length of all vertebrae. All pedicle screws were attempted to be placed as long as possible. The main intention was at least to engage the subcortical bone of the anterior vertebral cortex. Especially in the apical region, the screws were attempted to be inserted bicortically. The length, level, region, and side of each screw were recorded. Screws with 5-mm increments were called standard length screws (SLS), and middle-sized screws with 2.5-mm increments were called mid-length screws (MLS).

Results

Of 2,846 pedicle screws inserted, 1,575 (55.4%) were SLS and 1,271 (44.6%) were MLS, demonstrating a need for MLS in scoliosis surgery (p<0.05). The need for MLS increased significantly in the thoracic region, apical vertebrae, and convex side (p<0.05).

Conclusions

If anterior cortex engagement or longer placement of pedicle screws is intended during scoliosis surgery, for safer placement, screws with 2.5-mm increments should be available in posterior instrumentation systems.

The effect of patient positioning on the relative position of the aorta to the thoracic spine

PURPOSE

Detailed knowledge of the anatomy of the thoracic aorta is crucial for thoracolumbar spinal surgery. The purpose of the present study is to describe the relative displacement of the aorta to the spine in supine, prone and prone position with padding. Improved understanding of the magnitude and direction of this often-overlooked change could benefit preoperative planning and decision-making.

METHODS

A total of 200 patients underwent CT scan of the thoracic spine in the standard supine, prone and prone position with padding. Axial CT images from T4 to T12, in all three different positions, were selected and the following parameters were measured: (a) distance B connecting left pedicle entry point to the edge of the aortic wall and (b) projections Bx and By, representing the minimum AP depth and horizontal displacement of the aortic wall relative to the left pedicle entry point O.

RESULTS

There was a significant difference in the distance B between the three different positions across all thoracic vertebrae levels, confirming that positioning significantly affects aorta's relative position. Moreover, in the prone position with padding at the level of T6, the aortic wall lies at a minimum distance from the left pedicular axis and thus from the typical screw trajectory.

CONCLUSION

The results of this study show that prone positioning for posterior thoracolumbar approach affects significantly the anatomic relationship of the aorta to the spine. Surgeons should be aware that standard supine CT evaluation represents a static technique, which can differ considerably from surgical reality. These slides can be retrieved from electronic supplementary material.

Computed tomography morphometric analysis of anterior instrumentation in the pediatric thoracic spine

OBJECT The authors' goal in this paper was to quantify reference data on the dimensions and relationships of the maximum posterior screw angle and the thoracic spinal canal in different pediatric age groups. METHODS One hundred twelve pediatric patients were divided into 4 age groups, and their thoracic vertebrae were studied on CT scans. The width, depth, and maximum posterior screw angles with different screw entrance points were measured on a Philips Brilliance 16 CT. The statistical analysis was performed using the Student t-test and Pearson's correlation analysis. RESULTS The width and depth of the thoracic vertebrae increased from T-5 to T-12. The width ranged from 18.5 to 37.1 mm, while the depth ranged from 16.1 to 28.2 mm. The maximum posterior screw angle decreased from T-5 to T-12 in all groups. The ranges and mean angles at the entrance points were as follows: initial entrance point, 6.9° to 12.3° with a mean angle of 9.1°; second entrance point, 20.6° to 27.0° with a mean angle of 24.2°; and third entrance point, 29.2° to 37.5° with a mean angle of 33.7°. There were no significant age-related differences noted for the maximum posterior screw angles. CONCLUSIONS The angle decreased from T-5 to T-12. No significant age-related differences were noted in the maximum posterior screw angles. Screws should be placed between the initial and second points and parallel to the coronal section or at a slight anterior orientation.

Hemoptysis Due to Anterior Scoliosis Implants: A Case Report

CASE

A twenty-five-year-old man presented with recurrent episodes of hemoptysis requiring hospitalization and interventional embolization. Instrumentation that had been implanted ten years previously for anterior spinal correction and fusion to treat adolescent idiopathic scoliosis adjoined the medial border of the right lung. The instrumentation eroded the lung during respiration, which prompted the formation of adhesions and fibrosis. Because of the risk of additional hemoptysis events, we performed revision thoracotomy, removal of the spinal instrumentation, and partial lobectomy.

CONCLUSION

This rare and serious complication underscores the importance of meticulous surgical technique to ensure proper implant placement and of vigilant monitoring for late iatrogenic injury.

Aortic issues in scoliosis and scoliotic operations

The spatial relations between the aorta and vertebrae are changing with posture, surgical techniques, and operative maneuvers. "Risky screws" (within 1-3 mm proximity to the aorta or other adjacent tissues) were found in 5.8-15.2% screws. In order to avoid early and later aortic complications secondary to scoliotic operations, careful preoperative metrology of aorto-vertebrae relations is of crucial importance. Compared with patients with idiopathic scoliosis, Marfan-related scoliosis is characterized by faster progression and it is more bracing-resistant due to the particular developmental anomalies in Marfan syndrome, implying the refractory nature of the latter. The present study aims to highlight the clinical impact of preoperative aorto-vertebra metrology in the scoliotic operations.

Spontaneous lumbar curve correction in selective anterior instrumentation and fusion of idiopathic thoracic scoliosis of Lenke type C

BACKGROUND

Posterior pedicle screw instrumented correction and fusion have become the gold standard in the surgical treatment of thoracic scoliosis. However, in thoracic Lenke type C curves selective posterior fusion of the thoracic curve may lead to spinal imbalance. The aim of the study was to analyse the radiological results of selective anterior thoracic fusion using a standard open dual rod technique with special respect to spontaneous lumbar curve correction (SLCC).

METHODS

Twenty-eight patients (26 patients with Lenke 1C and 2 patients with Lenke 2C curves) with an average age of 15 years were surgically treated with an anterior dual rod system through a standard open double thoracotomy approach. Average clinical and radiological follow-up was 4 years (24-84 months).

RESULTS

Fusion was carried out mostly from end-to-end vertebra. The primary curve was corrected from 61.6° (average correction on reverse bending films 42.9 %) to 27.1° (56.0 % correction) with an average loss of correction of 2.2°. The secondary lumbar curve measured 47.7° preoperatively (40-56°, average correction on reverse bending films 66.2 %) and corrected spontaneously to 30.1° (36 % SLCC) and remained stable without any cases of deterioration or decompensation during follow-up. Lumbar apical vertebral translation increased minimally by an average of 4 mm directly, postoperatively, and returned to an average of preoperative values during follow-up. All but two curves remained as type C lumbar modifier at follow-up. Preoperatively, three patients showed a marked coronal imbalance of more than 3 cm (all left, average 4.0 cm); at follow-up, two patients were still out of balance by more than 3 cm (all to the left, average 3.4 cm). Preoperatively, a marked shoulder imbalance of more than 1.0 cm was found in 11 patients; this was corrected in all patients to <1.0 cm at follow-up. The apical vertebral rotation measured according to Perdriolle was corrected from 23.5° to 15.0° in the thoracic spine (36.2 % correction) with an average clinical reduction of the rib hump of 63.2 %. In the lumbar spine, there was no relevant radiological derotation; however, clinically, the lumbar hump corrected spontaneously by 44.3 %. Thoracic kyphosis measured 28.5° preoperatively and 32.3° at follow-up. All six patients with a preoperative hypokyphosis (<20°) of an average of 9.5° were successfully corrected to an average thoracic kyphosis of 23.8° at follow-up. There were no cases of junctional thoracolumbar kyphosis. There were neither reoperations nor implant failures with pseudarthrosis.

CONCLUSION

Selective anterior correction and fusion in primary thoracic curves with lumbar modifier type Lenke C resulted in a reliable and satisfactory SLCC. Advantages of anterior versus posterior techniques are the true segmental derotation with excellent rib hump correction and a superior restoration of thoracic kyphosis.

[Modified primary stable ventral derotation spondylodesis with Halm-Zielke instrumentation for the treatment of idiopathic scoliosis]

OBJECTIVE

Surgical technique with an anterior double-rod system for thoracic, thoracolumbar, or lumbar scoliosis. The aim of the system is to correct the coronal plane deformity and normalize the sagittal balance.

INDICATIONS

Scoliosis which should have a coronal Cobb measurement of at least 40 degrees and should usually not exceed 90 degrees in between T4 and L4. In the Lenke classification, the curve types 1 (main thoracic) and curve type 5 (thoracolumbar/lumbar) are amenable to anterior instrumentation and fusion.

CONTRAINDICATIONS

Osteoporosis. Infection. Allergic reaction to implants. Minor curves that do not correct to < 25 degrees on flexibility maneuvers. Structured kyphosis in the major curve. Severe sagittal plane malalignment with pathologic kyphosis cranial or caudal of the instrumented segments.

SURGICAL TECHNIQUE

The spine is exposed via an open thoracotomy or a thoracoabdominal approach. After completion of diskectomies at each level, the anterior double-rod system is fixed with two bicortical screws per vertebral body. The longitudinal components consist of a solid rod and a threaded rod. The rods are contoured to maintain normal sagittal and coronal contour. The proximal screws are engaged first and then a cantilever force is used to correct the deformity. Occasionally, a partial rod rotation maneuver or intersegmental compression is performed. Morselized autograft (typically rib) is placed in the disk spaces. Intraoperative radiographs are taken to evaluate the correction.

POSTOPERATIVE MANAGEMENT

Brace-free mobilization. Physiotherapy. Respiratory therapy.

RESULTS

Very high rate of successful spondylodesis. Excellent frontal correction of about 60-70%. Very good spontaneous correction of adjacent minor curves of around 40%. Restoration of a physiological profile. Correction angle and length of fusion comparable to modern transpedicular double-rod systems.

Approach-related lesions of the sympathetic chain in anterior correction and instrumentation of idiopathic scoliosis

During anterior scoliosis instrumentation with a dual-rod system, the vertebrae are dissected anterolaterally. After surgery, some patients report a change in temperature perception and perspiration in the lower extremities. Sympathetic lesions might be an explanation for this. The aim of this clinical study was to investigate sympathetic function after anterior scoliosis instrumentation. A total of 24 female patients with idiopathic scoliosis (mean age at follow-up, 23.8 years) who had undergone anterior instrumentation on average 6.6 years earlier were included. Due to the suspected relevance of the sympathetic L2 ganglion, two groups were created: a T12 group, in which instrumentation down to T12 was carried out (n = 12), and an L3 group, in which instrumentation down to L3 was done (n = 12). Sympathetic function was assessed by measuring skin temperature at the back of the foot, a plantar ninhydrin sweat test and sympathetic skin responses (SSRs) following electrical stimulation. The side on which the surgical approach was carried out was compared with the contralateral, control side. Health-related quality of life was investigated using the Scoliosis Research Society SRS-22 patient questionnaire. In the T12 group, mean temperatures of 29.6 degrees C on the side of the approach versus 29.5 degrees C on the control side were measured (P > 0.05); in the L3 group, the mean temperatures were 33.2 degrees C on the approach side versus 30.5 degrees C on the control side (P = 0.001). A significant difference between the T12 group and the L3 group (P < 0.001) was observed on the approach side, but not on the control side (P = 0.15). The ninhydrin sweat test showed reduced perspiration in 11 of 12 patients in the L3 group on the approach side in comparison with the control side (P = 0.002). In the T12 group, no significant differences were noted between the left and right feet. SSRs differed significantly between the two groups (P = 0.005). They were detected in all nine analyzable patients in the T12 group on both sides. In the L3 group, they were found on the approach side only in 4 of 11 analyzable patients versus 11 patients on the control side. The results of the SRS-22 questionnaire did not show any significant differences between the two groups. In conclusion, anterior scoliosis instrumentation with a dual-rod system including vertebrae down to L3 regularly leads to lesions in the sympathetic trunk. These are detectable with an increase in temperature, reduced perspiration and reduced SSRs. The caudal level of instrumentation (T12 vs. L3) has an impact on the extent of impairment, supporting the suspected importance of the L2 ganglion. The clinical outcome does not seem to be significantly limited by sympathetic trunk lesions.

[Posterior operative correction of idiopathic scoliosis. Value of pedicle screws versus hooks]

Posterior correction and fusion of scoliosis with multisegmental instrumentation systems was developed by Cotrel-Dubousset in the 1980s. Initially correction and instrumentation was performed using hooks only. Later pedicle screws were implemented first for the lumbar and then for the thoracic spine. Nowadays instrumentation based on pedicle screws only is well established for posterior scoliosis surgery. Biomechanical studies demonstrated higher pull-out forces for pedicle than for hook constructs.In clinical studies several authors reported better Cobb angle correction of the primary and the secondary curves and less loss of correction in pedicle screw versus hook instrumentations. Furthermore, pedicle screw instrumentation allows fewer segments to be fused, especially caudally, and thus saving mobile segments. In most of these publications there were no differences in operation time, blood loss and complication rates. In summary, there is better curve correction without an increased risk using multisegmental pedicle screw instrumentation in modern posterior scoliosis surgery.

[Anterior scoliosis surgery. State of the art and a comparison with posterior techniques]

For more than 2 decades ventral derotation spondylodesis (Zielke VDS) as a major improvement over Dwyer instrumentation (DI) was the gold standard of instrumented curve correction and stabilization from the anterior approach. As the first available system it enables a true three-dimensional curve correction. A disadvantage is the low internal stabilization capability with a need for long-term external stabilization by means of cast and brace treatment postoperatively. Meanwhile with the development of modern single and dual solid rod systems these disadvantages can be avoided completely. Video-assisted (thoracoscopic) anterior scoliosis surgery accounts for less than 2% of anteriorly treated scoliosis cases, mainly due to a long operating time and significant learning curve.From the posterior approach the Cotrel-Dubousset instrumentation (CDI) as a polysegmentally attached posterior hook threaded dual rod system used to be state of the art for a long time, since it eliminated the disadvantages of Harrington instrumentation (HI) in terms of only one-dimensional correction and low stabilization capabilities. However even with CDI effective derotation was impossible. In posterior scoliosis surgery there is a strong trend away from hook systems towards transpedicular segmentally fixed dual rod systems not only in the lumbar spine but also in the thoracic area. Advantages of these newer techniques are shorter fusion, improved correction, and less loss of correction over time.Advantages of modern anterior instrumentation systems in comparison to posterior transpedicular instrumented dual rod systems are less blood loss, better derotation, slightly shorter fusion levels, and a better influence on sagittal plane control or improvement especially for hypokyphotic thoracic scoliosis cases. Our data also document a superior spontaneous correction of the lumbar curve after selective anterior instrumented correction (Lenke 1B+C), although other studies could not find significant differences. In our experience the neurological risk of anterior instrumented correction is also lower than that of posterior scoliosis surgery, although the morbidity and mortality data of the Scoliosis Research Society could not prove that anymore in recent years. A negative effect of anterior transthoracic scoliosis surgery in comparison to posterior surgery is a more negative effect on lung function, which improves slower after surgery and does not quite reach the levels of posterior surgery at follow-up. But new data on posterior segmental transpedicular correction and fusion also prove a lordosating effect with negative effect on lung function.

Evaluation of thoracic pedicle screw placement in adolescent idiopathic scoliosis

Pedicle screw fixation is a challenging procedure in thoracic spine, as inadvertently misplaced screws have high risk of complications. The accuracy of pedicle screws is typically defined as the screws axis being fully contained within the cortices of the pedicle. One hundred and eighty-five thoracic pedicle screws in 19 patients that were drawn from a total of 1.797 screws in 148 scoliosis patients being suspicious of medial and lateral malpositioning were investigated, retrospectively. Screw containment and the rate of misplacement were determined by postoperative axial CT sections. Medial screw malposition was measured between medial pedicle wall and medial margin of the pedicle screw. The distance between lateral margin of the pedicle screw and lateral vertebral corpus was measured in lateral malpositions. A screw that violated medially greater than 2 mm, while lateral violation greater than 6 mm was rated as an "unacceptable screw". The malpositions were medial in 20 (10.8%) and lateral in 34 (18.3%) screws. Medially, nine screws were rated as acceptable. Of the 29 acceptable lateral misplacement, 13 showed significant risk; five to aorta, six to pleura, one to azygos vein and one to trachea. The acceptability of medial pedicle breach may change in each level with different canal width and a different amount of cord shift. In lateral acceptable malpositions, the aorta is always at a risk by concave-sided screws. This CT-based study demonstrated that T4-T9 concave segments have a smaller safe zone with respect to both cord-aorta injury in medial and lateral malpositions. In these segments, screws should be accurate and screw malposition is to be unacceptable.

Anterior-only approaches to scoliosis

Scoliosis is a three-dimensional spinal deformity for which surgery may be indicated when patients experience severe pain, curve progression, or progressive disability. Operative treatment has conventionally involved extensive posterior stabilization, either alone or in combination with anterior release procedures. Anterior-only approaches have a more limited role, but they should be considered in the appropriate setting when addressing this disease. Some advantages of anterior-only approaches to scoliosis include greater corrective ability with a greater fusion rate while mandating fewer motion segments to be involved in the instrumented construct. Preventing denervation of the posterior paraspinal musculature is also desirable and is inherently provided for by the anterior approach. Disadvantages include pulmonary morbidity associated with violating the thoracic cavity, as well as post-thoracotomy chronic pain. There are also limitations in the indications for which anterior-only surgery can be performed, and these will be discussed along with treatment options. Technological advances, including minimally invasive thoracic access as well as evolving instrumentation, may minimize the stated disadvantages and expand the scope of scoliosis cases that may be treated by anterior-only approaches. Hence, the enhanced corrective ability and biomechanical advantages of the anterior column can be used in the treatment of these patients. Although the indications for anterior-only strategies in scoliosis remain limited, such operations should be considered in the appropriate setting when addressing spinal deformity.

Accuracy of thoracic vertebral screw insertion in adolescent idiopathic scoliosis: a comparison between thoracoscopic and mini-open thoracotomy approaches

STUDY DESIGN

A cross-sectional study with axial computed tomography (CT) to compare the accuracy of vertebral screw insertion in the thoracic spine for adolescent idiopathic scoliosis (AIS) between the thoracoscopic and the mini-open thoracotomy approach.

OBJECTIVE

To evaluate the safety of vertebral screw placement in anterior instrumentation for thoracic AIS.

SUMMARY OF BACKGROUND DATA

Thoracoscopic anterior instrumentation has been used with good results for AIS. It is technically demanding especially for the insertion of vertebral screws. The important issue of whether the screws inserted thoracoscopically is as accurate and safe as those inserted through thoracotomy approach has not been well studied.

METHODS

Thirty-one patients with thoracic AIS receiving thoracoscopic or mini-open thoracotomy anterior instrumentation were included in this study. They were divided into Group A and B, respectively. Postoperative sequential CT scanning on the thoracic vertebral screws was carried out. The relative position between screws and the spinal canal, the aorta, and the bicortical purchase were analyzed with CT images. The percentage of screws in good position was defined and further analyzed.

RESULTS

Seventy-three and 162 thoracic vertebral screws were inserted in 10 patients in Group A and 21 patients in Group B, respectively. Eighty-nine percent of screw tips in Group A and 80.2% in Group B were distant from the aorta, 89.0% and 87.0% of screws achieved bicortical purchase in Group A and B, respectively. No significant difference was found in all thoracic levels including the upper thoracic, periapical, or lower thoracic vertebrae. Seventy-four percent and 66.7% of screws were in good positions in Group A and B, respectively and there was no statistically significant difference between the 2 groups.

CONCLUSION

The vertebral screws inserted through thoracoscopic approach were as accurate as those inserted through a mini-open thoracotomy approach. The accuracy could be enhanced by using screws with smaller increments, with special attention to the possible migration of aorta with anterior spinal instrumentation.

Surgical treatment of main thoracic scoliosis with thoracoscopic anterior instrumentation. a five-year follow-up study

BACKGROUND

The surgical outcomes in patients with scoliosis at two years following anterior thoracoscopic spinal instrumentation and fusion have been reported. The purpose of this study was to evaluate the results at five years.

METHODS

A consecutive series of forty-one patients with major thoracic scoliosis treated with anterior thoracoscopic spinal instrumentation was evaluated at regular intervals. Prospectively collected data included patient demographics, radiographic measurements, clinical deformity measures, pulmonary function, an assessment of intervertebral fusion, and the scores on the Scoliosis Research Society (SRS-24) outcomes instrument. Perioperative and postoperative complications were recorded. Patient data for the preoperative, two-year, and five-year postoperative time points were compared. In addition, a univariate analysis compared selected two-year radiographic, pulmonary function, and SRS-24 data of the study cohort and those of the patients lost to follow-up.

RESULTS

Twenty-five (61%) of the original forty-one patients had five-year follow-up data and were included in the analysis. Between the two-year and five-year follow-up visits, no significant changes were observed with regard to the average percent correction of the major Cobb angle (56% +/- 11% and 52% +/- 14%, respectively), average total lung capacity as a percent of the predicted value (95% +/- 14% and 91% +/- 10%), and the average total SRS-24 score (4.2 +/- 0.4 and 4.1 +/- 0.7). Radiographic evaluation of intervertebral fusion at five years revealed convincing evidence of a fusion with remodeling and trabeculae present at 151 (97%) of the 155 instrumented motion segments. No postoperative infections or clinically relevant neurovascular complications were observed. Rod failure occurred in three patients, and three patients required a surgical revision with posterior spinal instrumentation and fusion.

CONCLUSIONS

Thoracoscopic anterior instrumentation for main thoracic idiopathic scoliosis results in five-year outcomes comparable with those reported previously for open anterior and posterior techniques. The radiographic findings, pulmonary function, and clinical measures remain stable between the two and five-year follow-up time points. Thoracoscopic instrumentation provides a viable alternative to treat spinal deformity; however, the risks of pseudarthrosis, hardware failure, and surgical revision should be considered along with the advantages of limited muscular dissection and improved scar appearance.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.

The changes of relative position of the thoracic aorta after anterior or posterior instrumentation of type I Lenke curve in adolescent idiopathic thoracic scoliosis

The risk of impingement of the aorta associated with thoracic vertebral screw or pedicle screw instrumentation in the treatment of thoracic scoliosis has been an important concern. To understand this phenomenon more systematically, the relative position of the aorta with reference to the thoracic vertebrae in right thoracic adolescent idiopathic scoliosis (AIS) following anterior and posterior spinal instrumentation was analyzed in detail quantitatively; 34 patients underwent anterior (n = 14) or posterior (n = 20) spinal instrumentation were recruited in the present study. The relative position of the thoracic aorta, vertebral rotation, apical vertebral translation and thoracic kyphosis were measured from pre- and post-operative CT images from T5 to T12. The aorta was found to shift antero-medially in the anterior instrumentation group but not in the posterior spinal instrumentation group. It is likely that the disc removal, soft tissue release and spontaneous vertebral derotation of the scoliosis could account for the antero-medial shifting of the aorta. By the shifting, the space for contralateral screw penetration was reduced.

The anatomical relationship between the aorta and the thoracic vertebral bodies and its importance in the placement of the screw in thoracoscopic correction of scoliosis

Thoracoscopically-assisted anterior spinal instrumentation is being used widely to treat adolescent idiopathic scoliosis (AIS). Recent studies have showed that screws placed thoracoscopically could counter the aorta or entrance into the spinal canal. There are a few studies defining the anatomic landmarks to identify the relationship between the aorta and the thoracic vertebral body using quantitative measurement for the sake of safe placement of thoracoscopic vertebral screw in anterior correction for AIS. The CT scanning from T4 to T12 in 64 control subjects and 30 AIS patients from mainland China were analyzed manually. Parameters to be measured included the angle for safety screw placement (alpha), the angle of the aorta relative to the vertebral body (beta), the distance from the line between the left and the right rib heads to the anterior wall of the vertebral canal (a), the distance from the left rib head to posterior wall of the aorta (b), the vertebral body transverse diameter (c) and vertebral rotation (gamma). No significant differences were found between the groups with respect to age or sex. Compared with the control group, alpha angle from T7 to T10, beta angle from T5 to T10 and b value at T9, T10 were significantly lower in the scoliotic group. The a value was significantly lower in the scoliotic group. The c value showed no significant difference between the two groups. In conclusion, to place the thoracoscopic vertebral screw safely, at the cephalad thoracic spine (T4-T6), the maximum ventral excursion angle should decrease gradually from 20 degrees to 5 degrees , the entry-point of the screw should be close to the rib head. For apical vertebrae (T7-T9), the maximum ventral excursion angle increased gradually from 5 degrees to 12 degrees. At the caudal thoracic spine (T10-T12), the maximum ventral excursion angle increased, the entry-point should shift 3 approximately 5 mm ventrally.

Operative Therapie der idiopathischen Skoliose mittels ventraler Doppelstabinstrumentation

BACKGROUND

In the surgical treatment of idiopathic scoliosis both anterior and posterior correction and instrumentation techniques are available. The aim of the present study was to analyse the results of a new anterior dual rod instrumentation.

PATIENTS AND METHODS

Prospective analysis of radiometric and clinical parameters of 93 patients operated on between 1996 and 2004 using the Münster Anterior Dual Rod System.

RESULTS

The average curve correction was 65% (fusion length usually Cobb levels) with a preoperative Cobb angle of 59 degrees. Postoperative loss of correction amounted to 1.5 degrees (average follow-up of 36 months). Apical vertebral derotation averaged 45% in the thoracic and 53% in the lumbar spine with a subsequent correction of the rib hump of 66% and the lumbar hump of 81%. There were no revisions or neurological complications.

CONCLUSION

Anterior dual rod instrumentation enables an effective and safe three-dimensional curve correction in single structural curves with only minimal loss of correction.

The position of the aorta relative to the spine before and after anterior instrumentation in right thoracic scoliosis

STUDY DESIGN

Preoperative magnetic resonance images (MRI) and postoperative axial computed tomography (CT) scans in 25 consecutive patients with idiopathic right thoracic adolescent scoliosis (AIS) and anterior correction and fusion with a dual rod system were analyzed in a prospective study.

OBJECTIVES

Evaluation of the spatial relations between the vertebral body and the aorta and the relative migration of the aorta due to the anterior correction and instrumentation in right thoracic scoliosis patients.

SUMMARY OF BACKGROUND DATA

In anterior scoliosis surgery, bicortical screw purchase is performed to increase pullout strength. However, impingement of the aorta due to excessive contralateral screw penetration has been reported, especially after endoscopic instrumentation. For a safe screw placement, knowledge of both the preoperative topographic relation of aorta and vertebral body and its changes due to surgical correction is crucial. Recent studies reported on a more lateral and posterior position of the aorta in AIS patients. However, there are hardly any data on the changes of the aortic position after anterior curve correction available in the current literature.

METHODS

All 25 patients underwent an identical anterior surgical technique with standard open approach and dual rod instrumentation of the primary curve. Preoperative MRI and postoperative sequential CT scans of 180 vertebrae were analyzed with respect to following parameters: vertebral body width and depth, diameter of the aorta, closest distance between aorta and the vertebral body, the aorta-vertebral angle, and the position of the aorta in relation to the spinal canal.

RESULTS

Before surgery, the aorta is positioned posterolaterally with an aorta-vertebral angle of between 78 degrees and 92 degrees (between T5 and T10). Between T11 and L2, the aorta is positioned more anteromedially with an aorta-vertebral angle from 62 degrees (T11) to 16 degrees (L2). After surgery, the aorta has migrated from a posterolateral to a more anteromedial position. This migration is maximal at the apex vertebra with an average change of the aorta-vertebral angle of 31.4 degrees . Whereas the distance between the aorta and the vertebral body increases at the upper and lower fusion levels, the aorta moves significantly closer to the vertebral body at the curve apex due to surgical correction. In patients with thoracic hypokyphosis, the aorta is positioned significantly more posterior than in patients with hyperkyphosis.

CONCLUSIONS

This MRI and CT based study of 25 patients with thoracic AIS treated by standard open dual rod and dual screw instrumentation demonstrates a migration of the aorta by 31 degrees from a more posterolateral position before surgery to a more anteromedial position after surgery at the curve apex. Scoliosis surgeons should be aware of these changes; any excessive contralateral screw penetration must be avoided at any level.