Pedicle morphology of the thoracic spine in preadolescent idiopathic scoliosis: magnetic resonance supported analysis

Although several studies have been reported on the adult vertebral pedicle morphology, little is known about immature thoracic pedicles in patients with idiopathic scoliosis. A total of 310 pedicles (155 vertebrae) from T1 to T12 in 10–14 years age group were analyzed with the use of magnetic resonance imaging and digital measurement program in 13 patients with right-sided thoracic idiopathic scoliosis. Each pedicle was measured in the axial and sagittal planes including transverse and sagittal pedicle width and angles, chord length, interpedicular distance and epidural space width on convex and concave sides of the curve. The smallest transverse pedicle widths were in the periapical region and the largest were in the caudal region. No statistically significant difference in transverse pedicle widths was detected between the convex and concave sides. The transverse pedicle angle measured 15.56° at T1 and decreased to 6.32° at T12. Chord length increased gradually from the cephalad part of the thoracic spine to the caudad part as the shortest length was seen at T1 convex level with a mean of 30.45 mm and the largest length was seen at T12 concave level with a mean of 41.73 mm. The width of epidural space on the concave side was significantly smaller than that on the convex side in most levels of the curve. Based on the anatomic measurements, it may be reasonable to consider thoracic pedicle screws in preadolescent idiopathic scoliosis.     

胸椎椎弓根形态测量研究

目的:观察不同节段胸椎椎弓根形态特征,探讨其临床意义。方法:测量40具国人胸椎标本的椎弓根横径、矢状径、矢状面夹角、椎弓根间距、椎弓根后缘皮质到椎体前缘皮质距离及椎弓根-椎板夹角,观察椎弓根后缘中点与相应横突根部的关系。结果:（1）除T1外,各节段椎弓根矢状径均明显大于横径（P<0.01）;（2）椎弓根矢状面夹角从T1到T9逐渐减小,T10以下为负角;（3）椎弓根后缘皮质沿其轴线到椎体前缘的长度从T1到T7逐渐增加,T7到T12基本相同;（4）T1与T12椎弓根螺钉拟进钉点位于横突根部中点,T2及T11位于横突根部中上1/3点,其余各节段均位于横突根部上缘。结论:进行胸椎椎弓根螺钉固定时,应根据不同节段椎弓根形态特点,结合X线片或CT片,选择相应的螺钉直径、长度、进钉部位及方向。     

Analysis of anatomic morphometry of the pedicles and the safe zone for through-pedicle procedures in the thoracic and lumbar spine

Posterior instrumentation through the pedicle is a common surgery. Understanding the morphometry of the pedicle and the anatomy of adjacent neural structures should help decrease the risk of postoperative complications. T1–L5 segments from 15 sets of human vertebrae were separated into individual vertebrae and the morphometric characteristics of the thoracic and lumbar spine and the safe zone of the pedicle were analyzed. T11–L5 segments from six human cadavers were dissected. Measurements were taken from the pedicle to the dura and nerve roots superiorly, inferiorly, medially, and laterally, and the transverse angles of the nerve roots were measured. Pedicles were widest in L5 and narrowest in T4 in the transverse plane, and widest in T11 or T12 and narrowest in T1 in the sagittal plane. In individual pedicle, the ranges of the safe zone width and height were 3.4–7.7 and 8.6–13.7 mm, respectively, in T1–T10; and 7.2–17.8 and 13.9–16.7 mm, respectively, in T11–L5. The transverse angle of the pedicle decreases progressively from T1 to T12, then increase from L1 to L5. In sagittal angle, the largest angle localized at T2 and the smallest at L5. The mean distances from pedicles to adjacent neural structures were greater superiorly and laterally than inferiorly and medially. The lateral distance between nerve root and the pedicle ranged from 2.4 to 9.6 mm in lumbar spine. This study provides potential safe zones for the application of through-pedicle procedures to help decrease the risk of postoperative complications.     

Safety of thoracic pedicle screw application using the funnel technique in Asians: a cadaveric evaluation

The objective of this cadaveric study is to determine the safety and outcome of thoracic pedicle screw placement in Asians using the funnel technique. Pedicle screws have superior biomechanical as well as clinical data when compared to other methods of instrumentation. However, misplacement in the thoracic spine can result in major neurological implications. There is great variability of the thoracic pedicle morphometry between the Western and the Asian population. The feasibility of thoracic pedicle screw insertion in Asians has not been fully elucidated yet. A pre-insertion radiograph was performed and surgeons were blinded to the morphometry of the thoracic pedicles. 240 pedicle screws were inserted in ten Asian cadavers from T1 to T12 using the funnel technique. 5.0 mm screws were used from T1 to T6 while 6.0 mm screws were used from T7 to T12. Perforations were detected by direct visualization via a wide laminectomy. The narrowest pedicles are found between T3 and T6. T5 pedicle width is smallest measuring 4.1 ± 1.3 mm. There were 24 (10.0%) Grade 1 perforations and only 1 (0.4%) Grade 2 perforation. Grade 2 or worse perforation is considered significant perforation which would threaten the neural structures. There were twice as many lateral and inferior perforations compared to medial perforations. 48.0% of the perforations occurred at T1, T2 and T3 pedicles. Pedicle fracture occurred in 10.4% of pedicles. Intra-operatively, the absence of funnel was found in 24.5% of pedicles. In conclusion, thoracic pedicle screws using 5.0 mm at T1–T6 and 6.0 mm at T7–T12 can be inserted safely in Asian cadavers using the funnel technique despite having smaller thoracic pedicle morphometry.     

中国青少年特发性脊柱侧凸患者胸椎椎弓根形态学三维CT分析

目的 总结中国青少年特发性脊柱侧凸患者胸椎椎弓根形态学特点,与其他人种特发性脊柱侧凸患者胸椎椎弓根形态比较,为手术中胸椎安全置钉提供参考.方法 回顾性分析2007年7月至2012年6月期间56例于我院行术前CT扫描三维重建的青少年特发性脊柱侧凸(右胸弯)患者的资料,男10例,女46例;年龄10～18岁,平均14.8岁.Lenke分型:Ⅰ型28例、Ⅱ型12例、Ⅲ型14例、Ⅳ型2例.术前主胸弯Cobb角平均为55°(36°～90°).测量其胸椎两侧椎弓根在矢状面、冠状面、轴面的置钉长度、椎弓根宽度及角度等形态学指标,总结其变化规律,并与文献报道的其他人种数据进行对比.结果 主胸弯顶椎区凹侧椎弓根宽度小于凸侧,椎弓根置钉长度大于凸侧,椎弓根尾倾角度小于凸侧.椎弓根矢状面宽度自头端向尾端逐渐增加,平均值范围为0.68～1.36 cm;轴面椎弓根宽度平均值范围为0.30～0.70 cm.冠状面椎弓根最小径略小于轴面椎弓根宽度,平均值范围为0.28～0.67 cm.结论 与欧美人种相比,中国特发性脊柱侧凸患者椎弓根宽度较小.顶椎区凹侧置钉难度大、风险高,建议使用直径3.5 mm椎弓根螺钉或采用极外侧置钉法.     

Sagittal balance of thoracic lordoscoliosis: anterior dual rod instrumentation versus posterior pedicle screw fixation

Posterior pedicle screw fixation is now the standard treatment for surgical correction of idiopathic scoliosis and has largely replaced anterior techniques, but there have been reports describing a lordogenic effect of segmental pedicle screw instrumentation in the thoracic spine. This clinical study compared anterior dual rod instrumentation with posterior pedicle screw fixation for idiopathic thoracic lordoscoliosis, including 42 patients (7 male, 35 female; average age 16 years, range 12–34) who underwent posterior pedicle screw fixation (n = 20) or anterior dual rod instrumentation (n = 22) at two centers. The average follow-up period was 33 months (24–108 months). Inclusion criteria were a diagnosis of adolescent idiopathic scoliosis with a structural thoracic curve (Lenke 1–3) and thoracic hypokyphosis (T4–T12 < 20°). The main thoracic curve magnitude and sagittal profile on standing radiographs were evaluated. Thoracic kyphosis was significantly restored from preoperatively 10.2° to 23.4° postoperatively in the anterior group and from 7.6° to 12.9° in the posterior group (P < 0.005). Kyphosis improved significantly better in the anterior group than in the posterior group (P < 0.005). The preoperative and postoperative main thoracic curve values were 63° (48–80°) and 25.2° in the anterior group and 60.6° (50–88°) and 23.6° in the posterior group, with no significant differences between the groups. No neurological or other severe complications were observed. Anterior dual rod instrumentation in patients with thoracic lordoscoliosis allows significantly better restoration of thoracic kyphosis than posterior pedicle screw instrumentation.     

Morphometric analysis of thoracic and lumbar vertebrae in idiopathic scoliosis

STUDY DESIGN: Prospective study on the morphometry of 337 pedicles in 29 patients with idiopathic scoliosis. OBJECTIVES: To analyze by means of computed tomographic scans the vertebral morphometry in idiopathic scoliosis treated by pedicle screw instrumentation. SUMMARY OF BACKGROUND DATA: Although several studies exist on the vertebrae's morphometry in normal spines, little is known concerning the morphometry of scoliotic vertebrae. METHODS: The pedicles' morphometry between T5 and L4 was analyzed by computed tomographic scans in 29 surgically treated patients with idiopathic right thoracic scoliosis. Measurements included chord length, endosteal transverse pedicle width, transverse pedicle angle, and pedicle length. RESULTS: The endosteal transverse pedicle width was significantly smaller (P < 0.05) on the concavity in the apical region of the thoracic spine and measured between 2.5 and 4.2 mm in the middle thoracic spine (T5-T9) and between 4.2 and 5.9 mm in the lower thoracic spine (T10-T12). In the lumbar spine, the width varied between 4.8 and 9.5 mm without significant differences between the concave and convex sides (P > 0.05). The chord length was shortest at T5, measuring 37 mm and increased gradually to 50 mm at L3 with significantly larger dimensions in male patients and on the concavity of the apical region in the thoracic spine (P < 0.05). The pedicle length varied minimally, with a range of between 20 and 22 mm, and was relatively consistent throughout the thoracic and lumbar spine. The transverse pedicle angle varied between 6 degrees in the lower thoracic spine and 12 degrees in the upper thoracic and lower lumbar spine. CONCLUSION: The morphometry in scoliotic vertebrae is substantially different from that of vertebrae in normal spines, with an asymmetrical intravertebral deformity shown in scoliotic vertebrae. Pedicle screw instrumentation on the concavity in the apical region of thoracic curves appears critical because of the small endosteal pedicle width.     

Optimal entry points and trajectories for cervical pedicle screw placement into subaxial cervical vertebrae

The present study was performed to determine the optimal entry points and trajectories for cervical pedicle screw insertion into C3–7. The study involved 40 patients (M:F = 20:20) with various cervical diseases. A surgical simulation program was used to construct three-dimensional spine models from cervical spine axial CT images. Axial, sagittal, and coronal plane data were simultaneously processed to determine the ideal pedicle trajectory (a line passing through the center of the pedicle on coronal, sagittal, and transverse CT images). The optimal entry points on the lateral masses were then identified. Horizontal offsets and vertical offsets of the optimal entry points were measured from three different anatomical landmarks: the lateral notch, the center of the superior edge and the center of lateral mass. The transverse angle and sagittal angles of the ideal pedicle trajectory were measured. Using those entry points and trajectory results, virtual screws were placed into the pedicles using the simulation program, and the outcomes were evaluated. We found that at C3–6, the optimal entry point was located 2.0–2.4 mm medial and 0–0.8 mm inferior to the lateral notch. Since the difference of 1 mm is difficult to discern intra-operatively, for ease of remembrance, we recommend rounding off our findings to arrive at a starting point for the C3–6 pedicle screws to be 2 mm directly medial to the lateral notch. At C7, by contrast, the optimal entry point was 1.6 mm lateral and 2.5 mm superior to the center of lateral mass. Again, for ease of remembrance, we recommend rounding off these numbers to use a starting point for the C7 pedicle screws to be 2 mm lateral and 2 mm superior to the center of lateral mass. The average transverse angles were 45° at C3–5, 38° at C6, and 28° at C7. The entry points for each vertebra should be adjusted according to the transverse angles of pedicles. The mean sagittal angles were 7° upward at C3, and parallel to the upper end plate at C4–7. The simulation study showed that the entry point and ideal pedicle trajectory led to screw placements that were safer than those used in other studies.     

Analysis of the morphometric characteristics of the thoracic and lumbar pedicles

A total of 2,905 pedicle measurements were made from T1-L5. Measurements were made from spinal computerized tomography (CT) scan examinations and individual vertebral specimen roentgenograms. Parameters considered were the pedicle isthmus width in the transverse and sagittal planes, pedicle angles in the transverse and sagittal planes, and the depth to the anterior cortex in a line parallel to the midline of the vertebral body and along the pedicle axis. There was no significant difference between data obtained from CT scans and specimen roentgenograms. Pedicles were widest at L5 and narrowest at T5 in the transverse plane. The widest pedicles in the sagittal plane were seen at T11, the narrowest at T1. Due to the oval shape of the pedicle, the sagittal plane width was generally larger than the transverse plane width. The largest pedicle angle in the transverse plane was at L5. The posterolateral to anterolateral pedicle axis orientation in the transverse plane, seen at other levels throughout the thoracolumbar spine, reversed at T12. In the sagittal plane, the pedicles angled caudally at L5 and cephaladly from L3-T1. The depth to the anterior cortex was significantly longer along the pedicle axis than along a line parallel to the midline of the vertebral body at all levels with the exception of T12 and T11.     

椎弓根螺钉植入导向器的研制及体外应用研究

目的　分析自制椎弓根螺钉导向器提高椎弓根螺钉植入的准确性。　方法　根据椎弓根的解剖特点 ,研制椎弓根螺钉植入导向器。用多层螺旋 CT测量 2具胸椎标本 (T1 ～ T1 0 )椎弓根的三维定量解剖数据。依据其中轴的水平位角 (transverse section angle,TSA)和矢状位角 (sagittal section angle,SSA)值 ,调节导向器水平和矢状刻度盘角度。植入螺钉后拔出 ,用显影剂填充钉道。 CT测量显影钉道的 TSA和 SSA值。　结果　析因设计资料方差分析显示 ,椎弓根显影钉道的 TSA、SSA与其中轴的 TSA、SSA间差异无统计学意义 (P>0 .0 5 )。　结论　椎弓根螺钉导向器操作简便 ,其导向使钉道达到理想角度 ,能减少椎弓根穿破的发生。     

New parameters to represent the position of the aorta relative to the spine for pedicle screw placement

Parameters of the position of the aorta in previous reports were determined for anterior surgery. This study evaluated the relative position of the aorta to the spine by new parameters, which could enhance the safety of pedicle screw placement. Three parameters were defined in a new Cartesian coordinate system. We selected an entry point of a left pedicle screw as the origin. The transverse plane was determined to include both the bases of the superior facet and to be parallel to the upper endplate of the vertebral body. A line connecting the entry points of both sides was defined as the X-axis. The angle formed by the Y-axis and a line connecting the origin and the center of the aorta was defined as the left pedicle–aorta angle. The length of a line connecting the origin and the aorta edge was defined as the left pedicle–aorta distance. Distance from the edge of the aorta to the X-axis was defined as the pedicular line–aorta distance. These parameters were measured preoperatively in 293 vertebral bodies of 24 patients with a right thoracic curve. We simulated the placement of the pedicle screw with variable length and with some direction error. We defined a warning pedicle as that when the aorta enters the expected area of the screw. Sensitivity analysis was performed to find the warning pedicle ratio in 12 scenarios. The left pedicle–aorta angle averaged 29.7° at the thoracic spine and −16.3° at the lumbar spine; the left pedicle–aorta distance averaged 23.7 and 55.2 mm; the pedicular line–aorta distance averaged 18.3 and 51.0 mm, respectively. The ratio of warning pedicles was consistently high at T4–5 and T10–12. When a left pedicle screw perforates an anterior/lateral wall of the vertebral body, the aorta may be at risk. These new parameters enable surgeons to intuitively understand the position of the aorta in surgical planning or in placement of a pedicle screw.     

Morphometry of the lower thoracic and lumbar pedicles and its relevance in pedicle fixation

Purpose

To assess the pedicle morphology in the lower thoracic and lumbar spine in an Indian population and to determine the causes of pedicle wall violation by pedicle screws.

Methods

Computerised tomographic scans of 135 consecutive patients with thoracolumbar and lumbar spine fractures were prospectively analysed to determine the pedicle morphology. The transverse pedicle angle, pedicle diameter and screw path length at 527 uninjured levels were measured. Post-operative CT scans of 117 patients were analysed to determine the accuracy of 468 pedicle screws at 234 vertebrae.

Results

The lowest (mean ± SD) transverse pedicle width in the lower thoracic spine was 5.4 ± 0.70 mm, whereas in the lumbar spine it was 7.2 ± 0.87 mm. The shortest (mean ± SD) screw path length in lower thoracic pedicles was 35.8 ± 2.10 and 41.9 ± 2.18 mm in the lumbar spine. The mean transverse pedicle angle in the lower thoracic spine was consistently less than 5°, whereas it gradually increased from L1 through L5 from 8.5° to 30°. Forty-one screws violated the pedicle wall, due to erroneous angle of screw insertion.

Conclusions

In the current study, pedicle dimensions were smaller compared to the Western population. In Indian patients, pedicle screws of 5 mm diameter and 30 mm length, and 6 mm diameter and 35 mm length can safely be used in the lower thoracic and lumbar spine, respectively. However, it is important to assess the pedicle morphology on imaging prior to pedicle fixation.

     

Thoracic pedicle screw placement guided by computed tomographic measurements.

Cadaveric pedicle screw placement guided by the measurements from axial computed tomography (CT) scans in the thoracic spine was assessed in this study. Axial CT scans were performed on four cadaveric thoracic spines, and the measurements included the pedicle transverse angle, inner pedicle width, and distance between the midline of the vertebra and the pedicle axis on the dorsal aspect of the lamina. With utilization of the data from CT scans, screws were directly placed into the thoracic pedicle from T1 to T10. Screw penetration of the pedicle was determined by gross examination. The results showed that the largest pedicle transverse angle was found at the levels of T1-2, and the smallest occurred at the T3 through T8 levels. The value of the pedicle inner width was quite different between specimens with a minimum of 3.0 mm at T4 and a maximum of 9.2 mm at T10. Gross examination of the pedicle showed that 13 (16.3%) of 80 screws penetrated the pedicle wall, with a Grade I penetration in 11 pedicles and a Grade II penetration in 2 pedicles. Screw penetration of the medial wall was found in four pedicles and penetration of the lateral wall was noted in nine pedicles. No screw penetration of the superior and inferior walls of the pedicle was identified in any of the four specimens. Thoracic pedicle screw placement guided by the measurements from axial CT scans significantly reduced the incidence of pedicle penetration. Axial CT measurements of the pedicle inner diameter and transverse angle as well as the starting point for screw insertion are recommended if pedicle screw fixation is intended in the thoracic spine.     

胸椎经关节突关节椎弓根螺钉固定的可行性研究

 目的明确胸椎后路经关节突关节椎弓根螺钉固定的解剖学可行性和技术参数.为临床应用提供参考。方法取 20具胸椎标本.仔细解剖胸椎的后侧和前侧方.以清楚地暴露胸椎椎板和椎弓根。以椎板下缘向上、外缘向内各 7 mm为进钉点.在 T_1.2、T_5.6、T_9.10直视下置入经关节突关节椎弓根螺钉.通过直接的置钉和 CT重建.观察胸椎后路经关节突关节椎弓根螺钉实际置钉的可行性.测量经关节突关节椎弓根螺钉内固定进钉角度和钉道长度。结果所有胸椎后路经关节突关节椎弓根螺钉均由上位胸椎下关节突经关节突关节.进入下位胸椎的椎弓根.成功置入下位胸椎的椎体内。重建 CT测量发现螺钉在横断面的外倾角度为 2.1°±0.7°.在矢状面的尾倾角度为 41.4°±3.2°.在各节段间略有不同.但差异无统计学意义。平均的螺钉钉道长度为(40.6±4.9) mm.钉道长度由上胸椎向中、下胸椎呈逐渐增加趋势.差异有统计学意义(F=74.09, P<0.01)。结论胸椎后路经关节突关节椎弓根螺钉具有解剖学可行性.可以作为胸椎椎弓根螺钉固定的一种补充内固定方法.但置钉时要求较高的准确性。     

青少年特发性胸椎侧凸患者胸椎椎弓根横径的分型及其临床意义

目的 探讨胸椎椎弓根横径的测量及分型在青少年特发性胸椎侧凸患者治疗中的临床意义.方法 对2008年10月至2009年7月收治的30例青少年特发性胸椎侧凸患者(侧凸组)和2008年8月至2009年7月于本院就诊的20例年龄匹配的非侧凸青少年患者(对照组)采用螺旋CT行胸椎连续扫描,在图像编档和通信系统(PACS)上逐层阅片,选择胸椎椎弓根显示最清楚的层面对椎弓根横径进行测量,并根据测量结果将其分为4型.分别对侧凸组凹凸侧和对照组左右侧椎弓根横径进行对比,并对侧凸组与对照组椎弓根分型的构成比进行分析.结果 两组患者胸椎椎弓根横径T1～4逐渐减少,T5～12逐渐增加.对照组同节段双侧胸椎椎弓根横径差异无统计学意义(P>0.05).侧凸组顶椎区凹侧的椎弓根横径明显小于凸侧,差异有统计学意义(P<0.05).侧凸组中4型椎弓根的比例明显高于对照组,1型椎弓根的比例低于对照组,差异均有统计学意义(P<0.05).结论 青少年特发性胸椎侧凸患者胸椎椎弓根横径常较小,术前应根据CT胸椎椎弓根形态制定置钉策略,以减少经胸椎椎弓根置入螺钉的并发症的发生.     

椎弓根钉道参数的变异性及其相关因素的研究

目的研究椎弓根钉道相关参数的变异性及引起变异的具有临床意义的相关因素。方法用PickerPQ6000螺旋CT扫描仪对C3～L5椎体进行扫描。共扫描198例(男118例,女80例)的736个椎体。测量每个椎体的椎弓根横径、钉道长度、及e角(椎弓根轴线与矢状面夹角),观察椎体形态及椎体、棘突、人体三者各自矢状轴间的关系,如有异常则测量并记录。同时记录受检者的性别、身高、体重。以上数据用SPSS软件进行统计学处理。结果统计结果显示:每一节椎体的椎弓根宽度、钉道长度及e角均有较大的极差及四分位数间距。虽然t检验显示不同性别间的钉道长度、椎弓根宽度均有明显的统计学差异,但在进一步以协方差分析法分析各因素的交互效应时发现,在消除体重、身高两因素后,椎弓根宽度及钉道长度均与性别无关。泊松相关分析显示身高、体重均与椎弓根宽度及钉道长度呈显著正相关,而e角与后两者无显著相关性。对椎体畸变的观察显示:14(1.9%)个胸腰椎椎体矢状轴与人体矢状轴不一致;11(1.0%)个椎体棘突轴与椎体矢状轴不一致;T9以下,14(4.9%)个椎体的椎弓根横径小于4mm;4个椎体椎弓根外凸变形,影响置钉位置。结论人体椎弓根钉道参数具有较大的变异性,不同个体、不同节段水平均有显著不同;体重和身高是两个影响变异性重要的相关因素。偶发     

Computed tomographic-based morphometric study of thoracic spine and its relevance to anaesthetic and spinal surgical procedures

BackgroundTo collect a baseline computer software aided normative morphometric data of thoracic spine in the Indian population and analyze it to give pre-procedural guidelines to clinicians for safe surgical and anaesthetic procedures in the thoracic spine.MethodsCT scans of thoracic spine of patients free from spinal disorders were reviewed in a total of 600 vertebrae in 50 patients. Parameters recorded with the help of computer software were pedicle width, length and height, transverse pedicle angles, chord length, canal dimensions, body width and height, spinous process angle and transverse process length.ResultsPedicle width decreased from T1 (9.27 ± 1.01) to T4 (4.5 ± 0.93) and increased to T12 (8.31 ± 1.83). At T4 76% and at T5 62% of the pedicles were smaller than 5 mm and would not accept 4 mm screw with 1.0-mm clearance. However, at T1 2%, at T11 7% and at T12 8% would not accept a 4 mm screw. Chord length gradually increased in upper thoracic vertebrae and was relatively constant in middle and decreased in lower thoracic vertebrae. Shortest estimated chord length was at T1 (30.30 ± 2.11). On an average, from T1 to T6 and at T11 and T12, a screw length of 25–30 mm could be accommodated and from T7 to T10, 30–35 mm screw length could be accommodated. Transverse pedicle angle decreased from T1 (35.4 ± 2.21) to T12 (−9.8 ± 2.39). Canal dimensions were narrowest at T4/T5 (20.02 ± 1.23) in anteroposterior and 21.12 ± 1.23 in interpedicular diameters. Spinous process angle increased from T1 (30.11 ± 6.74) to T6 (57.89 ± 9.31) and decreased to 16.21 ± 7.38 at T12. Transverse process length increased from T1 to T7 (23.54 + 2.12 to 31.21 + 1.91) and then decreased to 12.11 + 2.3 at T12. Vertebral body dimensions showed increasing trends from T1 to T12.ConclusionsA thorough knowledge of anatomical and radiological characteristics of the spine and their variations is essential for the clinicians. Data collected in the present study provides baseline normative values in Indian population and will help in guiding safe and effective completion of both surgical and anaesthetic procedures in the thoracic spine. Computer software aided morphometric data can help in selecting appropriate size and optimal placement of the implant with minimal procedural difficulties and complications during spine surgery.     

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 (α), the angle of the aorta relative to the vertebral body (β), 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 (γ). No significant differences were found between the groups with respect to age or sex. Compared with the control group, α angle from T7 to T10, β 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° to 5°, 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° to 12°. At the caudal thoracic spine (T10–T12), the maximum ventral excursion angle increased, the entry-point should shift 3∼5 mm ventrally.     

The USS pedicle hook system: a morphometric analysis of its safety in the thoracic spine. Universal Spine System.

The Universal Spine System (USS) pedicle hook design includes a fixation screw that passes obliquely in the anterocranial direction in the pedicle. The addition of the fixation screw was to address concerns with rotation of the hook and hook disengagement. This study was designed to evaluate the safety of the USS screw locked pedicle hook. Eleven cadaveric thoracic spines were instrumented posteriorly with USS pedicle hooks from T1 to T12. Spinal instrumentation was performed by a spinal surgeon experienced with the USS system. Spinal deformity was created prior to instrumentation, ranging from 0 to 55 degrees in the horizontal plane (rotation) and from 0 to 50 degrees in the frontal plane (scoliosis). Radiographs, computed tomography (CT), and segmental dissection were used for data acquisition. Morphometric CT analysis before instrumentation demonstrated that the transverse pedicular diameter was the smallest at T5 with a mean of 3.7 mm. The transverse pedicular angle (TPA) was found to always point toward the midline. The largest TPA was observed at T1 with a mean TPA of 28.4 degrees. The pedicle with the least angular deviation from the midline was T11 with a mean TPA of 7 degrees. Postinstrumentation CT analysis and segmental dissection revealed perforations of the pedicle cortex by the fixation screw in 15% of instrumented pedicles (26/172). There were 6 medial and 20 lateral perforations. Medial perforations occurred exclusively in the three most proximal spinal segments, whereas the lateral perforations occurred throughout the thoracic spine. The mean encroachment of the fixation screw was 1.67 mm medially and 1.95 mm laterally. This study demonstrates the variation in caliber and direction of the thoracic pedicles. Medial and lateral perforations of the pedicle can occur with the USS pedicle hook instrumented system.     

Posterior fusion only for thoracic adolescent idiopathic scoliosis of more than 80°: pedicle screws versus hybrid instrumentation

The treatment of thoracic adolescent idiopathic scoliosis (AIS) of more than 80° traditionally consisted of a combined procedure, an anterior release performed through an open thoracotomy followed by a posterior fusion. Recently, some studies have reassessed the role of posterior fusion only as treatment for severe thoracic AIS; the correction rate of the thoracic curves was comparable to most series of combined anterior and posterior surgery, with shorter surgery time and without the negative effect on pulmonary function of anterior transthoracic exposure. Compared with other studies published so far on the use of posterior fusion alone for severe thoracic AIS, the present study examines a larger group of patients (52 cases) reviewed at a longer follow-up (average 6.7 years, range 4.5–8.5 years). The aim of the study was to evaluate the clinical and radiographic outcome of surgical treatment for severe thoracic (>80°) AIS treated with posterior spinal fusion alone, and compare comprehensively the results of posterior fusion with a hybrid construct (proximal hooks and distal pedicle screws) versus a pedicle screw instrumentation. All patients (n = 52) with main thoracic AIS curves greater than 80° (Lenke type 1, 2, 3, and 4), surgically treated between 1996 and 2000 at one institution, by posterior spinal fusion either with hybrid instrumentation (PSF–H group; n = 27 patients), or with pedicle screw-only construct (PSF–S group; n = 25 patients) were reviewed. There were no differences between the two groups in terms of age, Risser’s sign, Cobb preoperative main thoracic (MT) curve magnitude (PSF–H: 92° vs. PSF–S: 88°), or flexibility on bending films (PSF–H: 27% vs. PSF–S: 25%). Statistical analysis was performed using the t test (paired and unpaired), Wilcoxon test for non-parametric paired analysis, and the Mann–Whitney test for non-parametric unpaired analysis. At the last follow-up, the PSF–S group, when compared to the PSF–H group had a final MT correction rate of 52.4 versus 44.52% (P = 0.001), with a loss of −1.9° versus −11.3° (P = 0.0005), a TL/L correction of 50 versus 43% (ns), a greater correction of the lowest instrumented vertebra translation (−1.00 vs. −0.54 cm; P = 0.04), and tilt (−19° vs. −10°; P = 0.005) on the coronal plane. There were no statistically significant differences in sagittal and global coronal alignment between the two groups (C7-S1 offset: PSF–H = 0.5 cm vs. PSF–S = 0 cm). In the hybrid series (27 patients) surgery-related complications necessitated three revision surgeries, whereas in the screw group (25 patients) one revision surgery was performed. No neurological complications or deep wound infection occurred in this series. In conclusion, posterior spinal fusion for severe thoracic AIS with pedicle screws only, when compared to hybrid construct, allowed a greater coronal correction of both main thoracic and secondary lumbar curves, less loss of the postoperative correction achieved, and fewer revision surgeries. Posterior-only fusion with pedicle screws enabled a good and stable correction of severe scoliosis. However, severe curves may be amenable to hybrid instrumentation that produced analogous results to the screws-only constructs concerning patient satisfaction; at the latest follow-up, SRS-30 and SF-36 scores did not show any statistical differences between the two groups. Presented at 8th Annual Meeting of the Spine Society of Europe, October 2006, Istanbul, Turkey.