Analysis of vertebral morphology in idiopathic scoliosis with use of magnetic resonance imaging and multiplanar reconstruction

BACKGROUND: Several studies have provided data on the vertebral morphology of normal spines, but there is a paucity of data on the vertebral morphology in patients with idiopathic scoliosis. METHODS: The morphology of the pedicles and bodies of 307 vertebrae as well as the distance between the pedicles and the dural sac (the epidural space) in twenty-six patients with right-sided thoracic idiopathic scoliosis were analyzed with use of magnetic resonance imaging and multiplanar reconstruction. RESULTS: A distinct vertebral asymmetry was found at the apical region of the thoracic curves, with significantly thinner pedicles on the concave side than on the convex side (p < 0.05). The degree of intravertebral deformity diminished farther away from the apex, with vertebral symmetry restored at the neutral level. In the thoracic spine, the transverse endosteal width of the apical pedicles measured between 2.3 mm and 3.2 mm on the concave side and between 3.9 mm and 4.4 mm on the convex side (p < 0.05). In the lumbar spine, the pedicle width measured between 4.6 mm at the cephalad part of the curve and 7.9 mm at the caudad part of the curve. The chord length and the pedicle length gradually increased from 34 mm and 18 mm, respectively, at the fourth thoracic vertebra to 51 mm and 25 mm, respectively, at the third lumbar vertebra. The transverse pedicle angle measured 15 in the cephalad aspect of the thoracic spine, decreased to 7 at the twelfth thoracic vertebra, and increased again to 16 at the fourth lumbar vertebra. The width of the epidural space was <1 mm at the thoracic apical vertebral levels and averaged 1 mm at the lumbar apical vertebral levels on the concave side, whereas it was between 3 mm and 5 mm on the convex side (p < 0.05). CONCLUSION: Idiopathic scoliosis is associated with distinctive intravertebral deformity, with smaller pedicles on the concave side and a shift of the dural sac toward the concavity.     

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.     

青少年特发性脊柱侧凸胸椎形态学的MRI测量及临床意义

目的 通过磁共振成像(MRI)观察青少年特发性脊柱侧凸(AIS)和正常同年龄组青少年胸椎的形态学差异,探讨其临床意义.方法 胸椎轻度侧凸(MS)组患者10例(Cobb角15°～39°),胸椎中度侧凸(SS)组患者10例(Cobb角40°～75°).另选健康青少年10名作为对照(非侧凸组).所有研究对象均为女性,年龄13～14岁.用1.5 T磁共振扫描仪(Sonata,Siemens,Erlanger,德国)对所有研究对象进行全脊柱矢状面扫描,在图像工作站(Easy Vision,Philips Medical Systems,Best,荷兰)上重建脊柱矢状面图像,测量每个胸椎椎体前壁高度,后壁高度,棘突间高度,在横截面测量椎体横径长度,并进行对比分析.结果 椎体前后高度、宽度从T1到T12逐渐增加,并呈线性分布,脊柱侧凸组椎体高度普遍>正常同年龄非侧凸组患者.脊柱侧凸组患者椎体高度横径比值以及脊椎前后高度比值均>无侧凸组.胸椎侧凸顶椎区T6～T9椎体前方高度、椎体高度横径比值以及脊椎前后高度比值,脊柱侧凸组明显>非侧凸组,差异均有统计学意义(P<0.05).结论 AIS胸椎侧凸女性患者胸椎顶椎区存在显著的脊柱生长模式异常,与正常胸椎相比AIS的胸椎更高、并显得更为瘦长.     

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.     

Lumbar pedicle morphology in adolescent idiopathic scoliosis

Using computed tomography of lumbar spine pedicles, pedicle morphology was documented in 30 patients with adolescent idiopathic scoliosis. Lumbar pedicles are relatively symmetrical in patients with adolescent idiopathic scoliosis; however, a statistically significant difference was found between males and females at L2-L4. A trend for increased transverse pedicle width was observed on the concavity versus the convexity. At levels L3-L5, 90% of the pedicles were >5.5 mm but pedicles Li and 12 were smaller, only >5.5 mm in 34% and 42%, respectively. Safe insertion of 5.5-mm screws is possible at 13-15, but more cephalic pedicles necessitate caution.     

Clinical anatomy of vertebrae in scoliosis: global analysis in four different diseases by multiplanar reconstructive computed tomography

Background contextFew accurate analyses of clinically useful vertebral anatomy have been conducted, and most have focused on thoracic idiopathic scoliosis.PurposeTo evaluate the different anatomic characteristics in scoliosis by disease type and level.Study designObservational cohort study.Patient sampleForty-eight patients with scoliosis were included in this study.Outcome measuresSubjects underwent computed tomography (CT) of the whole spine.MethodsForty-eight patients with scoliosis were included in this study: 15 adolescent idiopathic, 11 cerebral palsy (CP), 10 muscular dystrophy (MD), and 12 congenital (CG) scoliosis patients with similar demographics. Subjects underwent CT of the whole spine, preoperatively. Eight anatomic parameters were measured in multiplanar reconstructive CT images, and statistical analysis was performed to investigate differences.ResultsIn general, values in the anatomic parameters were similar for the four diseases. Each parameter showed the unique change pattern according to the spinal level regardless of curvature shape, direction, or magnitude. In particular, chord length (CL) in MD and CG scoliosis was lower than in adolescent idiopathic scoliosis (AIS) and CP, and pedicle rib unit length was lower in CG scoliosis than in the other diseases (p<.05). Comparisons of convex and concave anatomies in AIS showed that inner pedicle width (PWI) and outer pedicle width (PWO) were wider for convex side, CL, pedicle width, and transverse pedicle angle were greater for concave side (p<.05), and differences were more significant at apices. However, in CP, PWI and PWO were similar between convex and concaves sides (p>.05). Although PWI and PWO were wider for convex sides and CL and pedicle length were greater for concave sides in MD (p<.05), differences were less significant at apices. Particularly, CG scoliosis showed severely deformed anatomy, with differences of seven parameters at apical vertebrae (p<.05).ConclusionClinical anatomies of vertebrae in scoliosis were found to differ significantly at different levels and in terms of convexity and disease type.     

The position of the aorta relative to the spine: a comparison of patients with and without idiopathic scoliosis

BACKGROUND: There is little information documenting the relationship of the aorta to the thoracic scoliotic spine. Recent studies have suggested that the ends of screws placed during an anterior spinal arthrodesis, and pedicle screws used for the treatment of right thoracic scoliosis, may be in proximity to the aorta. The purpose of this study was to analyze the anatomical relationship between the aorta and the spine in a comparison of patients with idiopathic right thoracic scoliosis and patients with a normal spine. METHODS: Thirty-six patients with adolescent idiopathic scoliosis with a right thoracic curve and forty-three with a normal straight spine were studied. Radiographs were analyzed to determine the Cobb angle, the apex of the curve, and the apical vertebral rotation for the patients with scoliosis. Axial magnetic resonance images from the fourth thoracic vertebra to the third lumbar vertebra at the midvertebral body level were used to measure the distance from the aorta to the closest point of the vertebral body cortex, the distance from the posterior edge of the aorta to the spinal canal, and the aorta-vertebral angle. RESULTS: No differences were found between the groups with respect to age or sex distribution. For the scoliosis and normal groups, boys had greater average vertebral body width and depth for all levels than did girls (p < 0.05). For the scoliosis group, the most common apical vertebra was the eighth thoracic vertebra, the average coronal curve measurement was 55.2 degrees, and the average apical rotation was 17.3 degrees. The average distance from the aortic wall to the vertebral body cortex at the apex of the curve was greater in the patients with scoliosis (4.0 mm) than at similar levels in the normal group (2.5 mm) (p < 0.05). The distance from the posterior aspect of the aorta to the anterior aspect of the spinal canal was less in the scoliosis group (11.1 mm) than in the normal group (19.2 mm) for the fifth to the twelfth thoracic level (p < 0.05). The aorta was positioned more laterally and posteriorly adjacent to the vertebral body at the fifth to the twelfth thoracic level in patients with scoliosis compared with that in normal patients as reflected in a smaller aorta-vertebral angle (p < 0.05). With an increasing coronal Cobb angle in the thoracic curve and apical vertebral rotation, the aorta was positioned more laterally and posteriorly (p < 0.05). CONCLUSION: In patients with right thoracic idiopathic scoliosis, the aorta is positioned more laterally and posteriorly relative to the vertebral body compared with that in patients without spinal deformity.     

Idiopathic scoliosis in three dimensions: a succession of two-dimensional deformities?

STUDY DESIGN: A geometric analysis of computerized three-dimensional (3-D) reconstructions of the spine of adolescents with idiopathic scoliosis. OBJECTIVES: To analyze and describe the 3-D location of scoliotic curves with respect to the global frontal, sagittal, and transverse planes of each subject. SUMMARY OF BACKGROUND DATA: Clinical two-dimensional (2-D) measurements cannot fully describe the 3-D deformity of a scoliotic spine because they are done in the 2-D frontal or sagittal plane projection of a subject and do not correspond to the actual deformity. METHODS: The spinal deformity from T1 to L5 of 50 adolescents with thoracic idiopathic scoliosis was reconstructed in 3-D using a multiplanar digital radiographic technique allowing the visualization of the vertebral line of the spine in any projection using auto CAD software. The curvature was segmented in three distinct curves for each subject: a high thoracic, a thoracic, and a lumbar. A regional plane passing through the two end-vertebrae and the apical vertebra was defined, and a series of geometric manipulations were performed to realign each regional plane with the global axis system of each subject. RESULTS: A total of 91% of the 147 curves studied were found to be entirely contained within its 2-D regional plane, and all scoliotic curves were found to be oriented in a 3-D location different from the classic frontal, sagittal, and transverse orthogonal planes of each subject. CONCLUSION: In thoracic idiopathic scoliosis the deformity of the spine is 3-D, but the regional deformity of each high thoracic, thoracic, or lumbar curve is almost always 2-D. The orientation in space of each 2-D plane is such that it cannot be seen in its true frontal or sagittal projection using standard frontal or sagittal radiologic views of the subject.     

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.     

Differences in early sagittal plane alignment between thoracic and lumbar adolescent idiopathic scoliosis

Background contextIt has previously been shown that rotational stability of spinal segments is reduced by posteriorly directed shear loads that are the result of gravity and muscle tone. Posterior shear loads act on those segments of the spine that are posteriorly inclined, as determined by each individual's inherited sagittal spinal profile. Accordingly, it can be inferred that certain sagittal spinal profiles are more prone to develop a rotational deformity that may lead to idiopathic scoliosis; and lumbar scoliosis, on one end of the spectrum, develops from a different sagittal spinal profile than thoracic scoliosis on the other end.PurposeTo examine the role of sagittal spinopelvic alignment in the etiopathogenesis of different types of idiopathic scoliosis.Study design/settingMulticenter retrospective analysis of lateral radiographs of patients with small thoracic and lumbar adolescent idiopathic scoliotic curves.Patients sampleWe included 192 adolescent idiopathic scoliosis patients with either a thoracic (n=128) or lumbar (n=64) structural curve with a Cobb angle of less than 20° were studied. Children with other spinal pathology or with more severe idiopathic scoliosis were excluded, because this disturbs their original sagittal profile. Subjects who underwent scoliosis screening and had a normal spine were included in the control cohort (n=95).Outcome measuresThoracic kyphosis, lumbar lordosis, T9 sagittal offset, C7 and T4 sagittal plumb lines, pelvic incidence, pelvic tilt, and sacral slope, as well as parameters describing orientation in space of each individual vertebra between C7 and L5 and length of the posteriorly inclined segment.MethodsOn standardized lateral radiographs of the spine, a systematic, semi-automatic measurement of the different sagittal spinopelvic parameters was performed for each subject using in-house developed computer software.ResultsEarly thoracic scoliosis showed a significantly different sagittal plane from lumbar scoliosis. Furthermore, both scoliotic curve patterns were different from controls, but in a different sense. Thoracic kyphosis was significantly decreased in thoracic scoliosis compared with both lumbar scoliosis patients and controls. For thoracic scoliosis, a significantly longer posteriorly inclined segment, and steeper posterior inclination of C7–T8 was observed compared with both lumbar scoliosis and controls. In lumbar scoliosis, the posteriorly inclined segment was shorter and located lower in the spine, and T12–L4 was more posteriorly inclined than in the thoracic group. The lumbar scoliosis cohort had a posteriorly inclined segment of the same length as controls, but T12–L2 showed steeper posterior inclination. Lumbar lordosis, pelvic incidence, pelvic tilt, and sacral slope, however, were similar for the two scoliotic subgroups as well as the controls.ConclusionsThis study demonstrates that even at an early stage in the condition, the sagittal profile of thoracic adolescent idiopathic scoliosis differs significantly from lumbar scoliosis, and both types of scoliosis differ from controls, but in different aspects. This supports the theory that differences in underlying sagittal profile play a role in the development of different types of idiopathic scoliosis.     

Pedicle morphology in thoracic adolescent idiopathic scoliosis: is pedicle fixation an anatomically viable technique?

STUDY DESIGN: A radiographic study of thoracic pedicle anatomy in a group of adolescent idiopathic scoliosis (AIS) patients. OBJECTIVE: To investigate the anatomic constraints of the thoracic pedicles and determine whether the local anatomy would routinely allow pedicle screw insertion at every level. SUMMARY OF BACKGROUND DATA: In spite of the clinical successes reported with limited thoracic pedicle screw-rod constructs for thoracic AIS, controversy exists as to the safety of this technique. MATERIAL AND METHODS: Twenty-nine patients with right thoracic AIS underwent preoperative thoracic CT scans and plain radiographs. Anatomic parameters were measured from T1 to T12. RESULTS: Information on 512 pedicles was obtained. The transverse width of the pedicles from T1 through T12 ranged from 4.6-8.25 mm. The medial pedicle to lateral rib wall transverse width from T1 through T2 ranged from 12.6 to 17.9 mm. Measured dimensions from the CT scans showed the actual pedicle width to be 1-2 mm larger than would have been predicted from the plain radiographs. Age, Risser grade, curve magnitude, and the amount of segmental axial rotation did not correlate with the morphology or size of the thoracic pedicles investigated. In no case would pedicle morphology have precluded the passage of a pedicle screw. CONCLUSION: Based on the data identified in this group of adolescent patients, it is reasonable to consider pedicle screw insertion at most levels and pedicle-rib fixation at all levels of the thoracic spine during the treatment of thoracic AIS.     

Structural vertebral changes in the horizontal plane in idiopathic scoliosis and the long-term corrective effect of spine instrumentation

Summary The rotation and structural changes of the apex vertebra in the horizontal plane as well as of the thoracic cage deformity were quantified by measurements on computed tomography (CT) scans from patients with right convex thoracic idiopathic scoliosis (IS). The CT scans were obtained from 12 patients with moderate scoliosis (mean Cobb angle 25.8°, r 13°–30°) and from 33 with severe scoliosis (mean Cobb angle 46.2°, r 35°–71°). In addition, CT scans of thoracic vertebrae from 15 patients without scoliosis were used as reference material. Ten of the scoliotic cases had had Cotrel-Dubousset instrumentation (CDI) and posterior fusion and had entered a longitudinal study on the effect of operative correction on the re-modelling of the apical vertebra. An increasingly asymmetrical vertebral body, transverse process angle, pedicle width and canal width were found in the groups with scoliosis as compared with the reference material. Vertebral rotation and rib hump index were significantly larger in patients with early and advanced scoliosis than in normal subjects. The modelling angle of the vertebral body, the transverse process angle index and the vertebral rotation in relation to the middle axis of the thoracic cage were significantly greater in patients with severe than with moderate scoliosis. The results of this longitudinal study suggest that the structural changes of the apical vertebra regress 2 years or more after CD instrumentation.     

The sagittal curvature of spine in idiopathic scoliosis--its morphological features and the correlation among sagittal and frontal curvatures and rotation of apical vertebra

The change in sagittal curvature especially in thoracic kyphosis of idiopathic scoliosis patients, was analyzed and discussed. Those patients who had scoliotic deformity with typical vertebral rotation only in thoracic spine (ST group), showed significant decrease compared to normal person in thoracic kyphosis, but no difference in lumbar lordosis. Those suffering from scoliotic deformities with typical vertebral rotation in thoracic and lumbar spine showed a significant decrease in thoracic kyphosis and an increase in lumbar lordosis. However those changes in sagittal curvature were not found in FT group patients, who had scoliotic deformity without vertebral rotation. In conclusion, it is not the frontal curvature but the vertebral rotation which influenced the sagittal curvature of spine in patients with idiopathic scoliosis.     

Pedicle anatomy in a patient with severe early-onset scoliosis: can pedicle screws be safely inserted?

OBJECTIVE: With the rapid increase in the use of pedicle screws in the thoracic spine for various pathologies, knowledge of the pedicle anatomy is critical. Previous authors, in discussing pedicle morphology, have usually reported their findings in nondeformed adult specimens. More recently, the use of pedicle screws in adolescent idiopathic scoliosis has been reported. METHODS: The authors studied the pedicle diameters in the spine of a patient with infantile idiopathic scoliosis who died at age 28 of cor pulmonale. The concave pedicles from T6 to L3 were measured both directly and with thin-section computed tomography (CT) scanning (the curve apex was T8-T11). RESULTS: By direct measurement, the concave pedicle width at its narrowest point (the isthmus) ranged from 2.9 (T9) to 6.7 (L1, L3) mm. Three apical concave pedicles (T8, T9, T10) had no cancellous cavity. By CT scan measurement, the four apical concave pedicles measured 3.4 (T8), 2.8 (T9), 2.6 (T10), and 3.4 (T11) mm, respectively. CONCLUSIONS: In conclusion, the authors confirm others' findings that the concave pedicles can be so small that pedicle screw insertion is impossible. We also found that these findings can be confirmed preoperatively with thin-section CT scanning. In such situations, extrapedicular screw placement should be considered.     

The Length and Proportions of the Thoracolumbar Spine in Children with Idiopathic Scoliosis

The length of the thoracolumbar spine was measured on standardized X-ray films from 274 children (61/2-181/2 years) with idiopathic scoliosis and 212 controls. Where possible, the height and width (transverse diameter) of two vertebral bodies (T-6 and L-4) were also measured.

Although a tendency towards longer spines in the scoliotics could be found, there was no significant difference between children with idiopathic scoliosis and controls in this respect. In girls the pubertal growth-spurt of the spine was found to start about 1 year earlier than in the controls and the growth of the spine seemed to cease later in the scoliotics.

The height and width of T-6 was significantly greater in the scoliotics than in the controls for girls under 13 years of age. In the older girls and in the boys no significant difference could be demonstrated. The height of L-4 tended to be greater in the scoliotic boys and younger girls, though the differences were not statistically significant. The index height/width was calculated for T-6 and L-4 in all groups of patients and higher values could be demonstrated in the scoliotics for all test groups.

The greater height of T-6 in scoliotics might indicate a longer thoracic spine in these children. The higher values of the height/width indices suggest that the thoracolumbar spine in children with idiopathic scoliosis has an increased slenderness compared with the spine in non-scoliotic children.     

Pathologic mechanism of experimental scoliosis in pinealectomized chickens

STUDY DESIGN: This study was designed to investigate the pathologic mechanisms of idiopathic scoliosis using experimentally induced scoliosis in chickens. OBJECTIVE: To understand the process of producing a scoliotic deformity in pinealectomized chickens. SUMMARY OF BACKGROUND DATA: Pinealectomy in chickens consistently produces scoliosis with anatomic characteristics similar to those of human idiopathic scoliosis. Pinealectomized chickens are an important animal model for the study of idiopathic scoliosis. METHODS: In this study, 40 chickens were divided into two groups; 20 chickens treated with pinealectomy and 20 with a sham operation as control subjects on the second after hatching. The chickens in both groups then were killed at intervals ranging from 1 to 20 weeks after surgery. Their spines were examined visually and radiologically for the presence of a scoliotic curve and vertebral deformities. RESULTS: Rotational lordoscoliosis developed in pinealectomized chickens. The chickens with severe scoliosis were characterized by apically wedge-shaped vertebrae. In contrast, no scoliosis with any vertebral deformity developed in any of the chickens that received a sham operation. CONCLUSIONS: Because there normally is evidence of lordosis in the thoracic spine of chickens, the rotational instability of the spine induced by pinealectomy may produce a scoliotic deformity as a secondary phenomenon. Pinealectomy in chickens consistently produces scoliosis with anatomic characteristics similar to those of human idiopathic scoliosis. The authors believe that disturbance of the equilibrium and the posture mechanism associated with a defect in melatonin synthesis after pinealectomy may promote the development of rotational lordoscoliosis.     

Pullout strength of pedicle screws versus pedicle and laminar hooks in the thoracic spine

While the biomechanical properties of pedicle screws have proven to be superior in the lumbar spine, little is known concerning pullout strength of pedicle screws in comparison to hooks in the thoracic spine. In vitro biomechanical pullout testing was performed to evaluate the axial pullout strength of pedicle screws versus pedicle and laminar hooks in the thoracic spine with regard to surgical correction techniques in scoliosis. Nine human cadaveric thoracic spines were harvested and disarticulated. To simulate a typical posterior segmental scoliosis instrumentation, standard pedicle hooks were used between T4 and T8 and supralaminar hooks between T9 and T12 and tested against pedicle screws. The pedicle screws were loaded strictly longitudinal to their axis; the hooks were loaded perpendicular to the intended rod direction. In total, 90 pullout tests were performed. Average pullout strength of the pedicle screws was significantly higher than in the hook group (T4-T8: 531 N versus 321 N, T9-T12: 807 N versus 600 N, p < 0.05). Both screw diameter and the bone mineral density (BMD) had significant influence on the pullout strength in the screw group. For scoliosis correction, pedicle screws might be beneficial, especially for rigid thoracic curves, since they are significantly more resistant to axial pullout than both pedicle and laminar hooks.     

胸椎椎弓根-肋骨复合体的解剖及影像学研究

目的 探讨胸椎椎弓根-肋骨复合体的解剖结构影像学特点及其临床意义.方法 取4具成人新鲜尸体胸椎脊柱标本.主要测量参数(数据)包括:椎弓根及椎弓根-肋骨复合体的横径、螺钉最长值、矢状角,以及椎弓根、椎弓根-肋骨复合体以及椎弓根-肋骨重叠的纵径.测量中将尸体标本与CT影像测量(含二维、三维重建)相结合.结果 椎弓根-肋骨复合体是一立体结构,椎弓根与肋骨不在同一平面,且两者位置关系随不同节段而发生变化.椎弓根-肋骨复合体纵径值T1最小,为(12.6±0.8)mm,T11最大,为(16.9±1.1)mm.椎弓根-肋骨重叠纵径值T1最小,为(7.2±0.3)mm,T10最大,为(11.8±1.0)mm.椎弓根纵径与椎弓根-肋骨复合体纵径间差异无统计学意义(P＞0.05),椎弓根纵径、椎弓根-肋骨复合体纵径均与椎弓根-肋骨重叠纵径间差异有统计学意义(P＜0.05).结论 椎弓根-肋骨复合体是一较复杂的立体结构,椎弓根-肋骨重叠纵径应被视为该复合体的真实或有效纵径.