三维CT血管造影对颅内肿瘤外科诊治价值

目的 探讨三维CT血管造影(3D-CTA)在颅内肿瘤外科诊治的价值及适应证。方法 颅内肿瘤患者30例(包括脑膜瘤16例、胶质瘤4例、垂体腺瘤3例、听神经瘤4例、血管母细胞瘤2例、皮样囊肿1例)，术前3D-CTA检查，以容积重建法(VR)及最大强度投影法(MIP)法等作图像三维重建处理，模拟手术入路。结果 本组所有病例3D-CTA图像均可较清楚地显示肿瘤的生长部位、形态、大小等；并立体地将肿瘤与血管、颅骨及周围结构呈现，与手术及病理检查吻合，与MRI诊断效能一致。结论 3D-CTA能作MPI的补充，对颅内肿瘤诊断及鉴别诊断、设计手术入路等有独到和重要的意义。     

国人下腰椎前方血管解剖结构特点和入路分型

目的研究国人下腰椎前方血管与椎间隙之间的解剖特点,并进行解剖结构分型,为下腰椎前路椎间融合手术入路,尤其是腹腔镜下手术入路的选择提供解剖学依据。方法随机抽取94例国人腰椎MRI片,观察腰3-4、腰4-5,腰5-骶1椎间隙横断面前方的大血管解剖结构,判断腹主动脉的分叉位置和左髂总静脉与下腔静脉汇合位置,并进行解剖结构分型。结果根据腹主动脉分叉、左髂总静脉与下腔静脉汇合点与腰。椎间隙的上边缘之间的关系,确定4种类型。21例(22.3％)被归为A类(低分叉／低汇合),34例(36．2％)被归为B类(高分叉／高汇合),38例(40．4％)被归为C类(高分叉／低汇合),1例(1．1％)被归为D类(低分叉／高汇合)。在腰5-骶1间隙腹主动脉均已分叉,左髂总静脉均未汇合。男女之间无显著性差异。结论下腰椎前方血管解剖位置具有多变性,以腰4-5椎间隙为著,使腹腔镜下手术入路变的复杂。术前常规腰椎。MRI图像能用来进行血管解剖位置的分类,并设计最佳的手术入路。     

CT血管造影三维血管重建在诊断透析血管通路狭窄中的应用

血管通路是长期血液透析患者的生命线，由于内瘘血管的长期穿刺，局部损伤等因素，瘘管可能出现狭窄，导致患者肢体远端肿胀．影响患者的日常生活及透析治疗。采用电子计算机断层扫描血管造影(CTA)，了解血管通路狭窄的部位、程度、走向等，可为进一步手术处理或数字减法血管造影(DSA)介入治疗提供帮助。     

三维螺旋CT血管造影检查在连头婴显微分离手术中的应用

目的 探讨三维螺旋CT血管造影在连头婴显微分离术术前影像检查中的作用。方法 采用表面遮盖显示法进行三维重建图像处理。结果 螺旋CT血管造影结果显示连头婴双头颅骨相互连续，连续部部分骨质，硬脑膜缺如；双侧脑组织相连，部分相融，双婴上矢状窦后1/3融合并汇入同一窦汇，两婴一侧横窦相融。结论 螺旋CT血管造影可以较清晰显示连头显颅脑，脑组织及颅内血管的变异尤其是颅内血管与颅骨的立体关系，有助于在手术中准确设计骨的立体关系，有助于在手术中准确设计骨瓣及手术入路，制定合理的手术计划。     

三维CT血管造影辅助下经枕下小脑幕上入路治疗松果体区脑膜瘤

目的 探讨三维CT血管造影(3D-CTA)辅助下枕下小脑幕上入路(Poppen入路)治疗松果体区脑膜瘤的方法及可行性.方法 2005年1月至2010年1月采用Poppen入路治疗松果体区脑膜瘤8例,其中男性3例,女性5例;年龄41～64岁,平均(54±10)岁.术前依照KPS评分标准进行生存质量评分(KPS):满意者(≥80)5例、不满意者(＜80)3例.8例均经MRI检查确诊,而后行3D-CTA检查了解脑膜瘤的血运及供血动脉以辅助手术治疗.手术时切开小脑幕及大脑镰,并根据3D-CTA提供的影像保护静脉复合体.对于术前并发的脑积水,给予随访观察;对术后无缓解者予分流手术.结果 8例患者脑膜瘤均予以分块全切除.术后发生颅内感染者1例,给予抗感染治疗后恢复良好;其余7例无并发症出现.术后随访6～24个月,术前并发脑积水的7例患者中,术后脑积水好转、继续随访观察者6例;脑积水加重而行分流手术者1例.8例在随访结束时复查MRI均未见脑膜瘤复发;患者评分:KPS≥80者7例、KPS＜80者1例.术前与术后KPS比较差异有统计学意义(χ2=1.33,P＜0.05).结论 对于松果体区脑膜瘤,3D-CTA能对脑膜瘤的血运、供血动脉及脑膜瘤与静脉复合体的解剖关系做出有效的判断,在其辅助下采用Poppen入路进行治疗,可获得满意的疗效.

Abstract：

Objective To evaluate the three-dimensional CT angiography(3D-CTA)assisted suboccipital transtentorial approach(Poppen' s approach)in the treatment of pineal region meningioma. Methods During the period of January 2005 to January 2010, 8 patients with pineal region meningioma were successfully treated using Poppen's approach through cerebral falx and tentorium. There were three male patients and five female patients were aged at a range of 41-64 years,average age was(54±10)years. According to the Karnofsky performance scale(KPS), 5 patients' KPS scores were more than or equal to 80 and 3 were less than 80. MRI was used for the diagnosis of meningioma. 3D-CTA was applied to detect meningioma staining and blood supply. For preoperative concurrent hydrocephalus, follow-up observations were given. If hydrocephalus didn't get better or even became worse, ventriculoperitoneal shunt should be considered. Results All the surgery were successfully performed, and venous complexes(VC)were well protected according to the CTA images. Out of the eight cases whose meningiomas were removed,one patient had got postoperative intracranial infection and recovered after given antibiotics. All patients were followed up for a period of 6-24 months. Preoperative concurrent hydrocephalus in 7 patients were improved. However, there was an aggravation of the hydrocephalus in one patient who was treated with ventriculoperitoneal shunt. The MRIs which were performed at the end of follow-up period, showed no recurrence of meningiomas, and preoperative symptoms were improved to varying degrees, 7 patients' KPS scores were more than or equal to 80 and 1 was less than 80. A χ2 test was used to analyze and to make comparisons between preoperative and postoperative KPS. The significance was indicated(χ2 = 1.33,P＜0.05). Conclusions For meningiomas in the pineal region, 3D-CTA is of great clinical value to distinguish the anatomic relationship among the meningioma, blood supply and VC. This case study has strongly supported using Poppen's approach assisted by 3D-CTA to proceed with the operation.     

CT三维血管造影诊断出血动脉瘤

目的 评价CT血管造影(CTA)在颅内动脉瘤破裂后蛛网膜下腔出血诊断中的价值及手术指导意义。方法 对63例急性蛛网膜下腔出血病人急诊行螺旋CT扫描,然后行脑血管三维成像。结果 发现颅内动脉瘤24例。有1例阴性经全脑血管造影(DSA)发现存在动脉瘤。诊断均以手术证实。结论 CTA对动脉瘤蛛网膜下腔出血是一种微创、快速、准确的诊断技术,对于急诊或危重病人应为首选。     

头部CT血管造影检查的护理配合

ＣＴ血管造影（ＣＴａｎｇｉｏｇｒａｐｈｙ，即ＣＴＡ）是由静脉注入造影剂后行病变部位ＣＴ连续薄层扫描，并通过后处理技术重建扫描区内血管结构，以显示病变的方法。广泛应用于头、肝、肺、肾等脏器血管病变的诊断。它免除了病人作数字减影血管造影（ＤＳＡ）检查时插...     

腰椎体后缘骨块的CT三维重建

作者利用螺旋ＣＴ具有的成像功能 ,重建腰椎体后缘骨块三维图像 ,可清晰显示出骨块的全貌 ,有助于辨别骨块来源和选择治疗方法。资料与方法　本组男 2例 ,女 3例 ,年龄 33～ 5 9岁 ,平均 45岁 ,均主诉有腰痛或下肢放射痛。采用ＰｈｉｌｉｐｓＴｏｍｏｓｃａｎＡＶＰＩ机器 ,常规扫描Ｌ3/ 4、Ｌ4/ 5、Ｌ5 /Ｓ1三个椎间隙 ,扫描层厚 3ｍｍ。显示屏上发现腰椎体后缘有骨块突入椎管后 ,在定标像上将该部位划出充分的范围重新扫描。由于椎体后缘骨块体积较小 ,扫描层厚越窄 ,生成的三维图像越清晰、平滑 ,故重新扫描时选择技术参数如下 :层厚 1 5…     

下腰椎前路腹腔镜椎体间融合术的血管应用解剖

目的 对下腰椎(L3-S1)前路血管进行解剖学研究，分析其变异情况并探讨下腰椎前路腹腔镜下椎体间融合术的可靠性和安全性。方法 解剖30例成人尸体标本(男15例、女15例)，记录腹主动脉的分叉点及髂总静脉的汇合点位置，以及动静脉血管的椎前走向；测量上述分叉点与汇合点到L5椎体下缘的距离；测量L5／S1椎间隙手术窗大小(即平椎间隙右髂总动脉与左髂总静脉之间的距离)；记录骶正中动脉的起始点，骶正中静脉汇入点及二者的走向。结果 腹主动脉分叉点、髂总静脉汇合点分布在L4-L5之间，腹主动脉行走于椎体左前方，下腔静脉行走于椎体右前方；腹主动脉分叉点到L5椎体下缘距离，男性平均3．5cm，女性平均3．6cm；髂总静脉汇合点到L5椎体下缘距离，男性平均2．2cm，女性平均2．4cm；L5／S1椎间隙手术窗大小，男性3．7cm，女性平均3．4cm；骶中动脉均起源于腹主动脉分叉部后壁，在骶前沿中线左或右侧下行，骶中静脉多与之伴行。结论 腹主动脉分叉点与髂总静脉汇合点均高于L5椎体下缘，L5／S1椎间隙手术窗大小男性平均3．7cm、女性平均3．4cm，腹腔镜下前路L5／S1椎间隙融合术是可靠及安全的；由于血管的遮盖，L3，4、L4，5，椎间隙经腹膜前路融合术没有足够的血管分离及牵开是无法进行的。     

下腰椎腹侧血管解剖及其临床意义

目的:为下腰椎前路手术提供其腹侧血管解剖学数据。方法:对40具成人尸体标本(男28具,女12具)的下腔静脉和腹主动脉进行解剖,重点观察记录其位于下腰椎腹侧的解剖形态和各个壁支的变异情况,并对比血管松解前后暴露椎间盘的情况。结果:腹主动脉分叉点和髂总静脉的汇合点距离L5/S1椎间盘上缘分别为5.6±2.2cm、2.9±1.8cm,动脉分叉点比静脉汇合点位置变异明显,但均位于静脉汇合点颅侧;腹主动脉各壁支起点、走行、外径相对恒定,大静脉各个壁支形态变异相对较大,尤其是髂腰静脉和腰升静脉的形态变异尤为明显;在椎前大血管充分松解并且牵拉状态下,L3/4、L4/5和L5/S1椎间盘的可操作空间占相应节段椎间盘横径的比例分别为96.2%、90.0%和97.6%。结论:腹主动脉分叉点和髂总静脉的汇合点主要影响L4/5和L3/4椎间盘的显露;椎前大静脉壁支变异多,应避免损伤而引起术中大出血;实际操作中L4/5椎间盘的可操作空间最小。     

Mini-open anterior spine surgery for anterior lumbar diseases

Minimally invasive surgeries including endoscopic surgery and mini-open surgery are current trend of spine surgery, and its main advantages are shorter recovery time and cosmetic benefits, etc. However, mini-open surgery is easier and less technique demanding than endoscopic surgery. Besides, anterior spinal fusion is better than posterior spinal fusion while considering the physiological loading, back muscle function, etc. Therefore, we aimed to introduce the modified “mini-open anterior spine surgery” (MOASS) and to evaluate the feasibility, effectiveness and safety in the treatment of various anterior lumbar diseases with this technique. A total of 61 consecutive patients (46 female, 15 male; mean age 58.2 years) from 1997 to 2004 were included in this study, with an average follow-up of 24–52 (mean 43) months. The disease entities included vertebral fracture (20), failed back surgery (13), segmental instability or spondylolisthesis (10), infection (8), herniated disc (5), undetermined lesion for biopsy (4), and hemivertebra (1). Lesions involved 13 cases at T12–L1, 18 at L1–L2, 18 at L2–L3, 22 at L3–L4 and 11 at L4–L5 levels. All patients received a single stage anterior-only procedure for their anterior lumbar disease. We used the subjective clinical results, Oswestry disability index, fusion rate, and complications to evaluate our clinical outcome. Most patients (91.8%) were subjectively satisfied with the surgery and had good-to-excellent outcomes. Mean operation time was 85 (62–124) minutes, and mean blood loss was 136 (minimal-250) ml in the past 6 years. Hospital stay ranged from 4–26 (mean 10.6) days. Nearly all cases had improved back pain (87%), physical function (90%) and life quality (85%). Most cases (95%) achieved solid or probable solid bony fusion. There were no major complications. Therefore, MOASS is feasible, effective and safe for patients with various anterior lumbar diseases.     

USS钉棒系统内固定结合椎体间植骨融合术治疗退行性腰椎不稳症

目的探讨USS钉棒系统内固定结合椎体间植骨融合术治疗退行性腰椎不稳症的疗效。方法对78例退行性腰椎不稳症患者采用USS钉棒系统内固定结合椎体间植骨融合术治疗。采用Oswestry功能障碍指数与JOA下腰痛评分对患者手术前和术后1年随访期进行评分;摄片观察植骨融合情况并统计术后内固定失败（钉棒松动、折断）的发生率。结果 6例术后出现顽固轻微手术区胀痛。所有患者均得到随访,时间13~36个月。术后3个月患者腰背痛明显缓解,术后半年基本可以恢复正常日常生活。随访期内无钉棒松动、折断发生。术后6~8个月骨性融合。术后1年,Oswestry功能障碍指数较低,JOA下腰痛评分较高,与术前比较差异有统计学意义（P〈0.05）。腰椎功能改善总有效率达100%。结论 USS钉棒系统内固定结合椎体间植骨融合术治疗退行性腰椎不稳症临床疗效满意。     

下腰椎极外侧椎体间融合术的应用解剖

目的：观测腰椎侧方血管和神经的解剖分布，为下腰椎极外侧椎体间融合术（extreme lateral intervertebra fusion，XLIF）提供解剖学依据。方法：解剖30具成人尸体的腰椎侧方血管和神经，观察腰动、静脉的位置及走行；测量椎间孔外口处L3～L5脊神经距相邻下位椎间盘、腹主动脉后缘（左侧手术窗）和下腔静脉后缘（右侧手术窗）的距离。结果：L1、L2、L3节段血管走行、分布比较恒定，走行于相应椎体的中央偏下水平；但L4动、静脉走行变异较大，其中36．7％（11例）走行于L4／5间隙表面；L3～L5椎间孔外口处脊神经距下位椎间盘的距离逐渐增大；L3～L5左、右侧手术窗均逐渐增大．且同一节段左侧手术窗大于右侧。结论：XLIF在L3／4、L4／5间隙可以顺利进行。     

Incidence and risk factors for postoperative ileus following anterior,posterior, and circumferential lumbar fusion

Background contextPostoperative ileus is a known complication of surgery. The incidence and risk factors for ileus after lumbar fusion surgery is not well characterized.PurposeTo determine rates of postoperative ileus, a population-based database was analyzed to identify incidence, mortality, and risk factors associated with anterior (ALF), posterior (PLF), and combined anterior/posterior (APLF) lumbar fusions.Study designThis was a retrospective database analysis.Patient sampleThe sample consisted of 220,522 patients from the Nationwide Inpatient Sample (NIS) database.Outcome measuresOutcome measures were incidence of postoperative ileus, length of stay (LOS), in-hospital costs, and mortality.MethodsData from the NIS were obtained from 2002 to 2009. Patients undergoing ALF, PLF, and APLF for degenerative pathologies were identified and the incidence of postoperative ileus was assessed. Patient demographics, Charlson comorbidity index (CCI), LOS, costs, and mortality were assessed. SPSS v.20 was used to detect statistical differences between groups and perform logistic regression analyses to identify independent predictors of postoperative ileus. A p value less than .001 denoted significance.ResultsA total of 220,522 lumbar fusions were identified in the United States from 2002 to 2009. There were 19,762 ALFs, 182,801 PLFs, and 17,959 APLFs. The incidence of postoperative ileus was increased in ALFs over PLFs (74.9 vs. 26.0 per 1,000; p<.001). Within PLF and APLF groups, CCI scores were increased in the presence of postoperative ileus (p<.001). Across cohorts, patients with postoperative ileus demonstrated greater LOS and costs (p<.001). PLF-treated patients with postoperative ileus demonstrated increased mortality (p<.001). Independent predictors of postoperative ileus included male gender, 3+ fusion levels, alcohol abuse, anemia, fluid/electrolyte disorders, and weight loss (p<.001).ConclusionsThe results of our study demonstrate increased incidence of postoperative ileus associated with anterior approaches for lumbar fusion. Across cohorts, postoperative ileus was associated with increased LOS and costs. To determine the mortality and resource use associated with postoperative ileus, we recommend preoperatively identifying and treating modifiable risk factors, especially when an anterior approach is used.     

Multidirectional flexibility analysis of anterior and posterior lumbar artificial disc reconstruction: in vitro human cadaveric spine model

The in vitro multidirectional flexibility analysis was conducted to investigate the initial biomechanical effect of biomimetic artificial intervertebral disc replacement from either anterior or posterior approach in a cadaveric lumbosacral spine model. Two designs of anterior total and posterior subtotal artificial discs were developed using bioactive three-dimensional fabric and bioresorbable hydroxyapatite/poly-l-lactide material (3DF disc). Both models were designed to obtain the stable interface bonding to vertebral endplates with maximum surface area occupation. Using seven cadaveric lumbosacral spines, the following three anterior reconstruction methods were sequentially performed at L4–5 level: anterior 3DF disc replacement; anterior BAK cages (BAK); and posterior pedicle screw fixation and anterior BAK cages combined (BAK + PS). The L2–3 level received two methods of posterior reconstructions: subtotal 3DF disc replacement (two implants), and posterior interbody cages and pedicle screw fixation (PLIF). Six unconstrained pure moments were applied and three-dimensional segmental motions were measured with an optoelectronic motion measurement system. The center of rotation (COR) calculation was conducted radiographically using flexion-extension films. Both anterior and posterior 3DF replacements statistically demonstrated equivalent range of motions (ROMs) in all loading modes compared to intact segment. Anterior BAK, BAK + PS, and PLIF demonstrated significantly lower ROMs when compared to intact and 3DF groups (P<0.05). The 3DF reconstruction tended to realign the COR to the posterior third or surrounding position at the operative disc level. The stand-alone lumbar 3DF disc replacement demonstrated biomechanical characteristics nearly equivalent to the intact spinal segments even through anterior or posterior approach in vitro, suggesting an excellent clinical potential.     

经椎间孔入路腰椎体间融合治疗下腰椎退变

目的总结经椎间孔入路腰椎体间融合治疗下腰椎退变的临床效果。方法采用半椎板或全椎板切除、经椎间孔入路腰椎体间融合、椎弓根螺钉固定治疗下腰椎退变患者26例。结果26例随访4~28个月,平均11个月。临床评价:优13例,良12例,尚可1例。无1例出现永久性神经损伤手术并发症。术后X线片显示植骨密度随术后时间的延长而加深,钛网融合器无下陷,椎间隙高度无丢失,椎弓根螺钉系统无断裂和移位。结论经椎间孔入路腰椎体间融合治疗下腰椎退变创伤小,并发症少,临床效果较好。     

L5/S1前路手术相关椎前大血管的影像解剖学研究

目的:通过腹部血管成像检查和腰骶椎CT三维重建观测腰骶椎前方大血管的局部解剖,为L5/S1前路手术提供术前血管解剖学评估依据.方法:62例正常成年人,男32例、女30例,行腹部血管成像检查和腰骶椎CT三维重建.观察髂血管间隙双侧髂血管的构成情况,测量髂间三角解剖参数:髂间三角顶点到L5椎体下缘的距离;L5椎体下缘、S1椎体上缘髂血管间距;髂间三角顶点偏离正中矢状面的距离;L5/S1椎间隙宽度.根据髂间三角顶点到L5椎体下缘的距离(＞1.2cm;0.6～1.2cm;＜0.6cm且＞0;≤0)定义Ⅰ、Ⅱ、Ⅲ、Ⅳ型髂间三角.计算髂间三角面积、L5/S1椎间盘显露百分比.结果:髂血管间隙由左侧髂静脉、右侧髂动脉组成占54例(87％);双侧均为髂动脉或髂静脉各占4例(6.45％)、2例(3.23％);左侧髂动脉、右侧髂静脉占2例(3.23％).Ⅰ、Ⅱ、Ⅲ、Ⅳ型髂间三角分别为42(67.7％)、11(17.7％)、7(11.3％)、2(1.6％)例.Ⅰ、Ⅱ、Ⅲ型各解剖参数比较,差异有显著性意义(P＜0.05).L5/S1椎间隙宽度为5.3±0.6cm.Ⅰ、Ⅱ、Ⅲ型髂间三角显露面积分别为5.00cm2 (1.42～11.90cm2)、1.04cm2(0.49～2.12cm2)、0.33cm2(0.10～0.92cm2),椎间盘显露百分比分别为78.3％、59.4％、42.5％.结论:腹部血管成像检查能够清晰显示腰骶椎前方大血管走行及分布情况,有助于L5/S1前路手术策略的制定.     

中线腰椎融合技术在老年退行性腰椎疾病应用的早期临床疗效及置钉注意事项

目的:探讨中线腰椎融合技术(midline lumbar fusion,MIDLF)治疗老年退行性腰椎疾病的效果、安全性及皮质骨轨迹(cortical bone trajectory,CBT)螺钉固定技术置钉注意事项。方法:回顾性分析我院2018年4月～9月收治的采用MIDLF治疗老年退行性腰椎疾病患者16例,男性8例,女性8例。年龄58～81岁,平均68.7±7.7岁。手术节段均为L4/5。术中均应用CBT螺钉固定技术。入钉点的选择参考上位节段的下关节突最尖端下移约5mm(a值)与峡部最窄处内移约4mm(b值)的交点,记录手术时间、术中出血量、手术并发症等。应用视觉模拟评分法(visual analogue scale,VAS)记录术前和末次随访时腰腿痛情况,应用腰椎JOA评估患者手术后功能改善情况,所有患者出院前及术后12个月均行腰椎CT扫描。通过Rao分级标准评价置钉准确性,置钉优良率=置钉优良数/总置钉数×100%。在术后出院前CT测量螺钉的外倾角、尾倾角、a值和b值。对未突破皮质组与突破皮质组上述4个参数进行比较。结果:手术时间平均174.3±27.9min (133～232min),术中出血量平均69.3±36.7ml(30～150ml),术后总引流量平均147.5±95.2ml(20～315ml),术后住院天数平均2.5±0.8d(2～4d)。术后随访时间平均15.1±2.0个月(12～20个月)。术后1例患者出现足下垂和血肿,有5枚CBT改为椎弓根螺钉固定。其他患者无术中和术后并发症。术前VAS腰痛评分4.5±1.7分,末次随访时为1.1±0.5分,差异有统计学意义(t=7.013,P0.001);术前VAS腿痛评分5.6±1.0分,末次随访时为1.1±0.9分,差异有统计学意义(t=13.006,P0.001);术前腰椎JOA评分15.7±2.4分,末次随访时为23.9±2.1分,差异有统计学意义(t=-16.364,P=0.000)。参考术后出院前CT进行Rao分级:0级46枚,1级4枚,2级3枚,3级6枚。置钉的优良率为84.7%(50/59),突破皮质骨的螺钉有13枚(13/59,22%),其中突破椎弓根内壁的3枚,突破椎体的10枚。未突破皮质骨组与突破皮质骨组比较分析显示螺钉外倾角有显著性差异(11.0°±3.7°vs 14.9°±3.8°,P=0.002),而尾倾角(15.0°±8.4°vs 16.9°±9.2°,P=0.502)、a值(5.6°±1.2°vs 5.7°±1.4°,P=0.687)、b值(4.1°±1.0°vs 4.4°±1.6°,P=0.459)未见显著性差异。结论:MIDLF技术应用于老年退行性腰椎疾病患者时,创伤小,可获得良好的手术效果,入钉点的选择参考上位节段的下关节突最尖端下移5.6～5.7mm(a值)与峡部最窄处内移4.1～4.4mm(b值)的交点,但是CBT螺钉置钉的容错率低,置钉技术要求高,置钉时螺钉外倾不要过大,角度11°为宜。