定量分析钢板及椎弓根钉固定脊柱骨折脱位后的应力松弛

背景：正常范围的应力松弛有利于各种骨折内外固定之后的再造和重建,一定的应力松弛可缓解过度的坚强固定而产生的应力遮挡效应。 目的：通过模拟脊柱L1~2骨折脱位,以钢板和髓内钉固定后对标本进行轴向压缩应力松弛实验,从流变学角度对临床治疗脊柱骨折脱位的2种固定器进行定量分析。 设计、时间及地点：配对检验设计实验,于2006-06/2007-02在吉林大学力学实验中心完成。 材料：实验所用8个正常国人尸体T8~L4脊柱标本由白求恩医科大学解剖教研室提供。 方法：将8个标本在椎体锯开,模拟L1椎体骨折脱位。分为2组,即钢板固定组及椎弓根钉固定组,n=4。分别将2组标本放入装有生理盐水的有机玻璃缸内,置于电子万能实验工作台上,驱动机器以50%/min的应变增加速度进行实验,设定时间为7 200 s,采集100个数据,达到设定时间后计算机自动输出实验数据和曲线。 主要观察指标：应力松弛数据和曲线,应力与时间的变化规律。 结果：得出了2组标本的应力松弛数据及归一化应力松弛函数数据和曲线,建立了归一化应力松弛函数方程。钢板组、椎弓根钉组的7 200 s应力松弛量分别为0.62,0.629 MPa,椎弓根钉组大于钢板组,但差异无显著性意义(P > 0.05)。 结论：回归分析的方法能准确地处理应力松弛实验数据,钢板及椎弓根钉的7 200 s应力松弛量差异不显著。     

三种固定器械置入固定胫骨骨折的生物力学分析☆

背景：胫骨骨折后以胫骨骨折髓内钉、钢板内固定和外固定支架固定后骨折断端的轴向压缩、弯曲、扭转力将发生怎样的变化？ 目的：对比观察胫骨轴向控制髓内钉,胫骨接骨钢板及胫骨外固定支架3种内外固定器械置入固定胫骨骨折的生物力学特性。 设计、时间及地点：观察性实验,于2007-08在吉林大学力学实验中心完成。 材料：新鲜胫骨标本9对,由白求恩医科大学解剖教研室提供;夹具由吉林大学力学实验中心提供;胫骨轴向控制髓内钉为上海浦卫医疗器械厂产品;胫骨接骨板(钢板)为常州华森医疗器械有限公司产品;胫骨外固定支架为常州市康辉医疗器械有限公司产品。 方法：9对新鲜尸体胫骨,随机分为髓内钉组,接骨板组和外固定支架组,每组3对。以线锯在胫骨中段锯开,制成DAT分类A1型骨折模型,分别以胫骨轴向控制髓内锁钉、钢板、外固定支架固定标本,在电子万能试验机上对3组标本进行轴向压缩实验和弯曲实验,在扭转试验机上进行扭转实验。 主要观察指标：标本承受轴向压缩、弯曲载荷时的位移值和在转矩作用下扭转角度。 结果：髓内钉组轴向压缩,弯曲位移小于接骨板组和外固定支架组,但差异无显著性意义(P > 0.05),髓内钉固定组扭转角度小于接骨板组和外固定支架组,差异有显著性意义(P < 0.05)。 结论：髓内钉内固定胫骨骨折组标本抗弯、抗扭、抗轴向压缩能力强,具有较好的力学特性。钢板固定组和外固定支架组抗弯和抗轴压缩能力也较强,虽抗扭转能力不如髓内钉组,但也具有较好的力学特性。     

滑动椎弓根钉棒系统的研制和生物力学测试

背景：现今临床上常用的椎弓根钉内固定系统为钉棒锁定结构系统，妨碍了处于生长发育期青少年脊柱的纵向生长，所以迫切需要一种能够滑动的椎弓根钉内固定系统，以减少或避免对脊柱生长的影响。 目的：对比观察自行研制的滑动椎弓根钉棒系统与传统锁定椎弓根钉棒系统固定脊椎的力学性能。 设计：对比观察。 单位：解放军第三军医大学新桥医院骨科，解放军第二一一医院骨科。 材料：实验于2007-06-29在哈尔滨工业大学材料科学院完成。自行设计的滑动椎弓根钉棒系统，材质是钛合金，由江苏省常州市武进第三医疗器械厂生产，包括滑动椎弓根钉、 矫形棒和横向连接装置三部分。新鲜猪脊椎标本12具，仔细剔除T1~L5椎体所附肌肉，保留主要韧带及后关节突结构的完整性。 方法：将标本随机分成滑动组和锁定组，每组6具标本。切除Tl2椎骨的部分椎板、周围韧带及T11~12、T12~Ll椎间双侧小关节造成脊柱失稳，再将滑动椎弓根钉系统和锁定椎弓根钉系统固定于各组的T10，T12，L2椎体上。将标本稳妥安装在夹具内，置于INSTAON-4505轴向压缩机上。将应变片连接于YJ-31静电电阻应变仪上，模拟人体脊柱载荷并加载于重心点，以便造成前屈、后伸、侧屈、轴向压缩等运动状态。载荷在100，200，300，400，500 N实施分级加载，在不同情况下测量T12椎体的位移。 主要观察指标：①在前屈、后伸、侧屈、轴向压缩情况下，主应变及位移变化。②脊柱固定强度和刚度。 结果：滑动组和锁定组在屈伸、侧屈、轴向压缩情况下，其主应变、位移变化及固定强度差异均无显著性性意义 (P > 0.05)。 结论：滑动椎弓根钉棒系统可以获得与锁定椎弓根钉棒系统相同的生物力学稳定性。滑动椎弓根钉系统将椎弓根钉与矫形棒之间的连接设计为滑动式，使之可随脊柱生长而延长，用于生长发育期脊柱侧凸的的治疗具有可行性。     

伤椎椎弓根置钉治疗胸腰椎压缩性骨折的三维有限元分析*

背景：有文献报道伤椎置钉技术较传统4钉跨阶段固定具有更强的牢固性,可有效避免内固定的松动断裂,但其生物力学机制研究尚显不足。 目的：构建脊柱胸腰椎单纯压缩性骨折的三维有限元模型,探讨伤椎附加椎弓根螺钉置入治疗胸腰椎压缩性骨折的生物力学效应。 方法：将一T12椎体压缩性骨折患者脊柱胸腰段超薄CT扫描数据输入Mimics软件中,构建T12椎体压缩性骨折的有限元模型,在此模型基础上模拟伤椎置6钉和跨节段4钉内固定,对两个模型分别施加垂直压缩、前屈、后伸、左屈及右旋载荷。 结果与结论：两组固定模式各种载荷下的应力均集中在螺钉根部,在垂直载荷下,螺钉的应力最小,右旋和左屈载荷下的应力最大;在垂直压缩、前屈、后伸、左侧弯及右旋运动下,上位螺钉较下位螺钉应力大(P < 0.05)。伤椎置6钉固定组螺钉应力较跨节段4钉固定组小(P < 0.05)。两组T11椎体最大位移无差别。表明伤椎附加椎弓根螺钉置入可以优化内固定的载荷,减少断钉率。     

骨水泥椎体强化椎弓根钉置入对骨质疏松脊柱生物力学稳定性的影响

背景：伴有骨质疏松患者的脊柱内固定松动、脱落是脊柱外科一个复杂而棘手的问题。用聚甲基丙烯酸甲酯骨水泥强化椎弓根螺钉可增加伴有骨质疏松患者的椎弓根螺钉防止椎弓根钉的松动及脱落。 目的：评价聚甲基丙烯酸甲酯骨水泥椎体强化后椎弓根钉固定对不稳定骨质疏松脊柱的生物力学稳定性影响。 设计、时间及地点：体外生物力学实验,于2008-03在上海大学生物力学实验室完成生物力学实验。 材料：12具新鲜老年女性尸体T10~L3椎体标本,制成T12、L1间的不稳定模型,采用椎弓根螺钉系统固定。 方法：将标本按照不同的处理方式分为4组。①对照组：为完整标本,只进行生物力学性能的测试。②一次固定组：对照组测试后随机选取6具不稳定模型,行T11~L2椎弓根钉固定。③二次固定组：一次固定组标本完成稳定性测试后,取出所有椎弓根螺钉,分别用注射器向T11~L2椎弓根钉道注入配制好的聚甲基丙烯酸甲酯骨水泥骨水泥2.0 mL后再次拧入螺钉固定。④强化固定组：将余下的6具标本于T11~L2双侧椎弓根分别以直径3.5 mm的钻头导孔,沿孔道插入直径3.5 mm的穿刺导管,插入深度为40 mm,用加压注射器经导管缓慢向椎体内加压注射配制好的聚甲基丙烯酸甲酯骨水泥3.5 mL后拧入螺钉固定。 主要观察指标：进行轴向压缩、前屈/后伸、左/右侧弯、左/右旋转7项非损伤性加载,比较上述4组不同状态下脊柱的相对运动范围变化。 结果：与一次固定组比较,二次固定组及强化固定组脊柱的相对运动范围增加(P < 0.05),强化固定组与二次固定组组间比较,差异无统计学意义(P > 0.05)。 结论：椎体成形强化椎弓根钉固定及钉道强化固定均可明显增强不稳定骨质疏松脊柱的稳定性。     

齿轮撑开式脊柱复位固定板装置的研制

背景: 目前临床应用的脊柱后路复位固定的钉棒系统存在一定程度的生物力学的缺陷,钉板系统更适合在患者中广泛使用。 目的：依据中国人脊柱的椎弓根间距、弧度、椎体及椎间隙高度的影像学测量结果,研制一种新型的脊柱后路复位内固定板装置。 方法：测量129例门诊查体的正常者的胸腰椎数据。依据影像学测量的结果,并在复习文献的基础上,对新型脊柱复位内固定器进行图纸设计及形状设计。取18具新鲜小牛腰椎标本随机分为实验组给予行齿轮撑开式脊柱复位内固定板装置固定,CD及Steffee组分别用CD及Steffee钢板固定,测量标本在受到轴向压缩、前屈、后伸及侧屈载荷状态下的位移、应变、刚度和破坏性能等测试,结果进行统计学处理。 结果与结论：齿轮撑开式脊柱复位内固定装置(GDP)能较好地满足人体强、刚度的要求。GDP组测得椎体固定的强度和刚度均比对照组CD和Steffee钢板系统优越(P < 0.05),腰椎的扭转力学性能比CD,Steffee钢板内固定分别高出13%和14%,腰椎的极限力学性能测试结果显示GDP能承载载荷,比CD,Steffee钢板更大(P < 0.05)。说明齿轮撑开式脊柱复位固定板装置的设计符合中国人脊柱的解剖规格,生物力学稳定性良好,可以显著促进椎骨骨折的愈合,防止脊椎后凸的复发和高度的丧失。     

腰椎椎弓根螺钉系统断裂的三维有限元分析

背景：椎弓根螺钉系统已是最为常用的脊柱内固定器械，但其钉棒断裂在临床上仍时有发生。 目的：利用三维有限元分析腰椎椎弓根螺钉系统在临床中断裂的并发症，以期提高手术成功率。 设计、时间及地点：三维有限元分析，于2007-11/2008-03在南方医科大学珠江医院完成。 对象：选择1名成年志愿者，年龄27岁，身高174 cm，体质量63 kg，经X射线检查排除脊柱疾病。 方法：建立腰椎椎弓根螺钉系统内固定的三维有限元模型，并分别施加压缩、前屈、后伸、侧屈及旋转5种生理载荷，对比分析不同载荷下螺钉、连接棒的应力分布。 主要观察指标：不同载荷下螺钉、连接棒各部分的应力。 结果：椎弓根螺钉系统各部分于垂直压缩下的应力远小于前屈、后伸、侧屈及旋转时所受压力。垂直压缩下应力主要集中在螺钉近棒段，而在前屈、后伸、侧屈及旋转时应力主要集中在连接棒上。 结论：椎弓根内固定系统设计及类型的选择，术中的规范操作，术后康复活动的指导及保护、适时取出内固定等对预防其断裂均十分重要。     

椎弓根螺钉及融合器应力分布在腰椎滑脱后路骨融合模型的三维有限元分析

背景：目前在脊柱外科的有限元分析多见于正常的腰椎模型,对术后病理状态的模型未见深入研究。 目的：建立L4/5滑脱不同融合术式的有限元模型,通过此模型对椎弓根螺钉和融合器上的应力分布及模型稳定性有无显著性差异进行生物力学评价。 方法：采集1名腰椎滑脱男性的腰椎螺旋CT数据借助mimics 10.01 软件,建立L4/5三维模型。将模型导入abaqus6.51软件,对模型进行网格划分,赋予材料属性。再分别建立椎弓根螺钉和融合器的有限元模型,然后根据临床术式组合成不同后路融合模型。设定边界条件在上述模型上分别施加垂直压缩载荷以及前屈、后伸、左屈、右旋等力矩载荷,并测定各种载荷下椎弓根螺钉、融合器上的应力及模型的位移,结果在SPSS13.0软件上进行统计学分析。 结果与结论：①两种模型在各种载荷中应力多集中在椎弓根螺钉与钛棒连接处,轴向压缩载荷下最小,在旋转时最大,融合器应力集中分布在前段及后断。②对比在5种载荷下两种模型位移后路椎体间融合组均小于后外侧融合(P < 0.05)。实验建立了L4椎体滑脱后路不同融合术式的有限元模型,模型加载后的应力分布和位移具有临床意义,椎体间融合的稳定性优于椎弓根螺钉内固定加后外侧植骨融合。     

短节段椎弓根螺钉置入内固定椎体成形治疗胸腰椎骨折的生物力学检测☆

背景：为避免单纯椎弓根螺钉置入内固定治疗胸腰段骨折出现的内固定物松动、断裂,及合并植骨时出现的骨折不愈合、后凸畸形丢失,而发展的短节段椎弓根螺钉合并椎体成形技术治疗胸腰段骨折,临床已有应用,但其生物力学方面鲜有研究。 目的：观察应用椎弓根螺钉置入内固定椎体成形治疗胸腰椎骨折的生物力学变化。 方法：12个冻存的新鲜胸腰段脊椎(T12~L2)标本,用于制备胸腰椎骨折模型,备测试。分为3组,经皮椎体成形术组：给予经单侧椎弓根注入低黏度的含对比剂骨水泥5~7 mL;椎弓根螺钉内固定组：于T12、L2椎弓根置入螺钉;强化组：行椎弓根螺钉内固定的同时行伤椎骨水泥椎体成形术,测试各组静态最大抗压强度及刚度。 结果与结论：骨水泥分布面积皆大于50%,经皮椎体成形术组和椎弓根螺钉内固定组最大静态抗压强度与刚度均小于强化组最大强度和刚度(P < 0.05)。椎弓根螺钉内固定组椎弓根螺钉较小强度下出现弯曲,而强化组在达到极性轴向压缩强度时才出现弯曲。提示应用短节段椎弓根钉置入内固定椎体成形治疗胸腰椎骨折提高了固定的强度及刚度,并且维持了复位伤椎高度,提高了稳定性,减少了椎弓根螺钉的并发症。     

颈前路钢板置入内固定加椎间植骨治疗Ⅱ型Hangman骨折的生物力学评价

背景：C2/3椎间盘切除，钢板置入内固定加椎间植骨是治疗Hangman骨折的常用术式。该术式在临床应用广泛，但目前尚缺乏相关实验评价钢板置入内固定治疗Hangman骨折的生物力学特点研究。 目的：评价钢板置入内固定+椎间植骨治疗Ⅱ型Hangman骨折的生物力学稳定性。 方法：6具正常成人新鲜冷冻颈椎，每一标本依次制作成以下3种状态组：即正常对照组、Ⅱ型Hangman骨折模型组、椎间植骨+钢板内固定组。按以上顺序应用脊柱三维运动试验机和三维激光扫描仪测试每一状态C2/3节段的三维运动范围。 结果与结论：与正常对照组比较，Ⅱ型Hangman骨折模型组C2/3节段前屈、后伸、旋转及侧弯关节活动度均显著增大(P < 0.05)，钢板内固定+椎间植骨组旋转方向关节活动度显著增大(P < 0.05)；与Ⅱ型Hangman骨折模型组相比，钢板内固定+椎间植骨组C2/3节段前屈、后伸及侧弯关节活动度均显著减小(P < 0.05)。结果提示钢板置入内固定能够在前屈、后伸及侧弯方向恢复Ⅱ型Hangman骨折的稳定性，然而在旋转方向缺乏稳定作用，术后需辅以外固定以确保融合。     

Functional Neuroanatomy of the Human Visual Fixation System

The regional cerebral blood flow correlates of the active fixation of an imagined target were studied in five healthy humans using the positron emission tomography activation paradigm. The fixation task was contrasted to a passive control condition, both tasks being performed in total darkness. Blood flow increases were observed in the frontal eye fields and supplementary eye fields and in the median cingulate gyrus. We suggest that the network of these activated regions mediates the interactions between ocular fixation, eye movements and directed visual attention.     

Atlantoaxial Rotatory Fixation in Adults Patient

Atlantoaxial rotatory fixation (AARF) in adult is a rare disorder that occurs followed by a trauma. The patients were presented with painful torticollis and a typical ''cock robin'' position of the head. The clinical diagnosis is generally difficult and often made in the late stage. In some cases, an irreducible or chronic fixation develops. We reported a case of AARF in adult patient which was treated by immobilization with conservative treatment. A 25-year-old female was presented with a posterior neck pain and limitation of motion of cervical spine after a traffic accident. She had no neurological deficit but suffered from severe defect on the scalp and multiple thoracic compression fractures. Plain radiographs demonstrated torticollis, lateral shift of odontoid process to one side and widening of one side of C1-C2 joint space. Immobilization with a Holter traction were performed and analgesics and muscle relaxants were given. Posterior neck pain and limitation of the cervical spine''s motion were resolved. Plain cervical radiographs taken at one month after the injury showed that torticollis disappeared and the dens were in the midline position. The authors reported a case of type I post-traumatic AARF that was successfully treated by immobilization alone.     

Fixation of the mandible changes masseter muscle activity associated with swallowing

The purpose of this study was to investigate the effect of mandibular fixation on activity of the swallowing-related muscles during swallowing. Electromyograms in the masseter muscle, orbicularis oris superior muscle, suprahyoid muscles, and infrahyoid muscles were recorded from seven healthy humans. Electromyographic activity during swallowing was compared between an experimental condition with mandibular fixation and an experimental condition without such fixation. Duration of the swallowing phase was prolonged with mandibular fixation. Mandibular fixation significantly delayed the onset of masseter muscle activity during swallowing, although no other muscle groups showed a delay. The amount of muscle activity during swallowing was not significantly different between the two experimental conditions in any of the muscle groups. In conclusion, mandibular fixation decreases the masseter muscle activity at the initial phase of swallowing. This may be due to decreased need of the masseter muscle activity against force pulling the mandible.     

Lumbo-sacro-pelvic Fixation Using Iliac Screws for the Complex Lumbo-sacral Fractures

Fractures of lumbo-sacral junction involving bilateral sacral wings are rare. Posterior lumbo-sacral fixation does not always provide with sufficient stability in such cases. Various augmentation techniques including divergent sacral ala screws, S2 pedicle screws and Galveston rods have been reported to improve lumbo-sacral stabilization. Galveston technique using iliac bones would be the best surgical approach especially in patients with bilateral comminuted sacral fractures. However, original Galveston surgery is technically demanding and bending rods into the appropriate alignment is time consuming. We present a patient with unstable lumbo-sacral junction fractures and comminuted U-shaped sacral fractures treated by lumbo-sacro-pelvic fixation using iliac screws and discuss about the advantages of the iliac screws over the rod system of Galveston technique.     

The Management of Bilateral Interfacetal Dislocation with Anterior Fixation in Cervical Spine : Comparison with Combined Antero-Posterior Fixation

Objective

Combined antero-posterior fixation has been a standard method for bilateral interfacetal dislocation in cervical spine. The purpose of this study is to evaluate the efficacy and complication of anterior cervical stabilization in treatment of bilateral interfacetal dislocation.

Methods

A total of 65 cases of traumatic bilateral interfacetal dislocation in cervical spine who were managed in our institution, from Mar. 1997 to Feb. 2006, were included in this study. Closed reduction was tried in all cases before operation. If closed reduction was accomplished successfully, only anterior cervical fixation was performed (Group I), and attempted to place screws bicortically as possible with unicortical screws. If failed, posterior open reduction with fixation was first tried, followed by anterior cervical fixation (Group II). All patients were evaluated for neurological outcome and radiological evidence of healing.

Results

The Group I included 47 patients and the Group II, 18 patients. The improvement of Frankel grade and increase of mean cervical lordosis angles were not statistically different between two groups. Screw-plate system used did not influence the outcome. On follow up, solid bone fusion was evident and there were no cases of instability in both groups.

Conclusion

Our study demonstrated that anterior cervical fixation on BID is safe and effective in comparison with combined antero-posterior cervical fixation.     

Radiographic Comparison of Four Anterior Fusion Methods in Two Level Cervical Disc Diseases : Autograft Plate Fixation versus Cage Plate Fixation versus Stand-Alone Cage Fusion versus Corpectomy and Plate Fixation

Objective

To evaluate radiographic results of anterior fusion methods in two-level cervical disc disease : tricortical autograft and plate fixation (ACDF-AP), cage and plate fixation (ACDF-CP), stand-alone cage (ACDF-CA), and corpectomy and plate fixation (ACCF).

Methods

The numbers of patients were 70 with a minimum 6 month follow-up (ACDF-AP : 12, ACDF-CP : 27, ACDF-CA : 15, and ACCF : 16). Dynamic simple X-ray and computed tomography were evaluated preoperatively, postoperatively, 6 month, and at the final follow-up. The fusion and subsidence rates at the final were determined, and global cervical lordosis (GCL), cervical range of motion, fused segment angle (FSA), and fused segment height (FSH) were analyzed.

Results

Nonunion was observed in 4 (25%) patients with ACDF-CA, 1 (8%) patient with ACDF-AP, 1 (4%) patient with ACDF-CP. The number of loss of FSH (%) more than 3 mm were 2 patients (16%) in ACDF-AP, 3 patients (11%) in ACDF-CP, 5 patients (33%) in ACDF-CA, and 3 patients (20%) in ACCF. The GCL was decreased with ACDF-CA and increased with others. The FSA was increased with ACDF-AP, ACDF-CP, and ACCF, but ACDF-CA was decreased. At the final follow-up, the FSH was slightly decreased in ACDF-CP, ACDF-AP, and ACCF, but ACDF-CA was more decreased. Graft related complication were minimal. Screw loosening, plate fracture, cage subsidence and migration were not identified.

Conclusion

ACDF-CP demonstrated a higher fusion rate and less minimal FSH loss than the other fusions in two-level cervical disc disease. The ACDF-AP and ACCF methods had a better outcome than the ACDF-CA with respect to GCL, FSA, and FSH.     

兔胫骨骨折模型的不同固定方法*★

背景：利用一种有效的固定方法维持骨折的稳定性是胫骨骨折动物模型成功制备的基础。 目的：观察4种不同的固定方法对兔胫骨骨折模型的固定效果。 方法：将日本大耳白兔截断胫骨骨干后随机分为4组，以4种方法分别固定：①直腿双托组：直腿双托石膏外固定。②塑形双托组：屈膝屈踝双托石膏外固定。③塑形管型组：屈膝屈踝管型石膏外固定。④内外固定组：克氏针内固定+屈膝屈踝双托石膏外固定。 结果与结论：相比其他3组，直腿双托组的外固定石膏脱落时间更早，损伤肢感染率更高(P < 0.05)。在骨折后第4周，内外固定组发生骨折断端移位的实验兔数量最少(P < 0.05)。证实只采用内固定+屈膝屈踝双托石膏外固定才能维持实验兔胫骨骨折的稳定性。     

Ocular Motor Fixation Deficits in Friedreich Ataxia

Friedreich ataxia (FRDA) is the most common genetic cause of ataxia with a prevalence of approximately 1 in 29,000. Ocular motor abnormalities are common in FRDA and include fixation instability, saccadic dysmetria, and vestibular dysfunction. It has not yet been determined whether aspects of spatial attention, which are closely coupled to eye movements, are similarly compromised in FRDA. This study examined attentional engagement and disengagement of eye movements in FRDA using a gap overlap task. Thirteen individuals with genetically confirmed FRDA and 12 age-matched unaffected controls participated in the experiment. The gap overlap paradigm was used to examine the effect of early (gap condition), simultaneous (null condition), or late (overlap condition) removal of a central fixation on saccadic latency to a peripheral target stimulus. Although the FRDA group showed a larger gap effect (i.e., difference in saccadic latencies between the overlap and gap condition), these participants demonstrated a greater difference in latencies in the overlap relative to the null condition, suggestive of deficits within the disengagement process of attentional orienting. We propose a role for the cerebellum in these deficits in the disengagement of spatial attention based on evidence of cerebellar connectivity with regions involved in exogenous shifts of attention. The significant correlations between saccadic latency and disease severity as measured by the Friedreich Ataxia Rating Scale further support the proposal that saccadic latency might be useful as a surrogate marker of disease severity and progression in future clinical trials in FRDA.     

The Use of Pedicle Screw-Rod System for the Posterior Fixation in Cervico-Thoracic Junction

Objective

In cervico-thoracic junction (CTJ), the use of strong fixation device such as pedicle screw-rod system is often required. Purpose of this study is to analyze the anatomical features of C7 and T1 pedicles related to screw insertion and to evaluate the safety of pedicle screw insertion at these levels.

Methods

Nineteen patients underwent posterior CTJ fixation with C7 and/or T1 included in fixation levels. Seventeen patients had tumorous conditions and two with post-laminectomy kyphosis. The anatomical features were analyzed for C7 and T1 pedicles in 19 patients using computerized tomography (CT). Pedicle screw and rod fixation system was used in 16 patients. Pedicle violation by screws was evaluated with postoperative CT scan.

Results

The mean values of the width, height, stable depth, safety angle, transverse angle, and sagittal angle of C7 pedicles were 6.9 ± 1.34 mm, 8.23 ± 1.18 mm, 30.93 ± 4.65 mm, 26.42 ± 7.91 degrees, 25.9 ± 4.83 degrees, and 10.6 ± 3.39 degrees. At T1 pedicles, anatomic parameters were similar to those of C7. The pedicle violation revealed that 64.1% showed grade I violation and 35.9% showed grade II violation, overall. As for C7 pedicle screw insertion, grade I was 61.5% and grade II 38.5%. At T1 level, grade I was 65.0% and grade II 35.0%. There was no significant difference in violation rate between the whole group, C7, and T1 group.

Conclusion

C7 pedicles can withstand pedicle screw insertion. C7 pedicle and T1 pedicle are anatomically very similar. With the use of adequate fluoroscopic oblique view, pedicle screw can be safely inserted at C7 and T1 levels.     

Fixation suppression of optokinetic nystagmus modulates cortical visual-vestibular interaction

Water activation positron emission tomography and statistical group analysis were used to evaluate differences in activation-deactivation patterns during small-field visual motion stimulation, eliciting rightward optokinetic nystagmus and its fixation suppression in 12 healthy volunteers. Bilateral patterns of activation in the visual cortex, including the motion-sensitive area MT/V5, and deactivations in an assembly of vestibular areas (posterior insula, thalamus, anterior cingulate gyrus) during optokinetic nystagmus was markedly diminished or totally absent during its fixation suppression. This finding agrees with the concept of a reciprocal inhibitory interaction between the visual-optokinetic and the vestibular systems, which takes place at a lower level during fixation suppression, because the potential mismatch between the two sensory inputs, visual and vestibular, is then reduced.