Biomechanical evaluation of occipital fixation

Many studies have shown a positive correlation among screw pullout strength, screw insertional torque, bone thickness, and areal bone mineral density (BMD) measured by dual-energy X-ray absorptiometry. Variations are significant in the anatomy of the occipital bone. But no studies have correlated these variables with respect to the two locations commonly used for plate fixation to the occiput. The purpose of this study was to determine the thickness and quality of the occipital bone and to correlate these variables with the insertional torque of screws and the pullout strength of plates secured into two different locations on the occiput. The occiputs of 12 adult human fresh frozen cadaveric specimens were used. The specimens were analyzed by dual-energy X-ray absorptiometry. Direct thickness measurements of the occiput were performed. Areal and volumetric BMD were measured. A simple pelvic reconstruction plate (3.2 mm) was fixed to the occiput either laterally or at the midline with bicortical 4-mm cancellous screws. Torque was recorded at the time of insertion of each screw. Axial pullout tests were performed on all specimens. The peak load, failure load, stiffness, and energy to failure were recorded for each construct. Statistical analysis showed that the average thickness of occipital bone is greater in the midline than laterally. Occipital bone is thicker and screw torque is greater close to the inion. There is a positive correlation between bone thickness, areal BMD as measured by dual-energy X-ray absorptiometry, screw insertional torque, and strength of fixation. A plate fixed in the midline region of the occiput provides more rigid fixation than a plate fixed laterally. Areal BMD correlates better than volumetric BMD with bone thickness and is a reliable predictor of the strength of occipital fixation.     

成人枕骨厚度解剖学和CT测量的相关性研究

目的了解枕骨厚度解剖学与CT两种测量结果的相关性,为枕颈融合术中螺钉长度的选择提供解剖学依据。方法对10具成人湿润颅骨标本进行CT和解剖学测量,测量方法参照McRac线,共66个点,每格相距1cm的矩阵,并对两组数据的相关性进行统计学分析。结果两组数据具有良好的相关性。最厚处位于枕骨粗隆部,最薄处位于小脑窝处,其中厚度大于8mm的区域位于水平线P5、6间ML线旁开2cm、P4、5间ML线旁开1cm及P3、4间ML线处的近似倒三角形区域;厚度介于6～8mm的区域位于上述倒三角形外周1cm的区域。结论各枕骨之间的厚度存在个体差异,CT和解剖学测量结果具有良好的相关性,术前CT测量结果可为术中螺钉长度选择提供参考依据。     

Morphologic and radiologic anatomy of the occipital bone.

Several diseases may cause craniovertebral instability warranting occiput-cervical fusion. As occipital screw and rod constructs are becoming more popular, requiring that screws be placed either medially or laterally in the occipital bone, the need for clearer anatomical and computed tomography (CT)-confirmed data regarding the relative thickness of the occiput in its various localities has become more critical. In 18 cadaveric specimens, the occipital bone was divided into 35 measurable segments. Transversely, the occipital bone was divided into five lines starting at the level of the inion; horizontal lines then proceeded inferiorly in 1-cm segments, 1, 2, 3, and 4 cm below the level of inion. In a comparable fashion, the occipital bone was divided vertically, starting at the midline, and proceeding laterally also in 1-, 2-, and 3-cm segments. Anatomical measurements of thickness were directly performed using a Vernier caliper. Results were directly correlated with axial CT measurements of bony thickness. Anatomical and CT measurements closely correlated within the same specimen, but there was significant interspecimen variability. The marked differences in the occipital bone anatomy noted between specimens indicates that patients undergoing occipital screw placement for cranial-cervical instability would benefit from preoperative occipital CT evaluations.     

Cadaveric morphometric analysis for atlantal lateral mass screw placement

OBJECTIVE: Atlantal lateral mass screws provide an alternative to C1/C2 transarticular screws and, in some cases, can obviate the need for extending a fusion to the occiput. For these reasons, C1 lateral mass screws are becoming increasingly popular. However, the critical local anatomy and unfamiliarity with this new technique can make C1 screw placement more challenging. METHODS: Morphometric analysis was performed on 74 cadaveric spines obtained from the Department of Anatomy at the Keck School of Medicine, University of Southern California. Critical measurements were determined for screw entry points, trajectories, and lengths for application of the technique described by Harms and Melcher. RESULTS: The mean height and width for screw entry on the posterior surface of the lateral mass were 3.9 and 7.3 mm, respectively. The maximum medialized screw trajectory ranged from 25 to 45 degrees (mean, 33 degrees). The mean maximal screw length to obtain bicortical purchase was 22.5 mm, and the mean minimum screw depth was 14.4 mm. Screw depths varied on the basis of the entry point, trajectory, and vertebral morphology. The overhang of the posterior arch averaged 11.4 mm (range, 6.9-17 mm). All specimens could accommodate 3.5-mm lateral mass screws bilaterally with proper preparation of the entry site. CONCLUSION: Significant variations in the morphology of C1 exist. However, the large size of the atlantal lateral mass makes screw placement forgiving. Preoperative computed tomographic scans and intraoperative fluoroscopy are useful in guiding proper screw placement. Close attention should be paid to preparation of the screw entry site.     

Occipital fixation: effect of inner occipital protuberance alignment on screw position.

Previous authors have demonstrated that the optimum position for screw placement in the occiput is in the inner occipital crest. The position of this structure is usually taken as being in the midline; however, this has not been previously validated. Computerized tomography (CT) of the occipital region was performed prospectively according to a standard protocol. The study included 100 patients (53 female and 47 male, 18-75 years of age). CT images were analyzed to determine the position of the inner occipital crest in relation to the midline. The inner occipital crest is located off the midline (> or = 2 degrees ) in 48% of patients. Preoperative CT evaluation may be helpful prior to occipitocervical fixation on the basis of this study.     

枢椎椎弓根螺钉进钉点的解剖定位研究

目的研究枢椎下关节突与枢椎椎弓根的位置关系,建立以枢椎下关节突为解剖标志的枢椎椎弓根螺钉进钉定位技术。方法取50套成人干燥枢椎标本,测量枢椎椎弓根的内、外缘和枢椎下关节突的内缘、中点、外缘分别与正中矢状线的垂直距离,以及枢椎椎弓根的宽度与高度。通过分析测量值间的关系,建立枢椎椎弓根螺钉的进钉定位技术。结果枢椎下关节突内缘在枢椎椎弓根内缘的外侧(3.67±0.41)mm处,枢椎下关节突中点在枢椎椎弓根外缘的外侧(1.15±0.44)mm处。建立了两种以枢椎下关节突为标志的进钉点定位方法,进钉点A位于枢椎下关节突内上象限,即中心点内、上各2mm处;进钉点B位于经枢椎下关节突内缘的纵垂线与枢椎下关节突中上1/4水平线的交点。结论枢椎下关节突与枢椎椎弓根间存在较恒定的解剖位置关系,枢椎下关节突可作为术中判断枢椎椎弓根位置和确定枢椎椎弓根螺钉进钉点的简易解剖学标志。     

髋臼前柱螺钉固定解剖学研究及导向器的设计

目的为经髋臼前柱螺钉固定提供解剖学依据。方法对22只成人尸体骨盆标本,共44侧髋臼进行解剖学研究,观测髋臼前柱横断面形状,测量髋臼前柱螺钉固定在髂骨翼外侧面的进针点、进针方向、钉道直径、进针点至闭孔沟的距离。结果髋臼前柱横断面呈近似直角三角形,钉道直径10.5±0.8mm;螺钉进针点位于髂骨翼后外侧面坐骨大切迹和髂前上棘连线上方9.2±2.4mm,距坐骨大切迹38.5±3.8mm;螺钉进针方向于水平面与中心线夹角为40.7±3.8°,矢状面向尾端成角54.2±5.5°。钉道长度84.1±6.2mm。并设计出髋臼前柱螺钉固定导向器。结论髋臼前柱可接受1枚直径6.5mm、长70mm的螺钉,螺钉进针点位于髂骨翼后外侧面坐骨大切迹和髂前上棘连线上方10mm,距坐骨大切迹40mm。螺钉进针方向于水平面与中心线夹角40°,矢状面向尾端成角55°。髋臼前柱螺钉固定导向器将提高前柱螺钉固定的安全性。     

Occipitocervical Revision Surgery Using the Bicortical Screw and Plate System for Failed Craniovertebral Junction Stabilization

BackgroundTo evaluate the clinical efficacy and safety of the modified technique utilizing the occipital bicortical screws and plate system in occipitocervical revision surgery.MethodsBetween October 2010 and May 2018, 12 consecutive patients were retrospectively evaluated. All patients had posterior occipitocervical resurgery utilizing modified technique of bicortical screws and occipital plate. The measurements of extracranial occiput on midline were conducted on computed tomography (CT) scans. The thickness of the occipital bone at the location of external occipital protuberance and below 15 mm were evaluated, respectively. For the procedure, the trajectory was drilled perpendicular to the external occipital protuberance for the specified depth with a depth‐limited drilling, 2 mm away from the internal bone plate, then the trajectory was deepened at intervals of 1 mm each time until reaching the internal bone plate. Meanwhile, a probe was used to explore all the walls of the trajectory. Bicortical screws were inserted to the occipital plate and the depth of penetration was less than 2 mm from the internal bone plate. Clinical efficacy and radiographic evaluation were followed up.ResultsThe thickest point was the external occipital protuberance, which was 15.49 ± 1.47 mm and decreased gradually on the midline to 13.41 ± 1.60 mm at below 15 mm. Twelve cases (mean age 41.17 years; range, 24–62 years), including five males and seven females, were followed up for 24.08 months (14–32 months). The interval time was 40.42 months (3–156 months) after the initial operation. At the final follow‐up, JOA score increased from 8.58 ± 2.53 before surgery to 12.67 ± 1.84 (P < 0.05) and VAS score improved from 6.17 ± 1.21 to 2.08 ± 1.32 (P < 0.05). Besides, clinical symptoms were relieved in all patients after revision surgery. All patients had rigid internal fixations with bone fusion and no major complications occurred.ConclusionsPosterior occipitocervical plate‐screw system with bicortical screws had the advantages of safety, simple and promising efficacy without excessive tissue release or intraspinal manipulation, proving that it''s valuable as a modified technique for occipitocervical revision surgery.     

后路经寰枕关节-斜坡螺钉枕颈固定技术的可行性研究

目的:探讨经寰枕关节-斜坡螺钉行后路枕颈固定的解剖学可行性。方法:回顾性分析2017年2月至2019年11月60例来院就诊并行枕颈区CT检查的成人CT影像资料,排除枕颈区域感染、损伤、肿瘤和畸形。利用CT扫描的Dicom数据在Mimics软件中进行解剖学参数测量,测量参数包括斜坡前缘、中部的高度和宽度,斜坡前方软组织最...     

The significance of anode location for stimulus-evoked electromyography during iliosacral screw placement

OBJECTIVES: To determine the effect of anode location on the current threshold required to provoke an electromyograph response during stimulus-evoked electromyography for iliosacral screw placement. DESIGN: Prospective cohort. SETTING: Level I trauma center. PATIENTS: Nineteen consecutive patients with 23 unstable posterior pelvic ring injuries treated with iliosacral screws. INTERVENTION: Iliosacral screws were inserted percutaneously over guidewires. Twenty-seven screws were inserted, all into the first sacral vertebrae. The guidewire was used as the cathode for constant-current, stimulus-evoked electromyography for all data collection. Stimulus-evoked electromyographs were obtained with the guidewire at four different stations: at the sacroiliac joint (station I), at the first sacral neuroforamen (station II), in the body of the sacrum (station III), and when the iliosacral screw was in final position over the guidewire (station IV). MAIN OUTCOME MEASURE: Stimulus-evoked electromyographs were obtained with the anode at four different locations for each of the implant stations. Location A had the anode adjacent to the percutaneous insertion site of the guidewire, location B at the ipsilateral anterior superior iliac spine, location C at the midline, and location D at the contralateral anterior superior iliac spine. RESULTS: Moving the anode from midline (location C) toward the entry point of the guidewire increased the current threshold required to provoke an EMG response as much as 67.1% (p < 0.05). Moving the anode from midline to the contralateral anterior superior iliac spine decreased thresholds as much as 3.4% (p > 0.05). In one case, anode placement close to the guidewire insertion site (locations A and B) failed to identify a potentially dangerous implant because current thresholds were >8 mA. With the anode at the midline, current thresholds were <8 mA, indicating unsafe guidewire position leading to redirection of the guidewire. CONCLUSION: The physical location of the anode during stimulus-evoked electromyography monitoring for iliosacral screw placement significantly changes the current thresholds required to provoke an electromyograph response. Current thresholds required to stimulate nerves increase as the anode is moved toward the stimulating electrode. Anode placement ipsilateral to the stimulating electrode may provide a false indication of safe guidewire placement. We recommend anode location at or beyond the midline for stimulus-evoked electromyography monitoring during iliosacral screw placement.     

经后路寰椎椎弓根螺钉固定的置钉研究

目的探讨经后路寰椎椎弓根螺钉固定的可行性. 方法利用20具颈椎尸体标本,模拟经后路寰椎椎弓根螺钉固定.在寰椎后弓后缘表面,经枢椎下关节突中心点纵垂线与寰椎后弓上缘下方3 mm水平线的交点作为进钉点,按内斜10度、上斜5度钻孔,经寰椎椎弓根置入直径3.5 mm的皮质骨螺钉.测量进钉点与寰椎椎弓根中线平面的距离、螺钉最大进钉深度、螺钉内斜角度和螺钉上斜角度等解剖指标,观察螺钉是否突破椎弓根和侧块骨皮质,以及椎动脉、硬膜、脊髓是否损伤等. 结果共放置40枚寰椎椎弓根螺钉,测得进钉点与寰椎椎弓根中线的平均距离为(2.20±0.42) mm,螺钉最大进钉深度平均(30.51±1.59) mm,螺钉内斜角度平均(9.70±0.67)度,上斜角(4.60±0.59)度.其中1枚螺钉因上斜角度过大穿破椎弓根上缘,8枚因后弓高度过小而突破椎弓根下缘,5枚进钉过深突破寰椎侧块前缘皮质,但均未对脊髓和椎动脉造成损伤. 结论经后路行寰椎椎弓根螺钉固定是安全可行的,但应注意进钉角度和深度.     

Biomechanical and morphometric evaluation of occipital condyle for occipitocervical segmental fixation

Two recent novel techniques of occipital fixation are the occipitoatlantal (C0-C1) transarticular screw technique and the direct occipital condyle screw technique. The present study evaluated and compared the biomechanical stability of the direct occipital condyle screw and C0-C1 transarticular screw with the established method for craniocervical spine fixation using the midline occipital keel screw and C1 lateral mass screw. Morphometric evaluation of the occipital condyle and the hypoglossal canal was performed to avoid hypoglossal nerve injury during the screw placement. Thirteen recently frozen cadaveric specimens were used. The occipital condyle anatomy and the hypoglossal canal dimension were measured using reconstructed computed tomography images. Insertion torque and pullout strength were evaluated to compare the midline occipital keel screw, C0-C1 transarticular screw, C1 lateral mass screw, and direct occipital condyle screw. The dimensions of the occipital condyle allow use of a 3.5 or 4.0-mm diameter screw. Mean pullout strength was 1619.6 N for the midline occipital keel screw, 870.7 N for the C0-C1 transarticular screw, 707.0 N for the C1 lateral mass screw, and 431.7 N for the direct occipital condyle screw. Mean insertion torque was 0.55 Nm for the midline occipital keel screw, 0.32 Nm for the C0-C1 transarticular screw, 0.14 Nm for the C1 lateral mass screw, and 0.11 Nm for the direct occipital condyle screw. The condylar anatomy allows direct insertion of the occipital condyle screw and C0-C1 transarticular screw. These techniques are suitable options for the treatment of craniovertebral junction instabilities in selected patients.     

枢椎后路椎板螺钉固定技术的可行性研究

目的:观察和测量国人枢椎椎板以获取形态学参数,探讨枢椎后路椎板螺钉固定的可行性及进针技术.方法:用电子游标卡尺、量角器测量28套正常成年人枢椎新鲜标本的相关参数,包括上位和下位椎板螺钉进针点距椎板上缘距离、枢椎椎板上、中、下部的厚度.枢椎椎板高度、上位和下位椎板螺钉的长度和进针角度、进针点至椎动脉孔及下关节突中心点距离等14项指标.并对测得的数据进行统计学分析.结果:上位和下位椎板螺钉进针点距椎板上缘距离分别为4mm和8 mm,枢椎椎板上、中、下部的厚度分别为3.2、6.7、5.5 mm,椎板高度为12.8mm,上位和下位椎板螺钉的长度分别为26.2mm和25.5mm.结论:枢椎后路椎板螺钉固定技术在国人解剖学上具有可行性,枢椎椎板螺钉固定可作为枢椎后路固定技术的补充.     

Axial computed tomography of the pedicle in the lower cervical spine

Using axial computed tomography (CT), we measured pedicle width, pedicle axis length, pedicle transverse angle, and distance between screw entry point and vertebrae midline in the cervical spines (C3-C7) of 40 patients. All measurements were greater in men than in women, and we noted significant sex differences at most levels of pedicle inner and outer widths (P < or = .05 or P < or = .01). Mean pedicle inner and outer widths for all levels and all patients ranged from 2.3 to 3.0 mm and from 5.0 to 6.0 mm, respectively. Mean distances between screw entry point and vertebrae midline ranged from 22.2 to 23.7 mm. Results of this study-along with axial CT measurements of individual pedicle diameter, pedicle transverse angle, and screw entry point-would be useful when considering and performing transpedicular screw fixation in the cervical spine.     

In vivo and in vitro CT analysis of the occiput

Arguments concerning the best procedure for occipito-cervical fusion have rarely been based upon occipital bone thickness or only based on in vitro studies. To close this gap and to offer an outlook on preoperative evaluation of the patient, 28 patients were analysed in vivo by means of spiral CT. Ten macerated human skulls were measured by means of CT and directly. Measurements were taken according to a matrix of 66 points following a grid with 1 cm spacing based upon McRae’s line. Maximum thickness in the patient group was met 4 cm above the reference plane in the median slice (11.87 mm; SD 3.41 mm) and 5 cm above it in the skull group (15.85 mm; SD 1.81 mm). Correlation between CT and direct measurements was good (91.79%). Intra-individual discrepancies from one side to the respective point on the other side are common (difference > 1 mm in 60%). Judging areas suitable for operative fixation using the 10% percentile value (6.68 mm for the maximum value of 11.87 mm) led to the conclusion that screws should only be inserted along the occipital crest in an area extending from 1.5 cm above the posterior margin of the foramen magnum to the external occipital protuberance (EOP). At the level of the EOP screws may also be inserted up to 1 cm lateral of the midline. A reduction of screw length to 7 mm (9 mm for the EOP) is proposed. Preoperative evaluation of the patient should be carried out by spiral CT with 1 mm slicing and sagittal reconstructions. Received: 19 February 1998 Revised: 13 July 1998 Accepted: 15 September 1998     

经前路枕颈融合术斜坡置钉的影像学研究

目的:探讨经前路枕颈融合术斜坡置钉的影像学参数.方法:2006年5月～2011年4月在我院行颅颈区多层螺旋CT扫描的患者中,排除:(1)＜20岁;(2)术后CT扫描;(3)枕颈部解剖异常,如先天性颅寰枕融合、颅底凹陷等;(4)肿瘤、外伤或感染患者.共有30例患者入选,男19例,女11例,年龄20～64岁,平均38.8岁.将30例患者的颅颈区CT扫描原始数据输入MXV工作站,进行多平面二维重建(MPR),重建好的图像保存于PACS系统并进行分析测量:在矢状位上确定颅底斜坡最佳进钉点A2再作水平线即为A线,斜坡最高点水平线即为C线,两线中点等距水平线即为B线,三线上分别有3个相距为3.5mm(即Zephir钢板螺钉孔直径)的进钉点,A线3个点作为最佳进钉点,B线3个点为候选进钉点,C线3个点为极限进钉点;在其矢状位图像上测量每个进钉点分别以水平角度(HA)、垂直角度(VA)以及极限向上倾斜角度(LA)进钉的安全角度和螺钉长度范围,并测量颅颈区内固定钢板或钛笼所需的折弯角度.结果:斜坡置钉相对安全的进钉范围呈一个不规则的梯形区域,在分别以A、B和C线的点为进钉点、以最佳进钉角度(VA)进钉时,平均钉道长度为(7.57±1.38)mm、(10.13±2.46)mm和(15.60±3.12)mm,三者间差异有显著性(P＜0.05).通过重建矢状位图像测量斜坡螺钉结果显示,29例患者在B线达到了VA,13例在C1和C2达到VA,12例在C3达到VA,其中1例在C1达到VA而在C2和C3处未达到,1例在C1和C2处达到但C3处未达到VA.矢状位图像测量中最佳进钉点、候补进钉点及极限进钉点的最大安全进钉角度分别为130.19°±8.00°、125.23°±13.24°和85.72°±24.33°,三者间差异有显著性(P＜0.05).内固定钢板或者钛笼所需的折弯角度为121.36°～140.18°(130.19°±8.00°).结论:经前路枕颈融合术在颅颈区斜坡置钉内固定是一种可行的选择,并且存在一个安全进钉角度和螺钉长度范围.     

螺旋CT个体化测量辅助下颈椎椎弓根置钉的实验研究

目的：探讨螺旋CT测量辅助下颈椎椎弓根个体化置钉的准确性。方法：成人颈椎标本10具行螺旋CT扫描重建，在其多平面截面图像上设计出理想进钉路线，此路线在后方侧块上的投影点（O点）即为理想的进钉点，测量出O点与侧块外缘的距离（HO），或到横突根部的距离（HT），与侧块下缘的距离（HL），或与侧块上缘的距离（HU）。同时测量此路线与椎体中轴线的夹角（Am）以及与椎体上终板的夹角（AE）；测量椎弓根峡部松质骨核心的长径（IL）与短径（IS），并测量其向内倾斜角度（f）。在标本上依据上述测量得到的数据找出椎弓根内固定的进钉点即O点。并根据测量的角度确定进钉方向后插入克氏针模拟置钉。将置钉后的标本进行CT扫描，判断其准确性。结果：共置入98枚克氏针，89枚（90．8％）完全在椎弓根内，9枚（9．2％）穿破椎弓根。结论：利用螺旋CT测量的数据辅助下颈椎椎弓根置钉有较高的准确性，但仍有一定的椎弓根穿破率。     

Trans-iliosacral plating for vertically unstable fractures of sacral spine associated with spinopelvic dissociation: A cadaveric study

Background:

The treatment algorithm for sacral fracture associated with vertical shear pelvic fracture has not emerged. Our aim was to study a new approach of fixation for comminuted and vertically unstable fracture pattern with spinopelvic dissociation to overcome inconsistent outcome and avoid complications associated with fixations. We propose fixation with well-contoured thick reconstruction plate spreading across sacrum from one iliac bone to another with fixation points in iliac wing, sacral ala and sacral pedicle on either side. Present biomechanical study tests the four fixation pattern to compare their stiffness to vertical compressive forces.

Materials and Methods:

Dissection was performed on human cadavers through posterior midline paraspinal approach elevating erector spinae from insertion with two flaps. Feasibility of surgical exposure and placement of contoured plate for fixation was evaluated. Ten age and sex matched computed tomography scans of pelvis with both hips were obtained. Reconstructions were performed with advantage windows 4.2 (GE Light Speed QX/I, General Electric, Milwaukee, WI, USA). Using the annotation tools, direct digital CT measurement (0.6 mm increments) of three linear parameters was carried out. Readings were recorded at S2 sacral level. Pelvic CT scans were extensively studied for entry point, trajectory and estimated length for screw placement in S2 pedicle, sacral ala and iliac wing. Readings were recorded for desired angulation of screw in iliac wing ala of sacrum and sacral pedicle with respect to midline. The readings were analyzed by the values of mean and standard deviation. Biomechanical efficacy of fixation methods was studied separately on synthetic bone. Four fixation patterns given below were tested to compare their stiffness to vertical compressive forces: 1) Single S1 iliosacral screw (7.5 mm cancellous screw), 2) Two S1 and S2 iliosacral screws, 3) Isolated trans-iliosacral plate, 4) Trans-iliosacral plate + single S1 iliosacral screw.

Statistical Analysis:

Mean of desired angulation for inserting screws and percentage of displacement on biomechanical testing was evaluated.

Results:

Mean angulations for inserting sacral pedicel were 12.3° (SD 2.7°) convergent to midline and divergent of 14° (SD 2.3°) for sacral ala screw and 23° (SD 4.9°) for iliac wing screw. All screws needed to be inserted at an angle of 90° to sacral dorsum to avoid violation of root canals. Cross headed displacement across fracture site was measured and plotted against the applied vertical shear load of 300 N in five cycles each for all the four configurations. Also, the force required for cross headed displacement of 2.5 mm and 5 mm was recorded for all configurations. Transmitted load across both ischial tuberosities was measured to resolve unequal distribution of forces. Taking one screw construct (configuration 1) as standard base reference, trans-iliosacral plate construct (configuration 3) showed equal rigidity to standard reference. Two screw construct (configuration 2) was 12% stronger and trans-iliosacral plate (configuration 4) with screw was 9% stronger at 2.5 mm displacing on 300 N force, while it showed 30% and 6%, respectively, at 5 mm cross-headed displacement.

Conclusions:

Trans-iliosacral plating is feasible anatomically, biomechanically and radiologically for sacral fractures associated with vertical shear pelvic fractures. Low profile of plate reduces the risk of hardware prominence and decreases the need for implant removal. Also, the fixation pattern of plate allows to spare mobile lumbosacral junction which is an important segment for spinal mobility. Biomechanical studies revealed that rigidity offered by plate for cross headed displacement across fracture site is equal to sacroiliac screws and further rigidity of construct can be increased with addition of one more screw. There is need for precountered thicker plate in future.     

峡部植骨修复拉力螺钉张力带固定治疗青少年下腰椎峡部裂

目的　探讨青少年下腰椎峡部裂的治疗中直接峡部植骨修复拉力螺钉张力带固定手术方法及其价值。　方法　共 12例 ,年龄范围 12 0～ 2 6 0岁 ,平均 18 4岁。术中暴露峡部并清理缺损区的纤维组织 ,分别切除两侧 1 0～ 2 0mm骨质 ,暴露新鲜骨界面 ,间隙内植入髂骨块 ,以椎板下缘中线旁开 8mm为进钉点 ,向头端和外侧各 30°倾斜安装长度 35 0～ 4 5 0mm ,直径 3 5mm钛质拉力螺钉 ,穿越峡部缺损和植骨块直至穿透椎弓根的外上缘皮质并紧固。峡部缺损表面植入条状植骨条 ,采用高强度尼龙线在螺钉尾部和横突基底部间形成张力带结构 ,关闭切口并留置负压引流。手术后石膏腰围固定 2个月。　结果　手术平均时间为 (10± 5 5 )min ,失血量为 170ml,术后随访 12～ 36个月 ,平均 17个月 ,所有修复的 2 2个峡部均在术后 3个月愈合。　结论　峡部植骨修复拉力螺钉张力带固定治疗青少年下腰椎峡部裂是一种简单、安全、可靠的术式 ,结合了生物力学和生物学过程 ,具有创伤小和保留病变节段运动功能的优点。     

Posterior stabilization of the lower cervical spine with lateral mass plates and screws

Posterior cervical fixation using lateral mass plates and screws is becoming increasingly used and accepted.Advantages include increased rigidity, ability to be used in cases where the lamina or spinous processes are deficient or missing, use across the occipito-cervical or cervico-thoracic junction, and need for less postoperative bracing. Safe placement of lateral mass screws requires complete exposure and identification of the boundaries of the lateral masses. The starting point for screw placement is 1 to 2 mm medial to the center of lateral mass. The screws are angulated outward 10 to 20 degrees and cranially 20 to 30 degrees to be parallel to the facet joints. An adjustable drill guide facilitates safe drilling and tapping techniques. All 102 patients with unstable cervical spines treated with AO reconstruction plates and autogenous bone graft had healed fusions based on flexion-extension radiographs. The reductions achieved postoperatively were maintained at follow-up. Two patients had transient radiculopathies secondary to screw placement. The indications for lateral mass fixation include cases where the lamina or spinal processes are deficient or missing, multilevel or rotational instabilities, when extension to the thoracic spine or occiput is required or when decreased bracing is beneficial.