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。     

Early complications after instrumentation of the lumbar spine using cortical bone trajectory technique

This retrospective chart review aimed to identify and report on a series of early complications that resulted from instrumentation of the lumbar spine using the cortical bone trajectory (CBT) technique. CBT technique is a novel method for fixation of the lumbar spine. Since it was first described in 2009 this technique has gained significant popularity. Here we report a series of early complications that have developed in patients who had lumbar spine fusion using the CBT technique. A retrospective chart review was performed in which all cases utilizing the CBT technique for instrumentation of the lumbar spine by two fellowship trained spine surgeons at our institution between July 2012 and May 2014 were reviewed. Medical records were reviewed to determine the number of patients who went on to develop an early complication after instrumentation with this technique. An early complication was defined as any of the following occurring within 3 months of surgery: (1) early screw loosening confirmed by post-operative CT scan, (2) evidence of fracture development confirmed by post-operative CT scan, (3) intra-operatively identified durotomy, (4) superficial or deep post-operative infection and (5) neurological injury. A total of 22 cases using the CBT technique were performed in our department. Of these cases two patients went onto develop early screw loosening, one developed an intra-operative pars fracture, one developed a dural tear and lastly, one patient developed both a pedicle fracture and early screw loosening. At our institution a total of five patients thus far have developed early complications after undergoing instrumentation of the lumbar spine using the CBT technique between 2012–2014.     

椎弓根螺钉植入物断裂18例相关因素分析*

目的：分析胸腰椎骨折中椎弓根螺钉断裂的相关因素。 方法：选择2001-03/2008-03桂林医学院附属医院脊柱外科收治的胸腰段骨折行椎弓根钉内固定患者374例,其中使用不锈钢材料的246例,使用钛合金材料的128例。术后出现椎弓根钉断裂患者18例(实验组),男8例,女10例;年龄19~61岁,平均38.6岁。随机抽取18例具有可比性的未断钉治疗效果良好的患者进行对比(对照组),男9例,女9例;年龄21~57岁,平均37.5岁。阅读所有观察对象的脊柱正侧位片,测量病椎的椎间隙高度、椎弓钉位置,观察骨性融合程度和横杆使用情况。 结果：246例使用不锈钢材料的患者中12例发生断钉,断钉率4.88%。128例使用钛合金材料的患者6例发生断钉,断钉率4.69%。两者相比,差异无显著性意义(P > 0.05),提示椎弓根钉的断钉和其材料无明显关系。通过对实验组和对照组4个观察指标的分析,病椎椎间隙的高度与椎弓根钉的断钉无明显关系,但是椎弓根钉置入的位置、植入骨的骨性融合程度及是否使用横杆和椎弓根钉的断钉有明显关系。 结论：胸腰椎骨折中螺钉断裂与其材料性质无明显关系,与椎弓根钉位置﹑骨性融合程度、横杆使用等因素密切相关,是多因素共同作用的结果。     

The Effects of Spinopelvic Parameters and Paraspinal Muscle Degeneration on S1 Screw Loosening

ObjectiveTo investigate risk factors for S1 screw loosening after lumbosacral fusion, including spinopelvic parameters and paraspinal muscles.MethodsWe studied with 156 patients with degenerative lumbar disease who underwent lumbosacral interbody fusion and pedicle screw fixation including the level of L5-S1 between 2005 and 2012. The patients were divided into loosening and non-loosening groups. Screw loosening was defined as a halo sign larger than 1 mm around a screw. We checked cross sectional area of paraspinal muscles, mean signal intensity of the muscles on T2 weight MRI as a degree of fatty degeneration, spinopelvic parameters, bone mineral density, number of fusion level, and the characteristic of S1 screw.ResultsTwenty seven patients showed S1 screw loosening, which is 24.4% of total. The mean duration for S1 screw loosening was 7.3±4.1 months after surgery. Statistically significant risk factors were increased age, poor BMD, 3 or more fusion levels (p<0.05). Among spinopelvic parameters, a high pelvic incidence (p<0.01), a greater difference between pelvic incidence and lumbar lordotic angle preoperatively (p<0.01) and postoperatively (p<0.05). Smaller cross-sectional area and high T2 signal intensity in both multifidus and erector spinae muscles were also significant muscular risk factors (p<0.05). Small converging angle (p<0.001) and short intraosseous length (p<0.05) of S1 screw were significant screw related risk factors (p<0.05).ConclusionIn addition to well known risk factors, spinopelvic parameters and the degeneration of paraspinal muscles also showed significant effects on the S1 screw loosening.     

Pilot study of oblique lumbar interbody fusion using mobile percutaneous pedicle screw and validation by a three-dimensional finite element assessment

The purpose of this study was to try oblique lateral interbody fusion (OLIF) using percutaneous pedicle screws (PPS) with mobility.Twelve patients who underwent single-level OLIF were observed for at least one year. These included 6 patients with conventional PPS (rigid group), and 6 with movable PPS (semi-rigid group). Mobile PPS used cosmicMIA, which is a load sharing system. The anterior and posterior disc height, screw loosening and bone healing period, and implant failure were evaluated at final observation by CT. Moreover, the stress on the vertebral body-cage, on the vertebral body-screw/rod and on the bone around the screw was estimated using a three-dimensional finite element assessment in both groups.There was no significant difference in surgical time, amount of bleeding, JOA score, or low back pain VAS between groups. There were no differences between groups in anterior and posterior disc height, screw loosening, and implant failure at final observation. The bone healing period was significantly shorter in the semi-rigid screw group (18.3 months vs 4.8 months, p = 0.01). The finite element analysis showed that the lower stress on the rod/screw would contribute to fewer implant fractures and that lower stress on the bone around the screw would reduce screw loosening, and that higher compressive force on the cage would promotes bone healing.OLIF combined with a movable screw accelerated bone healing by nearly 75%. We conclude that mobile PPS in combination with OLIF promotes bone healing and can be a better vertebral fusion technique.     

Pullout Strength after Expandable Polymethylmethacrylate Transpedicular Screw Augmentation for Pedicle Screw Loosening

Objective

Pedicle screw fixation for spine arthrodesis is a useful procedure for the treatment of spinal disorders. However, instrument failure often occurs, and pedicle screw loosening is the initial step of a range of complications. The authors recently used a modified transpedicular polymethylmethacrylate (PMMA) screw augmentation technique to overcome pedicle screw loosening. Here, they report on the laboratory testing of pedicle screws inserted using this modified technique.

Methods

To evaluate pullout strengths three cadaveric spinal columns were used. Three pedicle screw insertion methods were utilized to compare pullout strength; the three methods used were; control (C), traditional transpedicular PMMA augmentation technique (T), and the modified transpedicular augmentation technique (M). After control screws had been pulled out, loosening with instrument was made. Screw augmentations were executed and screw pullout strength was rechecked.

Results

Pedicle screws augmented using the modified technique for pedicle screw loosening had higher pullout strengths than the control (1106.2±458.0 N vs. 741.2±269.5 N; p=0.001). Traditional transpedicular augmentation achieved a mean pullout strength similar to that of the control group (657.5±172.3 N vs. 724.5±234.4 N; p=0.537). The modified technique had higher strength than the traditional PMMA augmentation technique (1070.8±358.6 N vs. 652.2±185.5 N; p=0.023).

Conclusion

The modified PMMA transpedicular screw augmentation technique is a straightforward, effective surgical procedure for treating pedicle screw loosening, and exhibits greater pullout strength than traditional PMMA transpedicular augmentation. However, long-term clinical evaluation is required.     

Posterior Atalntoaxial Fusion with C1 Lateral Mass Screw and C2 Pedicle Screw Supplemented with Miniplate Fixation for Interlaminar Fusion : A Preliminary Report

Objective

To investigate the feasibility of C1 lateral mass screw and C2 pedicle screw with polyaxial screw and rod system supplemented with miniplate for interlaminar fusion to treat various atlantoaxial instabilities.

Methods

After posterior atlantoaxial fixation with lateral mass screw in the atlas and pedicle screw in the axis, we used 2 miniplates to fixate interlaminar iliac bone graft instead of sublaminar wiring. We performed this procedure in thirteen patients who had atlantoaxial instabilities and retrospectively evaluated the bone fusion rate and complications.

Results

By using this method, we have achieved excellent bone fusion comparing with the result of other methods without any complications related to this procedure.

Conclusion

C1 lateral mass screw and C2 pedicle screw with polyaxial screw and rod system supplemented with miniplate for interlaminar fusion may be an efficient alternative method to treat various atlantoaxial instabilities.     

Focal hole versus screw stimulation to prevent false negative results in detecting pedicle breaches during spinal instrumentation

ObjectiveWe describe a stimulus-evoked EMG approach to minimize false negative results in detecting pedicle breaches during lumbosacral spinal instrumentation.MethodsIn 36 patients receiving 176 lumbosacral pedicle screws, EMG threshold to nerve root activation was determined using a focal probe inserted into the pilot hole at a depth, customized to the individual patients, suitable to position the stimulating tip at the point closest to the tested nerve root. Threshold to screw stimulation was also determined.ResultsMean EMG thresholds in 161 correctly fashioned pedicle instrumentations were 7.5 mA ± 2.46 after focal hole stimulation and 21.8 mA ± 6.8 after screw stimulation. Direct comparison between both thresholds in individual pedicles showed that screw stimulation was always biased by an unpredictable leakage of the stimulating current ranging from 10 to 90%. False negative results were never observed with hole stimulation but this was not true with screw stimulation.ConclusionsFocal hole stimulation, unlike screw stimulation, approaches absolute EMG threshold as shown by the lower normal limit (2.6 mA; p < 0.05) that borders the upper limit of threshold to direct activation of the exposed root.SignificanceThe technique provides an early warning of a possible pedicle breakthrough before insertion of the more harmful, larger and threaded screw.     

Fijación lumbar posterior empleando el sistema de imagen quirúrgica O-arm: experiencia inicial

ObjectThe use of transpedicular screw fixation has been widely accepted for the treatment of degenerative and traumatic pathology of the lumbar spine. Complications of spinal instrumentation can be serious. Screw misplacement can result in unintended durotomy, nerve root and/or cauda equina injury. In comparison to fluoroscopy-assisted screw placement, computer-assisted image guidance has been shown to achieve overall higher rates of accuracy. The O-arm is able to obtain computed tomography (CT)-type images with multiplanar reconstruction. In this study we evaluated a cohort of patients who underwent posterior lumbar fusion with pedicle screws utilizing the O-arm imaging system.MethodsA retrospective review of 40 consecutive patients who underwent posterior lumbar fusion surgery with O-arm utilization, was performed. The study population included 14 males and 26 females. Age range was 39-85 years with an average of 63.8 years. Twenty one patients had degenerative lumbar stenosis (52.5%) and 19 had spondylolisthesis (47.5%). Intraoperative CT-images were obtained. The mean time for surgery and screw placement was assessed.ResultsA total of 252 pedicle screws were sited using O-arm navigation system, with a mean of 6.3 screws per patient (range 4-10). On the basis of intraoperative CT, 3 screws were redirected, representing a 98.81% accuracy rate.The mean duration of surgery was 157.2 (90-240) minutes and the mean time for screw placement was 7.13 (3.08-15) minutes per screw.Three patients (7.5%) developed superficial wound infections which were treated conservatively. No patients required a return to the operating room because of screw malposition.ConclusionThe use of intraoperative O-arm imaging system with computer-assisted navigation significantly increases the surgical accuracy and safety of pedicle screw placement in lumbar fusion surgery.     

A Case of Pedicle Screw Loosening Treated by Modified Transpedicular Screw Augmentation with Polymethylmethacrylate

We report a case of pedicle screw loosening treated by modified transpedicular screw augmentation technique using polymethylmethacrylate (PMMA), which used the anchoring effect of hardened PMMA. A 56-year-old man who had an L3/4/5 fusion operation 3 years ago complained of continuous low back pain after this operation. The computerized tomography showed a radiolucent halo around the pedicle screw at L5. We augmented the L5 pedicle screw with modified pedicle screw augmentation technique using PMMA and performed an L3/4/5 pedicle screw fixation without hook or operation field extension. This modified technique is a kind of transpedicular stiffness augmentation using PMMA for the dead space around the loosed screw. After filling the dead space with 1-2 cc of PMMA, we inserted a small screw. Once the PMMA hardened, we removed the small screw and inserted a thicker screw along the existing screw threading to improve the pedicle screws'' pullout strength. At 10 months'' follow-up, x-ray showed strong fusion of L3/4/5. The visual analogue scale (VAS) of his back pain was improved from 9 to 5. This modified transpedicular screw augmentation with PMMA using anchoring effect is a simple and effective surgical technique for pedicle screw loosening. However, clinical analyses of long-term follow-up and biomechanical studies are needed.     

Pedicle Screw Placement in the Thoracolumbar Spine Using a Novel,Simple, Safe,and Effective Guide-Pin : A Computerized Tomography Analysis

ObjectiveTo improve pedicle screw placement accuracy with minimal radiation and low cost, we developed specially designed K-wire with a marker. To evaluate the accuracy of thoracolumbar pedicle screws placed using the novel guide-pin and portable X-rays.MethodsObservational cohort study with computerized tomography (CT) analysis of in vivo and in vitro pedicle screw placement. Postoperative CT scans of 183 titanium pedicle screws (85 lumbar and 98 thoracic from T1 to L5) placed into 2 cadavers and 18 patients were assessed. A specially designed guide-pin with a marker was inserted into the pedicle to identify the correct starting point (2 mm lateral to the center of the pedicle) and aiming point (center of the pedicle isthmus) in posteroanterior and lateral X-rays. After radiographically confirming the exact starting and aiming points desired, a gearshift was inserted into the pedicle from the starting point into the vertebral body through the center of pedicle isthmus.ResultsNinety-nine percent (181/183) of screws were contained within the pedicle (total 183 pedicle screws : 98 thoracic pedicle screws and 85 lumbar screws). Only two of 183 (1.0%) thoracic pedicle screws demonstrated breach (1 lateral in a patient and 1 medial in a cadaver specimen). None of the pedicle breaches were associated with neurologic or other clinical sequelae.ConclusionA simple, specially designed guide-pin with portable X-rays can provide correct starting and aiming points and allows for accurate pedicle screw placement without preoperative CT scan and intraoperative fluoroscopic assistance.     

Current trends in pedicle screw stimulation techniques: lumbosacral, thoracic, and cervical levels

Unequivocally, pedicle screw instrumentation has evolved as a primary construct for the treatment of both common and complex spinal disorders. However an inevitable and potentially major complication associated with this type of surgery is misplacement of a pedicle screw(s) which may result in neural and vascular complications, as well as impair the biomechanical stability of the spinal instrumentation resulting in loss of fixation. In light of these potential surgical complications, critical reviews of outcome data for treatment of chronic, low-back pain using pedicle screw instrumentation concluded that "pedicle screw fixation improves radiographically demonstrated fusion rates;" however the expense and complication rates for such constructs are considerable in light of the clinical benefit (Resnick et al. 2005a). Currently, neuromonitoring using free-run and evoked (triggered) electromyography (EMG) is widely used and advocated for safer and more accurate placement of pedicle screws during open instrumentation procedures, and more recently, guiding percutaneous placement (minimally invasive) where the pedicle cannot be easily inspected visually. The latter technique, evoked or triggered EMG when applied to pedicle screw instrumentation surgeries, has been referred to as the pedicle screw stimulation technique. As concluded in the Position Statement by the American Society of Neurophysiological Monitoring (ASNM), multimodality neuromonitoring using free-run EMG and the pedicle screw stimulation technique was considered a practice option and not yet a standard of care (Leppanen 2005). Subsequently, the American Association of Neurological Surgeons/Congress of Neurological Surgeons (AANS/CNS) Joint Section on Disorders of the Spine and Peripheral Nerves published their "Guidelines for the Performance of Fusion Procedures for Degenerative Disease of the Lumbar Spine" (Heary 2005, Resnick et al. 2005a, Resnick et al. 2005b). It was concluded that the "primary justification" of intraoperative neuromonitoring"... is the perception that the safety and efficacy of pedicle screw fixation are enhanced..." (Resnick et al. 2005b). However in summarizing a massive (over 1000 papers taken from the National Library of Medicine), contemporary, literature review spanning nearly a decade (1996 to 2003), this invited panel (Resnick et al. 2005b) recognized that the evidence-based documents contributing to the parts related to pedicle screw fixation and neuromonitoring were "... full of potential sources of error ..." and lacked appropriate, randomized, prospective studies for formulating rigid standards and guidelines. Nevertheless, current trends support the routine use and clinical utility of these neuromonitoring techniques. In particular free-run and triggered EMG have been well recognized in numerous publications for improving both the accuracy and safety of pedicle screw implantation. Currently, treatment with pedicle screw instrumentation routinely involves all levels of the spine - lumbosacral, thoracic, and cervical. Significant historical events, various neuromonitoring modalities, intraoperative alarm criteria, clinical efficacy, current trends, and caveats related to pedicle screw stimulation along the entire vertebral column will be reviewed.     

Navigated minimally invasive facet fusion during percutaneous lumbar pedicle screw insertion: Technical note

ObjectiveMinimally invasive surgery (MIS), or percutaneous, lumbar pedicle screw placement is commonly done, but the percutaneous nature of this makes posterior arthrodesis extremely difficult. Many times, surgeons will simply forego posterior arthrodesis, place posterior pedicle screws, and rely only on the interbody area for arthrodesis. We describe our technique of adding facet arthrodesis via the same corridor through which the pedicle screw is inserted with minimal addition of time or steps.MethodsWe demonstrate our technique of how we use navigation and tubular retractors to perform posterior facet arthrodesis during percutaneous pedicle screw placement. We illustrate this technique with a case of a patient with scoliosis, intraoperative photos, and an illustrative video. We also show an intraoperative computed tomography image to help visualize the arthrodesis surfaces. With this technique, we show how there are a few additional steps that are not very time consuming to add posterior arthrodesis.ResultsMIS facet fusion can be performed in a relatively straightforward manner during percutaneous pedicle fixation without significant addition of intraoperative time or steps.ConclusionsIt is possible to add posterior arthrodesis to percutaneous lumbar pedicle screw fusion with few added steps and minimal addition of time using navigation and MIS tubular retractors.     

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。     

上颈椎骨折脱位侧块钛板椎弓根螺钉内固定置入与宿主的生物相容性

目的：探讨上颈椎骨折脱位颈椎侧块钛板椎弓根螺钉内固定置入后的疗效及生物相容性特点。　 方法：应用计算机检索Medline database (1991/2006)、中国期刊全文数据库(CNKI：1991/2006),由作者对文献进行筛选、资料收集和质量评价,总结颈椎侧块钛板椎弓根螺钉内固定置入治疗上颈椎骨折脱位的疗效及生物相容性特点。并选择2003-01/2008-01右江民族医学院附属医院脊柱骨病外科收治上颈椎骨折脱位19例进行临床验证,车祸伤10例,高处坠落伤 6例,重物砸伤3例。颈椎损伤节段：C1 8例,C2 11例,病程3 h~10 d 。其中16例合并脊髓神经根损伤, Frankle 分级,A 级4例,B级3例,C级4例,D级2例,E级3例(合并神经根损伤伴有手、肩麻木),均行小关节植骨融合、侧块钛板内固定置入治疗;置入后摄X射线片观察植骨融合、颈椎活动及内固定稳定情况,并按Frankle分级法评定神经功能恢复情况。　 结果：纳入的21篇文章结果显示,采用侧块钛板椎弓根螺钉内固定置入治疗不稳定性的上颈椎骨折脱位,是上颈椎骨折脱位手术方法中稳定上颈部最为符合生物力学方式的骨折-固定方法。临床验证结果显示,X 射线片可见颈椎侧块间隙,后弓与椎板间隙植骨融合,时间为3~6个月。术后6个月X射线片显示内固定牢固稳定,无折断松动等并发症。16例脊髓神经根损伤者中,按Frankel分级,术前A级4例中,术后3例为B级,1例为C级;术前B级3例中,术后为C级2例,D级1例;术前C级4例中,术后D级3例,E级1例;术前D级2例中,术后均为E级;3 例E级术后无变化,3例合并神经根损伤,术后短期内手、肩麻木消失。与人体组织的生物相容性好,术后2年随访,无血液、免疫、组织等反应,无囊膜形成及细胞质的转变;亦无钛合金腐蚀、磨损等材料反应的发生。 结论：颈椎侧块钛板椎弓根螺钉后路短节段固定保留了枕寰和C2~3 的关节功能,最大限度地保留上颈椎的运动功能单位,钛板椎弓根螺钉固定在颈椎后部的关节柱上,对过伸过屈损伤有良好的稳定作用,与人体组织的生物相容性好,无血液、免疫、组织等反应及腐蚀、磨损等材料反应发生。     

Application of different thresholds for instrumentation device testing in minimally invasive lumbosacral spine fixation

The main aim of this study was evaluating the reliability of stimulus-evoked electromyography (using different thresholds for stimulation of the instrumentation devices) for minimally invasive pedicle screw placement in the lumbosacral spine. A threshold of 5 mA was applied for the pedicle access needle. 7 mA was applied for the tapscrew and pedicle screw stimulation. The existence of threshold differences between vertebral levels was also assessed. All patients underwent postoperative computed tomography (CT) to determine the accuracy of pedicle screw placement. A total of 172 percutaneous pedicle screws were placed in 52 patients. 94.1% of screws were placed at L4, L5 and S1 vertebral levels. No statistically significant differences existed in thresholds of the pedicle access needles, tapscrews and pedicle screws between vertebral levels. In four instances, the pedicle access needle stimulation had a threshold of 5 mA (no breaches were associated). In the rest of occasions, the pedicle access needles had stimulation thresholds above 5 mA. In all instances, tapscrew and pedicle screw thresholds were above 7 mA; the tapscrews and pedicle screws had significantly greater thresholds than the pedicle access needles. No statistically significant differences existed in thresholds between tapscrews and pedicle screws. Postoperative CT imaging revealed one lateral pedicle violation. Both breach rate and false negative rate were 0.5%. No false positive cases were observed. No patients experienced postoperative pedicle screw–related neurologic deficits. A threshold of 5 mA for the pedicle access needle stimulation seems to be safe. Greater than 7 mA should be used for the tapscrew and pedicle screw stimulation.     

Image-guided pedicle screws using intraoperative cone-beam CT and navigation. A cost-effectiveness study

Image-guided surgery using intraoperative cone-beam CT and navigation improves screw placement accuracy rates. However, this technology is associated with high acquisition costs. The aim of this study is to evaluate the costs of revision surgery from symptomatic pedicle screw malposition to justify whether the costs of acquiring intraoperative navigation justify the expected benefits. This is a retrospective cost-effectiveness analysis of consecutive patients who had pedicle screw instrumentation using intraoperative cone-beam CT and navigation compared with patients who underwent freehand pedicle screw instrumentation at our institution over 4 years. The costs associated with revision surgery for symptomatic pedicle screw malposition (excess length of stay, intensive care, theatre time, implants and additional outpatient appointments) were calculated. A total of 19 patients had symptomatic screw malpositioning requiring revision surgery. None of these patients had screws inserted under navigation. Revision surgery accounted for an extra 304 bed days and an additional 97 h theatre time. The total extra spent over 4 years was £464,038. When compared to the costs of revision surgery for screw malpositioning, it was cost neutral to acquire and maintain this technology. Intraoperative image-guided surgery reduces reoperation rates for symptomatic screw malposition and is cost-effective in high volume centers with improved patients outcomes. High acquisition and maintenance cost of such technologies is economically justifiable.     

Bilateral versus unilateral instrumentation in spinal surgery: Systematic review and trial sequential analysis of prospective studies

Lumbar fusion surgical intervention is often followed by bilateral pedicle screw fixation. There has been increasing support for unilateral pedicle screw fixation in an attempt to reduce complications and costs. The following study assesses the efficacy and complications of bilateral versus unilateral pedicle screw fixation in open and minimally invasive lumbar interbody fusion techniques. A systematic review with meta-analysis and trial sequential analysis was performed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and recommendations. In comparison with existing meta-analyses, trial sequential analysis was implemented to reduce the potential for type I error. Of the 1310 citations screened, four observational studies and 13 randomised controlled trials were used comprising 574 bilateral cases and 549 unilateral cases. Statistical analysis showed no difference in fusion rates, total complications, dural tear rates, Visual Analogue Scale (VAS) score for back pain, VAS for leg pain, Oswestry Disability Index scores, and length of stay between bilateral and unilateral instrumentation. Unilateral instrumentation was significantly shorter in duration (P < 0.00001) and led to significantly lower blood volume loss (P = 0.0002). These results were the same for both open and minimally invasive surgical approaches. Unilateral pedicle screw fixation appears to have similar post-operative outcomes as bilateral fixation and improved efficacy in regards to procedure duration and blood volume loss.     

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.     

Evaluation of the implantation of transpedicular screws in spinal instrumentation with free-hand technique and navigation-assisted with intraoperative computed tomography: An analytical-positional study

BackgroundSpinal instrumentation using transpedicular screws has been used for decades to stabilize the spine. In October 2018, an intraoperative CT system was acquired in the Neurosurgery service of the University Hospital Complex of Vigo, this being the first model of these characteristics in the Spanish Public Health System, so we began a study from January 2015 to December 2019 to assess the precision of the transpedicular screws implanted with this system compared with a control group performed with the classical technique and final fluoroscopic control.MethodsThe study was carried out in patients who required transpedicular instrumentation surgery, in total 655 screws were placed, 339 using the free-hand technique (Group A) and 316 assisted with intraoperative CT navigation (Group B) (p > 0.05). Demographic characteristics, related to surgery and the screw implantation grades were assessed using the Gertzbein–Robbins classification.Results92 patients were evaluated, between 12 and 86 years (average: 57.1 years). 161 thoracic screws (24.6%) and 494 lumbo-sacral screws (75.4%) were implanted. Of the thoracic screws, 33 produced a pedicle rupture. For the lumbo-sacral screws, 71 have had pedicle violation. The overall correct positioning rate for the free-hand group was 72.6% and for the CT group it was 96.5% (p < 0.05).ConclusionThe accuracy rate is higher in thoracic-lumbar instrumentation in the navigation group versus free-hand group with fluoroscopic control.