Capture of the screw during percutaneous screw insertion

The simple technique to maintain the engagement of the screw and the screw driver during percutaneous locking screw insertion is presented. The method can capture the screw when the screw becomes disengaged. This will be helpful when percutaneous screw insertion is performed in the narrow and deep location of the bone such as a locking screw at the upper part of the femur during retrograde femoral nailing.     

Interference screw fixation using bioabsorbable screw as void filler

We evaluated interference screw fixation in a plug-tunnel construct using bioabsorbable screws as void fillers with different percentages of the screw removed. Nine-millimeter tunnels in a closed-cell foam block were filled with a 10-mm bioabsorbable screw, and 10-mm revision tunnels were placed in parallel with tunnel overlap resulting in removal of 10%, 25%, or 50% of the screw diameter. Synthetic bone plugs were fashioned to fit 10-mm tunnels. In all groups, the plugs were secured in standard interference fixation with a 9-mm metal screw between the void-filling bioabsorbable screw and plug. Failure loads for the control group (no revision tunnel) averaged 926 +/- 44 N, 10% (1024 +/- 129 N) and 25% (932 +/- 129 N) groups were not significantly different; failure load in the 50% diameter group (780 +/- 72 N) was significantly lower than all other groups (p < 0.001). Using a bioabsorbable screw as void filler provided mean load to failure not different from that of standard reconstruction when 10 and 25% of the diameter of the void-filling screw was removed. Load to failure was significantly lower when 50% of the void-filling screw diameter group was removed. This may be applicable in anterior cruciate ligament reconstruction where a previous tunnel void has to be addressed.     

Complications of the variable screw plate pedicle screw fixation

In this study, 124 consecutive cases of posterior spinal fusion with variable screw plate fixation were reviewed. In 33 patients (27%), 41 complications were identified. Urinary tract infection without sequelae developed in 13 patients. Dural tear occurred in seven patients and wound hematoma in five. Wound infection developed in three patients; one was subfascial requiring instrument and graft removal. Neurologic deficit developed in seven patients (6%), in five of whom the deficit was due to manipulation and reduction of neural elements. Two of the seven deficits were believed to be caused by misplaced pedicle screws. Variable screw plate fixation is a formidable procedure with a significant complications rate.     

Iliosacral screw complications

Potential complications due to iliosacral screws are numerous. Problems occur as a result of poor preoperativeplanning, inadequate intraoperative fluoroscopic imaging, inaccurate posterior pelvic reductions, posterior pelvic anatomical variations, and other reasons. Local nerve or vascular structures are at risk during screw insertions, and fixation failures are associated with insufficient anterior and posterior pelvic stability. Inadequate fixation may result in screw failure and/or delayed or nonunions. Removal of intact or broken screws can also be difficult.     

寰椎椎弓根螺钉技术和侧块螺钉技术的临床疗效比较

目的：探讨寰椎椎弓根螺钉和侧块螺钉固定技术的临床疗效。方法：2006年1月-2010年1月,行寰椎椎弓根螺钉固定技术32例（A组）,行寰椎侧块螺钉固定技术28例（B组）。通过术中失血量,手术时间,颈枕区疼痛缓解,JOA评分和术后植骨融合情况评定疗效。结果：两组患者在JOA评分,颈枕区疼痛缓解WAS评分）和植骨融合率方面无明显差异。A组术中失血量和手术时间明显低于B组,有统计学意义。B组中有3例术后出现颈枕区疼痛加重。结论：寰椎椎弓根螺钉固定技术显露范围小,简化了操作程序,减少了术中、术后的并发症。在设计手术方案时,应优先考虑椎弓根螺钉技术,而侧块螺钉技术可以作为一种补充。     

Transpedicular screw fixation

Spinal fixation employing transpedicular screws has recently been the focus of increased attention at various institutions throughout the world, but concerns about the safety and efficacy of transpedicular screws linger. This study was undertaken to address some of these concerns. The study included evaluation of the internal and external morphology of the vertebral pedicles, which revealed that adequate bone stock is generally available at T2, T7, T12, and L1-L5 spinal levels to accept screws in the 4-7-mm diameter range. The pedicle was observed to be composed of abundant cancellous bone internally with relatively thick cortical walls. The method of pilot hole preparation for pedicle screws was also examined. Screws inserted in pilot holes prepared with a 3.4-mm blunt probe (ganglion knife) resulted in higher pullout forces in eight of 10 trials as compared with those with pilot holes prepared using a 3.2-mm drill. Furthermore, the probes afford greater control of hole depth and alignment. Fatigue studies on three screw designs revealed a graduation of strength between a 7.0-mm pedicle screw, a 5.5-mm pedicle screw, and a modified 6.5-mm cancellous lag screw. The modified cancellous lag screw has an inherent stress riser that affected fatigue life. It was noted that extreme care must be exercised to prevent bending of the pedicle screws during implantation. If bending occurs one can expect a 50% reduction in the number of cycles to failure.     

Syndesmosis transfixation screw

Instability of the distal tibia-fibular joint necessitates the implant of a fibular tibial transfixation screw. The screw should be placed 2 cm above the anterior syndesmosis. The angle of insertion is 30 degrees upwards from dorsal in relation to the frontal plane. If tibiofibular stability cannot be maintained following anatomical reconstruction of the fibula the transfixation screw must engage the medial tibial cortex. This is imperative, since the transfixation screw cannot withstand the biomechanical forces during motion and bearing of load if the screw penetrates only three corticals.     

椎弓根螺钉内固定术中X线测量椎弓根螺钉横断面倾角

目的探讨术中利用C形臂X线机测量椎弓根螺钉横断面倾角(STA)的临床应用价值。方法选取胸腰椎椎弓根螺钉内固定术患者43例,术中利用C形臂X线机正位像测量椎体旋转度(VRD)、椎弓根螺钉空间旋转度(SSR),并计算STA(STA=SSR-VRD);术后利用CT横断面图像测量椎弓根螺钉实际STA。选取同一术者手术的20例患者的20枚椎弓根螺钉(每例1枚),分别在初始位(目标显像在图像中央)、球管高移位、球管低移位、球管左移位、球管右移位、球管头移位、球管尾移位、球管头倾斜照位及球管尾倾斜位照位9个不同透视机投照位置下测量VRD、SSR并计算STA,分析测量者测量结果的内部差异性。另选取20例患者的20枚椎弓根螺钉,由3名不同医生依上述方法测量VRD、SSR并计算STA,分析测量者间测量结果的差异性。结果椎弓根螺钉CT测量STA范围为-4.5°~27.3°(内倾为正角度),术中X线机测量值与术后CT测量值差距为-2.7°~3.2°,2组间差异无统计学意义(P0.05)。测量者测量结果的内部差异性分析结果显示,球管左移或右移时VRD、SSR及STA测量值与初始位置测量值差异存在统计学意义(P0.05),其他不同位置测量值与初始位置测量值差异无统计学意义(P0.05)。测量者间差异性分析显示,3名医生测量结果差异无统计学意义(P0.05)。结论术中利用C形臂X线机能较准确地评估STA。当术者遇到置钉困难时,可利用该方法测量STA并指导置钉,提高术者置钉信心及手术安全性。     

膨胀式椎弓根螺钉与骨水泥强化方法增强螺钉稳定性的比较研究

[目的]比较膨胀式椎弓根螺钉(expansive pedicle screw,EPS)与骨水泥(polymethylmethacrylate,PM-MA)强化方法在体外增强螺钉稳定性的效果,并观察各方法中的钉道界面情况.[方法]45个新鲜成年绵羊腰椎随机分为3组.CPS组:直接拧入普通椎弓根螺钉;PMMA-PS组:向钉道内注入PMMA后拧入普通椎弓根螺钉;EPS组:直接拧入EPS.24 h后,对所有标本进行轴向拔出实验、X线和micro-CT检查.[结果]EPS组和PMMA-PS组中螺钉的稳定性均显著强于CPS组(P<0.05),而EPS组和PMMA-PS组之间的差异无统计学意义(P>0.05).X线检查示各组中螺钉位置良好.CPS组中骨组织包裹螺钉,形成"螺钉-骨质"界面;PMMA-PS组中,PMMA包裹螺钉,阻碍了螺钉与骨质的接触,形成了"螺钉-PMMA-骨质"界面;EPS组中,骨小梁直接包裹螺钉,形成"螺钉-骨质"界面.螺钉的前端明显膨胀,形成一个"爪状"结构.螺钉前端胀开的两翼挤压周围骨质,使膨胀部分周围的骨质较非膨胀部分更加致密.[结论]EPS可以显著提高螺钉的稳定性,其效果与目前临床上常用的PMMA强化方法接近.同时,EPS可以有效的避免因增加螺钉直径和使用PMMA可能带来的椎弓根骨折和渗漏、压迫等风险.另外,EPS的置入并不增加手术时间和手术创伤.作为一种有效、安全和操作简便的方法,EPS在临床上的广泛应用具有巨大的潜力.     

动力髁螺钉与动力髋螺钉治疗股骨转子下骨折

2004年1月～2007年12月,笔者采用动力髁螺钉(DCS)和动力髋螺钉(DHS)手术治疗股骨转子下骨折35例,疗效满意.     

Arthroscopic and percutaneous bone screw techniques with a new screw system]

A new screwdriver is presented with which small titanium screws can be introduced into a joint under arthroscopic guidance. The screws are centrally cannulated, 2.7 mm thick (thread diameter), and available with and without a washer (5 mm in diameter, serrated and convex, flexible but not removable). The screwdriver has a special screw-holding device which allows the screw to be grasped and released making it possible to remove a screw already implanted in the joint at an earlier time. This arthroscopic screwing system has been used in 81 cases to date. In 59 patients with shoulder instability, arthroscopic refixation of the detached labrum-capsule complex was performed. In the first 32 of these cases an intra-articular screwing technique was used and in the following 27 cases an extra-articular screwing technique was applied. In addition, in 9 patients a fractured and displaced greater tuberosity was reduced and fixated percutaneously under the guidance of an image intensifier by means of this screwdriver. Other fields of application were the knee joint (type III fracture of the intercondylar eminence in 5 patients) and the ankle (displaced fracture of the talus in 2 patients and osteochondritis dissecans in 1). Complications were seen only in the patients with shoulder instability who were treated by the intra-articular screwing technique (screw loosening in 4 patients). This was the reason why the intra-articular technique was replaced by the extra-articular method. Since that time no further complications caused by the screws have been seen. Redislocation of the shoulder joint occurred in 1 case 7 months after operation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Assessment of different screw augmentation techniques and screw designs in osteoporotic spines

This is an experimental study on human cadaver spines. The objective of this study is to compare the pullout forces between three screw augmentation methods and two different screw designs. Surgical interventions of patients with osteoporosis increase following the epidemiological development. Biomechanically the pedicle provides the strongest screw fixation in healthy bone, whereas in osteoporosis all areas of the vertebra are affected by the disease. This explains the high screw failure rates in those patients. Therefore PMMA augmentation of screws is often mandatory. This study involved investigation of the pullout forces of augmented transpedicular screws in five human lumbar spines (L1–L4). Each spine was treated with four different methods: non-augmented unperforated (solid) screw, perforated screw with vertebroplasty augmentation, solid screw with vertebroplasty augmentation and solid screw with balloon kyphoplasty augmentation. Screws were augmented with Polymethylmethacrylate (PMMA). The pullout forces were measured for each treatment with an Instron testing device. The bone mineral density was measured for each vertebra with Micro-CT. The statistical analysis was performed with a two-sided independent student t test. Forty screws (10 per group and level) were inserted. The vertebroplasty-augmented screws showed a significant higher pullout force (mean 918.5 N, P = 0.001) than control (mean 51 N), the balloon kyphoplasty group did not improve the pullout force significantly (mean 781 N, P > 0.05). However, leakage occurred in some cases treated with perforated screws. All spines showed osteoporosis on Micro-CT. Vertebroplasty-augmented screws, augmentation of perforated screws and balloon kyphoplasty augmented screws show higher pullout resistance than non-augmented screws. Significant higher pullout forces were only reached in the vertebroplasty augmented vertebra. The perforated screw design led to epidural leakage due to the position of the perforation in the screw. The position of the most proximal perforation is critical, depending on screw design and proper insertion depth. Nevertheless, using a properly designed perforated screw will facilitate augmentation and instrumentation in osteoporotic spines.