寰椎后路单或双层皮质骨螺钉固定强度的生物力学评价

目的:测量单层皮质骨和双层皮质骨寰椎侧块螺钉固定与寰椎椎弓根螺钉固定的强度,为临床选择寰椎后路螺钉固定的方式提供生物力学依据。方法:利用12例新鲜的寰椎和第三颈椎标本,进行单层皮质骨和双层皮质骨的椎弓根螺钉或侧块螺钉固定,测试并比较其螺钉拔出强度。结果:双层皮质骨寰椎椎弓根螺钉固定的拔出力最大,为1757.0±318.7N;单层皮质骨寰椎椎弓根螺钉固定(1192.5±172.6N)与双层皮质骨寰椎侧块螺钉固定(1243.8±350.0N)及单层皮质骨C3椎弓根螺钉固定(1121.6±224.6N)的拔出力之间均无明显差异。结论:应用寰椎侧块螺钉固定时宜选用双层皮质骨螺钉固定,而寰椎椎弓根螺钉固定选用单层皮质骨螺钉即可。     

Biomechanical analysis of anterior cervical spine plate fixation systems with unicortical and bicortical screw purchase

Anterior plate fixation with unicortical screw purchase does not involve the risk of posterior cortex penetration and possible injuries of the spinal cord. However, there are very few biomechanical data about the immediate stability of non-locking plate fixation with unicortical or bicortical screw placement. The aim of the present study was to evaluate the immediate biomechanical properties in terms of flexibility of a non-locking anterior plate system with 4.5-mm screw fixation and unicortical or bicortical screw purchase applied to a single destabilized cervical spine motion segment. Using fresh cadaveric cervical spine specimens C3-C7, multidirectional flexibility was measured at the level C4-C5 before and after destabilization and fixation with an anterior plate with either unicortical or bicortical screw purchase. The results showed that fixed cervical spine segments with anterior plate and bicortical screw purchase were more rigid than intact specimens in all modes of testing. The difference was statistically significant for flexion and extension (P<0.001). Plate fixation with unicortical screw purchase had statistically significant decreased ranges of motion compared to the intact specimen only in extension. Neither unicortical nor bicortical screw purchase decreased the range of motion significantly in axial rotation compared to the intact specimens. This in vitro study documented that neither unicortical nor bicortical screw purchase with non-locking plate fixation can increase stability in all modes of testing, in axial rotation in particular. Direct comparison between the group with uni- and that with bicortical screw fixation did not reveal significant differences, and therefore no advantage was shown for either type of screw fixation. Therefore, we demonstrated that both uni- and bicortical screw purchase with non-locking plate fixation can decrease immediate flexibility of the tested motion segment, with better results for bicortical purchase. No significant differences were found comparing the two groups of screw fixation. These data suggest that unicortical screw fixation can be used for anterior plate fixation with a comparable immediate stability to bicortical screw fixation.Supported by the German Research Foundation, DFG, Bonn, Germany     

Dynamic compression plate fixation: a biomechanical comparison of unicortical vs bicortical distal screw fixation

The use of unicortical screws instead of bicortical screws in the extreme outer holes of dynamic compression plates (DCPs) has been recommended to minimize the stress riser effect at the end of the plates. The authors examined in vitro two groups of paired canine femurs after compression plates had been applied to the anterolateral diaphyseal surface bilaterally. Group I: intact paired femurs with bicortical peripheral screws in one DCP and unicortical peripheral screws in the other; Group II: osteotomized paired femurs again comparing unicortical and bicortical peripheral DCP screws. All specimens were torsion tested to failure and the torque, stiffness, energy, rotation, and failure fracture length were calculated. Unicortical screws did not enhance the torsional strength in either group, and significantly compromised stiffness, energy, and rotation in the osteotomized group. The only apparent benefit of unicortical peripheral screws in a DCP was a shorter, less comminuted fracture upon failure.     

C1侧块C2椎板螺钉固定与C1-2关节螺钉固定的生物力学性能比较

目的 比较1侧块C2椎板螺钉固定与后路C1-2关节螺钉固定的牛物力学性能,为枢椎交叉椎板螺钉的临床应用提供参考依据.方法 收集新鲜成年人尸体颈椎标本(C0-C4)10具,男6具,女4具,平均年龄58岁(50～72岁).分别制备成C1-2完整状态的模型(M0)、C1-2失稳的模型(M1)、C1,侧块螺钉C2交义椎板螺钉固定模型(M2)及后路C1-2关节螺钉固定模型(M3),进行三维生物力学测试,记录各组模型在屈伸、轴向旋转和侧屈的运动范围(ROM)和中性区(NZ).结果 屈伸模式下M0、M1、M2、M3的ROM和NZ分别为:(20.4±9.2)°、(10.4±5.8)°;(46.3±17.2))°、(34.5±14.1)°;(4.1±0.9)°、(1.9±0.8)°;(4.3±1.0)°、(2.1±0.7)°.轴向旋转模式下 M0、M1、M2、M3的ROM和NZ分别为:(65.3±12.9)°、(40.8±11.2)°;(91.7±10.5)°、(72.3±12.6)°;(8.9±2.1)°、(4.7±1.8)°;(8.4±2.5)°、(4.4±2.3)°.侧屈模式F M0、M1、M2、M3的ROM和NZ分别为:(11.5±4.3)°、(7.2±3.2)°;(35.0±12.9)°、(21.9±11.8)°;(2.9±1.1)°、(1.4±0.8)°;(2.5±1.4)°、(1.3±1.0)°.在三维运动模式下M2和M3力学稳定性均明显优于M1和M0,然而M2和M3,的差异无统计学意义(P>0.05).结论 C1侧块C2椎板螺钉固定拥有良好的生物力学稳定性,可作为C1-2关节螺钉固定的良好替代.     

A comparison of unicortical and bicortical end screw attachment of fracture fixation plates.

Plate fixation is considered by many clinicians to be the treatment of choice for displaced diaphyseal fractures of the forearm. One possible complication associated with plate fixation is refracture with the plate in situ or after plate removal. With the plate in situ, refracture typically occurs through the last screw hole near the end of the plate. Some clinicians have advocated the use of unicortical end screws to minimize the risk of such refractures. In this study, we performed a series of in vitro tests to compare the breaking strength of plated bone analogues that used either unicortical or bicortical end screws. The plated constructs that used unicortical end screws were significantly weaker in the two most important physiologic loading modes. Based on these results, we conclude that the use of unicortical end screws may result in a greater risk of refracture with the plate in situ.     

Biomechanical evaluation of locking plate radial shaft fixation: unicortical locking fixation versus mixed bicortical and unicortical fixation in a sawbone model

PURPOSE: Compression plating is a commonly accepted technique for treating diaphyseal forearm fractures. The purpose of this study was to evaluate the stabilizing effects of two hybrid fixations that replace the end screws of a locked unicortical fixation with bicortical (locked or unlocked) screws and to compare these hybrid fixations to an unlocked bicortical fixation. METHODS: Sixteen composite radius sawbones were equally divided into 4 groups. We performed a midshaft osteotomy and plate fixation on the volar surface with 1 of 4 different constructs: 3 unlocked bicortical screws on each side (unlocked bicortical), 3 locked unicortical screws on each side (locked unicortical), or with 2 unicortical locked screws near the fracture and 1 bicortical unlocked (unlocked hybrid) or locked (locked hybrid) screw distant from the fracture on each end (LCP system, Synthes USA, Paoli, PA). Specimens were tested in nondestructive 4-point bending and torsion on a servo-hydraulic material testing system. The construct stiffness was obtained from the linear portion of the load-displacement curves after 3 cycles of preconditioning. The results from all groups were compared using analysis of variance and post hoc Bonferroni tests. RESULTS: Under torsional loads, replacing the end screws of a locked unicortical configuration with bicortical screws significantly improved the construct stiffness: 57.6% increase for the locked screws and 51.6% increase for the unlocked. In anteroposterior (AP) bending, the highest improvement over the locked unicortical configuration came from the locked hybrid constructs (42.9% increase). When compared with the unlocked bicortical configuration, both hybrid constructs provide equivalent stability in torsion but superior stability in AP bending. CONCLUSIONS: Replacing a single set of unicortical locked screws with locked or unlocked bicortical screws distant from the fracture site improves torsional stability of the construct by more than 50%, giving stability equal to standard unlocked plating. The hybrid fixation, however, with locked bicortical end screws has the best stability in AP bending.     

寰枢椎前路侧块螺钉内固定的生物力学测试

目的比较寰枢椎前路侧块螺钉和前路钛网、前路钢板内固定后颈椎标本的稳定性,分析不同前路内固定方法对寰枢椎各个方向运动的控制作用,为临床选择应用提供参考。方法 5具新鲜冷冻保存的尸体标本,快速分离出C0～T1节段,去除表面肌肉组织,放射测定,排除骨溶解、骨折及有其他病变的标本,以自凝型牙托粉包埋C2～7节段。包埋好的标本以特殊夹具固定于三思牌测力机上进行前屈、后伸和左右侧屈刚度的测试。旋转刚度在自制的测力机上测定。结果与正常组和损伤组相比,三种内固定方法均能明显提高寰枢椎各向活动的刚度,统计检验P<0.05;术式间的比较前路螺钉组的活动刚度明显高于前路钢板(各个方向P<0.05)和前路钛网(各个方向P<0.05);前路钢板的活动刚度明显高于前路钛网(各个方向P<0.05)。结论体外颈椎标本的生物力学实验表明,无论与正常组或损伤组相比前路双侧块螺钉、前路钢板和前路钛网内固定均能提高寰枢椎的稳定性,其中前路双侧块螺钉内固定提供的稳定性最强,与简单外固定配合使用可满足临床需要,当必须行寰枢椎前路内固定时应优先考虑使用。前路钢板和前路钛网单独使用稳定性较差,虽与后路内固定术式联用或改进设计可提高稳定性,但提高了并发症风险和经济负担。     

Biomechanical analysis of bicortical versus unicortical locked plating of mid-clavicular fractures

Objectives  

Operative fixation of displaced mid-shaft clavicle fractures has been shown to improve the functional outcomes and decrease the likelihood of non-union; however, little is known about the need for locking screws versus traditional screws. We, therefore, evaluated the strength of unicortical locked plating versus traditional bicortical non-locking fixation methods.     

A comparison of three screw types for unicortical fixation in the lateral mass of the cervical spine.

STUDY DESIGN: In vitro comparison of three different screws for unicortical fixation in lateral masses of the cervical spine. OBJECTIVES: To compare the axial load-to-failure of cervical lateral mass screws and their revision screws in a cadaveric model. SUMMARY OF BACKGROUND DATA: Lateral mass screws are used for posterior fixation of the cervical spine. Risks to neurovascular structures have led many surgeons to advocate unicortical application of these screws, although fixation strength may vary with screw design. METHODS: Screws from three posterior cervical fixation systems were used: Axis, Starlock/Cervifix, and Summit. Tested were 3.5-mm cancellous screws, along with revision screws for each system. The C3-C6 vertebrae from three cadaveric specimens were fixed with screws inserted into the lateral masses at a depth of 10 mm with 30 degrees cephalad and 20 degrees lateral angulation. Coaxial pullout force was recorded for each primary and revision screw. RESULTS: Axial load-to-failure (mean +/- SD) of the screws was 459 +/- 60 N for Axis screws, 423 +/- 78 N for Starlock screws, and 319 +/- 97 N for Summit screws. The Axis and Starlock screws were significantly stronger than Summit screws (P = 0.017 and P = 0.067, respectively). The load-to-failure of revision screws was much lower than that of primary screws (Axis 54%, Starlock 56%, Summit 63% of the primary screw), without significant difference between screw types. CONCLUSIONS: The Axis and Starlock screws resisted significantly greater axial load-to-failure than did the Summit screws. For all three systems, the revision screws could not restore the load-to-failure of the primary screw in this model. The tested unicortical screws had a consistently higher load-to-failure than those previously tested under similar conditions, suggesting that currently available screws may be superior to those previously tested.     

Fixation strength of unicortical versus bicortical C1–C2 transarticular screws

BACKGROUND CONTEXT: The internal carotid artery and hypoglossal nerve lie over the anterior aspect of the lateral mass of the atlas and are at risk from bicortical C1-C2 transarticular screws. This has led to the recommendation for unicortical screws if the neurovascular structures are in close proximity to the proposed exit point. No data are available on strength of unicortical versus bicortical C1-C2 transarticular screws. PURPOSE: To compare the biomechanical pullout strength of unicortical versus bicortical C1-C2 transarticular screws in a cadaveric model. STUDY DESIGN: Biomechanical study. METHODS: Fifteen cervical spine specimens underwent axial pullout testing. A unicortical C1-C2 transarticular screw was placed on one side with a contralateral bicortical screw. Data were analyzed to reveal any significant differences in strength. RESULTS: Mean pullout strength for the bicortical C1-C2 transarticular screws was 1,048.8 (+/-360.1) N versus 939.2 (+/-360.6) for unicortical screws (p=.22). There was no significant difference in the pullout strength of unicortical and bicortical screws. CONCLUSIONS: In cases with satisfactory bone quality, it appears reasonable to use unicortical screws to avoid the risk of neurovascular injury from penetrating the anterior cortex of C1.     

寰椎前弓双皮质螺钉固定相关解剖学测量

目的 :通过测量寰椎前弓双皮质螺钉固定相关解剖结构数据,为设计出更契合寰椎解剖结构的双皮质可调螺钉提供可靠的数据支持。方法:回顾性分析2017年4月～2018年8月门诊及住院部行上颈椎CT三维重建检查的就诊患者99例。其中男性54例,年龄31～81岁,平均56.67±10.56岁,身高159～180cm,平均172.24±4.95cm,体重55～90kg,平均70.24±7.57kg;女性45例,年龄46～77岁,平均59.84±8.29岁,身高154～171cm,平均163.11±5.24cm,体重40～80kg,平均59.31±8.48kg。通过三维测量软件,对前结节中点与齿状突后缘中点距离(前后距离)、双侧垂直钛板螺钉孔方向置钉长度(垂直长度)、双侧向齿状突后缘中点方向置钉长度(斜行长度)、双侧向齿状突后缘中点方向置钉尾端外倾角度(尾端外倾角度)和双侧置钉处前弓高度等进行测量。按照不同性别将患者分组,两组定量资料的比较采用t检验(方差齐)或Satterthwaite t′检验(方差不齐);左右侧比较采用配对t检验。年龄和各数值的相关性采用简单线性回归分析,身高、体重和各数值的关系采用Pearson相关系数和简单线性回归描述。结果:垂直长度、斜行长度、尾端外倾角度及置钉处前弓高度的左右侧数值差异均无统计学意义(P0.05)。男性前后距离、垂直长度、斜行长度、尾端外倾角度、置钉处前弓高度的均数分别为21.33±1.12mm、8.92±1.48mm、8.37±1.49mm、13.20°±0.93°、12.44±0.48mm;女性前后距离、垂直长度、斜行长度、尾端外倾角度、置钉处前弓高度的均数分别为20.01±1.33mm、8.18±1.56mm、7.67±1.58mm、13.88°±1.38°、12.08±0.75mm;男性患者垂直长度、斜行长度、前后距离及置钉处前弓高度大于女性患者,女性患者尾端外倾角度大于男性患者,有统计学意义(P0.05)。身高和垂直长度及斜行长度在不同性别组中均无相关性(P0.05)。Pearson相关分析显示,身高和尾端外倾角度在不同性别组中均呈负相关(r=-0.123,P0.05)。年龄和各数值的相关性没有统计学意义(P0.05)。结论:男性患者垂直长度、斜行长度、前后距离及置钉处前弓高度大于女性患者,女性患者尾端外倾角度大于男性患者。术者可根据患者性别,参考所得置钉参数选择合适的螺钉,从而提高了寰椎前弓置钉的准确率和安全性。     

Biomechanical evaluation of C1 lateral mass and C2 translaminar bicortical screws in atlantoaxial fixation: an in vitro human cadaveric study

Background Context

Atlantoaxial fixation with C1 lateral mass-C2 translaminar bicortical (C1LM-C2TB) screws has been reported to afford good stability with the least risk of injury to vertebral artery. However, no comparative in vitro studies have been conducted to evaluate the biomechanical stability of this method.

Freehand C1 lateral mass screw fixation technique: our experience

Background

Although C1 lateral mass fixation technique is frequently performed in upper cervical instabilities, it requires the guidance of fluoroscopic imaging. The fluoroscopy guidance is time-consuming and has the risks of accumulative radiation. Biplane fluoroscopy is also difficult in upper cervical pathologic conditions because of the use of cranial fixations. This study aimed to demonstrate that unicortical C1 lateral mass screws could be placed safely and rapidly without fluoroscopy guidance.

Methods

Between 2002 and 2008, 32 C1 lateral mass screws were inserted in 17 consecutive patients with various pathologic conditions involving either atlantoaxial or occipitocervical instability.

Results

C1 screw lengths ranged from 18 to 32 mm. The atlantoaxial fixation was performed in 13 patients, and C1 lateral mass screws were added to the occipitocervical construct in 3 patients, to the posterior cervical construct in 2 patients, and to the cervicothoracic construct in 1 patient. In 2 patients, because C1 lateral mass screws could not be inserted unilaterally, C1 pedicle screw analogs were inserted. There were no screw malpositions or neurovascular complications related to screw insertion. Operation time and intraoperative bleeding of the isolated atlantoaxial fixations were retrospectively evaluated. The mean follow-up was 32.3 months (range, 7-59 months). No screw loosening or construct failure was observed within this period. Postoperatively, 4 patients complained of hypoesthesia, whereas one patient had superficial wound infection.

Conclusion

C1 lateral mass screws may be used safely and rapidly in upper cervical instabilities without intraoperative fluoroscopy guidance and the use of the spinal navigation systems. Preoperative planning and determining the ideal screw insertion point, the ideal trajections, and the lengths of the screws are the most important points.     

Biomechanical evaluation of subcortical versus bicortical screw purchase in anterior cervical plating

Summary The purpose of this in vitro study is to compare the stabilities provided by anterior cervical H-plating with screws purchased either subcortically or bicortically on porcine cervical spines.Nine porcine cervical spines (C3–C4) were challenged by 12 Nm in extension followed by 6 Nm in flexion in 6 consecutive steps, i.e., (1) when disc was intact, (2) after discectomy. Subsequently, a tricortical bone graft was inserted to simulate interbody fusion. Each specimen was tested again (3) when plated with 16 mm screws to purchase subcortically and (4) after cyclic loading (f=0.5 Hz, n=1000), (5) when plated with 30 mm screws to purchase bicortically and (6) after cyclic loading. Neutral zone and range of motion were parameters normalized for comparison.The results showed comparable stability in constructs plated with screws purchased either subcortically or bicortically before cyclic loading. Cyclic loading deteriorated construct-bone relation in both groups, yet bicortically purchased screws rendered additional stability in anterior cervical plating.