枢椎棘突螺钉与椎弓根螺钉固定的生物力学拔出力比较

目的 比较枢椎棘突螺钉和椎弓根螺钉的生物力学拔出力强度.方法 取8具新鲜尸体枢椎标本(C2).于椎体两侧随机进行枢椎棘突螺钉和椎弓根螺钉固定,置入直径为4.0 mm的皮质骨螺钉.枢椎棘突螺钉进钉点选择为棘突的基底部、棘突及椎板的交界处,进钉角度为水平置钉,螺钉由对侧棘突基底部穿出,形成双层皮质固定;枢椎椎弓根螺钉在直视椎弓根下置钉.置钉后行拔出强度实验,比较2种螺钉的最大轴向拔出力强度.结果 枢椎棘突螺钉的平均拔出力强度为(387.56±137.73)N,稍小于枢椎椎弓根螺钉的平均拔出强度(465.25±214.32)N,差异无统计学意义(t=-0.862,P =0.403);枢椎棘突螺钉的平均钉道长度为(21.42±1.14) mm,稍短于枢椎椎弓根螺钉的(23.16±1.01) mm,差异有统计学意义(t=4.368,P ＜0.05). 结论 枢椎棘突螺钉具有椎弓根螺钉相近的生物力学拔出力强度,枢椎棘突螺钉在生物力学上具有应用可行性.     

两种长度的颈椎椎弓根螺钉与侧块螺钉拔出试验比较

目的:比较两种长度的颈椎椎弓根螺钉和侧块螺钉的抗拔出力,探讨颈椎经椎弓根短螺钉固定的可行性。方法:5具C3~C5共15节新鲜颈椎标本,用长度为28mm和20mm的皮质骨螺钉分别置入椎弓根,并用20mm的螺钉行侧块双皮质固定,螺钉进入侧块深度约14mm。行拔出试验,比较螺钉的最大轴向拔出力。结果:椎弓根长螺钉的最大拔出力为650N,椎弓根短螺钉为585N,两者比较无显著性差异(P>0.01);侧块螺钉的最大拔出力为360N,与椎弓根短螺钉比较有显著性差异(P<0.0001)。结论:颈椎椎弓根短螺钉固定可提供足够的稳定性,其安全性相对较高。     

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。     

寰椎侧块螺钉与寰椎椎弓根螺钉的解剖与生物力学对比研究

目的对寰椎侧块螺钉和寰椎椎弓根螺钉进行解剖和生物力学研究,为临床选择寰椎螺钉的固定方式提供依据。方法利用12例新鲜标本的寰椎进行单皮质和双皮质的椎弓根螺钉或侧块螺钉固定,测试比较其螺钉拔出强度和钉道长度。结果寰椎椎弓根螺钉的最大进钉长度为29·79mm±1·68mm,其中10·15mm在寰椎后弓内,19·65mm在寰椎侧块内。寰椎侧块螺钉的最大进钉长度为24·88mm±0·41mm,其进钉点与寰椎后弓后缘的平均距离为9·93mm±1·35mm。双皮质寰椎椎弓根螺钉的拔出力量最大,平均1757·0N±318·7N;单皮质寰椎椎弓根螺钉(1192·5N±172·6N)与双皮质寰椎侧块螺钉(1243·8N±350·0N)无明显差异,单皮质寰椎侧块螺钉最小(794·5N±314·8N)。结论在同时适用寰椎椎弓根螺钉和寰椎侧块螺钉固定的患者,宜首先选择寰椎椎弓根螺钉固定,次选寰椎侧块螺钉固定。     

颈椎椎间孔螺钉、椎弓根螺钉与侧块螺钉钉道的影像学测量比较

目的测量下颈椎椎间孔螺钉的钉道长度及角度参数,并与椎弓根螺钉和侧块螺钉进行比较。方法选取2018年1月至2018年6月连续进行健康查体的受检者,共50名(男25名,女25名)的颈椎CT影像资料,年龄(56.00±15.90)岁(范围:29～89岁)。对受检者的CT数据进行三维重建,依据椎间孔螺钉、椎弓根螺钉、侧块螺钉(Magerl法)置钉技术的进钉点和钉道设计在三维重建模型上选定后进行调整,在调整完毕的重建图像上分别对C3～C7节段进行钉道长度和进钉角度测量,记录其最大内倾角、最适内倾角、最小内倾角、最适钉道长度、椎弓根宽度等参数测量值。间隔2周由同1名脊柱外科医生对各影像学参数再次进行测量,取两次测量的平均值。结果颈椎椎间孔螺钉总体最适钉道长度和内倾角分别为C3 10.65 mm,21.12°;C4 10.12 mm,22.62°;C5 9.82 mm,23.66°;C6 9.19 mm,24.13°和C7 9.10 mm,27.54°。C3节段总体最适钉道长度最长;C7节段总体最适钉道长度最短(F=19.287,P <0.001),但与C6节段的差异无统计学意义(P=0.67...     

颈胸段脊柱侧块螺钉和椎弓根螺钉的抗拔强度的研究

目的　分析颈胸段脊柱后路不同置钉方法的拔出强度。方法　 5例新鲜尸体脊柱C6～T4椎骨 ,分解为单个椎体 30个 ,共 6 0个椎弓根。对其中的颈椎分为两组 ,分别为侧块螺钉固定组 (Roy -Camille法 ,Magerl法 ,Anderson法 ,自行设计侧块螺钉植入法 )和椎弓根螺钉固定组。将 6 0个椎弓根分组进行拔出测试 (5mm/min的速度垂直方向拔出 )。胸椎全部用椎弓根螺钉固定。结果　Roy-Camille法和Magerl法最大的拔出力接近 ,自行设计侧块螺钉植入法较Magerl法明显增加 ,而椎弓根螺钉抗拔出力最大。结论　选用侧块后正中线中下 1 / 3作为进针点 ,其抗拔出强度明显增加 ,钉道增加 ,操作简便 ;而颈胸椎椎弓根螺钉的拔出强度均大于侧块螺钉     

颈椎经关节椎弓根螺钉固定与标准椎弓根螺钉固定的生物力学比较

目的 比较颈椎经关节椎弓根螺钉固定和标准椎弓根螺钉固定的拔出强度.方法 取10具新鲜尸体颈椎标本(C_3～T_1),游离成三个颈椎运动节段(C_(3,4),C_(5,6),C_7T_1).在椎体两侧随机进行经关节椎弓根螺钉固定或标准椎弓根螺钉固定,置入直径3.5 mm皮质骨螺钉.经关节椎弓根螺钉固定以上位椎骨侧块外下象限中点为进钉点,在直视椎弓根下,螺钉在冠状面内倾约45°、矢状面尾倾约50°.由上位椎骨下关节突经关节突关节、下位椎骨的椎弓根,进入下位椎骨的椎体内.标准椎弓根螺钉固定以侧块外上象限中点为进钉点,在直视椎弓根下,螺钉方向参考CT测量结果 ,尽量与椎弓根倾斜角度保持一致,在横断面上内倾约45°、矢状面上螺钉指向椎体的上1/3.在生物力学试验机上行拔出强度试验,比较两种螺钉固定的最大轴向拔出力.结果 颈椎经关节椎弓根螺钉固定平均最大轴向拨出力为(694±42)N,标准椎弓根螺钉固定为(670±36)N,两者比较差异有统计学意义(P<0.05).结论 颈椎后路经关节椎弓根螺钉固定的拔出强度大干标准椎弓根螺钉固定,从生物力学强度方面考虑经关节椎弓根螺钉固定可以作为标准椎弓根螺钉固定的一种补充方法.     

枢椎后路3种螺钉固定技术生物力学测试的对比研究

目的：评价单皮质和双皮质枢椎椎弓根螺钉、枢椎侧块螺钉和枢椎椎板螺钉的固定强度,为临床选择后路螺钉的固定方式提供生物力学依据。方法：利用30具新鲜尸体枢椎标本,进行单皮质和双皮质的枢椎椎弓根螺钉、枢椎侧块螺钉、枢椎椎板螺钉固定,测试比较其螺钉拔出强度。结果：双皮质枢椎椎弓根螺钉的拔出力量最大,为（1255.8±381.9）N;单皮质枢椎椎弓根螺钉[（901.8±373.3）N]、双皮质枢椎侧块螺钉[（776.1±306.8）N]和双皮质枢椎椎板螺钉[（640.8±302.9）N]之间差异无统计学意义。结论：枢椎后路螺钉固定宜首选椎弓根螺钉,枢椎侧块螺钉和枢椎椎板螺钉可作为枢椎后路补充固定技术,且以双皮质骨固定为宜。     

上胸椎椎板螺钉的生物力学研究

 目的比较上胸椎椎板螺钉(translaminar screw.TLS)、椎板关节突螺钉(translaminar facet screw.TLFS)和椎弓根螺钉(transpedicle screw.TPS)固定的拔出强度。方法取 9具新鲜尸体上胸段(T1~T3)完整脊柱标本.双能 X线骨密度仪测量后.游离成 3个独立完整节段(T1、T2、T3).在椎体两侧随机进行 TPS、标准 TLS和 TLFS置入.螺钉直径均为 4.0 mm。分别进行旋入扭距和拔出试验.比较三种固定方式的最大轴向扭矩和拔出力。结果上胸椎 TPS的平均最大扭矩为(0.40±0.01) N.m.TLS的平均最大扭矩为(0.35±0.01) N.m.TLFS的平均最大扭矩为(0.43±0.01) N.m;TPS与 TLS间差异无统计学意义(t=1.94,P >0.05).TPS与 TLFS间差异无统计学意义(t=-1.28, P>0.05).TLFS与 TLS间差异有统计学意义(t=-13.86, P0.05). TPS与 TLFS间差异无统计学意义(t=0.924, P >0.05).TLFS与 TLS差异有统计学意义(t=9.907, P约 0.05)。螺钉的旋入最大扭矩与螺钉的拔出力呈正相关性。结论上胸椎椎板螺钉、椎板关节突螺钉与椎弓根螺钉固定拔出强度差异并不明显。椎板关节突螺钉固定的拔出强度明显大于椎板螺钉。椎板螺钉和椎板关节突螺钉固定可以作为椎弓根螺钉固定的一种补充方法。     

枢椎椎板螺钉与椎弓根螺钉抗拔出强度的比较

目的:比较枢椎椎板螺钉与枢椎椎弓根螺钉的抗拔出强度,为临床应用枢椎椎板螺钉固定提供生物力学依据。方法:在7具成年男性新鲜尸体枢椎标本上进行枢椎单皮质椎弓根螺钉和双皮质椎板螺钉固定,测试螺钉拔出力。结果:单皮质枢椎椎弓根螺钉的最大拔出力平均为875.3±403.2N,双皮质枢椎椎板螺钉的最大拔出力平均为679.5±308.2N;椎弓根螺钉的最大拔出力大于椎板螺钉,但二者之间无统计学差异。结论:枢椎椎板螺钉进行双皮质固定具有可靠的力学固定强度,可作为枢椎椎弓根螺钉的补充固定技术。     

Pullout strength of anterior spinal instrumentation: a product comparison of seven screws in calf vertebral bodies

A lot of new implant devices for spine surgery are coming onto the market, in which vertebral screws play a fundamental role. The new screws developed for surgery of spine deformities have to be compared to established systems. A biomechanical in vitro study was designed to assess the bone–screw interface fixation strength of seven different screws used for correction of scoliosis in spine surgery. The objectives of the current study were twofold: (1) to evaluate the initial strength at the bone–screw interface of newly developed vertebral screws (Universal Spine System II) compared to established systems (product comparison) and (2) to evaluate the influence of screw design, screw diameter, screw length and bone mineral density on pullout strength. Fifty-six calf vertebral bodies were instrumented with seven different screws (USS II anterior 8.0 mm, USS II posterior 6.2 mm, KASS 6.25 mm, USS II anterior 6.2 mm, USS II posterior 5.2 mm, USS 6.0 mm, USS 5.0 mm). Bone mineral density (BMD) was determined by quantitative computed tomography (QCT). Failure in axial pullout was tested using a displacement-controlled universal test machine. USS II anterior 8.0 mm showed higher pullout strength than all other screws. The difference constituted a tendency (P = 0.108) when compared to USS II posterior 6.2 mm (+19%) and was significant in comparison to the other screws (+30 to +55%, P < 0.002). USS II posterior 6.2 mm showed significantly higher pullout strength than USS 5.0 mm (+30%, P = 0.014). The other screws did not differ significantly in pullout strength. Pullout strength correlated significantly with BMD (P = 0.0015) and vertebral body width/screw length (P < 0.001). The newly developed screws for spine surgery (USS II) show higher pullout strength when compared to established systems. Screw design had no significant influence on pullout force in vertebral body screws, but outer diameter of the screw, screw length and BMD are good predictors of pullout resistance.     

Pullout strength of self-tapping screws inserted to different depths

OBJECTIVES: The purpose of this study was to determine whether the depth of insertion through the far cortex of self-tapping screws significantly affects pullout strength. DESIGN: Fifty, Synthes, 3.5-mm, self-tapping screws were inserted into synthetic bone blocks and divided into 5 groups. Group 1 had screws with their tips inserted 1 mm short of the far cortex. Group 2 had screws inserted flush with the far cortex. Groups 3, 4, and 5 had screws inserted 1 mm, 2 mm, and 3 mm past the far cortex respectively. Pullout strength was then tested. SETTING: Institutional research laboratory. MAIN OUTCOME MEASUREMENTS: Pullout strength (peak force) was measured for each group and analyzed using a single factor analysis of variance-balanced incomplete block design. RESULTS: Peak force values presented as mean +/- SD for the 5 groups were as follows: group 1 (1380 +/- 69 N), group 2 (1566 +/- 137 N), group 3 (1956 +/- 137 N), group 4 (2013 +/- 184 N), group 5 (2044 +/- 174 N). With a P < or = 0.05, it was found that groups I and II had statistically different pullout strengths than all other groups. However, there was no significant difference in pullout strength between groups 3, 4, and 5. CONCLUSIONS: Synthes self-tapping screws exhibit their highest pullout strength when inserted 1 mm past the far cortex, and there is no significant increase in pullout strength with deeper insertion depths.     

Pullout strength of misplaced pedicle screws in the thoracic and lumbar vertebrae - A cadaveric study

Background:

The objective of this cadaveric study was to analyze the effects of iatrogenic pedicle perforations from screw misplacement on the mean pullout strength of lower thoracic and lumbar pedicle screws. We also investigated the effect of bone mineral density (BMD), diameter of pedicle screws, and the region of spine on the pullout strength of pedicle screws.

Materials and Methods:

Sixty fresh human cadaveric vertebrae (D10–L2) were harvested. Dual-energy X-ray absorptiometry (DEXA) scan of vertebrae was done for BMD. Titanium pedicle screws of different diameters (5.2 and 6.2 mm) were inserted in the thoracic and lumbar segments after dividing the specimens into three groups: a) standard pedicle screw (no cortical perforation); b) screw with medial cortical perforation; and c) screw with lateral cortical perforation. Finally, pullout load of pedicle screws was recorded using INSTRON Universal Testing Machine.

Results:

Compared with standard placement, medially misplaced screws had 9.4% greater mean pullout strength and laterally misplaced screws had 47.3% lesser mean pullout strength. The pullout strength of the 6.2 mm pedicle screws was 33% greater than that of the 5.2 mm pedicle screws. The pullout load of pedicle screws in lumbar vertebra was 13.9% greater than that in the thoracic vertebra (P = 0.105), but it was not statistically significant. There was no significant difference between pullout loads of vertebra with different BMD (P = 0.901).

Conclusion:

The mean pullout strength was less with lateral misplaced pedicle screws while medial misplaced pedicle screw had more pullout strength. The pullout load of 6.2 mm screws was greater than that of 5.2 mm pedicle screws. No significant correlation was found between bone mineral densities and the pullout strength of vertebra. Similarly, the pullout load of screw placed in thoracic and lumbar vertebrae was not significantly different.     

Increasing bending strength and pullout strength in conical pedicle screws: biomechanical tests and finite element analyses

STUDY DESIGN: Comparative in vitro biomechanical study and finite element analysis. OBJECTIVES: To investigate the bending strength and pullout strength of conical pedicle screws, as compared with conventional cylindrical screws. SUMMARY OF BACKGROUND DATA: Transpedicle screw fixation, the gold standard of spinal fixation, is threatened by screw failure. Conical screws can resist screw breakage and loosening. However, biomechanical studies of bending strength have been lacking, and the results of pullout studies have varied widely. METHODS: Ten types of pedicle screws with different patterns of core tapering and core diameter were specially manufactured with good control of all other design factors. The stiffness, yielding strength, and fatigue life of the pedicle screws were assessed by cantilever bending tests using high-molecular-weight polyethylene. The pullout strength was assessed by pullout tests using polyurethane foam. Concurrently, 3-dimensional finite element models simulating these mechanical tests were created, and the results were correlated to those of the mechanical tests. RESULTS: In bending tests, conical screws had substantially higher stiffness, yielding strength, and fatigue life than cylindrical screws (P<0.01), especially when there was no step at the thread-shank junction. In pullout tests, pullout strength was higher in screws with a conical core and smaller core diameter and also in situations with higher foam density (P<0.01). In finite element analysis, the maximal deflection and maximal tensile stress were closely related to yielding strength (r=-0.91) and fatigue life (r=-0.95), respectively, in the bending analyses. The total reaction force was closely related to the pullout strength in pullout analyses (r=0.84 and 0.91 for different foam densities). CONCLUSIONS: Conical screws effectively increased the bending strength and pullout strength simultaneously. The finite element analyses reliably predicted the results of the mechanical tests.     

Stability of pedicle screws after kyphoplasty augmentation: an experimental study to compare transpedicular screw fixation in soft and cured kyphoplasty cement

OBJECTIVE: The goal of this cadaver study was to compare the stability of pedicle screws after implantation in soft or cured kyphoplasty cement. METHODS: Pedicle screws were inserted in a total of 30 thoracolumbar vertebrae of 10 different human specimens: 10 screws were implanted in nonaugmented vertebrae (group 1), each 10 screws were placed in soft (group 2) and cured (group 3) cement. Pedicle screws were than evaluated for biomechanical axial pullout resistance. RESULTS: Mean axial pullout strength was 232 N (range 60-600 N) in group 1, 452 N (range 60-1125 N) in group 2 and 367 N (range 112-840 N) in group 3. The paired Student t-test demonstrated a significant difference between pullout strength of groups 1 and 2 (P = 0.0300). Between pullout strength of groups 1 and 3 and between groups 2 and 3 no significant difference was seen. CONCLUSION: We achieved a 1.9 times higher pullout strength with kyphoplasty augmentation of osteoporotic vertebrae compared with the pullout strength of nonaugmented vertebrae. Implantation of pedicle screws in cured cement is a sufficient method. With this method we found a 1.6 times higher pullout strength then in nonaugmented vertebrae.     

Improving the pullout strength of pedicle screws by screw coupling

The objective of this study was to determine the effect of pedicle screw coupling on the pullout strength of pedicle screws in the osteoporotic spine. The vertebral bone mineral density (BMD) of 33 cadaveric lumbar vertebrae were measured by quantitative computed tomography. Pedicle screws were inserted into each pedicle. The pullout strength and displacement of the screws, without coupling and with single or double couplers, were studied, and the relationship between pullout strength and BMD was analyzed. The average pullout strength of the pedicle screws without screw coupling was 909.3 +/- 188.6 N (n = 9), that coupled with a single coupler was 1,409.0 +/- 469.1 N (n = 9), and that with double couplers was 1,494.0 +/- 691.6 N (n = 9). The pullout strength of the screws coupled with single or double couplers was significantly greater than that of screws without couplers (p < 0.01); however, there was no significant difference between the groups of single and double couplers. The improvement of pullout strength by screw coupling was significant in a test group with BMD of more than 90 mg/ml (p < 0.01), but was not in the group with BMD less than 90 mg/ml (p = 0.55). These results suggest that the coupling of pedicle screws improves pullout strength; however, the effect tends to be less significant in severely osteoporotic spines.     

Pullout strength of pedicle screws versus pedicle and laminar hooks in the thoracic spine

While the biomechanical properties of pedicle screws have proven to be superior in the lumbar spine, little is known concerning pullout strength of pedicle screws in comparison to hooks in the thoracic spine. In vitro biomechanical pullout testing was performed to evaluate the axial pullout strength of pedicle screws versus pedicle and laminar hooks in the thoracic spine with regard to surgical correction techniques in scoliosis. Nine human cadaveric thoracic spines were harvested and disarticulated. To simulate a typical posterior segmental scoliosis instrumentation, standard pedicle hooks were used between T4 and T8 and supralaminar hooks between T9 and T12 and tested against pedicle screws. The pedicle screws were loaded strictly longitudinal to their axis; the hooks were loaded perpendicular to the intended rod direction. In total, 90 pullout tests were performed. Average pullout strength of the pedicle screws was significantly higher than in the hook group (T4-T8: 531 N versus 321 N, T9-T12: 807 N versus 600 N, p < 0.05). Both screw diameter and the bone mineral density (BMD) had significant influence on the pullout strength in the screw group. For scoliosis correction, pedicle screws might be beneficial, especially for rigid thoracic curves, since they are significantly more resistant to axial pullout than both pedicle and laminar hooks.     

Biomechanical comparison of pedicle screws versus spinous process screws in C2 vertebra: A cadaveric study

Background:

Biomechanical studies have shown C2 pedicle screw to be the most robust in insertional torque and pullout strength. However, C2 pedicle screw placement is still technically challenging. Smaller C2 pedicles or medial localization of the vertebral artery may preclude safe C2 pedicle screw placement in some patients. The purpose of this study was to compare the pullout strength of spinous process screws with pedicle screws in the C2.

Materials and Methods:

Eight fresh human cadaveric cervical spine specimens (C2) were harvested and subsequently frozen to −20°C. After being thawed to room temperature, each specimen was debrided of remaining soft tissue and labeled. A customs jig as used to clamp each specimen for screw insertion firmly. Screws were inserted into the vertebral body pairs on each side using one of two methods. The pedicle screws were inserted in usual manner as in previous biomechanical studies. The starting point for spinous process screw insertion was located at the junction of the lamina and the spinous process and the direction of the screw was about 0° caudally in the sagittal plane and about 0° medially in the axial plane. Each vertebrae was held in a customs jig, which was attached to material testing machine (Material Testing System Inc., Changchun, China). A coupling device that fit around the head of the screw was used to pull out each screw at a loading rate of 2 mm/min. The uniaxial load to failure was recorded in Newton''st dependent test (for paired samples) was used to test for significance.

Results:

The mean load to failure was 387 N for the special protection scheme and 465 N for the protection scheme without significant difference (t = −0.862, P = 0.403). In all but three instances (38%), the spinous process pullout values exceeded the values for the pedicle screws. The working distances for the spinous process screws was little shorter than pedicle screws in each C2 specimen.

Conclusion:

Spinous process screws provide comparable pullout strength to pedicle screws of the C2. Spinous process screws may provide an alternative to pedicle screws fixation, especially with unusual anatomy or stripped screws.