海绵质骨螺旋钉拔出试验之生物力学分析

评估螺旋钉设计优劣的简便方法之一为拔出试验。虽然比较用之海绵质骨试件可取自相同部位，自同一方向植入螺旋钉，并具有相同基准。然而因各处海绵质骨骼结构不尽相同，至今尚未有人探讨如使用不同之海绵质骨结构，例如近似等向性之杆状结构，或是板与杆组合之有强列方向排列者，对于螺旋钉拔出之最大力量有多大影响？采用牛股骨远端部位及牛颈椎Ｃ２～Ｃ６作为不同结构特性之试体。并各由两相互垂直之方向旋入螺旋钉，来做拔出试验。最后并建立一三维有限元素模型，用以研究螺纹周围之变形模式及其预测拔出最大力量的准确性。模型分析中以应变能密度准则作为破坏之参考标准。     

Tensile Behavior of High-Strength,Strain-Hardening Cement-Based Composites (HS-SHCC) Reinforced with Continuous Textile Made of Ultra-High-Molecular-Weight Polyethylene

The paper at hand presents an investigation of the tensile behavior of high-strength, strain-hardening cement-based composites (HS-SHCC), reinforced with a single layer of continuous, two-dimensional textile made of ultra-high molecular weight polyethylene (UHMWPE). Uniaxial tension tests were performed on the bare UHMWPE textiles, on plain HS-SHCC, and on the hybrid fiber-reinforced composites. The bond properties between the textile yarns and the surrounding composite were investigated in single-yarn pullout experiments. In order to assess the influence of bond strength between the yarn and HS-SHCC on the tensile behavior of the composites with hybrid fiber reinforcement, the textile samples were analyzed both with, and without, an additional coating of epoxy resin and sand. Compared to the composites reinforced with carbon yarns in previous studies by the authors, the high elongation capacity of the UHMWPE textile established the higher strain capacity of the hybrid fiber-reinforced composites, and showed superior energy absorption capacity up to failure. The UHMWPE textile limited the average crack width in comparison with that of plain HS-SHCC, but led to slightly larger crack widths when compared to equivalent composites reinforced with carbon textile, the reason for which was traced back to the lower Young’s modulus and the higher elongation capacity of the polymer textile.     

Biological Safety Evaluation and Surface Modification of Biocompatible Ti–15Zr–4Nb Alloy

We performed biological safety evaluation tests of three Ti–Zr alloys under accelerated extraction condition. We also conducted histopathological analysis of long-term implantation of pure V, Al, Ni, Zr, Nb, and Ta metals as well as Ni–Ti and high-V-containing Ti–15V–3Al–3Sn alloys in rats. The effect of the dental implant (screw) shape on morphometrical parameters was investigated using rabbits. Moreover, we examined the maximum pullout properties of grit-blasted Ti–Zr alloys after their implantation in rabbits. The biological safety evaluation tests of three Ti–Zr alloys (Ti–15Zr–4Nb, Ti–15Zr–4Nb–1Ta, and Ti–15Zr–4Nb–4Ta) showed no adverse (negative) effects of either normal or accelerated extraction. No bone was formed around the pure V and Ni implants. The Al, Zr, Nb, and Ni–Ti implants were surrounded by new bone. The new bone formed around Ti–Ni and high-V-containing Ti alloys tended to be thinner than that formed around Ti–Zr and Ti–6Al–4V alloys. The rate of bone formation on the threaded portion in the Ti–15Zr–4Nb–4Ta dental implant was the same as that on a smooth surface. The maximum pullout loads of the grit- and shot-blasted Ti–Zr alloys increased linearly with implantation period in rabbits. The pullout load of grit-blasted Ti–Zr alloy rods was higher than that of shot-blasted ones. The surface roughness (Ra) and area ratio of residual Al₂O₃ particles of the Ti–15Zr–4Nb alloy surface grit-blasted with Al₂O₃ particles were the same as those of the grit-blasted Alloclassic stem surface. It was clarified that the grit-blasted Ti–15Zr–4Nb alloy could be used for artificial hip joint stems.     

Locking plates for displaced fractures of the lateral end of clavicle: Potential pitfalls

Roughly a quarter of all clavicle fractures occur at the lateral end. Displaced fractures of the lateral clavicle have a higher rate of nonunion. The management of fractures of the lateral clavicle remains controversial. Open reduction internal fixation with a superiorly placed locking plate is a recently developed technique. However, there are no randomized controlled trials to evaluate the efficacy of this procedure. We present a series of four cases which highlight the technical drawbacks with this method of fixation for lateral clavicle fractures. Two cases show that failure of the plate to negate the displacing forces at the fracture site can lead to plate pullout. Two cases illustrate an unusual complication of an iatrogenic injury to the acromioclavicular joint capsule which led to joint instability and dislocation. We advise caution in using this method of fixation. Recent studies have described the success of lateral clavicle locking plate fixation augmented with a coracoclavicular sling. This augmentation accounts for the displacing forces at the fracture site. We would recommend that when performing lateral clavicle locking plate fixation, it should be reinforced with a coracoclavicular sling to prevent plate failure by lateral screw pullout.     

三种不同长度全螺纹松质骨螺钉最大轴向拔出强度的测试

目的探讨螺钉长度对全螺纹松质骨螺钉轴向最大拔出强度（Axial maximum pullout strength）的影响。方法分三种螺钉长度组，每组八个螺钉，总共24个全螺纹松质骨螺钉。三具福尔马林液防腐固定尸体脊柱段标本（T10-L5），并行X-线（X-rays）检查和应用美国Norland公司的XR-36型双能X线吸收骨密度仪[Dual-energy X-rays absorptiometry bone（DEXA）densitometer]测试椎体骨密度（BMD）。根据骨密度值选出12个椎体，并根据骨密度分成四个骨密度段。在每个骨密度段内，每个椎体中随机植入2个不同长度的螺钉固定在材料实验机（Material testing system machine）上分别进行轴向拔出强度的测试。结果A组（18mm）和B（20mm）组的拔出强度之间无显著性差异（P=0．407），B组（20mm）和C组（24mm）的拔出强度之间无显著性差异（P=0．092），A组（18mm）和C组（24mm）的拔出强度之间有显著性差异（P＜0．05）。结论本实验数据分析24mm长的全螺纹松质骨螺钉比18mm长的螺钉具有更强的握持力（Holding power）。螺钉轴向最大拔出强度与螺钉长度明显相关，在临床中，为提高螺钉的最大拔出强度尽可能应用长的螺钉。     

Experimental analysis of screw hold as judged by operators v pullout strength

An analysis of the accuracy of the operators' assessments of the hold of bone screws is reported. These assessments of screw hold were compared with measurements from pullout testing. Four operators, encompassing a range of experiences in terms of screw insertion, prepared the pilot holes, and inserted a number of screws, assigning each with a score from 0 to 10 on the basis of how good the hold was felt to be. The pullout strength for each screw was then measured using a tensometer. The results were analysed and correlation coefficients calculated. Significant correlation was observed in all four subjects, with P < 0.001 in two out of the four subjects, and 0.01 > P > 0.001 in the other two. The conclusions were that there is a strong correlation between the subjective assessment of screw hold and actual pullout strength within the four subjects analysed.     

经肋横突结合区入路生物力学研究

目的 测量肋横突结合区螺钉的生物力学特性并与椎弓根螺钉的进行比较.方法 取3具冷冻成人胸椎标本,在椎体的一侧按常规方法置入椎弓根螺钉,对侧经肋横突结合区置入螺钉,然后测量每颗螺钉的最大拔出力.结果 测量了57枚螺钉的最大轴向拔出力,其中肋横突结合区螺钉30枚,椎弓根螺钉27枚.肋横突结合区螺钉平均最大轴向拔出力为(805.99±169.3)N,椎弓根螺钉平均最大轴向拔出力为(808.40±183.5)N,两者之间差异无显著性.结论 肋横突结合区螺钉足以为脊柱提供坚强的固定.     

Impact of bone quality on the performance of integrated fixation cage screws

Background Context

Commercially available lumbar integrated fixation cages (IFCs) have variable designs. For example, screw-based designs have up to four screws inserted at different locations across the vertebral end plate as well as at different angles in the sagittal and transverse planes. This is important as end plate and trabecular bone quality may vary across the vertebra and may affect the screw's fixation ability, particularly if bone purchase at the bone-screw interface is poor.

Screw orientation and plate type (variable- vs. fixed-angle) effect strength of fixation for in vitro biomechanical testing of the Synthes CSLP

BACKGROUND CONTEXT: Two common justifications for orienting cervical screws in an angled direction are to increase pullout strength and to allow use of longer screws. This concept is widely taught and has guided implant design. Fixed- versus variable-angle systems may offer strength advantages. Despite these teachings, there is a paucity of supporting biomechanical evidence. The purpose of our study is to test the influence of screw orientation and plate design on the maximum screw pullout force. PURPOSE: This study evaluates the effect of screw orientation and plate type (fixed- vs. variable-angle) on screw pullout strength. STUDY DESIGN: Anterior cervical plates of both a fixed- and variable-angle CSLP, were tested for peak pullout strength in a direct plate pullout model using polyurethane foam bone, which models osteoporotic bone. METHODS: Self-tapping, locking screws (4.0x14mm and 4.0x16mm) were used. Screws were oriented in the fixed-angle plate in the standard fashion. In the variable plate, screws were instrumented in three different orientations. Biomechanical testing was performed on an Instron DynaMight 8841 servohydraulic testing machine, measuring maximum pullout force under a displacement-controlled pullout rate of 1mm/min. Five samples were tested per group. RESULTS: When all screws were placed 90 degrees to the plate, there was a significantly increased peak pullout strength (412.8+/-22.2N) compared with when all screws were placed 12 degrees "up and in" (376.2+/-24.3N, p less than or equal to .03). When the 90 degrees construct was reproduced using 14-mm screws and compared with 16-mm screws oriented 12 degrees "all up and in," there was still significantly higher pullout strength with the all 90 degrees construct (434.2+/-28.7N vs. 376.2+/-24.3N, p less than or equal to .009). The fixed-angle plate had a significantly decreased peak pullout strength (288.2+/-15.7N) compared with the variable-angle plate (416.6+/-12.6N) (p less than .00001) when the screws were placed in the same orientation. Overall, the variable-angle plate, regardless of the orientation of screws, had a significantly greater pullout strength than the fixed-angle plate (p less than .001). CONCLUSIONS: In this system, a variable-angle plate has greater pullout strength than a fixed-angle plate, regardless of the orientation of screws. With the variable-angle plate, a construct of all screws 12 degrees "up and in" is the weakest configuration. We found that with the 90 degrees construct, both 16- and 14-mm screws performed significantly better than 16-mm convergent screws. These findings are remarkable because they contradict the current doctrine. This may be a function of plate-dependent factors and should not be applied universally to all plate systems. Further study of screw orientation in additional plating systems is warranted.     

Comparison of pullout strength of small-diameter cannulated and solid-core screws

The purpose of this study was to determine the difference in pullout strength between cannulated and solid-core small-diameter bone screws. Cannulated screws from different manufacturers were compared against solid-core screws with 2.0-mm, 2.4-/2.5-mm, and 3.0-mm diameters. A synthetic material made to simulate bicortical bone was used as the test medium. The screws were extracted under servohydraulic control. There was no statistically significant difference between any of the cannulated and solid-core 2.0-mm screws used in this study (P < .05). In the 2.4-/2.5-mm screw tests, both of the cannulated screw designs had a significantly higher pullout strength when compared with the solid-core screw (P < .05). In the testing of 3.0-mm screw test, 1 of the cannulated screw designs showed a significantly higher pullout strength than the other cannulated and solid-core screws that were tested (P < .05). The results of this study suggest that small-diameter cannulated bone screws are similar in mechanical pullout strength to solid-core screws.