经口寰枢椎单侧与双侧侧块螺钉内固定的有限元分析

目的采用有限元分析方法比较经口寰枢椎单侧与双侧侧块螺钉内固定的生物力学特性。方法选取1名健康成年男性志愿者进行颈椎CT扫描,获取数据建立正常模型,并置入单侧钛合金螺钉建立单钛钉模型,置入双侧钛合金螺钉建立双钛钉模型,比较3种模型在1、5、10 N·m扭矩下受到的Mises应力与位移情况。结果在10 N·m扭矩下各个模型Mises应力与位移最大,单钛钉模型中单钛合金螺钉Mises应力2 000.3 MPa,位移2.29 mm,寰枢柱其他部位Mises应力754.7 Mpa;双钛钉模型中双钛合金螺钉Mises应力699.1 MPa,位移0.79 mm,寰枢柱其他部位Mises应力211.1 Mpa;正常模型寰枢柱其他部位Mises应力104.4 Mpa。双钛钉模型10 N·m扭矩下应力及位移云图与正常模型相似度更高。结论经口寰枢椎双侧侧块螺钉内固定稳定性好,能最大程度地保留颈椎活动度。     

异体皮质骨板联合不同螺钉治疗股骨干骨折生物力学研究

目的测量和探究异体皮质骨板联合可吸收螺钉加捆绑带固定治疗股骨干骨折的力学强度及机制。方法采用新鲜山羊股骨为材料,X线排除骨病后,制作接骨板及骨折模型。分别用可吸收螺钉加捆绑带(A组)、钛合金螺钉(B组)、钛合金螺钉加捆绑带(C组)、可吸收螺钉(D组)4种固定方式固定骨板。使用万能电子力学实验机进行垂直压缩实验、骨板侧及非骨板侧三点弯曲实验,记录模型极限载荷结果。结果 A组垂直压缩及三点弯曲极限载荷与C组接近(P0.05),且高于B、D两组(P0.05)。A组的垂直压缩、骨板侧三点弯曲和非骨板侧三点弯曲极限载荷分别为(1.51±0.33)k N、(0.80±0.31)k N、(0.82±0.11)k N;C组分别为(1.67±0.28)k N、(0.97±0.19)k N、(0.98±0.16)k N;B组(1.47±0.31)k N、(0.73±0.27)k N、(0.73±0.23)k N;D组为(1.13±0.23)k N、(0.70±0.21)k N、(0.75±0.18)k N。结论异体皮质骨板联合可吸收螺钉及捆绑带可满足山羊股骨骨折术后即刻固定强度;在骨折模型中可吸收螺钉可承受与钛合金螺钉接近的极限载荷;增加捆绑带可以提高整个骨折固定强度。     

基于有限单元法的股骨干粉碎性骨折锁定板内固定优化仿真

目的研究粉碎性股骨干骨折采用锁定板内固定时选择不同螺钉位置固定情况下锁定板及螺钉最大应力情况。方法通过64层螺旋CT扫描采集27名健康志愿者左侧股骨数据并导入Mimics软件,建立骨骼3D模型并依据CT值为股骨赋材料属性。用三坐标测量仪扫描锁定板,并将生成的点云文件导入Geomagic Studio生成光顺曲面及实体文件;将股骨及锁定板文件导入有限元分析软件Abaqus进行装配,施加压力和扭矩载荷,并对锁定板及螺钉的应力分布进行求解。结果对于粉碎性股骨干骨折,在压力和力矩载荷作用下,不同螺钉位置组合时的锁定板及螺钉上应力峰值均出现在最内侧螺钉处,即最靠近骨折线处;并且随着最内侧固定螺钉外移,锁定板及螺钉上分布的应力峰值均逐渐增大。结论对于粉碎性股骨干骨折锁定板内固定,使用较多的螺钉固定可使螺钉及锁定板上的应力峰值减小,同时最内侧螺钉尽量靠近骨折端。     

肱骨内植物材料选择及预紧力影响的参数化研究

背景：目前,关于肱骨及接骨板的生物力学研究较多,但甚少将两者组合为一个骨折固定模型并将材料及预紧力作为参数进行研究。〈br〉 目的：通过带接骨板的肱骨骨折有限元模型的生物力学仿真,比较不同接骨板和螺钉材料、预紧力对举重过程中接骨板及螺钉失效可能性的影响,以及对骨折应力遮挡效率的影响。〈br〉 方法：利用肱骨点云数据和接骨板及螺钉几何数据进行装配,得到带接骨板的肱骨骨折有限元模型,将举重动作逆向动力学仿真得到的关节力和肌肉力作为有限元仿真的载荷边界条件。采用相同的有限元模型进行参数化研究,比较不同接骨板和螺钉材料及预紧力对接骨板、螺钉、骨折缝及其周围肱骨应力变化的影响。〈br〉 结果：相同预紧力下,采用不锈钢材料接骨板和螺钉的应力大于钛合金和钛材料,即采用不锈钢材料接骨板和螺钉失效的危险性大于钛合金和钛材料;采用不锈钢材料时肱骨的应力遮挡率大于钛合金和钛材料;采用相同材料时,增加预紧力会导致接骨板和螺钉的应力增加,但会减小肱骨的应力遮挡率。〈br〉 结论：接骨板和螺钉的材料属性及预紧力大小等因素均对接骨板、螺钉以及骨的应力分布有一定影响。本文建立的分析方法同样适用于其它部位骨折固定的应力分析。     

低弹性模量接骨板固定股骨干骨折的有限元分析

目的 探讨不同弹性模量接骨板内固定对股骨干骨折应力及其分布的影响. 方法采用64排螺旋CT对一名健康成年男性股骨进行层厚为0.5 mm的扫描,获得股骨CT数据,再通过软件三维反求得到股骨有限元模型.模拟股骨中段骨折模型,分别采用Ti-6Al-4V(高弹性模量组,弹性模量为110 GPa)和Ti2448(低弹性模量组,弹性模量为30 GPa)两种材料的8孔接骨板进行固定.分析两种不同弹性模量接骨板内固定在轴向压缩、四点前后弯曲和扭转载荷下股骨的应力分布情况,并以应力云图的方式直观地显示应力分布规律. 结果在3种载荷下,两组均在断端接触部位出现最大应力.在轴向压缩载荷下,低弹性模量组最大应力值为30.00 MPa,大于高弹性模量组(21.68 MPa);螺孔内最大应力值(11.47 MPa)小于高弹性模量组(13.89 MPa),应力云图显示:高弹性模量组骨组织呈多个应力梯度分布,而低弹性模量组骨组织应力分布较均匀.在四点前后弯曲载荷下,低弹性模量组最大应力值为11.23 MPa,大于高弹性模量组(7.96 MPa).在扭转载荷下,两组股骨应力分布均较均匀,低弹性模量组最大应力值(63.82 MPa)大于高弹性模量组(43.97 MPa),螺孔内最大应力值(11.47MPa)小于高弹性模量组(31.24 MPa). 结论低弹性模量接骨板内固定股骨干骨折,其骨折断端应力刺激增大,螺孔内应力集中减轻,接骨板的应力遮挡效应减小.     

镁合金中空螺钉固定治疗ⅡA型齿状突骨折的三维有限元分析

目的:建立正常枢椎及中空螺钉固定ⅡA型齿状突骨折的三维有限元模型,分析镁合金螺钉固定ⅡA型齿状突骨折的稳定性.方法:通过CT扫描l例正常成年男性志愿者颈椎获取枢椎的空间结构信息,导入三维重建软件Mimics 10.01、Solidworks 2010,建立正常枢椎及中空螺钉固定ⅡA型齿状突骨折的三维有限元模型.在有限元软件Ansys 13.0中分析正常枢椎模型、ⅡA型齿状突骨折中空螺钉(镁合金螺钉、钛合金螺钉)固定模型,分别模拟颈椎后伸、前屈时受到水平载荷50N、100N、150N、200N的作用力及颈椎旋转时分别受到50N· mm、100N· mm、150N· mm、300N· mm扭矩时,测量齿状突的最大位移与最大应力、枢椎椎体的最大应力及螺钉的最大应力.钛合金螺钉弹性模量为108000MPa,屈服强度为930MPa;镁合金螺钉弹性模量为45000MPa,屈服强度为193MPa.结果:所建正常枢椎及ⅡA型齿状突骨折中空螺钉固定有限元模型外形逼真,几何相似性好.颈部前屈、后伸、旋转三种活动状态下,受到不同载荷时镁合金螺钉的最大应力均小于钛合金螺钉,两种螺钉的最大应力均小于其屈服强度;两种材料中空螺钉固定的ⅡA型齿状突骨折模型中齿状突、枢椎椎体的最大应力均小于皮质骨应力阀值(200MPa),齿状突的最大位移是正常枢椎齿状突最大位移的5～8倍,均小于1 mm(有限元模型中网格大小为1mm).结论:应用CT扫描获取枢椎空间结构信息建立的枢椎三维有限元模型可用于生物力学实验,镁合金中空螺钉在固定ⅡA型齿状突骨折时足以维持其稳定性.     

可灌注骨水泥椎弓根螺钉的生物力学研究

目的 探讨可灌注骨水泥椎弓根螺钉(novel perfusional pedicle screw,NPPS)在骨质疏松椎体内的生物力学稳定性.方法 选取平均年龄73岁的完整湿润脊柱标本(T11～L5)6具,共42个椎体,平均骨密度为(0.696±0.14)g/cm2.所有椎体均任取一侧椎弓根置入可灌注螺钉后,使用配套的骨水泥推杆和灌注筒向椎体内灌注骨水泥2ml,对侧椎弓根置入常规螺钉,作为对照组.随机选取3个椎体,剖开椎体观察骨水泥分布情况.余39个椎体随机分成3组,每组13个,分别行最大轴向拔出力、最大旋出力矩、周期抗屈试验.另取10个可灌注螺钉和10个对照组螺钉行三点弯曲实验.结果 所有椎体均没有观察到骨水泥渗漏.可灌注螺钉的最大轴向拔出力为(760±178)N,对照组为(355±87)N;可灌注螺钉的最大旋出力矩为(1.347±0.377)N·m,对照组为(0.488±0.205)N·m.4枚(4/13,占30.8%)可灌注螺钉发生松动,其平均载荷为(150±46)N;未松动的螺钉中,松动位移半均(0.661±0.289)mm,对照组中所有的螺钉在最大负荷介于50～200 N时开始松动(位移>2.000 mm),平均载荷(104±35)N.可灌注螺钉的平均极限弯曲载荷为(3082±144)N,对照组螺钉为(3357±263)N.结论 可灌注椎弓根螺钉,结合骨水泥推杆和灌注筒能有效控制骨水泥渗漏,明显增强椎弓根螺钉在骨质疏松椎体内的稳定性.     

具有可扩张翼的动力髋螺钉固定股骨转子间骨折的三维有限元分析

目的运用三维有限元法探讨具有可扩张翼的动力髋螺钉固定股骨转子间骨折的生物力学稳定性。方法基于正常成人股骨及动力髋螺钉的CT扫描数据,利用Mimics 13.0、Freeform、Ansys 14.0软件建立具有可扩张翼的动力髋螺钉和普通动力髋螺钉固定的股骨转子间骨折有限元模型;运用有限元分析软件Ansys 14.0,模拟70 kg正常人缓慢行走单腿站立状态的轴向压缩试验及在股骨近端加载一定扭转力矩的扭转实验,比较两组内固定和股骨的应力分布情况,分析两种内固定的生物力学稳定性。结果在轴向压缩试验中,两种骨折内固定模型应力分布情况相似,两组股骨模型的总体应力分布较均匀,两组内固定模型在拉力螺钉与侧方钢板套筒连接部位可见应力集中;在扭转试验中,具有可扩张翼的动力髋螺钉固定的股骨转子间骨折有限元模型可抵抗25 N·m以上、50 N·m以下的扭矩,而普通动力髋螺钉固定的股骨转子间骨折有限元模型只能抵抗5 N·m以上、10 N·m以下的扭矩。结论具有可扩张翼的动力髋螺钉固定股骨转子间骨折的生物力学稳定性较普通动力髋螺钉更具优势。     

表面置换和全髋关节置换股骨近段应力遮挡的比较

目的试图验证表面置换术能否有效避免类似于全髋关节置换术所出现的股骨侧应力遮挡并发症。方法采集8具青年正常新鲜髋关节标本,选择静止单腿站立的股骨头受力模型。依次测16根正常股骨在1000N载荷下股骨头表面置换前、后的应力值,以及全髋关节假体置换后的应力值,根据公式η=(1-δ全板/δ未板)×100%(η为应力遮挡率),计算两种不同假体在各点的应力遮挡率。结果全髋关节置换后的股骨张力侧(外侧)应力遮挡率在15%~17%之间变化。压力侧应力遮挡率在30%~34%之间变化。表面置换后的股骨颈应力遮挡最大为3%~5%,股骨近段和中部应力遮挡为0·1%~0·6%。结论表面置换能有效维持近段股骨的正常应力传递,能有效避免类似于全髋关节置换后的股骨近段应力遮挡性骨吸收,从而能有效保留近段股骨的骨量,为日后翻修提供良好条件。     

腰椎单侧椎弓根螺钉固定的三维有限元分析

目的:建立人正常L3～L5节段三维有限元模型,分析腰椎单侧椎弓根螺钉固定融合的生物力学特性.方法:基于人正常L3～L5节段的CT扫描数据,利用Geomagic Studio 9.0、Simpleware 2.0、Abaqus 6.7软件建立人正常L3～L5三维有限元模型(INT),并在此基础上分别建立L4/5单侧椎弓根螺钉内固定加后外侧植骨融合模型(M1)、单侧椎弓根螺钉内固定加单枚融合器置入模型(M2)及双侧椎弓根螺钉内固定加单枚融合器置入模型(M3).在L3上表面施加500N预载荷,再施加10N·m的力矩模拟腰椎前屈、后伸、侧屈及旋转等生理活动,观察不同工况下L4-L5节段角位移、椎弓根螺钉及融合器应力分布情况.结果:各工况下M1、M2、M3角位移均较INT减少,M3减少最明显;除右屈和后伸外,其他工况下M2与M3的角位移减少程度相当,而M1在左、右侧屈及左、右旋转时稳定性较差.M1的螺钉应力峰值明显高于M2和M3,尤以左屈及后伸载荷时螺钉应力峰值最大,M2螺钉应力峰值高于M3.M2椎间融合器的应力峰值在各种工况下均高于M3.结论:单侧椎弓根螺钉固定不能很好地控制侧屈和旋转载荷,椎弓根螺钉承受较大的应力;附加单枚融合器置入可以重建融合节段的稳定性,明显减少螺钉的应力.     

抗滑动钢板治疗Letenneur Ⅰ型Hoffa骨折的生物力学研究

目的 通过对Letenneur Ⅰ型Hoffa骨折使用抗滑动钢板(使用锁定螺钉和松质骨螺钉两组)与松质骨螺钉(由前向后和由后向前固定两组)四种固定方式固定Letenneur Ⅰ型Hoffa骨折的力学进行比较,探讨抗滑动钢板在Hoffa骨折中的应用.方法 20个模型股骨造成相同的Letenneur Ⅰ型Hoffa骨折,随机分为四组,每组5个.A组使用由前向后两枚松质骨螺钉固定,B组使用由后向前两枚松质骨螺钉固定,C组使用抗滑动钢板加锁定螺钉固定,D组使用抗滑动钢板加松质骨螺钉固定.所有标本通过循环负荷试验和最大失效负荷试验,对最大位移平均值和最大失效负荷平均值进行比较.结果 在循环负荷试验中,第10、100、1000、10 000周期下,四组骨折块最大位移平均值间差异均无统计学意义(P>0.05).而在最大失效负荷试验中,A组[(1224±72)N]和C[(2183±227)N]、D组[(2124±235)N]差异有统计学意义(P<0.05),B组[(1405±235)N]和C、D组差异有统计学意义(P<0.05),A组和B组、c组和D组差异均无统计学意义(P>0.05). 结论对于简单的Hoffa骨折,固定后初期给予适当保护条件,四种固定方式都能取得满意的力学稳定性和强度.但对于预计骨折愈合时间长、体质量指数大、患者依从性差的患者,建议使用抗滑动钢板.     

Comparison of metacarpal plating methods

PURPOSE: Most metacarpal fractures are stable and can be treated with nonsurgical stabilization. However, some metacarpal fractures are treated with open reduction and internal fixation because of an open fracture, instability, or multiple fractures. Newer plate designs have emerged that allow a shorter plate and screw construct. We sought to determine the relative strength of 3 different methods of metacarpal plating for unstable fractures. METHODS: We tested our hypothesis in a transverse metacarpal fracture model using fourth-generation, biomechanical testing grade composite sawbones (Sawbones; Pacific Research Laboratories, Vashon, WA). The metacarpals were divided into 3 groups of 15 bones. Group 1 was plated with a standard 6-hole, 2.3-mm plate with 6 nonlocking bicortical screws in standard AO fashion. Group 2 was plated with a 6-hole, double-row, 3-dimensional (3D) plate with 3 nonlocking screws on either side of the fracture aiming for convergence of the screws. Group 3 was plated with a 2.4-mm plate using 6 nonlocking screws and standard AO technique. The metacarpals were then tested to failure in cantilever bending mode. RESULTS: All constructs broke through the bone. No plate failure or screw pullout was seen. Group 1 had a load to failure of 264 N +/- 14. Group 2 had a load to failure of 302 N +/- 17. Group 3 had a load to failure of 274 N +/- 20. The load to failure was highest in group 2 (3D plate). All differences were statistically significant. CONCLUSIONS: All 3 methods produced a strong construct. The load to failure was highest in group 2 (3D plate). Double-row plates with converging screws provide adequate or superior strength of fixation when compared with standard plate constructs.     

Locking plates increase the strength of dynamic hip screws

INTRODUCTION: Failure of a dynamic hip screw (DHS) fixation leads to decreased mobility of the patient and frequently to a decrease in general health. The most common mode of failure of a DHS is cut out of the lag screw from the femoral head. The second most common mode of failure is lift-off of the plate from the femur. The aim of this laboratory-based experimental study was to determine whether a DHS secured to an osteoporotic femur with a locking screw plate would provide a stronger construct than the standard DHS plate. METHOD: The standard DHS design was compared to a DHS with fixed angle locking screws holding the DHS plate to the femur. Standard dynamic compression plates (DCP) and locking compression plates (LCP) were attached to synthetic, osteoporotic bone. A load was applied to replicate the forces occurring following the fixation of unstable, intertrochanteric hip fractures. A bracket on the proximal end of the plate replicated the lag screw in the femoral head. The constructs were cyclically loaded by a screw-driven material-testing machine and the number of cycles before failure occurred was determined. RESULTS: The mean number of cycles to failure for the locking plate construct was 2.6 times greater than for the standard screw construct (285 versus 108 cycles, respectively p=0.016). CONCLUSION: A dynamic hip screw with fixed angle locking screws would reduce the risk of DHS failure. A locking screw DHS would be particularly useful in patients with osteoporotic bone, and in patients with less stable fracture configurations.     

骨质疏松性肱骨近端骨折PMMA骨水泥强化螺钉钢板固定的有限元分析

目的：借助有限元分析的方法探讨肱骨近端聚甲基丙烯酸甲酯（polymethyl methacrylate,PMMA）骨水泥强化螺钉钢板固定对骨质疏松性肱骨近端骨折内固定稳定性的影响。方法：制作肱骨近端2部分骨折伴干骺端骨缺损的不稳定肱骨近端骨折数字化模型,分别建立肱骨近端骨水泥强化螺钉钢板固定及普通螺钉钢板固定的有限元模型,分析螺钉周围松质骨应力、整体刚度、钢板最大应力及螺钉最大应力。结果：肱骨近端骨水泥强化螺钉钢板固定的头端6枚螺钉周围松质骨最大应力分别为：1号钉1.07 MPa,2号钉0.43 MPa,3号钉1.16 MPa,4号钉0.34 MPa,5号钉1.99 MPa,6号钉1.57 MPa,普通螺钉钢板固定为：1号钉2.68 MPa,2号钉0.67 MPa,3号钉4.37 MPa,4号钉0.75 MPa,5号钉3.30 MPa、6号钉2.47 MPa。两组模型的整体刚度分别为：骨水泥结构448 N/mm、普通结构434 N/mm。钢板的最大应力均出现在结合孔：骨水泥结构701 MPa、普通结构420 MPa。螺钉的最大应力均出现在4号钉的尾端：骨水泥结构284 MPa、普通结构...     

Bone resorption triggered by high radial stress: The mechanism of screw loosening in plate fixation of long bone fractures

Screw loosening is a common complication in plate fixation. However, the underlying mechanism is unclear. This study investigated screw loosening mechanisms by finite element analysis (FEA) simulation and clinical X‐ray feature analysis. Two FEA models incorporated bone heterogeneity and orthotropy, representing fracture fixation using dynamic compression plate (DCP) and locking compression plate (LCP), were developed. These models were used to examine the volume of bone exceeding a certain stress value around each screw under physiologically‐relevant loading conditions. These damaged bone was then separated and compared by the axial stress and radial stress of each screw. In addition, features of patients’ X‐ray images showing screw loosening were analyzed to validate the loosening features simulated by the models. The FEA study showed that more damaged bone was found at the central two screws which gradually decreased toward the two end screws in all groups. More bone was damaged by the radial stress of each screw than by the axial stress. The radiological analysis of screw loosening showed that bone loss occurred at the screw closest to the fracture line first then subsequent bone loss at the screws further away from the fracture line occurred. This study found that the two screws nearest to the fracture line are more vulnerable to loosening. The radial stress of the screw plays a larger role in screw loosening than the axial stress. Bone resorption triggered by the high radial stress of screws is indicated as the mechanism of screw loosening in the diaphyseal plate fixation. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1498–1507, 2019.     

The effect of an angle-stable plate-screw connection and various screw diameters on the stability of plate osteosynthesis. An FE model study

In a finite element model of a human femur with an attached stainless steel six-hole plate exposed to a load equivalent to that set up by standing on one leg, pressures on the face of the screw holes, bending stresses in the screws, and axial bone stresses in the mid-plate transverse section were determined. The calculations were performed for minor thread diameters of 3 mm, 5 mm and 8 mm. Further calculations were done assuming a fixator-like rigid screw-plate connection. As a model of a fracture a medial bone defect was chosen. The results show a definitive influence of the screw diameter and the screw-plate connection on the load distribution in the system. Increasing screw diameter makes for lower bone stresses combined with increased bending stability, a larger part of the load being carried by the plate. The rigid screw-plate connection (plate fixator) causes less bone stresses, but high bending stresses are set up the points of screw-plate fixation. Maximal stresses for screw and bone are found at the end of the plate, caused by the large difference in the E-module between the steel plate and the bone. End-plate bone and screws are loaded in excess of their material limits when 3 mm core diameters are used, and sometimes when 5 mm core diameters are used, under the assumed conditions. When a medial bone defect reducing the bone cross-sectional area by 44% is present, the loads on the inner screws increase by a factor of 3 and the loads of the distant screws, by a factor of only 1.3. The maximal pressure in the bone cross section increases 4-fold.     

Screw pull-out force is dependent on screw orientation in an anterior cervical plate construct

Two common justifications for orienting cervical screws in an angled direction is to increase pull-out 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. The purpose of our study is to test the influence of screw orientation and plate design on the maximum screw pull-out load. Variable and fixed angle 4.0 x 15 mm and 4.0 x 13 mm self-tapping screws were used to affix a Medtronic Atlantis cervical plate to polyurethane foam bone samples (density 0.160/cm). This synthetic product is a model of osteoporotic cancellous bone. The fixed angle screws can only be placed at 12 degrees convergent to the midline and 12 degrees in the cephalad/caudal ("12 degrees up and in") direction. Three groups were tested: (1) all fixed angle screws, (2) variable angle, all screws 12 degrees up and in, (3) variable angle, all screws 90 degrees to the plate. Plate constructs were pulled off with an Instron DynaMight 8841 servohydrolic machine measuring for maximum screw pull-out force. There was no difference between group 1, fixed angle (288.4 +/- 37.7 N) (mean +/- SD) and 2, variable angle group (297.7 +/- 41.31 N P< or =0.73). There was a significant increase in maximum pull-out force to failure for the construct with all screws at 90 degrees (415.2+/-17.4 N) compared with all screws 12 degrees "up and in" (297.4 +/- 41.3 N, P< or =0.0016). Group 3 done with 13 mm screws, showed a trend toward better pull-out strength, compared to group 2 w/15 mm screws (345.2 +/- 20.5 vs. 297.4 +/- 41.3, P< or =0.06). In this plate pull-out model, screw orientation influences maximum force to failure. When all 4 screws are 90 degrees to the plate the construct has the greatest ability to resist pullout. Fixed angle designs show no advantage over variable angle. These findings are contrary to current teaching.     

肱骨近端骨折3种不同固定方式重建内侧柱的有限元分析

目的 采用有限元分析肱骨近端骨折锁定钢板联合内侧支撑螺钉、锁定钢板联合腓骨支撑及外侧锁定钢板联合内侧钢板重建内侧柱3种内固定模型的生物力学稳定性.方法 选取1名健康女性志愿者进行肱骨近端CT扫描,按照肱骨解剖颈下5 mm截骨,建立肱骨近端内侧柱缺失型骨折模型,按不同内固定方式分为PC组、PF组、PP组.PCO组单纯应用...     

Bioabsorbable vs. titanium screws for first tarsometatarsal joint arthrodesis: An in-vitro study

BackgroundThe TMT-1 joint arthrodesis is a common repair for severe hallux valgus. Two crossing interfragmental screws, usually titanium or steel, and a locking plate or a plate with a compression screw are the most common fixation methods for first TMT joint arthrodesis. The qualities of an ideal fixation material include adequate strength and rigidity, biocompatibility, lack of interference with bone healing, lack of visibility and palpability, and a low risk of surgical removal. We sought to determine whether bioabsorbable cannulated screws would perform as well as titanium screws in anatomical models.MethodsIdentical anatomical TMT-1 arthrodesis was created with a saw by making a straight cut in 30 anatomical models (Sawbone®). The bioabsorbable and titanium screws were placed one at a time in exactly the same location in each model according to careful measurements. All 30 models were analyzed with a material testing machine (MTS Insight 30, Eden Prairie, USA). Each model was oriented 15° to the platform to simulate its position to the ground during mid-stance.ResultsIn the single-cycle load-to-failure test, the mean yield load was 61.4 N ± 5.7 N (range, 50.1 N–70.3 N) in the bioabsorbable screw group and 81.2 N ± 12 N (range, 61.7 N–113.4 N) in the titanium screw group (P < .001). The respective values for the stiffness of the fixation were 8.1 N/mm ± 0.8 N/mm (range, 6.7 N/mm to 9.1 N/mm) and 9.7 N/mm ± 1.8 N/mm (range, 6.9 N/mm to 12.6 N/mm) for the bioabsorbable and titanium groups (P = .004). The mean maximum failure loads in the bioabsorbable group were 85.1 N ± 8.5 N (range, 67.1 N–97.2 N) and in the titanium group 120.6 N ± 13.2 N (range, 96.7 N–136.7 N), respectively (P < .001). Analysis of the failure models shows bioabsorbable fixation failures caused by bending occur more often than in the titanium group.ConclusionIn biomechanical testing, titanium screws were stronger than bioabsorbable screws in the TMT-1 arthrodesis model tested, although bioabsorbable cannulated screws may be an alternative to titanium screws in the fixation Lapidus procedure.