后凸成形和传统钉道骨水泥强化对骶骨钉松动的生物力学作用（英文）

背景：后凸成形骨水泥强化可应用于骨质疏松患者的腰椎椎弓根钉固定。目的：评价松动的骶骨钉经后凸成形和传统钉道骨水泥强化后的固定强度。方法：纳入9具骨质疏松症患者的新鲜尸体标本。在同一骶骨标本上,分别测试单皮质和双皮质骶骨椎弓根钉最大拔出力后,分别建立传统钉道骨水泥强化与后凸成形骨水泥强化椎弓根钉固定模型。在MTS材料试验机上,对螺钉尾部施加2 000次周期性压力载荷后,进行螺钉最大拔出力测试。结果与结论：9个标本的骨密度均值为0.71 g/cm2（0.61～0.77 g/cm2）。4种骶骨钉固定技术单皮质、双皮质、传统钉道骨水泥强化和后凸成形骨水泥强化骶骨钉的平均最大拔出力分别为203,325,437及565 N。双皮质骶骨钉的拔出力显著高于单皮质钉（P〈0.05）;但此2固定均显著低于骨水泥强化组（P〈0.05）。后凸成形骨水泥强化组的拔出力显著高于传统钉道骨水泥强化组（P〈0.05）。此外,4种骶骨钉固定技术的最大拔出力与骨密度值均呈现显著的正相关（P〈0.05）。结果证实,传统钉道骨水泥强化技术和后凸成形骨水泥强化技术均可做为骶骨椎弓根钉松动的补救手段,但后凸成形骨水泥强化可获得更为坚强的锚定。     

骶骨S2椎弓根外进钉固定的生物力学分析

背景：模拟骶骨骨折S2椎弓根钉外进钉固定拔出力与在拔出椎弓钉时的应变电测分析鲜有报道。目的：测量S2椎弓根外进钉固定拔出力与骶骨应变分布,为临床提供生物力学参数。方法：取正常国人新鲜尸体骶骨标本,以椎弓根钉外进钉方法固定于S2椎弓根,以小型力传感器与椎弓根钉固定装置连接测量椎弓根钉的拔出力,同时以动静态电阻应变仪,对预先粘贴在4个椎弓根螺栓固定边缘部位和骶骨不同部位的应变片进行应变电测量。1号进钉点位置为左侧第1骶后孔下缘最低点,2号进钉点位置为右侧第1骶后孔下缘最低点,3号进钉点为左侧第1骶后孔连线与骶外侧嵴的交点,4号进钉点为右侧第1骶后孔连线与骶外侧嵴的交点。测量椎弓根螺钉最大拔出力和骶骨各测点应变值。结果与结论：外进钉1号螺钉拔出力为（399.0±7.2）N,2号螺钉拔出力为（281.0±5.2）N,3号螺钉拔出力为（196.0±4.3）N,4号螺钉拔出力为（220.1±4.6）N。应变电测量最小应变发生在2号螺钉8号测点,应变为（13.5±1.1）με;最大应变发生在1号螺钉1号测点,应变为（96.8±6.5）με。提示S2椎弓根钉外进钉固定方法符合生物力学原理。     

骶骨S2椎弓根外进钉固定的生物力学分析

背景:模拟骶骨骨折S2椎弓根钉外进钉固定拔出力与在拔出椎弓钉时的应变电测分析鲜有报道。目的:测量S2椎弓根外进钉固定拔出力与骶骨应变分布,为临床提供生物力学参数。方法:取正常国人新鲜尸体骶骨标本,以椎弓根钉外进钉方法固定于S2椎弓根,以小型力传感器与椎弓根钉固定装置连接测量椎弓根钉的拔出力,同时以动静态电阻应变仪,对预先粘贴在4个椎弓根螺栓固定边缘部位和骶骨不同部位的应变片进行应变电测量。1号进钉点位置为左侧第1骶后孔下缘最低点,2号进钉点位置为右侧第1骶后孔下缘最低点,3号进钉点为左侧第1骶后孔连线与骶外侧嵴的交点,4号进钉点为右侧第1骶后孔连线与骶外侧嵴的交点。测量椎弓根螺钉最大拔出力和骶骨各测点应变值。结果与结论:外进钉1号螺钉拔出力为(399.0±7.2)N,2号螺钉拔出力为(281.0±5.2)N,3号螺钉拔出力为(196.0±4.3)N,4号螺钉拔出力为(220.1±4.6)N。应变电测量最小应变发生在2号螺钉8号测点,应变为(13.5±1.1)με;最大应变发生在1号螺钉1号测点,应变为(96.8±6.5)με。提示S2椎弓根钉外进钉固定方法符合生物力学原理。     

影响椎弓根螺钉拔出力的相关因素

椎弓根螺钉的松动和轴向脱出是导致脊柱内固定失败的主要原因,螺钉的松动、脱出与螺钉的拔出力有关,螺钉的拔出力与椎弓根螺钉直径、螺纹设计、骨密度及螺钉的操作技术有关。拔出强度随外径的增加而增加,螺钉越长,拔出强度越大。椎弓根螺钉的稳定性在骨质疏松时明显降低,对于骨质疏松患者,单纯增加螺钉直径较为困难,一般需进一步强化椎弓根螺钉的稳定性,聚甲基丙烯酸甲酯骨水泥强化骨质疏松椎弓根螺钉能显著增加螺钉的稳定性和抗屈强度,但由于骨水泥聚合产生高热可导致组织损伤,体内长期留置会产生毒性和致癌作用,具有良好生物相容性的新型添加材料,如羟基磷灰石骨水泥、磷酸钙骨水泥等将逐渐替代聚甲基丙烯酸甲酯骨水泥。同时螺钉置入过程中准确的进钉点、进钉方向和置入位置可以减少因螺钉重新拧入而导致的把持力下降,提高螺钉的拔出强度和稳定性。     

腰椎内固定中两种椎弓根钉加强技术与骨水泥的应用

背景：骨质疏松伴腰椎退行性病变行椎弓根钉固定骨质疏松的椎体后可能会出现螺钉的松动、脱落,使用固化材料强化椎弓根钉能提高治疗效果。目的：比较骨质疏松患者腰椎内固定中使用聚甲基丙烯酸甲酯骨水泥和可注射硫酸钙骨水泥加强椎弓根钉两种技巧的临床效果。方法：腰椎滑脱、腰椎失稳、严重腰椎管狭窄合并骨质疏松的患者共61例,根据治疗方式分为2组：传统聚甲基丙烯酸甲酯强化椎弓根钉组和可注射硫酸钙骨水泥强化椎弓根钉组。结果与结论：两组患者治疗操作时间、出血量、治疗前后目测类比评分、日本骨科协会评估治疗分数评分及改善率比较差异均无显著性意义（P〉0.05）。聚甲基丙烯酸甲酯组中2例患者出现了注入的骨水泥渗漏,随访未造成新的神经损伤。聚甲基丙烯酸甲酯组患者治疗后骨密度随着随访时间的延长未出现逐渐的增强趋势;硫酸钙骨水泥组患者治疗后骨密度出现渐进性的改善,与患者治疗后日本骨科协会评估治疗分数改善率呈线性相关。两组患者未出现螺钉松动、拔出及神经功能的异常。表明与聚甲基丙烯酸甲酯相似,硫酸钙骨水泥能增加椎弓根螺钉的稳定性。     

成人颈椎椎弓根螺钉在儿童腰椎应用的可行性

背景:由于1～3岁幼年儿童椎体发育未完全成熟,各种解剖径线相对较成人小得多,尚无幼儿专用的椎弓根螺钉固定器械,现有能够利用的直径最小的椎弓根螺钉是用于成人颈椎侧块或椎弓根固定的钉棒系统。目的:观察将成人颈椎椎弓根螺钉应用到成年猪颈椎与幼猪腰椎固定后的生物力学对比。方法:将6具完整新鲜成年猪颈段C3～C6脊椎标本和6具完整8周龄新鲜幼猪腰段脊柱标本自椎间盘及关节处离断,游离成单个椎体,共54个椎体108侧椎弓根。按照标准操作将成人颈椎椎弓根螺钉分别安置在成年猪颈椎标本和幼猪腰椎标本的椎弓根上,应用生物力学方法测试螺钉的最大轴向拔出力。结果与结论:颈椎标本最大轴向拔出力高于腰椎标本,但差异无显著性意义(P>0.05);L1椎弓根螺钉的拔出力均值明显小于L3椎弓根螺钉的拔出力均值(P<0.05);C5椎弓根螺钉的拔出力均值明显大于C3椎弓根螺钉的拔出力均值(P<0.05);颈椎和腰椎标的骨密度差异有显著性意义(P<0.01),椎体椎弓根力学数值与椎体骨密度之间存在线性正相关。说明取得了成人颈椎椎弓根螺钉在轴向拉力方面适应于幼儿腰椎的初步实验依据。     

骨水泥椎体强化椎弓根钉置入对骨质疏松脊柱生物力学稳定性的影响

背景:伴有骨质疏松患者的脊柱内固定松动、脱落是脊柱外科一个复杂而棘手的问题.用聚甲基丙烯酸甲酯骨水泥强化椎弓根螺钉可增加伴有骨质疏松患者的椎弓根螺钉防止椎弓根钉的松动及脱落.目的:评价聚甲基丙烯酸甲酯骨水泥椎体强化后椎弓根钉固定对不稳定骨质疏松脊柱的生物力学稳定性影响.设计、时间及地点:体外生物力学实验,于2008-03在上海大学生物力学实验室完成生物力学实验.材料:12具新鲜老年女性尸体T10-L3椎体标本,制成T12、L1间的不稳定模型,采用椎弓根螺钉系统固定.方法:将标奉按照不同的处理方式分为4组.①对照组:为完整标本,只进行生物力学性能的测试.②一次固定组:对照组测试后随机选取6具不稳定模型,行T11～L2椎弓根钉固定.③二次固定组:一次固定组标本完成稳定性测试后,取出所有椎弓根螺钉,分别用注射器向T11～L2椎弓根钉道注入配制好的聚甲基丙烯酸甲酯骨水泥骨水泥2.0 mL后再次拧入螺钉固定.④强化固定组:将余下的6具标本于T11～L2双侧椎弓根分别以直径3.5 mm的钻头导孔,沿孔道插入直径3.5 mm的穿刺导管,插入深度为40 mm,用加压注射器经导管缓慢向椎体内加压注射配制好的聚甲基丙烯酸甲酯骨水泥3.5 mL后拧入螺钉固定.主要观察指标:进行轴向压缩、前屈,后伸、左,右侧弯、左,右旋转7项非损伤性加载,比较上述4组不同状态下脊柱的相对运动范围变化.结果:与一次固定组比较,二次固定组及强化固定组脊柱的相对运动范围增加(P<0.05),强化固定组与二次固定组组间比较,差异无统计学意义(P>0.05).结论:椎体成形强化椎弓根钉固定及钉道强化固定均可明显增强不稳定骨质疏松脊柱的稳定性.     

短节段椎弓根螺钉置入内固定椎体成形治疗胸腰椎骨折的生物力学检测

背景:为避免单纯椎弓根螺钉置入内固定治疗胸腰段骨折出现的内固定物松动、断裂,及合并植骨时出现的骨折不愈合、后凸畸形丢失,而发展的短节段椎弓根螺钉合并椎体成形技术治疗胸腰段骨折,临床已有应用,但其生物力学方面鲜有研究。目的:观察应用椎弓根螺钉置入内固定椎体成形治疗胸腰椎骨折的生物力学变化。方法:12个冻存的新鲜胸腰段脊椎(T12～L2)标本,用于制备胸腰椎骨折模型,备测试。分为3组,经皮椎体成形术组:给予经单侧椎弓根注入低黏度的含对比剂骨水泥5～7mL;椎弓根螺钉内固定组:于T12、L2椎弓根置入螺钉;强化组:行椎弓根螺钉内固定的同时行伤椎骨水泥椎体成形术,测试各组静态最大抗压强度及刚度。结果与结论:骨水泥分布面积皆大于50%,经皮椎体成形术组和椎弓根螺钉内固定组最大静态抗压强度与刚度均小于强化组最大强度和刚度(P<0.05)。椎弓根螺钉内固定组椎弓根螺钉较小强度下出现弯曲,而强化组在达到极性轴向压缩强度时才出现弯曲。提示应用短节段椎弓根钉置入内固定椎体成形治疗胸腰椎骨折提高了固定的强度及刚度,并且维持了复位伤椎高度,提高了稳定性,减少了椎弓根螺钉的并发症。     

骶2椎弓根钉内进钉固定拧紧力与骶骨的应变分布规律

背景:国内外学者对骶骨骨折术式和骶2椎弓根钉固定方法进行了一定的研究,但对于骶2椎弓根钉固定螺钉拧紧力及在最大螺钉拧紧力作用下骶骨不同部位的应变分布规律研究少见报道.目的:研究骶2椎弓根钉固定拧紧力与骶骨应变分布,为临床骶2椎弓根钉固定术提供生物力学参数.设计、时间及地点:观察性实验,于2008-08在吉林大学力学实验中心完成.材料:取自正常国人新鲜尸体4具,均为男性,年龄25-30岁,由白求恩医科大学解剖教研室提供.方法:取正常国人新鲜尸体骶骨标本,以椎弓根钉内进钉方法固定于骶2椎弓根,以小型力传感器与椎弓根钉固定装置连接测量椎弓根钉的拧紧力,同时以动静态电阻应变仪对预先黏贴在4个椎弓根螺检固定边缘部位和骶骨不同部位的应变片进行应变电测量.1号进钉点位置为左侧第一骶后孔下缘最低点,2号进钉点位置为右侧第一骶后孔下缘最低点,3号进钉点为左侧第一骶后孔连线与骶外侧嵴的交点,4号进钉点为右侧第一骶后孔连线与骶外侧嵴的交点.主要观察指标:椎弓根螺钉最大拧紧力和骶骨各测点应变分布值.结果:内进钉1号螺钉拧紧力为(68.7±7.8)N,2号螺钉拧紧力为(81.1±5.6)N,3号螺钉拧紧力为(56.9±4.6)N,4号螺钉拧紧力为(57.5±6.5)N.应变电测量最小应变发生在1号螺钉8号测点应变为(18.6±2.6)×10<-6>,最大应变发生在2号螺钉2号测点应变为(92.6±6.4)×106.结论:骶2椎弓根钉术式符合生物力学原理.     

磷酸钙骨水泥强化椎弓根螺钉固定的生物力学特性

背景:聚甲基丙烯酸甲酯能改善椎弓根螺钉和周围骨质间界面的情况、显著提高螺钉固定强度,但它在术中和术后伴有聚合热损伤效应、毒性和不可吸收等缺点。磷酸钙骨水泥具有生物相容性和生物安全性好、可降解、不产生聚合热等优点,是一种较理想的聚甲基丙烯酸甲酯替代材料。目的:从生物力学方面评价磷酸钙骨水泥对椎弓根螺钉固定的强化作用。设计:随机对照,重复观察测量。单位:南京医科大学第二附属医院骨科。材料:实验于2002-08/2003-02在华中科技大学同济医学院完成。①由同济医科大学解剖教研室提供两具新鲜男性尸体椎骨,一具52岁,一具50岁。各取10个椎骨(T8～12,L1～5)分别构成52岁组和50岁组。摄X线片排除先天性畸形、骨折和肿瘤等病变。两组椎骨均为Ⅰ级骨质疏松,符合实验要求。②磷酸钙骨水泥固相主要成分是磷酸四钙和磷酸三钙超细粉末,液相主要成分是枸橼酸盐溶液,使用时按1g固相:1mL液相的比例进行配制,初步凝固时间15min,最终凝固时间12h,最大压缩强度介于45～57MPa。③椎弓根螺钉自制,螺钉直径5mm,螺纹段长34mm,螺距2mm,螺纹深0.8mm。方法:①磷酸钙骨水泥最终凝固时强化椎弓根螺钉固定的生物力学测试:取50岁组椎骨作为测试对象。对照侧:钉道直接置入椎弓根螺钉;强化侧:填入磷酸钙骨水泥再置入椎弓根螺钉。置钉后的椎骨在37℃恒温箱里放置12h,然后测定椎弓根螺钉的最大轴向拔出力。②磷酸钙骨水泥初步凝固时强化椎弓根螺钉固定的生物力学测试:取52岁组椎骨作为测试对象。用同样方法在椎弓根对照侧直接置入椎弓根螺钉,强化侧填入骨水泥后再置入椎弓根螺钉,37℃恒温箱里放置15min,测定椎弓根螺钉初步凝固时的最大轴向拔出力。③磷酸钙骨水泥强化松动椎弓根螺钉固定的生物力学测试:取测试后的50岁组椎骨,用磷酸钙骨水泥重新固定12h后拔松的椎弓根螺钉,测定其两侧的最大轴向拔出力。主要观察指标:①磷酸钙骨水泥最终凝固时强化椎弓根螺钉固定的生物力学测试结果。②磷酸钙骨水泥初步凝固时强化椎弓根螺钉固定的生物力学测试结果。③磷酸钙骨水泥强化松动椎弓根螺钉固定的生物力学测试结果。结果:①50岁组对照侧和强化侧的椎弓根螺钉最大轴向拔出力中位数分别为620N和1136N,强化侧较对照侧增加83%(P<0.01)。强化骨-螺钉界面的抗剪切应力中位数从1.16N/mm2增加到2.13N/mm2。②52岁组对照侧和强化侧的椎弓根螺钉最大轴向拔出力中位数分别为554.5N和859.5N,强化侧较对照侧增加55%(P<0.01)。强化骨-螺钉界面的抗剪切应力中位数从1.039N/mm2增加到1.61N/mm2。③50岁组椎骨对照侧和强化侧重新固定12h后最大轴向拔出力中位数分别为517N和876N,和同侧松动后轴向拔出力中位数比较,分别增加了63.6%和54.2%(P均<0.01)。结论:磷酸钙骨水泥初步凝固和最终凝固时能强化椎弓根螺钉的固定,并且椎弓根螺钉松动后使用磷酸骨水泥能使螺钉重新获得固定。椎体强化侧的椎弓根螺钉均从骨-螺界面剥离开来,不伴周边骨质和椎弓根的严重损害,有利于螺钉松动、拔出后的二次置入。     

Biplanar fixation of a locking plate in the diaphysis improves construct strength

Background

Elevation of a locking plate over the bone surface not only supports biological fixation, but also decreases the torsional strength of the fixation construct. Biplanar fixation by means of a staggered screw hole arrangement may combat this decreased torsional strength caused by plate elevation. This biomechanical study evaluated the effect of biplanar fixation on the torsional strength of locking plate fixation in the femoral diaphysis.

Methods

Custom titanium plates were manufactured with either a linear or staggered hole pattern to evaluate planar and biplanar fixation, respectively. Fixation strength under torsional loading was evaluated in surrogates of the femoral diaphysis representative of osteoporotic and non-osteoporotic bone. Furthermore, fixation strength was determined for plate fixation with unicortical or bicortical locking screws. Five specimens per configuration were loaded to failure in torsion to determine their strength, stiffness, and failure mode.

Findings

In osteoporotic bone, biplanar fixation was 32% stronger (P = 0.01) than planar fixation when unicortical screws were used and 9% stronger (P = 0.02) when bicortical screws were used. In non-osteoporotic bone, biplanar fixation was 55% stronger (P < 0.001) than planar fixation when unicortical screws were used and 42% (P < 0.001) stronger when bicortical screws were used.

Interpretation

A biplanar screw configuration improves the torsional strength of diaphyseal plate fixation relative to a planar configuration in both osteoporotic and normal bone. With biplanar fixation, unicortical screws provide the same fixation strength as bicortical screws in non-osteoporotic bone.     

Biomechanical evaluation of fixation strength of conventional and expansive pedicle screws with or without calcium based cement augmentation

Background

The expansive pedicle screw was originally developed to be installed in the bone of compromised quality, but there are some concerns whether it can provide enough fixation strength in the spine with osteoporosis or severe osteoporosis.

Methods

Twelve fresh human cadaver spines were stratified into four levels: normal, osteopenia, osteoporosis and severe osteoporosis. The vertebra was bilaterally instrumented with pedicle screws according to four protocols, including conventional pedicle screw without augmentation, expansive pedicle screw without augmentation, conventional screw with augmentation and expansive screw with augmentation. Screw pullout tests were conducted.

Findings

Given the same specimen, the fixation strength of expansive screw was significantly higher than that of the conventional screw. When the same type of screw was used, the fixation strength of the calcium based cement augmented group was stronger than that of the non-augmented group. The pullout strength and stiffness of the expansive screw, augmented conventional screw and augmented expansive screw groups at the osteoporotic level were comparable to those of the conventional pedicle screw group at the osteopenic level. However, under the severely osteoporotic bone environment, the pullout strength of pedicle screw with whatever placement protocol was significantly lower than that of the conventional screw group at the osteopenic level.

Interpretation

Our results demonstrate that (i) the expansive pedicle screw appears feasible and safe in either osteopenic or osteoporotic spine; (ii) calcium based cement augmentation can offer improved initial fixation strength of pedicle screws.; and (iii) no screw placement protocol we examined is efficacious in the bone at the severely osteoporotic level.     

A bicortical pedicle screw in the caudad trajectory is the best option for the fixation of an osteoporotic vertebra: An in-vitro experimental study using synthetic lumbar osteoporotic bone models

BackgroundIn pedicle screw fixation, the optimal depth and trajectory of insertion are controversial, and this might be because of the wide variations in specimens. The present study aimed to investigate the biomechanically optimal depth and trajectory of screw insertion using synthetic lumbar osteoporotic vertebrae.MethodsA total of 27 synthetic osteoporotic lumbar vertebrae (L3) were used to ensure standard vertebral quality and shape. Pedicle screws having two different lengths (unicortical: to the center of the vertebra; bicortical: to the anterior cortex of the vertebra) were inserted in the following three different trajectories: 1) straight-forward (parallel to the superior endplate), 2) cephalad (toward the anterosuperior corner), and 3) caudad (toward the anteroinferior corner). Maximum insertional torque and pull-out strength were measured.FindingsFor the straight-forward, cephalad, and caudad trajectories, the maximum insertional torque (Ncm) values of unicortical screws were 144.4, 143.1, and 148.9, respectively, and those of bicortical screws were 205.5, 156.2, and 207.8, respectively. The maximum insertional torque values were significantly higher for bicortical screws than unicortical screws (p < 0.001). Additionally, regarding bicortical screws, the maximum insertional torque values were significantly lower for the cephalad trajectory than other trajectories (p = 0.002). The pull-out strength (N) values of bicortical screws for the straight-forward, cephalad, and caudad trajectories were 703.3, 783.9, and 981.3, respectively. The pull-out strength values were significantly lower for the straight-forward trajectory than other trajectories (p = 0.034).InterpretationA bicortical pedicle screw in the caudad trajectory might be the best option to improve fixation in an osteoporotic lumbar vertebra.     

Are the terms "biology" and "osteosynthesis" contradictory?

Biology and Osteosynthesis may, at first glance, appear to be contradictory. The disadvantages of the surgical procedure are offset by improved recovery of blood supply across a fracture zone and by stimulation of callus formation due to (controlled and slight) instability (elastically flexible fixation). Biological internal fixation is a principle in its own right; its technique is to some extent incompatible with conventional compression fixation. Locked screws provide better anchorage of the implant in both biological and compression internal fixation techniques. This generally offers improved potential in the treating fractures in osteoporotic bone. Because locked screws offer improved anchorage, the use of unicortical screws is made possible with the effect that the medullary circulation is damaged less. Locked unicortical screws, especially if they are self-drilling and self-cutting, offer important surgical advantages in minimally invasive percutaneous osteosynthesis (MIPO) whereas bicortical screws are required for epi- and metaphyseal anchorage.     

Pullout strength for cannulated pedicle screws with bone cement augmentation in severely osteoporotic bone: Influences of radial hole and pilot hole tapping

Background

Pedicle screw fixation in a severely osteoporotic spine remains a challenge for orthopedic surgeons. The previous literature does not adequately address the effects of radial holes for cannulated screws with cement injection and pilot hole tapping on the bone/screw interfacial strength.

Methods

Specially designed cannulated pedicle screws, with or without radial holes, were installed in tapped and untapped pilot holes and then injected with cement. A uniform synthetic bone (test block) was used to provide a platform for each screw design. Specimens with inserted screws were then tested for axial pullout failure.

Findings

(1) Cannulated screws with cement augmentation significantly increased the pullout strength in comparison to solid screws. Additionally, the amount of cement exuded from the cannulated screws increased with an increasing number of radial holes, leading to an increase in the average ultimate pullout strength for cannulated screws with a large number of radial holes. (2) Radiological examination indicated that the cement was exuded from the most proximal holes at the very beginning of its flow path, whereas no cement exudation was found at the remaining distal holes. (3) Cement exudation from the holes of cannulated screws into the open cell of the test block led to a composite (cement/bone) structure at the area of cement exudation. Observations of the failed specimens indicated that failure occurred at the composite/bone interface, while the composite was well bonded to the screws. This implies that the screw/composite interfacial strength was much higher than the composite/bone interfacial strength. (4) Tapping pilot holes decreased the pullout strength of the screws. Generally, larger standard deviations were found for the tapped cases, implying that untapped cases results are more repeatable than tapped cases results.

Interpretation

Cannulated pedicle screws with radial holes combined with PMMA cement augmentation but without tapping may be a viable clinical option for achieving fixation in severely osteoporotic bone.     

Biomechanical analysis of pedicle screw thread differential design in an osteoporotic cadaver model

Background

Pedicle screw fixation, the standard surgical care for posterior stabilization in the thoraco-lumbar spine has a high rate of failure in osteoporotic individuals. Screw design factors and insertion techniques have been shown to influence the biomechanical performance of pedicle screws. Our objective was to investigate the biomechanical characteristics of pedicle screw fixation in osteoporotic bone by comparing standard screws with newly designed differential crest thickness dual lead screws.

Methods

An in-vitro spinal-level paired factorial study design was used to examine thoraco-lumbar spine biomechanical outcomes for differential pedicle screw thread designs. Six cadaveric human spines (T8-L5) were tested for six groups (n = 20) consisting of 2 different crest thickness and 3 different insertion techniques. Bone mineral density was assessed and peak insertion torque measured while placing one screw of new design and control on the contralateral side. Screw pullout properties were measured from classical American Society for Testing and Materials protocols.

Findings

The screws designed specifically for osteoporotic bone showed significantly larger insertion torque compared with the standard screw design irrespective of insertion technique. Much of the variability in pullout failure and stiffness was explained by bone mineral density. The osteoporotic screws of different crest thickness were statistically similar to each other in all outcome measures.

Interpretation

Compared with standard pedicle screws, the dual lead osteoporotic-specific pedicle screws demonstrated significantly larger insertion torques and similar pullout properties. Non-significant increased biomechanical strength was observed for thin crest compared to thick crest dual lead pedicle screws indicating their enhanced purchase in osteoporotic bone.     

骨水泥强化椎弓根螺钉固定对骨质疏松患者有利无弊？

背景：在对伴骨质疏松的腰椎疾病患者进行椎弓根螺钉固定手术时,椎体添加骨水泥可有效增加内固定稳定性,但对相邻节段的影响尚不明确. 目的：观察伴骨质疏松的腰椎疾病患者进行椎体骨水泥强化内固定后,早中期随访中骨水泥强化对相邻节段的影响. 方法：以87例伴骨质疏松的腰椎疾病患者为研究对象,均行椎弓根螺钉系统固定＋后路椎管减压术,并分为3组：常规螺钉组,常规螺钉＋骨水泥组,可灌注骨水泥螺钉＋骨水泥组.样本平均随访6-18个月,平均随访为9个月.测量术前、术后3 d、末次随访的Oswestry功能障碍指数评分、固定节段上位相邻椎间隙高度、固定节段上位相邻椎体变形指数、固定节段椎体上缘终板及相邻上位椎体下缘终板凹陷角度、固定节段Cobb角. 结果与结论：①常规螺钉组、常规螺钉＋骨水泥组、可灌注骨水泥螺钉＋骨水泥组3组内末次随访功能障碍指数评分均较前明显减小（P〈0.05）,组间两两对比无显著差异（P〉0.05）.表明骨质疏松患者脊柱后路固定时,是否添加骨水泥及不同添加方式,对早中期主观疗效影响无显著差异,且均可明显改善患者生活质量.②常规螺钉＋骨水泥组、可灌注骨水泥螺钉＋骨水泥组2组末次随访对术后3 d固定节段Cobb角变化小于常规螺钉组（P 〈0.05）,常规螺钉＋骨水泥组、可灌注骨水泥螺钉＋骨水泥组2组组间差异无统计学意义（P 〉0.05）.表明添加骨水泥辅助的内固定稳定性明显优于未添加骨水泥常规手术.③常规螺钉＋骨水泥组、可灌注骨水泥螺钉＋骨水泥组2组术后3 d出现上终板凹陷角度增大;末次随访观察到相邻上位椎体下终板凹陷角度、椎体矩形指数及相邻椎间隙均减小,且前两项指标的改变程度明显大于常规螺钉组.表明添加骨水泥辅助内固定对相邻椎间盘退变程度无显著影响,但明显改变了相邻椎体终板及椎体的形态,增加了相邻椎体发生骨折的风险.     

注入骨水泥治疗胸腰椎骨质疏松性骨折：成熟技术中的常见问题

背景：注入骨水泥是胸腰椎骨质疏松性骨折常用的固定方法之一。目的：评估注入骨水泥内固定胸腰椎骨质疏松性骨折的生物力学性能以及固定效果。方法：选取骨质疏松胸腰椎标本,测定骨密度以及最大压力载荷、位移、刚度等力学性能指标,建立骨折模型,注入骨水泥固定后,再次测定最大压力载荷、位移、刚度指标,比较注入骨水泥固定前后生物性能的变化,同时与椎弓根螺钉固定胸腰椎骨质疏松性骨折的生物学性能进行比较。对注入骨水泥固定胸腰椎骨质疏松性骨折的患者进行随访观察,通过评估患者缓解疼痛程度、胸腰椎体高度恢复程度以及骨水泥注入量和骨水泥外渗等情况,明确注入骨水泥固定治疗的效果。结果与结论：生物力学实验测定注入骨水泥固定胸腰椎骨质疏松性骨折后的最大载荷为2285N,比骨折前承受的最大载荷1954N强度增加了近16．9％,注入骨水泥固定胸腰椎骨质疏松性骨折后的刚度为427N,比骨折前刚度349N增加了近22．1％,显示出良好的生物性能。对应用注入骨水泥固定胸腰椎骨质疏松性骨折的患者以及应用闭合复位注入骨水泥固定胸腰椎骨质疏松性骨折的患者进行随访观察,结果发现2种方法均可以使患者的疼痛得到明显的缓解,而闭合复位注入骨水泥固定胸腰椎骨质疏松性骨折时骨水泥注入量、局部后凸角以及椎体高度恢复情况均更好,表明闭合复位辅助下注入骨水泥固定是胸腰椎骨质疏松性骨折安全有效的治疗方法。