Screw design alters the effects of stress relaxation on pullout

Stress relaxation during pullout of a pedicle screw decreases the peak load and stiffness of the bone-screw interface. However, it is unknown whether this can be generalized to all types of screw designs. This study aimed to show whether screw design altered the effects of stress relaxation on the mechanical performance of the pedicle screw during pullout. Twelve calf vertebrae were obtained: six vertebrae were instrumented with 7.5x40 mm conical pedicle screws and the other six with 5.0x40 mm cylindrical pedicle screws. The screws with two different designs were pulled out using either a standard pullout or a stress relaxation pullout protocol. Both bone-screw interfaces had lower stiffness in the stress relaxation pullout model than in the standard pullout model, but it was significant in only the cylindrical design group (P<0.05). However, the stress relaxation and standard pullout models did not yield any difference in peak loads in either screw type. Although stress relaxation at the bone-screw interface can alter the mechanical performance of the screw, this may be eliminated by modifying the screw design. A better understanding of viscoelastic properties of the bone-screw interface may help improve implant design and thus, clinical outcomes.     

膨胀式椎弓根螺钉脊柱后路内固定的生物力学测试

目的　测试并比较自行设计的膨胀式椎弓根螺钉 (expansivepediclescrew ,EPS)与USS ,Tenor ,CDH椎弓根螺钉的最大轴向拔出力 ,评价EPS螺钉的椎弓根固定作用。方法　将 6 0个新鲜小牛腰椎随机分成 3组 ,每组 2 0个椎体(4 0侧椎弓根 ) ,每组均随机在一侧拧入EPS螺钉 ,对侧则分别拧入USS ,Tenor ,CDH螺钉 ,进行螺钉拔出实验 ,测试并记录最大轴向拔出力。结果　EPS ,USS ,Tenor ,CDH螺钉的最大轴向拔出力分别为 2 6 5 8 4N± 816 7N ,192 9 9N±4 84 9N ,184 9 8N± 5 75 9N ,1980 9N± 836 4N。EPS螺钉和其它三种螺钉的最大轴向拔出力相比均有非常显著差异 (P <0 0 1)。结论　EPS螺钉较目前使用的USS ,Tenor ,CDH非膨胀椎弓根螺钉有更好的固定作用。     

The effect of screw insertion angle and thread type on the pullout strength of bone screws in normal and osteoporotic cancellous bone models

Screw fixation can be extremely difficult to achieve in osteoporotic (OP) bone because of its low strength. This study determined how pullout strength is affected by placing different bone screws at varying angles in normal and OP bone models. Pullout tests of screws placed axially, and at angles to the pullout axis (ranging from 10° to 40°), were performed in 0.09 g cm^?3, 0.16 g cm^?3 and 0.32 g cm^?3 polyurethane (PU) foam. Two different titanium alloy bone screws were used to test for any effect of thread type (i.e. cancellous or cortical) on the screw pullout strength. The cancellous screw required a significantly higher pullout force than the cortical screw (p < 0.05). For both screws, pullout strength significantly increased with increasing PU foam density (p < 0.05). For screws placed axially, and sometimes at 10°, the observed mechanism of failure was stripping of the internal screw threads generated within the PU foam by screw insertion. For screws inserted at 10°, 20°, 30° and 40°, the resistance to pullout force was observed to be by compression of the PU foam material above the angled screw; clinically, this suggests that compressed OP bone is stronger than unloaded OP bone.     

骨水泥和纳米骨浆强化椎弓根螺钉植入固定骨质疏松椎体的生物力学特点

背景：纳米骨浆和骨水泥注入是强化椎弓根螺钉固定的两种常用方法,但目前关于两种加强方法的强化效果比较的报道相对较少。 目的：对比骨水泥或纳米骨浆强化椎弓根螺钉植入固定骨质疏松椎体的生物力学特点。 方法：取24个人尸体椎弓根,均符合骨质疏松标准,随机均分为3组,对照组仅植入椎弓根螺钉,骨水泥组在钉道内注入骨水泥后植入椎弓根螺钉,纳米骨浆组在钉道内注入纳米骨浆后植入椎弓根螺钉。植入2 h后,检测各组标本最大轴向拔出力和最大旋出力矩。 结果与结论：骨水泥组、纳米骨浆组的最大轴向拔出力和最大旋出力矩均大于对照组(P < 0.05),并且骨水泥组的最大轴向拔出力和最大旋出力矩大于纳米骨浆组(P < 0.05)。表明骨水泥和纳米骨浆强化可有效提高椎弓根螺钉植入固定骨质疏松椎体的最大轴向拔出力和最大旋出力矩,且骨水泥强化效果更明显。 中国组织工程研究杂志出版内容重点：生物材料;骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性;组织工程     

变牙厚椎弓根螺钉的生物力学测试

目的　评价不同变牙厚椎弓根螺钉（transitional thread pedicle screw, TTPS）对螺钉拔出力的影响。 方法 取新鲜小牛胸腰椎标本（T11~L4）5具,共30个椎体(60侧椎弓根),剔除周围肌肉、筋膜,注意保持骨结构完整,解离成单个椎骨。平均骨密度为（1.186±0.182）g/cm2。TTPS规格有6种：A0（牙厚保持不变）、A1（逐牙加厚0.01mm）、A2（逐牙加厚0.02 mm）、A3（逐牙加厚0.03 mm）、A4（逐牙加厚0.04 　mm）、A5（逐牙加厚0.05 mm）。每种螺钉随机置入10侧椎弓根,将标本包埋好并用夹具固定在材料试验机上,设置椎弓根螺钉长轴与拔出力轴线方向重合。设置材料试验机加载速率为0.08 mm/s进行拔出实验,结果输出拔出力-位移曲线、最大轴向拔出力（Fmax）。计算拔出刚度。 结果　A0至A5 6种螺钉的最大轴向拔出力分别为（983.99±324.19）、（1119.84±362.47）、（1067.67±398.00）、（900.04±255.89）、（799.07±406.79）、（850.71±408.11）N。6种不同规格TTPS轴向拔出力间无显著差异（组间差异P=0.216）。6种不同规格的TTPS的拔出刚度间无显著差异（组间差异P=0.07）。 结论　小范围增加螺纹牙厚,对椎弓根螺钉抗拔出力没有显著影响。     

不同角度置钉对椎弓根螺钉稳定性的影响

背景：有研究表明经皮椎弓根螺钉置入的准确性及手术效果要优于开放手术,但既往研究中对置钉角度与螺钉稳定性的关系尚不清楚。 目的：观察不同角度置钉对椎弓根螺钉稳定性的影响。 方法：选取成年猪椎体标本30个,分别按照不同的冠状面及矢状面角度置钉,通过机器测试各标本螺钉的最大拔出力,并绘制载荷-位移曲线,进行统计分析。 结果与结论：10°及15°冠状面及矢状面角度置钉的螺钉最大拔出力及最大能量明显优于0°角组(P < 0.05)。当应力超出最大拔出力时,螺钉的拔出力呈现缓降趋势,冠状面及矢状面10°及15°夹角组曲线相似,斜率优于0°角组(P < 0.05)。结果证实,置钉角度为经皮椎弓根螺钉稳定性提供有力帮助,螺钉开始松动后,把持力呈现稳步下降趋势。 中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程     

钉道局部点状固化技术强化椎弓根螺钉固定的生物力学研究

目的探讨钉道局部点状固化技术在体外强化椎弓根螺钉固定的效果。方法选用30个新鲜成年山羊腰椎。每一个椎体一侧椎弓根常规置钉(空白组);另一侧对钉道局部进行点状固化处理后拧入螺钉(实验组)。24h后,随机选取10个椎体行轴向拔出实验,其余20个椎体行周期抗屈实验。结果螺钉最大轴向拔出力(Fmax):空白组(637.60±109.95)N,实验组(816.50±134.88)N;螺钉拔出的能量吸收值:空白组(1.268±0.252)J,实验组(1.631±0.269)J,两组间差异均有统计学意义(P<0.05)。周期抗屈试验中,实验组的螺钉能够耐受更大的负荷或者在同等负荷下所产生的位移较小。结论钉道局部点状固化技术可以显著增加椎弓根螺钉固定的稳定性,为临床解决螺钉松动问题提供了新的研究方向,具有较好的临床应用前景。     

Comparison of Bioabsorbable Suture Anchor Fixation on the Tibial Side for Anterior Cruciate Ligament Reconstruction Using Free Soft Tissue Graft: Experimental Laboratory Study on Porcine Bone

Purpose

The use of graft tissue fixation using bioabsorbable interference screws (BISs) in anterior cruciate ligament (ACL) reconstruction offers various advantages, but limited pullout strength. Therefore, additional tibial fixation is essential for aggressive rehabilitation. We hypothesized that additional graft tissue fixation using bioabsorbable suture anchors (BSA) would provide sufficient pull-out strength.

Materials and Methods

Twenty four fresh frozen porcine distal femur and patellar tendon preparations were used. All specimens were divided into three groups based on additional fixation methods: A, isolated BIS; B, BIS and BSA; and C, BIS and post cortical screw. Tensile testing was carried out under an axial load. Ultimate failure load and ultimate failure load after cyclic loading were recorded.

Results

The ultimate failure loads after load to failure testing were 166.8 N in group A, 536.4 N in group B, and 438 N in group C; meanwhile, the ultimate failure loads after load to failure testing with cyclic loading were 140 N in group A, 466.5 N in group B, and 400 N in group C. Stiffness after load to failure testing was 16.5 N/mm in group A, 33.5 N/mm in group B, and 40 N/mm in group C. An additional BSA fixation resulted in a significantly higher ultimate failure load and stiffness than isolated BIS fixation, similar to post screw fixation.

Conclusion

Additional fixation using a BSA provided sufficient pullout strength for ACL reconstruction. The ultimate failure load of the BSA technique was similar to that of post cortical screws.     

椎体骨微结构参数与椎弓根螺钉固定强度的相关性

目的 测量不同骨密度（bone mineral density, BMD）条件下椎体松质骨显微结构参数,并与椎弓根螺钉拔出力作相关性分析,以了解与螺钉稳定性相关的骨显微结构参数,进一步明确螺钉松动的原因。方法 采用新鲜尸体脊柱标本,根据BMD检测结果,按临床诊断标准分为骨质正常、骨量减少、骨质疏松和重度骨质疏松4个水平。然后植入椎弓根螺钉,进行螺钉轴向拔出实验,测定最大拔出力（maximum pullout strength, MPS）。收集螺钉拔出实验后椎体标本,在椎体中央部钻取松质骨柱状样本,对样本进行显微CT扫描,获取椎体松质骨显微结构参数,并进行各项指标的不同BMD水平间的比较分析,在了解这些指标随骨质疏松程度加重的变化规律的基础上,再对骨显微结构参数与所对应的螺钉MPS开展相关性分析。结果BMD水平从正常下降到重度疏松程度,MPS随之显著性下降。随BMD水平的依梯次下降,即骨质疏松程度进行性加重,椎体松质骨显微结构参数发生相应明显变化,存在BMD水平间的显著性差异。广泛的相关性存在于BMD、显微CT参数和螺钉MPS指标之间。其中,螺钉MPS与显微CT扫描所得的骨体积分数（BV/TV）、骨小梁厚度（Tb.Th）和小梁间隙（Tb.Sp）呈高度相关性。结论 随BMD下降,骨组织会同时发生质的退变;螺钉MPS与部分骨显微结构参数高度相关。     

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5~7 mL;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。     

个体化3D打印导向模板辅助上颈椎椎弓根螺钉置入的实验研究

目的 评价个体化3D打印导向模板辅助上颈椎椎弓根螺钉置入的准确性和安全性。方法 纳入2013年10月—2015年9月蚌埠医学院第二附属医院CT中心的13例上颈椎疾病患者术前CT检查数据,利用Mimics 15.0、Geomagic Studio 2013、NX 8.5三种计算机软件设计出寰枢椎椎弓根螺钉置钉导向模板,并运用3D打印技术打印出颈椎等比例实体模型和上颈椎椎弓根置钉导向模板。每例颈椎模型3D打印2份,分为两组:实验组利用导向模板辅助置入寰枢椎椎弓根螺钉;对照组采用影像学透视徒手置入寰枢椎椎弓根螺钉。两组上颈椎椎弓根螺钉均由同一名脊柱外科主任医师负责置入。以术后CT扫描数据评估上颈椎椎弓根螺钉置钉导向模板辅助置钉的准确性,对螺钉置入情况分类,依据螺钉在矢状面和横断面穿破椎弓根皮质程度以及是否需要翻修将其分为3类,其中Ⅰ类和Ⅱ类螺钉为可接受置钉,Ⅲ类螺钉为不可接受置钉。结果 实验组设计并打印出上颈椎3D打印导向模板19块,辅助置入螺钉37枚,其中Ⅰ类33枚(86.49%)、Ⅱ类2枚(8.11%)、Ⅲ类2枚(5.40%);模拟手术置入1枚螺钉平均时间为(5.37±1.26) min,X线机透视次数为(5.48±1.19)次,螺钉长(28.38±2.98)mm。对照组使用C形臂X光机透视下徒手置入上颈椎椎弓根螺钉合计37枚,其中Ⅰ类23枚(62.16%)、Ⅱ类3枚(8.11%)、Ⅲ类11枚(29.73%);模拟手术置入1枚螺钉平均时间为(11.48±2.32) min,X线机透视次数平均为(17.85±2.96)次,螺钉长(28.65±2.83)mm。实验组与对照组螺钉置入的成功率分别为94.60%(35/37)和70.27%(25/37),差异有统计学意义(Z=-5.790, P<0.05);实验组与对照组使用螺钉长度差异无统计学意义(t=0.399, P>0.05);实验组置入单枚螺钉用时和X光机透视次数均明显少于对照组,差异均有统计学意义(t=-14.078、-23.586, P值均<0.01)。结论 个性化导向模板辅助上颈椎置钉显著提高了置钉的安全性和准确性,尤其适用于严重畸形的上颈椎椎体。3D打印个体化上颈椎椎弓根螺钉置钉导板体现了个体化置钉原则,置钉成功率高、安全、有效、可行,有临床推广价值。     

骶髂螺钉LX 固定方式的生物力学特性分析

目的　研究骶髂螺钉LX固定方式与目前常规骶髂螺钉固定方式的拔出强度、刚度、能量吸收，确定比较符合人体生物力学要求的固定方式。方法　8具甲醛固定湿润成人尸体的正常骨盆标本，平均年龄23~45岁。骨密度测量排除骨质疏松，排除畸形、肿瘤、外伤等异常。将骨盆等分锯成两半，左侧组采用骶髂螺钉LX固定，置入正、负应力骶髂拉力螺钉，沿着骶髂关节复合体的压力带和张力带轴线，分别置入骶髂关节复合体的张力带和压力带；右侧组置入常规骶髂拉力螺钉。测量拧紧力矩、轴向拔出力、相对位移、应变、能量吸收。结果　拧紧力矩与骨密度、拧紧力矩与轴向拔出力、轴向拔出力与骨密度之间存在明显的正相关关系(P<0.05)。左侧组拔出力为(1158.10±29.20)N，比右侧组(791.2±44.6)N高32%(P<0.05)。右侧组的吸收能量为(6.52±0.78)J，左侧组的吸收能量为(11.75±1.45)J，左右两侧总的能量相比，左侧比右侧大(P<0.05)。结论　骶髂螺钉LX固定方式的强度和刚度均高于常规骶髂螺钉固定，拔出螺钉需要的能量亦大，具有生物力学优势，有利于骶髂复合体修复，更符合人体工程学要求。     

骨水泥加固椎弓根螺钉的生物力学特性

背景：由于骨质原因及结构特点导致椎弓根螺钉经常出现把持力下降,从而发生松动、拔出,导致内固定失败,因此提高椎弓根螺钉的稳定性显得尤为重要。 目的：检测可注射骨水泥空心椎弓根螺钉椎弓根螺钉生物力学稳定性,为优化骨水泥使用量提供参考。 方法：选取7具新鲜成人尸体T₁₁-L₄椎体标本共40个椎体,随机分为可注射骨水泥空心椎弓根螺钉及DTPS^TM椎弓根螺钉组,各20个,置钉后分别注入1,2,3,5 mL骨水泥,通过影像学观察骨水泥弥散分布情况,并测得最大轴向拔出力进行比较。 结果与结论：骨水泥用量为1-3 mL时,可注射骨水泥空心椎弓根螺钉组螺钉平均最大轴向拔出力显著高于DTPS^TM组(P < 0.05)。骨水泥用量为5 mL时,2组平均最大轴向拔出力差异无显著性意义(P > 0.05)。可注射骨水泥空心椎弓根螺钉组的直线回归方程为Y=25.269X+133.681(R²=0.837),DTPS^TM椎弓根螺钉组的直线回归方程为Y=32.039X+99.251(R²=0.936)。骨水泥用量在1-5 mL时,2组螺钉最大轴向拔出力与骨水泥量高度正相关(|R| > 0.8)。说明骨水泥强化椎弓根螺钉可显著提高螺钉稳定性,椎弓根螺钉最大轴向拔出力与骨水泥使用量呈高度正相关,可注射骨水泥空心椎弓根螺钉在达到满意的内固定强化效果同时,减少骨水泥使用量,降低了骨水泥泄漏风险,相比DTPS^TM椎弓根螺钉更具有优势。中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程     

The effect of flexion angle on the macro and microscopic appearance of the rupture surface of the ACL of rabbits

This study investigated how knee flexion angle affects the appearance of the rupture surface of the anterior cruciate ligament (ACL) using rabbit knees. Specimens were failed at flexion angles of 45 degrees and 90 degrees at displacement rates of 10 and 500 mm/min. Video recordings and scanning electron microscopy (SEM) studied the appearance of the rupture surfaces. At the displacement rate of 10 mm/min, the major mode of failure was fibre pullout for all flexion angles. At displacement rate of 500 mm/min, which more closely approximated loading conditions during trauma, we found that all modes of failure were exhibited. At 45 degrees flexion, the majority of specimens tested failed by avulsion. The reverse was true for specimens tested at 90 degrees where the majority of failures were fibre pullouts. At 45 degrees, there were more pulled-out fibres on rupture surfaces of specimens tested at 10 mm/min than at 500 mm/min. At 90 degrees, little difference was seen in the appearance of ruptures from both rates. SEM revealed that the waviness of collagen fibres was more pronounced at 10 mm/min. Therefore, the appearance of rupture surfaces of ACLs are affected by both flexion angle and displacement rate.     

微创L5椎弓根钉进钉点的有效性分析

背景：在临床应用中,第5腰椎人字嵴结构不清,往往需扩大显露范围,通过横突、上下关节突等结构明确进钉点,增加了创伤和医源性上位椎间退变的风险。因此有必明确一个微创的L₅椎弓根钉进钉点。 目的：通过影像学评价以L5乳突“斜坡”作为进钉点的L₅椎弓根螺钉置入准确性。 方法：第5腰椎上关节突基底部的乳突向后突起的最高点向内下方延伸过程中形成一斜面,将其定义为乳突“斜坡”;其内侧为椎弓根部内上缘,向外比邻横突根部,位于人字嵴结构顶点的略上方,“斜坡”是椎旁肌间隙入路时可最先触及且显露的骨性部位。以乳突“斜坡”为进钉点,对50例腰椎退行性疾病患者行L5椎弓根螺钉置入内固定,根据术前CT和X射线透视确定椎弓根钉矢状面和横断面的进钉方向。椎弓根钉直径均为6.5 mm。修复过程中评价其一次性置钉成功率,置钉后行腰椎正侧位X射线片和CT检查,评价置钉准确率。 结果与结论：应用乳突“斜坡”定位法的一次性置钉成功率为96%(96/100);于L₅椎体内共置入100枚椎弓根螺钉,根据Gertzbein等推荐的标准,95枚(95%)螺钉完全位于椎弓根内,5枚(5%)螺钉均向内侧穿透椎弓根皮质,其中3枚(3%)螺钉穿透距离< 2 mm,2枚(2%)螺钉穿透距离为2-4 mm,均未出现神经根损伤等并发症。提示L5乳突“斜坡”定位法的一次性置钉成功率高,结合置钉前的X射线片和CT评价可获得较高的置钉准确率。中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程     

A parametric study of cylindrical pedicle screw design implications on the pullout performance using an experimentally validated finite-element model

The present study aims to the design of a finite-element model simulating accurately the pullout behaviour of cylindrical pedicle screws and predicting their pullout force. Three commercial pedicle screws, subjected to pure pullout from synthetic bone, were studied experimentally. The results were used for the design, calibration and validation of a finite-element model. Special attention was paid to the accurate simulation of the failure inside the host material under shear. For this purpose, a bilinear cohesive zone material model was adopted, controlling the mode-II debonding of neighbouring elements in the vicinity of the screw. Comparison between experimental and numerical results proved that the implementation of this approach can significantly enhance the accuracy of the numerical simulation of a screw's mechanical behaviour under pure pullout loads. The numerical model was used for the parametric study of various factors affecting the pullout performance of a cylindrical pedicle screw. It was concluded that the major parameter influencing the pullout force is the outer radius (increasing its value by 36% increases the pullout force by 34%). The influence of the purchase length of the screw is of similar quantitative nature. The respective dependence on the thread inclination, depth and pitch was significantly weaker.     

Biomechanical study of expandable pedicle screw fixation in severe osteoporotic bone comparing with conventional and cement-augmented pedicle screws

Pedicle screws are widely utilized to treat the unstable thoracolumbar spine. The superior biomechanical strength of pedicle screws could increase fusion rates and provide accurate corrections of complex deformities. However, osteoporosis and revision cases of pedicle screw substantially reduce screw holding strength and cause loosening. Pedicle screw fixation becomes a challenge for spine surgeons in those scenarios. The purpose of this study was to determine if an expandable pedicle screw design could be used to improve biomechanical fixation in osteoporotic bone. Axial mechanical pull-out test was performed on the expandable, conventional and augmented pedicle screws placed in a commercial synthetic bone block which mimicked a human bone with severe osteoporosis. Results revealed that the pull-out strength and failure energy of expandable pedicle screws were similar with conventional pedicle screws augmented with bone cement by 2 ml. The pull-out strength was 5-fold greater than conventional pedicle screws and the failure energy was about 2-fold greater. Besides, the pull-out strength of expandable screw was reinforced by the expandable mechanism without cement augmentation, indicated that the risks of cement leakage from vertebral body would potentially be avoided. Comparing with the biomechanical performances of conventional screw with or without cement augmentation, the expandable screws are recommended to be applied for the osteoporotic vertebrae.     

快速建立小牛椎体骨质疏松模型

背景：目前用于脊柱生物力学研究的骨质疏松动物模型是以去势雌性动物或服药动物为代表的动物模型,但存在建立时间长、可靠性差的问题。 目的：利用Shandon TBD-1脱钙法快速建立牛椎体骨质疏松模型。 方法:选取新鲜小牛脊柱第6~11节椎体,共24个椎体,测量骨密度后,随机分为3组：预实验组采用Shandon TBD-1浸泡椎体,脱钙组将Shandon TBD-1注入椎体一侧钉眼内,对照组不做脱钙处理。脱钙后再次测量骨密度,将相同规格的椎弓根螺钉拧入双侧椎弓根,测试其最大轴向拔出力。 结果与结论：预实验组椎体脱钙后椎体骨密度随着脱钙时间的延长而降低;脱钙组骨密度值、椎弓根螺钉最大轴向拔出力均低于对照组( P < 0.01),且骨密度与椎弓根螺钉最大轴向拔出力存在线性正相关。说明应用Shandon TBD-1脱钙剂对小牛椎体脱钙是一种快速制备骨质疏松动物模型的方法,并能够很好模拟骨质疏松的力学性能。     

生物力学评价颈椎前路椎弓根螺钉植入骨质疏松椎骨内的稳定性

背景：前路颈椎间盘切除植骨融合是治疗颈椎病的有效术式,该术式能够提供坚强固定且植骨融合率相对较高。但是,对于2个节段以上同时受累的颈椎,由于植骨跨度较大,内固定和植骨块稳定性较差,容易产生植骨融合失败、假关节形成等并发症,影响疗效。 目的：观察颈椎前路椎弓根螺钉植入骨质疏松椎骨内的生物力学稳定性。 方法：纳入12具人颈椎骨,包括6具骨密度正常颈椎骨和6具骨质疏松颈椎骨,共60个椎骨标本资料进行分析,将30个骨质疏松椎骨标本植入颈椎前路椎弓根螺钉设为颈椎前路椎弓根螺钉组,将30个骨密度正常椎骨标本植入前路椎体螺钉设为前路椎体螺钉组。从上述两组中根据骨密度值抽取40个椎骨,分别设置为即时正常骨密度组、即时骨密度疏松组、疲劳正常骨密度组以及疲劳骨质疏松组,每组10个椎骨。采用双能X射线骨密度仪测定各椎体骨密度值,采用ElectroForce 3510材料试验机对两种螺钉进行生物力学指标测试。 结果与结论：颈椎前路椎弓根螺钉组骨矿盐含量、椎体螺钉拔出力、椎体螺钉拔出刚度、椎弓根螺钉拔出力、椎弓根螺钉拔出刚度均显著高于前路椎体螺钉组(P < 0.05)。颈椎前路椎弓根螺钉即时正常骨密度标本最大轴向拔出力、即时骨质疏松标本最大轴向拔出力、疲劳正常骨密度标本最大轴向拔出力、疲劳骨质疏松标本最大轴向拔出力均显著高于高于前路椎体螺钉(P < 0.05)。结果证实,与颈椎前路椎体螺钉相比,颈椎前路椎弓根螺钉在骨质疏松椎骨内生物力学性能更加稳定。中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程     

Biomechanical evaluation of bending strength of spinal pedicle screws,including cylindrical,conical, dual core and double dual core designs using numerical simulations and mechanical tests

Pedicle screws are used for treating several types of spinal injuries. Although several commercial versions are presently available, they are mostly either fully cylindrical or fully conical. In this study, the bending strengths of seven types of commercial pedicle screws and a newly designed double dual core screw were evaluated by finite element analyses and biomechanical tests. All the screws had an outer diameter of 7 mm, and the biomechanical test consisted of a cantilever bending test in which a vertical point load was applied using a level arm of 45 mm. The boundary and loading conditions of the biomechanical tests were applied to the model used for the finite element analyses. The results showed that only the conical screws with fixed outer diameter and the new double dual core screw could withstand 1,000,000 cycles of a 50–500 N cyclic load. The new screw, however, exhibited lower stiffness than the conical screw, indicating that it could afford patients more flexible movements. Moreover, the new screw produced a level of stability comparable to that of the conical screw, and it was also significantly stronger than the other screws. The finite element analysis further revealed that the point of maximum tensile stress in the screw model was comparable to the point at which fracture occurred during the fatigue test.