椎弓根螺钉骨水泥强化固定治疗腰椎退行性变的临床效果

目的 探讨椎弓根螺钉骨水泥强化固定治疗腰椎退行性变的临床效果.方法 对56例腰椎退行性变患者行椎弓根螺钉骨水泥强化固定、椎间植骨融合,术前测量拟固定椎体的骨密度,术中测量螺钉的最大旋入力偶矩后取出螺钉,钉道注入聚甲基丙烯酸甲酯（PMMA）3ml再次置入螺钉并测量螺钉的最大旋入力偶矩,椎体固定后减压并行椎体间植骨融合.结果 患者均获随访,时间6~24（14.4±3.6）个月,均未发生内固定物松动、断钉及断棒等并发症.影像学评估：骨水泥分布于钉道周围松质骨中无明显椎体外渗.末次随访时按改良Macnab标准评价临床疗效：优27例,良22例,可7例;椎弓根螺钉的最大旋入力偶矩经术中骨水泥强化固定后由（0.61±0.23）N·m增至（1.35±0.32） N·m,差异有统计学意义（P〈0.05）.结论椎弓根螺钉骨水泥强化固定治疗腰椎退行性变可以明显增强螺钉的稳定性.     

骨水泥强化椎弓根螺钉固定治疗老年退行性腰椎不稳的临床疗效分析

目的:探讨用聚甲基丙烯酸甲(polymethylmethacrylate,PMMA)骨水泥强化椎弓根螺钉内固定治疗老年退行性腰椎不稳的临床疗效.方法:回顾性分析2002年3月～2009年6月收治的23例老年腰椎退行性不稳患者的临床资料,其中:男6例,女17例;年龄62～77岁,平均71岁;均采用PMMA骨水泥强化椎弓根螺钉内固定、椎体间植骨融合治疗,术前测量待置人螺钉之椎体的骨密度,术中测量螺钉的最大旋入力偶矩;取出螺钉后经钉道注入3ml粘稠的PMMA,再拧入螺钉,10min后拧紧螺钉并测量螺钉的最大旋入力偶矩;减压后行植骨融合内固定.结果:所有患者随访7～24个月,平均17个月,腰腿痛治愈好转率达87%,无手术并发症发生.PMMA强化椎弓根螺钉后,螺钉的最大旋入力偶矩由0.591±0.213N·m增至1.332±0.377N·m,差异有显著性(P<0.01):影像学表现为骨水泥分布于钉道周嗣松质骨中,未出现椎体外渗漏.结论:骨水泥强化椎弓根螺钉内固定治疗老年退行性腰椎不稳能明显增强螺钉的稳定性;正确掌握进钉技术及螺钉强化技术是手术成功的关键.     

强化骨质疏松椎弓根螺钉治疗老年腰椎疾患

目的评价骨水泥强化骨质疏松椎弓根螺钉治疗老年腰椎疾患的临床疗效。方法对22例老年腰椎疾病患者行骨水泥强化椎弓根螺钉、椎间植骨融合。术前测量待植入螺钉之椎体的骨密度;术中测量螺钉的最大旋入力偶矩;用3ml骨水泥强化椎弓根螺钉,测量螺钉的最大旋入力偶矩;减压后行椎间植骨融合术。结果患者均未发生手术并发症,睽腿痛治愈、好转20例,2例症状无明显改善。强化椎弓根螺钉后,螺钉的最大旋入力偶矩由（0．591±0．213）Nm增至（1．332±0．377）Nm．差异有显著性（P〈0．01）。影像学表现为骨水泥分布于钉道周围松质骨中,未出现椎体外渗漏。结论骨水泥强化骨质疏松椎弓根螺钉治疗老年腰椎疾患能明显增强螺钉的稳定性。     

后凸成形骨水泥强化技术对骶骨钉固定强度的生物力学影响

目的评价后凸成形骨水泥(Polymethylmethacrylate,PMMA)强化技术对骨质疏松情况下骶骨钉固定强度的生物力学影响,为骶骨钉松动选择坚强的补救技术提供依据。方法11具新鲜骶骨标本用于实验,并采用DEXA评价标本骨密度。在同一骶骨标本上,依次建立非PMMA强化和PMMA强化骶骨钉的固定模型如下,A组:单皮质椎弓根钉;B组:双皮质椎弓根钉;C组:传统PMMA强化单皮质椎弓根钉;D组:后凸成形PMMA强化椎弓根钉;E组:后凸成形PMMA强化侧翼钉。在MTS试验机上对五种骶骨钉依次进行轴向拔出测试,记录最大拔出力并比较。结果11具标本的平均骨密度为0.71±0.08g/cm2。A组的螺钉拔出力(508N)显著低于其他4种固定组(P0.05)。B组的螺钉拔出力(685N)与E组(702N)无显著差异(P0.05),但是,两者的拔出力均显著低于C和D组(P0.05)。重要的是,D组(986N)的拔出力显著高于C组(846N)。结论在骨质疏松患者的骶骨固定中,双皮质骶骨椎弓根钉较单皮质具有显著的力学优势。骶骨椎弓根钉一旦发生松动,传统的和后凸成形PMMA强化技术均可成为补救手段,并且后凸成形PMMA强化骶骨椎弓根钉可获得最坚强的锚定。     

PMMA提高椎体钉固定强度的体外实验研究

[目的]探讨骨水泥(PMMA)强化后椎体钉穿透单侧椎体固定的可行性。[方法]选用新鲜成人尸体标本32个,按骨密度分为骨质正常组和骨质疏松组分别进行实验。实验组为骨水泥(PMMA)强化后椎体钉穿单侧椎体皮质固定;对照组为无骨水泥强化,椎体钉穿透双侧椎体皮质固定。应用螺钉拔出实验,记录螺钉最大拔出力。[结果]在骨质正常组中,PMMA组和对照组拉出力分别为1758.42±32.63N和843.25±65.35N,增加109%±33%。在骨质疏松组中,PMMA组和对照组拉出力分别为811.19±188.58N和374.21±77.66N,增加122%±56%。差异有显著性P<0.01。[结论]应用PMMA固化椎体钉,减少手术并发症是可行的。     

geneX骨水泥强化骨质疏松椎体椎弓根钉的生物力学研究

目的评估骨质疏松情况下geneX骨水泥强化椎弓根钉的固定强度。方法应用微量注射泵对30个新鲜小牛腰椎标本注射稀盐酸建立骨质疏松椎体模型。60个椎弓根分为四组:geneX骨水泥组,硫酸钙骨水泥(CSC)组,聚甲基丙烯酸甲酯骨水泥(PMMA)组,对照组。随机选择一侧注射2.5 ml骨水泥,然后置入螺钉;另一侧行正常螺钉固定对照,应用材料试验机进行轴向拔出力测试,记录各组的轴向最大拔出力和能量吸收值并进行比较。结果 geneX组与CSC组两组拔出力及能量吸收值比较,差异无统计学意义(P>0.05),两组均显著低于PMMA组(P<0.05),两组均显著高于对照组(P<0.05)。结论 geneX骨水泥强化椎弓根钉可显著提高椎弓根固定强度,geneX骨水泥可用作椎弓根强化螺钉的填充材料。     

不同椎弓根螺钉固定及骨水泥强化方法在骨质疏松骶骨上锚定强度的比较

目的:通过比较不同椎弓根螺钉固定及骨水泥强化方法在骨质疏松骶骨上的锚定强度,探讨骶骨椎弓根螺钉松动后的理想补救技术.方法:应用11具成人新鲜骶骨标本,经骨密度测试确认为骨质疏松后,在同一骶骨标本上,依次建立5种骶骨螺钉固定模型,A组,单皮质椎弓根螺钉固定(左侧):B组,双皮质椎弓根螺钉固定(右侧);C组,PMMA钉道强化后单皮质椎弓根螺钉固定(建立于A组螺钉拔出后);D组,PMMA钉道强化后侧翼钉固定(右侧);E组,后凸成形技术支持下的PMMA强化后侧翼钉固定(左侧).应用MTS材料测试机进行轴向拔出测试,记录各种骶骨螺钉固定技术的最大拔出力并进行比较.结果:11具标本的骨密度为0.55～0.79g,cm~2,平均0.71±0.08g/cm~2.A～E组最大拔出力分别为508±128N、685±126N、846±230N、543±121N和702±144N.A组与D组间无显著性差异(P>0.05),且均显著低于B、C和E组(P<0.05);B组与E组间无显著性差异(P>0.05),但两组的拔出力均显著低于C组(P<0.05).结论:在骨质疏松患者的骶骨固定中,双皮质骶骨椎弓根钉较单皮质具有更高的锚定强度.骶骨椎弓根钉一旦发生松动,PMMA钉道强化和后凸成形技术支持下的PMMA强化后的侧翼钉固定均可成为理想的补救手段.     

通用型脊柱内固定系统椎弓根螺钉的生物力学测试

目的测试自行设计的通用型脊柱内固定系统(generalspinesystem,GSS)椎弓根螺钉以及SOCON和CCD螺钉置入正常成人椎体标本的最大轴向拔出力及最大旋入力矩,评价GSS螺钉对椎弓根的锚固作用。方法将27个正常成人腰椎椎体标本随机分为3组,每组9个椎体(18侧椎弓根),分别置入GSS、SOCON和CCD椎弓根螺钉,行螺钉拔出试验,测试并记录螺钉的最大旋入力矩和最大轴向拔出力。结果三组螺钉的最大旋入力矩分别为(1.83±0.27)Nm、(2.09±0.51)Nm和(1.66±0.34)Nm,最大轴向拔出力分别为(1131.0±255.4)N、(1034.0±262.3)N和(886.1±152.9)N。GSS螺钉最大轴向拔出力最大,且与CCD螺钉相比差异有非常显著性意义(P<0.01)。结论GSS螺钉具有很强的椎弓根锚固作用。     

通用型脊柱内固定系统椎弓根螺钉翻修作用的生物力学研究

目的测试自行设计的通用型脊柱内固定系统(generalspinesystem,GSS)椎弓根螺钉以及SOCON、TSRH和Diapason螺钉置入椎体的拔出力及旋入力矩,评价GSS螺钉的翻修作用。方法将36个正常成人腰椎椎体标本随机分为三组,每组12个椎体(24侧椎弓根)。各组标本每个椎体的每侧椎弓根均先拧入CCD螺钉(直径6.0mm,长45mm),行螺钉拔出试验,测试并记录螺钉的最大旋入力矩和最大轴向拔出力。然后各组标本每个椎体均随机选择一侧椎弓根经原钉道拧入GSS螺钉(直径6.5mm,长45mm);第一组另一侧拧入SOCON螺钉(直径7.0mm,长45mm),第二组另一侧拧入TSRH螺钉(直径7.0mm,长45mm),第三组另一侧拧入Diapason螺钉(直径6.7mm,长45mm)。分别测试螺钉最大旋入力矩及最大轴向拔出力。结果第一组GSS螺钉最大轴向拔出力为CCD螺钉的114%,SOCON螺钉为CCD螺钉的108%;GSS螺钉最大轴向拔出力大于SOCON螺钉,差异无显著性(P>0.05);GSS螺钉最大旋入力矩小于SOCON螺钉,差异无显著性(P>0.05)。第二组GSS螺钉最大轴向拔出力为CCD螺钉的127%,TSRH螺钉为CCD螺钉的64%;GSS螺钉最大轴向拔出力大于TSRH螺钉,差异有显著性(P<0.01);GSS螺钉最大旋入力矩大于TSRH螺钉,差异有显著性(P<0.01)。第三组GSS螺钉最大轴向拔出力为CCD螺钉的122%,Diapason螺钉为CCD螺钉的8     

CPC提高椎体钉固定强度的体外实验研究

目的探讨磷酸钙骨水泥(calcium phosphate cement,CPC)强化骨质疏松椎体钉后穿透单侧椎体皮质固定的可行性。方法选用新鲜成人尸体胸腰段骨质疏松标本24个,实验组为骨水泥(PMMA)和磷酸钙骨水泥灌注后椎体钉穿透单侧椎体皮质固定;对照组为无骨水泥强化,螺钉穿透双侧椎体皮质固定。应用螺钉拔出实验,记录螺钉最大拔出力并观察椎体破坏形态。结果三组拉出力值PMMA组(811.19±188.58N)、CPC组(541.89±101.44N)、对照组(374.21±77.66N)差异有显著性,P<0.01。分别增加122%±56%和50%±37%。对照组(8例)螺钉拔出破坏时均为螺钉抽出,在8例PMMA强化椎体中所有椎体均有不同程度骨折。而在8例CPC强化椎体中仅1例发生椎体骨折。结论应用CPC强化骨质疏松椎体钉简化手术步骤、增加手术安全性是可行的。     

Polymethylmethacrylate augmentation of the pedicle screw: the cement distribution in the vertebral body

Many studies have proven that the polymethylmethacrylate (PMMA) augmentation of the pedicle screw can significantly increase stiffness and strength of spinal fixation. Some major complications have also been reported. However, there are no reports discussing cement distribution and its morphology in the osteoporotic vertebral body, which is critical in the analysis of the biomechanical strength of the pedicle screw and the risk of cement leakage after pedicle screw augmentation. In this study, we used computed tomography (CT) to evaluate the cement distribution in the osteoporotic vertebral body after PMMA augmentation of a pedicle screw and to analyze the factors leading to cement leakage. Two groups of patients were studied. Group A consisted 25 osteoporotic patients (mean age of 73 years) with spinal instrumentation who had a total of 145 pedicle screws and cement augmentation with biopsy needles. Group B consisted of 23 osteoporotic patients (mean age of 74.6 years) with spinal instrumentation who had a total of 125 cannulated pedicle screws with cement augmentation. All patients had CT evaluation of the cement distribution in the vertebral body after the surgery. The cement distribution in the vertebrae was divided into four zones in the axial CT view: anterior one-third, middle third, and posterior third of vertebral body, and the pedicle. The morphology of the cement distribution around the pedicle screw was defined as scattered type or concentrate type. The leakage pattern was divided to anterior–lateral, posterior–lateral, and canal leakage. The correlations among bone mineral density (BMD), the cement leakage rate, and cement distribution morphology were also analyzed. The results showed that most augmented pedicle screws had cement extension into three of the four zones of the vertebral body (66.3%), followed by two zones (20%), all four zones (11.5%), and only one zone (2.2%). Overall, 123 screws (84.8%) in Group A and 108 screws (86.4%) in Group B had cement concentrate type distribution. The cement leakage rate in Group A is 18.3% and 13.6% in Group B. Patients with a BMD <0.6 g/cm² had significantly higher rates of cement leakage and tended toward a scattered cement distribution. There was only one patient who had a symptomatic leakage (sciatica) in Group B. We concluded that the cement distribution after pedicle screw augmentation with biopsy needle or cannulated screw technique was mostly localized in three zones of the vertebral body, and patients with lower BMD had a higher risk of cement leakage and scattered cement distribution.     

Evaluation of calcium sulfate paste for augmentation of lumbar pedicle screw pullout strength.

BACKGROUND CONTEXT: Many authors have evaluated the components responsible for ultimate pullout strength of pedicle screws. In these studies, one important variable has been the screw fixation. Because pedicle screw fixation has increased in popularity over recent years, so has the need for augmentation in difficult situations. Polymethylmethacrylate (PMMA) has been established as the gold standard in terms of strength of fixation but has the potential for severe complications when applied in spine surgery. Calcium sulfate is an alternative to PMMA, because it lacks the exothermic reaction, is potentially osteoconductive and is resorbed by the body in 30 to 60 days. PURPOSE: To determine the strength of a new calcium sulfate cement in terms of pedicle screw augmentation. The purpose was to evaluate calcium sulfate versus PMMA in terms of pullout strength. PMMA was considered the gold standard in terms of strength for this experiment. STUDY DESIGN: Lumbar vertebrae implanted with pedicle screws were subjected to axial pullout tests. The force required to cause implant failure was measured and compared for three methods of fixation. OUTCOME MEASURES: Force to failure (Newtons) for each pedicle test was recorded and analyzed with results from similarly augmented pedicles. METHODS: Lumbar vertebrae were harvested from four cadavers and implanted with pedicle screws. These screws were either placed in native bone or augmented with either calcium sulfate paste or PMMA. In those pedicles that had augmentation, the material was permitted to set for a minimum of 24 hours. Axial pullout tests were then performed using an MTS (Materials Testing System Corporation, Minneapolis, MN) testing machine. The screws were pulled out over a distance of up to 6 mm at 0.25 mm/sec. This rate and distance ensured failure in each case. The load to failure was recorded for each pedicle. RESULTS: Calcium sulfate augmentation improved pedicle screw pullout strength significantly when compared with native bone (p=.0003). This represented an average increase of 167% over the native bone. Likewise, PMMA improved the pullout strength significantly over native bone (p<.0001) for an average increase of 199%. There were no significant differences between the calcium sulfate and PMMA augmentation (p=.0791), although the PMMA averaged 119% of the strength of calcium sulfate. CONCLUSIONS: Although PMMA is considered the gold standard in terms of fixation strength, its use around the spine has been limited because of concern over complications. The calcium sulfate bone paste tested in this study demonstrated strength similar to PMMA without the major risks to the spinal cord. In addition, the calcium sulfate paste allows for possible osteoconduction to aid in spinal fusion. Further study is needed to determine the applicability of this calcium sulfate paste in the clinical setting of spine surgery.     

Augmentation of anterior vertebral body screw fixation by an injectable, biodegradable calcium phosphate bone substitute.

STUDY DESIGN: A biomechanical study to evaluate the effects of a biodegradable calcium phosphate (Ca-P) bone substitute on the fixation strength and bending rigidity of vertebral body screws. OBJECTIVES: To determine if an injectable, biodegradable Ca-P bone substitute provides significant augmentation of anterior vertebral screw fixation in the osteoporotic spine. SUMMARY OF BACKGROUND DATA: Polymethylmethacrylate (PMMA) augmented screws have been used clinically; however, there is concern about thermal damage to the neural elements during polymerization of the PMMA as well as its negative effects on bone remodeling. Injectable, biodegradable Ca-P bone substitutes have shown enhanced fixation of pedicle screws. METHODS: Sixteen fresh cadaveric thoracolumbar vertebrae were randomly divided into two groups: control (no augmentation) (n = 8) and Ca-P bone substitute augmentation (n = 8) groups. Bone-screw fixation rigidity in bending was determined initially and after 10(5) cycles, followed by pullout testing of the screw to failure to determine pullout strength and stiffness. RESULTS: The bone-screw bending rigidity for the Ca-P bone substitute group was significantly greater than the control group, initially (58%) and after cyclic loading (125%). The pullout strength for Ca-P bone substitute group (1848 +/- 166 N) was significantly greater than the control group (665 +/- 92 N) (P < 0.01). Stiffness in pullout for the Ca-P bone substitute groups (399 +/- 69 N/mm) was significantly higher than the control group (210 +/- 51 N/mm) (P < 0.01). CONCLUSION: This study demonstrated that augmentation of anterior vertebral body screw fixation with a biodegradable Ca-P bone substitute is a potential alternative to the use of PMMA cement.     

Biomechanical study of pedicle screw fixation in severely osteoporotic bone.

BACKGROUND CONTEXT: Obtaining adequate purchase with standard pedicle screw techniques remains a challenge in poor quality bone. The development of alternate insertion techniques and screw designs was prompted by recognition of potential fixation complications. An expandable pedicle screw design has been shown to significantly improve fixation compared to a conventional screw in poor quality bone. PURPOSE: The purpose of this study was to determine if polymethylmethacrylate (PMMA) bone cement augmentation of an expandable pedicle screw can further improve fixation strength compared to the expandable screw alone in severely osteoporotic bone. A technique for cement insertion into the pedicle by means of the cannulated central portion of the expandable screw is also described. STUDY DESIGN: The axial pullout strength, stiffness and energy absorbed of cemented and noncemented expandable pedicle screws was determined in cadaveric vertebrae. METHODS: Twenty-one fresh unembalmed vertebrae from the thoracolumbar spine were used. Radiographs and bone mineral density measurements (BMD) were used to characterize bone quality. Paired cemented and noncemented pedicle screw axial pullout strength was determined through mechanical testing. Mechanical pullout strength, stiffness and energy to failure was correlated with BMD. RESULTS: Overall, there was a 250% increase in mean pullout strength with the cemented expandable screw compared with a noncemented expandable screw including a greater than twofold increase in pullout strength in the most severely osteoporotic bone. The mean stiffness and energy absorbed to failure was also significantly increased. A cemented conventional screw achieved a pullout strength similar to the noncemented expandable screw. CONCLUSIONS: PMMA cement augmentation of the expandable pedicle screw may be a viable clinical option for achieving fixation in severely osteoporotic bone.     

松质骨螺钉骨水泥强化的生物力学和组织学研究

目的通过动物实验观察不同骨水泥强化松质骨螺钉的生物力学和组织学变化动态,为骨质疏松骨折患者内固定提供理论基础。方法在10只杂种犬胫骨近端制作松质骨螺钉植入的动物模型,分别采用碳酸化羟基磷灰石水泥(CHC)和聚甲基丙烯酸甲酯(PMMA)强化,分别于术后5d、4、8、12和16周处死动物,观察螺钉拔出的生物力学和组织学变化。结果CHC强化的螺钉拔出力随手术后时间的延长而逐渐升高,16周时达到(512.5 14.5)N,而PMMA强化组螺钉拔出力则随手术后时间的延长而逐渐降低。CHC-骨界面结合紧密,并且随时间延长出现CHC降解和骨长入,而PMMA-骨界面形成一层纤维组织。结论CHC强化能够提高松质骨螺钉植入体内的稳定性,并且随植入时间延长而逐渐升高。     

Pedikelschraubenaugmentation aus biomechanischer Sicht

Severe osteoporosis is a serious problem in the instrumentation during spine surgery. Besides kyphosis, adjacent vertebral fractures and of course pedicle screw loosening and implant pullout are frequent challenges in instrumentation of the osteoporotic spine. In addition to screw diameter and length, bone mineral density has the most important impact on the stability of a pedicle screw. In cases of severe osteoporosis cement augmentation increases the stability of a pedicle screw. Pullout force can be increased with augmentation by 96–278%. Nowadays, there are two different procedures for augmentation: cement augmentation of the vertebra before inserting the screw into the soft, fresh cement or augmentation via a perforated screw that has already been inserted. The main problem in augmentation techniques are cement leakages. In both techniques leakages may occur. The problem of leakages seems to be less severe in the augmentation technique via the perforated screw, because cement application can be stopped immediately if the onset of leakage is noticed. Even surgical revision of cement augmented screws is not a major clinical problem based on recent biomechanical studies. The revision screw can be chosen 1 mm thicker and can be cement augmented again without technical problems.     

四种骶骨钉固定技术的生物力学比较

目的通过骨质疏松骶骨标本对4种骶骨椎弓根钉（双皮质、三皮质、标准骨水泥强化和终板下骨水泥强化）载荷后的下沉位移进行比较。方法取自11具新鲜骨质疏松尸体的骶骨标本用于实验。采用DEXA测定骨密度后在同一骶骨的左右侧随机置入直径7mm的双皮质和三皮质骶骨椎弓根钉。使用MTS试验机对螺钉进行30～250N压力加载2000次后取出螺钉。钉道内注入骨水泥（polymethylmethacrylate,PMMA）,将比双皮质或三皮质固定短5mm的螺钉再次置人（分别定义为标准和终板下PMMA强化）,并重复上述加载。记录加载后螺钉的下沉位移,进行比较。结果11具标本的骨密度为0．55～0．78g／cm^2,平均0．7lg／cm^2。三皮质和标准PMMA强化椎弓根钉间的下沉位移差异无统计学意义,此2种固定技术的下沉位移显著低于双皮质固定。终板下PMMA强化椎弓根钉的下沉位移显著低于其他固定技术。结论在骨质疏松状态下PMMA强化可显著提高骶骨钉一骨界面的结合强度。在上述4种骶骨固定技术中终板下PMMA强化椎弓根钉可获得最坚强的锚定。     

Characteristics of immediate and fatigue strength of a dual-threaded pedicle screw in cadaveric spines

Background contextNovel dual-threaded screws are configured with overlapping (doubled) threads only in the proximal shaft to improve proximal cortical fixation.PurposeTests were run to determine whether dual-threaded pedicle screws improve pullout resistance and increase fatigue endurance compared with standard pedicle screws.Study design/settingIn vitro strength and fatigue tests were performed in human cadaveric vertebrae and in polyurethane foam test blocks.Patient sampleSeventeen cadaveric lumbar vertebrae (14 pedicles) and 40 test sites in foam blocks were tested.Outcome measuresMeasures for comparison between standard and dual-threaded screws were bone mineral density (BMD), screw insertion torque, ultimate pullout force, peak load at cyclic failure, and pedicular side of first cyclic failure.MethodsFor each vertebral sample, dual-threaded screws were inserted in one pedicle and single-threaded screws were inserted in the opposite pedicle while recording insertion torque. In seven vertebrae, axial pullout tests were performed. In 10 vertebrae, orthogonal loads were cycled at increasing peak values until toggle exceeded threshold for failure. Insertion torque and pullout force were also recorded for screws placed in foam blocks representing healthy or osteoporotic bone porosity.ResultsIn bone, screw insertion torque was 183% greater with dual-threaded than with standard screws (p<.001). Standard screws pulled out at 93% of the force required to pull out dual-threaded screws (p=.42). Of 10 screws, five reached toggle failure first on the standard screw side, two screws failed first on the dual-threaded side, and three screws failed on both sides during the same round of cycling. In the high-porosity foam, screw insertion torque was 60% greater with the dual-threaded screw than with the standard screw (p=.005), but 14% less with the low-porosity foam (p=.07). Pullout force was 19% less with the dual-threaded screw than with the standard screw in the high-porosity foam (p=.115), but 6% greater with the dual-threaded screw in the low-porosity foam (p=.156).ConclusionsAlthough dual-threaded screws required higher insertion torque than standard screws in bone and low density foam, dual-threaded and standard pedicle screws exhibited equivalent axial pullout and cyclic fatigue endurance. Unlike single-threaded screws, the mechanical performance of dual-threaded screws in bone was relatively independent of BMD. In foam, the mechanical performance of both types of screws was highly dependent on porosity.