Bisphosphonate coating on titanium screws increases mechanical fixation in rat tibia after two weeks

Recently published data indicate that immobilized N-bisphosphonate enhances the pullout force and energy uptake of implanted stainless steel screws at 2 weeks in rat tibia. This study compares titanium screws with and without a bisphosphonate coating in the same animal model. The screws were first coated with an approximately 100-nm thick crosslinked fibrinogen film. Pamidronate was subsequently immobilized into this film via EDC/NHS-activated carboxyl groups within the fibrinogen matrix, and finally another N-bisphosphonate, ibandronate, was physically adsorbed. The release kinetics of immobilized (14)C-alendronate was measured in buffer up to 724 h and showed a 60% release within 8 h. Mechanical tests demonstrated a 32% (p = 0.04) and 48% (p = 0.02) larger pullout force and energy until failure after 2 weeks of implantation, compared to uncoated titanium screws. A control study with physically adsorbed pamidronate showed no effect on mechanical fixation, probably due to a too small adsorbed amount. We conclude that the fixation of titanium implants in bone can be improved by fibrinogen matrix-bound bisphosphonates.     

Raloxifene and alendronate containing thin mesoporous titanium oxide films improve implant fixation to bone

This study tested the hypothesis that osteoporosis drug-loaded mesoporous TiO₂ implant coatings can be used to improve bone–implant integration. Two osteoporosis drugs, Alendronate (ALN) and Raloxifene (RLX), were immobilized in nanoporous oxide films prepared on Ti screws and evaluated in vivo in rat tibia. The drug release kinetics were monitored in vitro by quartz crystal microbalance with dissipation and showed sustained release of both drugs. The osteogenic response after 28 days of implantation was evaluated by quantitative polymerase chain reaction (qPCR), removal torque, histomorphometry and ultrastructural interface analysis. The drug-loaded implants showed significantly improved bone fixation. In the case of RLX, stronger bone-remodelling activity was observed compared with controls and ALN-loaded implants. The ultrastructural interface analysis revealed enhanced apatite formation inside the RLX coating and increased bone density outside the ALN coating. Thus, this novel combination of a thin mesoporous TiO₂ carrier matrix and appropriate drugs can be used to accelerate implant fixation in trabecular bone.     

Simple coating with fibronectin fragment enhances stainless steel screw osseointegration in healthy and osteoporotic rats

Metal implants are widely used to provide structural support and stability in current surgical treatments for bone fractures, spinal fusions, and joint arthroplasties as well as craniofacial and dental applications. Early implant-bone mechanical fixation is an important requirement for the successful performance of such implants. However, adequate osseointegration has been difficult to achieve especially in challenging disease states like osteoporosis due to reduced bone mass and strength. Here, we present a simple coating strategy based on passive adsorption of FN7-10, a recombinant fragment of human fibronectin encompassing the major cell adhesive, integrin-binding site, onto 316-grade stainless steel (SS). FN7-10 coating on SS surfaces promoted α5β1 integrin-dependent adhesion and osteogenic differentiation of human mesenchymal stem cells. FN7-10-coated SS screws increased bone-implant mechanical fixation compared to uncoated screws by 30% and 45% at 1 and 3 months, respectively, in healthy rats. Importantly, FN7-10 coating significantly enhanced bone-screw fixation by 57% and 32% at 1 and 3 months, respectively, and bone-implant ingrowth by 30% at 3 months compared to uncoated screws in osteoporotic rats. These coatings are easy to apply intra-operatively, even to implants with complex geometries and structures, facilitating the potential for rapid translation to clinical settings.     

锁定加压钢板置入内固定治疗胫骨骨折的力学分析

背景：锁定加压钢板结合了传统钢板和支架原理,即头部有锁定螺纹的螺钉和钢板锁钉孔构成的内固定支架锁定单元,又有传统螺钉和动力加压孔构成的内固定支架加压单元,在骨折的内固定治疗方面具有很多优势。 目的：分析锁定加压钢板置入内固定治疗胫骨骨折的生物力学特点,以及在胫骨骨折治疗中的疗效。 方法：锁定加压钢板是依靠钢板与螺钉的成角稳定性和螺钉与骨之间的把持力来实现骨折内固定的。骨髓腔细小时应避免螺钉尖端损伤近端皮质的骨螺纹,应更换为双皮质自攻螺钉至少在对侧骨皮质获得把持力。骨质疏松植入螺钉,由于单皮质骨螺钉产生的工作长度减少,在所有骨折块均使用双皮质自攻螺钉,以提高螺钉工作长度。当长骨轴线与钢板对线不良时,要么打入长自攻螺钉,要么改变角度打入标准螺钉。锁定加压钢板应选择适宜的长度,钢板的长度取决钢板跨越比和钢板螺钉密度,钢板与螺钉间的应力还受螺钉数量和位置的影响。 结果与结论：锁定加压钢板置入内固定可应用于骨干或干骺端的简单骨折、粉碎性骨折、关节内及关节周围骨折、骨折延迟愈合、闭合或开放截骨术和不适合髓内钉固定的骨干骨折,对于骨质疏松骨折和假体周围骨折的内固定有很好的成角稳定性和把持力。锁定加压钢板置入内固定治疗胫骨骨干骨折均取得满意的疗效,符合生物力学固定原理。需要术者熟练掌握锁定加压钢板的内固定技术,避免由于失误导致内固定的失败。     

Poly(D,L-lactide) coating is capable of enhancing osseous integration of Schanz screws in the absence of infection

Pin loosening is a major complication in external fixation. Biological and mechanical conditions play an important role in the maintenance and enhancement of the implant-bone interface in fracture fixation. It is thought that biodegradable coatings may be capable of preventing pin track infection and pin loosening. The goal of this study was therefore to analyze the influence of a biodegradeable coating on the osseous integration of Schanz' screws during fracture treatment. Standardized osteotomies (3-mm fracture gap) of the right tibiae were performed on 16 sheep and stabilized by an AO mono-lateral external fixator. Additional, mechanically less loaded Schanz' screws were also mounted. All screws were randomly coated with biodegradable poly(D,L-lactide). The sheep were sacrificed after 9 weeks. All screws were removed and rolled on blood agar plates for microbiological analysis. Histological sections of the pin tracks were histochemically and morphometrically analyzed. Clinically, no signs of severe infection were visible. Microbiological analysis revealed 14.8% colonization by Staphylococcus aureus in the coated and 29% in the uncoated screws. Histomorphometry of the bone surrounding the Schanz' screws revealed that significantly more osseous integration had occurred on poly(D,L-lactide)-coated screws in the absence of bacterial colonization. Significantly more bone remodeling and a higher osteoclastic activity was seen near the screw-bone interface in the uncoated screw group. Up to a threefold increase in new bone formation and more severe remodeling was observed around the screw entry compared to the pin exit in all groups. Loaded screws showed significantly more callus formation around the exit sites than their less loaded counterparts. In the present study, poly(D,L-lactide) coating of Schanz' screws was found to enhance osseous integration in the absence of bacterial colonization in sheep by causing less cortical remodeling and less osteoclastic activity in the cortices compared to uncoated screws. Additionally, the coating appeared to reduce the instances of pin track infections. Mechanical loading showed an adverse effect on bone formation and remodeling. It has been shown that both biological and mechanical factors play an important role in the maintenance of osseous integrity of the pin-bone interface. Poly(D,L-lactide) coating of Schanz' screws does not prevent osseous destruction and severe bacterial colonization along the pin tracts, but can improve osseous integration of Schanz' screws in the absence of infection.     

Cortical bone screw fixation in ionically modified apatite cements

Hydroxyapatite cements are used in reconstruction of the face; usually in well-defined cavities where the cement can be stabilized without the need for internal fixation. A hydroxyapatite cement that could enable screw fixation and some loading therefore has considerable potential in maxillofacial reconstruction. It has been demonstrated recently that water demand of calcium phosphate cements can be reduced by ionically modifying the liquid component. This study investigated the capacity of an ionically modified precompacted apatite cement to retain self-tapping cortical bone screws. Screw pullout forces were determined in the direction of the screw long axis and perpendicular to it, using cortical bone and polymethylmethacrylate cement as a control. In bending pullout tests, measured forces to remove screws from ionically modified precompacted cement were insignificantly different from cortical bone. However, pullout forces of bone screws from hydroxyapatite cement decreased with aging time in vitro.     

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     

A randomised RSA study of Peri-Apatite HA coating of a total knee prosthesis

BACKGROUND: In total knee replacement, sound early fixation of the prosthesis is crucial for achieving a good long-term result and for minimising the risk of loosening. Various types of prosthetic material, different surface textures and shapes and the incorporation of screws or pegs have been used to achieve good fixation, particularly in the uncemented knee. Hydroxyapatite (HA) coating of prosthetic joint components is another technique used to enhance early stability and so to improve the longevity of the prosthesis-bone fixation. HA ceramic coatings are mostly plasma sprayed onto the fixation surface of the implant. Plasma spraying is largely a 'line of sight' technique and as such there are difficulties involved when covering three-dimensional planes, such as porous beaded fixation surfaces typically found on several knee prostheses. The objective of this study was to assess the clinical performance of the solution-deposited HA coating, Peri-Apatite , with regard to its ability to stimulate an endurable and stable implant fixation. PATIENTS AND METHODS: We randomised 60 patients into two groups; one group received the porous coated prosthesis with solution-deposited HA, and the other group received a prosthesis without HA. Radiostereometric examination was used as the primary tool for measuring migration in the prosthetic components. RESULTS: There was a lower incidence of early subsidence in the Peri-Apatite group. At 24 months there were no differences in clinical scorings or maximal total point motion. CONCLUSION: Addition of solution-deposited HA coating appears to provide better early stable fixation in a porous coated knee prosthesis.     

In vivo comparison of the osseointegration of vacuum plasma sprayed titanium- and hydroxyapatite-coated implants

For the last 15 years, orthopedic implants have been coated with hydroxyapatite (HA) to improve implant fixation. The osteoconductive effect of HA coatings has been demonstrated in experimental and clinical studies. However, there are ongoing developments to improve the quality of HA coatings. The objective of this study was to investigate whether a rough and highly crystalline HA coating applied by vacuum plasma spraying (VPS) had a positive effect on the osseointegration of special, high-grade titanium (Ti) implants with the same surface roughness. Ti alloy implants were coated (VPS) with special, high-grade Ti or HA. The osseointegration of the implants was evaluated by either light microscopy or pullout tests after 1, 2, and 4 weeks of unloaded implantation in the cancellous bone of 18 sheep. The interface shear strength increased significantly over all time intervals. By 4 weeks, values had reached approximately 10N/mm(2). However, the difference between the coatings was not significant at any time interval. Direct bone-implant contact was significantly different between the coatings after 2 and 4 weeks, and reached 46% for Ti and 68% for HA implants by 4 weeks. This study indicates that the use of a rough and highly crystalline HA coating, applied by VPS, enhances early osseointegration. Accelerated establishment of secondary implant fixation decreases the risk of early loosening.     

Prevention of pin track infection in external fixation with silver coated pins: clinical and microbiological results

Pin tract infection is a frequent complication of external fixation; according to literature its frequency ranges from 2-30%. The recent introduction of silver coating of polymeric materials was found to decrease bacterial adhesion; its clinical use with Foley catheters and central venous catheters led to significant results. To verify the ability of the same silver coating to decrease the bacterial colonization on external fixation screws, a prospective randomized study was carried out on 24 male patients; a total of 106 screws were implanted in the lower limb to fix femoral or tibial diaphyseal fractures: 50 were coated with silver and 56 were commercially available stainless steel screws. Although the coated screws resulted in a lower rate of positive cultures (30.0%) than the uncoated screws (42.9%), this difference was not statistically significant (p = 0.243). The clinical behavior of the coated screws did not differ from that of the uncoated ones. Furthermore, the implant of silver-coated screws resulted in a significant increase in the silver serum level. These results led us to consider it ethically unacceptable to continue this investigation.     

Axial cyclic behavior of the bone-screw interface

Screw fixation strength is investigated by using a pullout test. Despite many screw pullout studies, the effects of loading rate on the pullout behavior of pedicle screws are not known. The objective of this study was to assess the effects of loading rate on the pullout stiffness and strength of pedicle screws. Sixty pedicle screws were inserted in foam blocks and pulled out at four different rates: 0.1, 1, 5 and 50 mm/min. Twenty of these 60 screws were cycled non-destructively at four different rates sequentially, i.e., 0.1, 1, 5 and 50 mm/min prior to pullout. Ten additional pedicle screws were inserted in five calf lumbar vertebrae, cycled as in foam group, and pulled out at a rate of either 0.1 or 50 mm/min. The results showed that the stiffness was higher at all rates compared to 0.1 mm/min in foam model but in bone model only 1 and 5 mm/min groups were higher compared to 0.1 mm/min. The pullout strength in 50 mm/min group was higher than that in 0.1 mm/min group in both foam and bone model. The results suggested that loading rate influenced the mechanics of the bone-screw interface. Therefore, a fair comparison between the pullout studies can be achieved under same loading rate conditions. Moreover, the cycling of the pedicle screws in axial direction within a pre-yield region showed an unusual hysteresis curve. Further studies are needed for a better understanding of the mechanics of the screw-bone interface.     

Effect of zinc ions on improving implant fixation in osteoporotic bone

Abstract

The application of titanium (Ti) and its alloys in tooth restoration and joint replacement for aged patients with unfavorable conditions is gaining popularity. Therefore, strategies aiming at improving the fixation of Ti-based implants are worth investigating. This study was designed to observe whether modification of Ti implants by zinc (Zn) could enhance the fixation capability in osteoporotic bone. Two kinds of implants, hydroxyapatite (HA) coated Ti and Zn-incorporated HA (ZnHA) coated Ti, were inserted into the femoral metaphysis longitudinally in ovariectomized (OVX) rats. Specimens were harvested and subjected to double fluorescence labeling examination at week 6 after surgery. At week 12, samples were evaluated with histomorphometry, micro-CT (μCT) analysis and biomechanical test. Compared to the HA coated implants, ZnHA coating improved mineral apposition rate (MAR) of peri-implant bone, which was revealed by double fluorescence labeling; bone area ratio (BA) and bone-to-implant contact (BIC) were also higher for the latter group by histomorphometry. μCT images suggested that more bone mass was formed around the ZnHA coated implants as compared to the HA coated implants. Biomechanical push-out test showed that the ZnHA coated implants demonstrated higher strength of osseointegration than the HA group. The current study suggested that Zn ions could enhance bone formation and improve implant fixation in OVX rats.     

AFM force spectroscopy of the fibrinogen adsorption process onto dental implants

Protein binding to implants is governed by the physicochemical properties of the biomaterial surface. The adhesion of a protein onto a solid surface is nonspecific. The aim of this study was to assess the adsorption process of fibrinogen at two different dental implants. The first biomaterial has a sand-blasted titanium surface, whereas the second one is covered by a calcium phosphate coating. After scanning electron microscopy and atomic force microscopy characterization of the implant surfaces, force spectroscopy has been used to determine the unbinding force of fibrinogen adsorbed at the two different substrates. Force-measurement findings indicate that the detachment force of fibrinogen adsorbed onto both surfaces varies as a function of the interaction time. The mean strength of the unbinding forces increases with the interaction time (100 and 1,000 ms, respectively). However, experimental data suggest that fibrinogen fixes to the two studied biomaterials by different mechanisms. Moreover, it appears that, after an interaction time of 1,000 ms, the detachment force of the adsorbed protein is quite larger for the titanium surface than for the calcium phosphate coating.     

Effect of bone mineral density and amorphous diamond coatings on insertion torque of bone screws

In this study, the potential of high-quality amorphous diamond (AD) coatings in reducing the torque and failures of bone screws was studied. Torque values were recorded for 32 stainless steel screws, 2.7 or 3.5 mm in diameter and 60 mm in length. Half of the screw sets were coated with the AD coating before installing in predrilled holes of human cadaveric femoral bone samples. The bone samples were selected from two groups of four persons with mean ages of 34 years (range 25-41 years) and 75 years (range 73-77 years), respectively. The bone mineral density (BMD) values of the samples were determined exactly at the screw insertion site by peripheral quantitative computed tomography (pQCT). In the mechanical tests, insertion and removal torques were measured. BMD had a significant effect on insertion torque; the maximum torque (adjusted with respect to the screw diameter) was significantly higher for the young bone than for the old bone (p < 0.05). By using a polished AD coating, insertion torque was decreased even up to 50% in comparison with the screws without coating. The results suggest that AD coating provides a stable, smooth surface and reduces the risk of screw failures.     

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.     

Molecular barriers to biomaterial thrombosis by modification of surface proteins with polyethylene glycol

For cardiovascular biomaterials, thrombosis, thromboembolism and vascular graft occlusion are believed to be precipitated by the adsorption of proteins containing adhesive ligands for platelets. Polyethylene-glycol-diisocyanate(PEG-diisocyanate, 3400 MW) may potentially react with protein amines to form molecular barriers on adsorbed proteins on biomaterials, thereby masking adhesive ligands and preventing acute surface thrombosis. To test this notion, PE, PTFE, and glass microconduits were pre-adsorbed with fibrinogen and treated with PEG-diisocyanate, non-reactive PEG-dihydroxyl, or remained untreated. Following perfusion of 111In-labeled platelets in whole human blood for 1 min (wall shear rate = 312 s(-1)), PEG-diisocyanate treated surfaces experienced 96%(PE), 97%(PTFE) and 94% (glass) less platelet deposition than untreated surfaces. Similar reductions were seen for PEG-diisocyanate versus PEG-dihydroxyl treatment. Low shear perfusions of plasma for one hour prior to blood contact did not reduce the inhibitory effect of PEG-diisocyanate. Platelet adhesion onto collagen coated glass coverslips and platelet deposition onto preclotted Dacron was also reduced by treatment with PEG-diisocyanate (93 and 91%, respectively). Protein-reactive PEG may thus have utility in forming molecular barriers on surface associated proteins to inhibit acute thrombosis on cardiovascular biomaterials.     

Local delivery of bisphosphonate from coated orthopedic implants increases implants mechanical stability in osteoporotic rats

Patients with osteoporosis and joint disabilities represent a constant growing and challenging population to be treated in the musculoskeletal clinical field. Especially in the case of total hip arthroplasty, new solutions should be developed to compensate for the double negative factors, peri-implant osteolysis, and osteoporotic bone loss, affecting the quality of implant outcome. The goal of this study was then to establish a proof of concept for orthopedic implant used as Zoledronate delivery in osteoporotic rats, and in particular, to verify if this approach could increase the initial implant stability. Twenty-five female 6-month-old Wistar rats were ovariectomized 6 weeks before the implantation to induce osteoporosis. The animals were randomly separated in five groups representing the different Zoledronate concentrations in the HA coating: 0, 0.2, 2.1, 8.5, and 16 microg/implant. Histomorphometric measures and peri-implant bone volume fraction were assessed and mechanical stability tests were performed. Bone volume fraction and biomechanical results clearly illustrate the positive effect of Zoledronate coated implants in the osteoporotic rats. A remarkable result was to show the existence of a window of Zoledronate content (0.2 to 8.5 microg/implant) in which the mechanical fixation of the implant increased. We were able to establish the proof of concept for orthopedic implants used as a drug delivery system in osteoporotic rats. The local bisphosphonate delivery from a calcium phosphate coating allowed increase of the mechanical fixation of an orthopedic implant. This study shows that orthopedic implants containing bisphosphonates could be beneficial for osteoporotic patients in need of a total joint replacement.     

金属椎弓根螺钉植入物及其新型替代材料的研究与进展

背景：椎弓根螺钉内固定系统广泛应用于脊柱骨折、退行性变、肿瘤等疾病之中,螺钉的材料、整体设计及结合新型生物材料强化等方面的研究有了很大进展。 目的：对国内外椎弓根螺钉的设计进展作一综述。 方法：由第一作者检索1994/2010中国期刊全文数据库及 1959/2010 Pubmed数据库中关于椎弓根螺钉的文章,在标题和摘要中以“椎弓根螺钉,生物力学,设计,生物材料”或“pedicle screw,biomechanics,design, biomaterial”为检索词进行检索。选择文章内容与椎弓根螺钉设计有关者,同一领域文献则选择近期发表或发表在权威杂志文章。最终入选36篇文献进入结果分析。 结果与结论：采用钛合金材料,增加螺钉的直径及长度,使用特殊设计的螺钉,如可膨胀椎弓根螺钉,或运用生物材料强化椎弓根螺钉,可以提高螺钉的固定强度。此外,不同螺钉形状、螺纹形状、螺纹倾角、螺纹深度、间距与其固定强度密切相关。设计螺钉时应充分考虑到各个因素,以便于研究出更完美的椎弓根螺钉。     

In vitro and in vivo evaluation of the surface bioactivity of a calcium phosphate coated magnesium alloy

Magnesium has shown potential application as a bio-absorbable biomaterial, such as for bone screws and plates. In order to improve the surface bioactivity, a calcium phosphate was coated on a magnesium alloy by a phosphating process (Ca–P coating). The surface characterization showed that a porous and netlike CaHPO₄·2H₂O layer with small amounts of Mg²⁺ and Zn²⁺ was formed on the surface of the Mg alloy. Cells L929 showed significantly good adherence and significantly high growth rate and proliferation characteristics on the Ca–P coated magnesium alloy (p < 0.05) in in-vitro cell experiments, demonstrating that the surface cytocompatibility of magnesium was significantly improved by the Ca–P coating. In vivo implantations of the Ca–P coated and the naked alloy rods were carried out to investigate the bone response at the early stage. Both routine pathological examination and immunohistochemical analysis demonstrated that the Ca–P coating provided magnesium with a significantly good surface bioactivity (p < 0.05) and promoted early bone growth at the implant/bone interface. It was suggested that the Ca–P coating might be an effective method to improve the surface bioactivity of magnesium alloy.     

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。