数字散斑法测量加载100 N与500 N肱骨干骨折钢板固定下的位移

背景：目前国际上还没有统一骨组织力学性能测试的试验标准。以往将传统传感器引入骨折位移的研究,存在精度低、高消耗成本等问题。 目的：采用数字散斑法测量肱骨骨折内固定后钢板螺钉的位移特点。 方法：取8根肱骨,于其中点横断,制造肱骨中段骨折模型。将标本用8孔钢板固定,骨折线两端各使用4枚螺钉。将实验模型设计成5种状态进行对比分析：状态a是骨折后加压钢板坚强内固定组(未锯断,模拟骨折愈合),状态b是在状态a锯断后基础上近端去1枚螺钉,状态c是在状态b的基础上远端去1枚螺钉,状态d是在状态c的基础上近端去1枚螺钉,状态e是在状态d的基础上远端去1枚螺钉。螺钉编号顺序从上到下依次为1-8号,即骨折线上位螺钉为1-4号,骨折线下位螺钉为5-8号。用电子万能试验机进行加载100 N与500 N测量,通过相关软件计算位移。 结果与结论：在不同载荷间的总位移比较,差异有显著性意义(F=49.155,P < 0.001),即随着加载力的增大,5种模拟状态下第4钉、第5钉的总位移值均呈逐渐增大趋势。提示骨折线两端的2枚螺钉是承受较多应力的部位(应力集中),易于发生断裂,应选用比现有螺钉直径增大1-2.5 mm的螺钉,增加骨折线旁固定螺钉的稳定性以避免断钉等后遗症。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;组织工程全文链接：     

First clinical and biomechanical results of the Trochanteric Fixation Nail (TFN).

Conventional osteosynthesis of proximal femur fractures is still affected by serious complication rates between 4-18%, even though advanced implant modifications and surgical techniques are common practice. In terms of increasing age and co-morbidity of patients this complication ratio is expected to increase even further in the immediate future. One major reason for implant failure is the decreasing stability potential of the implant due to a loss in mechanical properties of cancellous bone. Therefore, efforts in new intramedulary techniques specifically focus on the load bearing characteristics of the implant by developing new geometries to improve the implant-tissue interface. This investigation discusses first clinical results of the trochanteric fixation nail TFN (145 patients) and a biomechanical analysis of the blade/femur head interaction under different static loading conditions. The TFN shows promising performance in first clinical results. In the clinical study the overall complication rate was significantly lower compared to other similar osteosynthesis. For the investigation of the biomechanical stability of the helical TFN blade the following experiments were performed: Analysis of the axial load required for insertion of the blade by free rotation; measurement of the corresponding rotation angle for total insertion (32 mm) (n = 8); pull-out forces with suppressed rotation (n = 4); loads for rotational overwinding of the implant in the fully inserted condition (n = 4). All investigations were performed on human femoral heads. The bone mineral densities of the specimens were detected by QCT-scans. Prior to cadaveric testing the experimental set-up was validated (n = 8) by the use of synthetic foam blocks (Sawbone).     

Biocompatibility and osseointegration of beta-TCP: histomorphological and biomechanical studies in a weight-bearing sheep model

The aim of the study was to investigate the biocompatibility, degradation, and biomechanical properties of beta-TCP (Cerasorb) in a weight-bearing sheep model. beta-TCP implant prototypes were implanted in the tibial head of adult merino sheep. After 6 and 12 months material explants were harvested for biomechanical, histological, and histomorphometrical analysis. Corresponding bone specimens of the intact bone of the contralateral leg were used as controls in the biomechanical test. Compression tests showed higher values for maximum fracture load, yield strength, and compression modulus after 6 and 12 months compared to control. Microscopically, the implants showed good osteoconduction and were incorporated into the bone; however, relevant amounts of beta-TCP were still present after 12 months. Histomorphological results revealed that beta-TCP had partially degraded between implantation and 6 months, but its share remained constant between 6 and 12 months. The bone volume fraction in the area of the implant (46% +/- 6.5%) was initially higher than in the corresponding bone area of the contralateral leg (31% +/- 9.6%), but after 12 months declined to 29% +/- 9.4% (control: 33% +/- 8.3%), while the share of beta-TCP remained constant at 36% +/- 12.2%. These findings were supported by microradiographic data. In conclusion, in a weight bearing implantation model beta-TCP showed good biocompatibility, osseointegration and beginning degradation, even though it was not further degraded between 6 and 12 months.     

The primary stability of pelvic reconstruction after partial supraacetabular pelvic resection due to malignant tumours of the human pelvis: A biomechanical in vitro study

BackgroundUp until now, reconstructions after partial supraacetabular pelvic resection have been done with the use of megaprostheses or allo-/autografs, including screws. The literature states complications in up to 100%. Therefore, the university hospital of Muenster has successfully established a reconstruction using poly-axial screws and titanium rods in combination with a Palacos^® shroud. The aim of this study was to gather data on primary stability of five different types of reconstruction.MethodsUsing a biomechanical model Load (N), displacement (mm) and stiffness (N/mm) were recorded in load cycles from 100 N up to 1050 N.FindingsThe data shows that reconstructions with poly-axial screws, titanium rods and Palacos^® can bear a load of up to 1050 N without structural damages. The same is valid with an additional bone graft and for a full metal prosthesis. Referring to reconstructions with just bone graft or without graft and Palacos^® the load-bearing capacity is significantly worse. Additionally, structural damages were recorded in those reconstructions from 700 N onwards.InterpretationDue to the biomechanical results and the save and easy handling, reconstructions with poly-axial screws, titanium rods and Palacos^® (and, if necessary, bone graft) can be recommended achieving high primary stability for pelvic ring reconstruction after partial supraacetabular pelvic resection.     

Computational simulations of stress shielding and bone resorption around existing and computer-designed orthopaedic screws

Failure of an orthopaedic fixation due to stress shielding and consequent screw loosening is a major concern among surgeons: the loosened screws could not only interfere with the healing process but also endanger adjacent anatomical structures. In this study, the effect of the screw's engineering design (dimensions, profile shape and material properties) on the load sharing with adjacent bone and consequent bone resorption was tested, using a set of two-dimensional computational (finite element) models. An algorithm simulating local bone adaptation to strain energy density (SED) mechanical stimuli was developed and used to evaluate the biomechanical performances of different commercial screws. Two new designs, a ‘graded-stiffness’ composite screw, with a reduced-stiffness titanium core and outer polymeric threads, and an active-compression hollow screw that generates compressive stresses on the surrounding bone, were also evaluated. A dimensionless set of stress transfer parameters (STPs) were utilised for ranking the performances of the different screws according to the expected screw-bone load sharing and its evolution with adaptation of the surrounding tissue. The results indicated that commercial wide (6mm thread diameter) trapezoidal and rectangular screw profiles have superior biomechanical compatibility with bone (i.e. predicted to be stable after 2 years). The graded-stiffness and active-compression screws provided the best biomechanical performances: bone loading around them was predicted to decrease by no more than 15% after 3 years, compared with a decrease of 55–70% in bone loading around commercially available screws. Computer simulations of bone adaptation around orthopaedic screws are demonstrated to be effective means for objective and quantitative evaluation of the biomechanical aspects of implant-tissue compatibility.     

Fixation strength of four headless compression screws

To promote a quicker return to function, an increasing number of patients are treated with headless screws for acute displaced and even non-displaced scaphoid fractures. Therefore, it is imperative to understand and optimize the biomechanical characteristics of different implants to support the demands of early mobilization. The objective of this study was to evaluate the biomechanical fixation strength of 4 headless compression screws under distracting and bending forces. The Acutrak Standard, Acutrak Mini, Synthes 3.0, and Herbert-Whipple screws were tested using a polyurethane foam scaphoid fracture model. Implants were inserted into the foam blocks across a linear osteotomy. Custom fixtures applied pull-apart and four-point bending forces until implant failure. Pull-apart testing was performed in three different foam densities in order to simulate osteoporotic, osteopenic, and normal bone. The peak pull-apart forces varied significantly between implants and were achieved by (from greatest to least): the Acutrak Standard, Synthes 3.0, Acutrak Mini, and Herbert-Whipple screws. The fully threaded screws (Acutrak) failed at their proximal threads while the shanked screw (Synthes and Herbert Whipple) failed at their distal threads. Similarly, the screws most resistant to bending were (from greatest to least): the Acutrak Standard, Acutrak Mini, Herbert-Whipple, and Synthes. Although the amount of force required for pull-apart failure increased with each increasing simulated bone density (a doubling in density required triple the amount of pull apart force), the mode and sequence of failure was the same. Overall, the fully threaded, conical design of the Acutrak screws demonstrated superior fixation against pull-apart and bending forces than the shanked designs of the Synthes and Herbert-Whipple. We also found a strong relationship between simulated bone density and pull-apart force.     

Factors affecting stability after medial opening wedge high tibial osteotomy using locking plate: A cadaveric study

ObjectivesTo investigate the effect of screw length, lateral hinge fracture, and gap filling on stability after medial opening wedge high tibial osteotomy (MOW HTO) using a locking plate.MethodsForty tibiae from fresh-frozen cadavers were randomly allocated into five groups. Group A was bicortically fixated, while Group B and Group C were unicortically fixated: 90% and 55% of drilled tunnel length, respectively. Group D was fixated using 90% length screws with a fractured lateral hinge. Group E was fixated using 90% length screws with gap filling using a bone substitute. Operated tibiae were tested under axial compressive load using a material testing machine. The medial gap changes under the serial axial load of 100–600 N and ultimate failure load were measured.ResultsGroup D showed the biggest medial gap change and lowest failure load, while Group E presented the smallest gap change and highest failure load. The medial gap changes tended to increase with shorter screw length, but the difference was not significant between Groups A, B, and C. Group C and Group D showed greater medial gap change and lower failure load compared with Group E, while not differing from Group A and Group B.ConclusionsUnicortical fixation in proximal screw holes of a locking plate was not inferior to bicortical fixation regarding axial stability in MOW HTO, although proximal screws that are too short should be avoided. Lateral hinge fracture decreased, while gap filling with bone substitute increased axial stability.     

植入位点及轴向对上颌中切牙即刻种植即刻负重应力影响的三维有限元分析

目的 探讨不同牙槽窝形态上颌中切牙即刻种植即刻负重时,植入位点及轴向对种植体周围骨界面应力分布的影响。方法 参照1名健康成年人口腔锥体束计算机断层(cone beam computed tomography, CBCT)影像资料,建立偏唇型、中间型、偏腭型3种牙槽窝形态的上颌中切牙即刻种植即刻负重三维有限元模型;模拟不同植入位点(根尖位点、偏腭/唇侧位点)及轴向(牙长轴、牙槽骨长轴);对已建模型以100 N力进行不同角度(0°、30°、45°、60°、90°)的应力加载;应用ANSYS软件分析种植体周围牙槽骨的应力情况。结果 成功建立12个不同牙槽窝形态上颌中切牙即刻种植即刻负重三维有限元模型。偏唇型及中间型牙槽窝形态行即刻种植即刻负重时,沿牙槽骨长轴方向偏腭位点植入种植体更易获得良好的种植体骨界面生物力学特性;偏腭型牙槽窝形态行即刻种植即刻负重时,在偏唇位点植入,不论是沿牙长轴方向还是沿牙槽骨长轴方向植入种植体,种植体周牙槽骨所受等效应力远小于根尖位点植入。结论 不同牙槽窝形态、植入位点及轴向都会对上颌中切牙即刻种植即刻负重种植体骨界面生物力学特点产生影响。临床中,应针对不同牙槽窝形...     

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.     

Enhancing the mechanical integrity of the implant-bone interface with BoneWelding technology: determination of quasi-static interfacial strength and fatigue resistance

The BoneWelding technology is an innovative bonding method, which offers new alternatives in the treatment of fractures and other degenerative disorders of the musculoskeletal system. The BoneWelding process employs ultrasonic energy to liquefy a polymeric interface between orthopaedic implants and the host bone. Polymer penetrates the pores of the surrounding bone and, following a rapid solidification, forms a strong and uniform bond between implant and bone. Biomechanical testing was performed to determine the quasi-static push-out strength and fatigue performance of 3.5-mm-diameter polymeric dowels bonded to a bone surrogate material (Sawbones solid and cellular polyurethane foam) using the BoneWelding process. Fatigue tests were conducted over 100,000 cycles of 20-100 N loading. Mechanical test results were compared with those obtained with a comparably-sized, commercial metallic fracture fixation screw. Tests in surrogate bone material of varying density demonstrated significantly superior mechanical performance of the bonded dowels in comparison to conventional bone screws (p < 0.01), with holding strengths approaching 700 N. Even in extremely porous host material, the performance of the bonded dowels was equivalent to that of the bone screws. For both cellular and solid bone analog materials, failure always occurred within the bone analog material surrounding and distant to the implant; the infiltrated interface was stronger than the surrounding bone analog material. No significant decrease in interfacial strength was observed following conditioning in a physiological saline solution for a period of 1 month prior to testing. Ultrasonically inserted implants migrated, on average, less than 20 microm over, and interfacial stiffness remained constant the full duration of fatigue testing. With further refinement, the BoneWelding technology may offer a quicker, simpler, and more effective method for achieving strong fixation and primary stability for fracture fixation or other orthopaedic and dental implant applications.     

种植体联合牙半切剩余牙体共同支持下颌磨牙的三维有限元分析

BACKGROUND: Tooth hemisection contributes to preserving partial tooth structure and periodontal ligament that are able to reduce the resorption of alveolar bone. However, the traditional fixed partial denture (FPD) for dental restoration after hemisection jeopardizes the health of abutment tooth. Given this, the use of dental implant offers a new option for tooth restoration. OBJECTIVE: To analyze the feasibility of preserving a mandibular molar after hemisection by combining an inserted dental implant with the residual tooth by means of finite element analysis. METHODS: Based on the image data of a volunteer, three models with different ways of restorations were created: the model of combining implant and residual tooth after hemisection to support a molar crown (combined model), the model of implant to support a molar crown (implant model) and the model of FPD. Densities of two kinds of spongy bones were assigned respectively. Vertical load of 100 N was applied on the prosthesis. Biomechanical properties of different models were analyzed. RESULTS AND CONCLUSION: (1) Displacement of the tooth and implant: As the decrease of the density of spongy bone, displacements of the tooth and implant increased in the combined model. The implant displacement was higher in the combined model as compared with the implant model. For the combined model, the implant displacement was lower than that of the residual tooth. (2) Stress in the cortical bone: Stress in the cortical bone in models with low-density spongy bone was higher than that in the corresponding models with high-density spongy bone. Under the condition of high-density spongy bone, the highest values were obtained in the implant model, followed by the combined model and FPD model. Under the condition of low-density spongy bone, the highest values were obtained in the combined model, followed by the implant model and FPD model. (3) Strain in the spongy bone: Strain in the spongy bone in models with low-density spongy bone was higher than that in the corresponding models with high-density spongy bone. Under the condition of high-density spongy bone, the highest values were obtained in the FPD model, followed by the combined model and implant model. Under the condition of low-density spongy bone, the highest values were obtained in the combined model, followed by the FPD model and implant model. From the biomechanical point of view, it can be concluded that the combined use of an implant and residual molar after tooth hemisection is an acceptable treatment option under the condition of high-density spongy bone.     

数字散斑法测量加载100 N与400 N肱骨干骨折钢板固定下的位移

背景：将光学测量技术数字散斑相关方法应用到生物医学领域中,能更精确地分析螺钉断裂的特点。 目的：以数字散斑法测量肱骨钢板螺钉的位移。 方法：取4根肱骨制造肱骨中段骨折模型。将骨折标本进行复位,用8孔钢板固定,骨折线两端各使用4枚螺钉固定。分别在100及400 N拉力下,将模型设计成骨折前后的5种状态,即状态a是未骨折加压钢板坚强内固定组(模拟骨折愈合,未锯断);状态b是骨折后近端去1枚螺钉;状态c是在状态b的基础上远端去1枚螺钉;状态d是在状态c的基础上近端去1枚螺钉;状态e是在状态d的基础上远端去1枚螺钉。分别测量骨折线两端两枚螺钉的位移,通过相关软件计算位移。 结果与结论：在100 N及400 N拉力下,骨折线旁对称分布的两枚螺钉随着其他螺钉的减少,所产生的位移差异存在显著性意义(P < 0.01);骨折线旁成对称分布的两枚螺钉所承受的应力差异无显著性意义(P > 0.05)。提示骨折线两端的2枚螺钉是承受较多应力的部位(应力集中),易于发生断裂,应选用比现有螺钉的直径增大1.0~2.5 mm的螺钉,增加骨折线旁的固定螺钉稳定性以避免断钉等后遗症。     

Tissues at the surface of the new composite material titanium/glass-ceramic for replacement of bone and teeth

A new composite implant material titanium/glass-ceramic was tested in rabbits using light microscopy, histomorphometry, and biomechanical testing methods. Two rabbit implant models were used. The first premolar tooth was replaced and cylinders inserted into the trabecular bone of the distal femur below the patella sliding plane. There was bone bonding to the glass-ceramic component and additional mechanical interlocking, due to bone ingrowth between the titanium matrix into secondary pores. This was proved by measuring the tensile strength at the interface of the new composite material which was in the same range as compared to pure glass-ceramic implants. In tooth replacement there was a tight attachment of gingival epithelium and stroma to composite titanium/glass-ceramic. These results are of particular clinical interest: physicochemical bone bonding and additional mechanical interlocking result in a resistance of the implant material against shear and tensile loads at the interface. Therefore this new composite material should be suitable for further load-bearing applications.     

In vivo investigations on composites made of resorbable ceramics and poly(lactide) used as bone graft substitutes.

Porous composites made of poly(L, DL-lactide) (PLA) and alpha-tricalcium phosphate (alpha-TCP) or the glass ceramic, GB14N, respectively, were investigated in a loaded implant model in sheep. Six, 12 and 24 months after implantation histological and biomechanical evaluation were performed and compared to autogenous bone transplants. No significant differences were observed between the composites. After 6 months, the interconnecting pores of the alpha-TCP-composite and the GB14N-composite were filled with newly formed bone (14 +/- 5% or 29 +/-15% of the implant, respectively) and soft tissue (30 +/-9% or 21 +/-12% of the implant, respectively). Only a mild inflammatory response was observed. The reaction was similar after 12 months. However, after 24 months a strong inflammatory reaction was seen. The newly formed bone was partly osteolytic. The adverse reaction occurred simultaneously to a significant reduction of the PLA component. The histological results were reflected by the biomechanical outcomes. Both composites showed compression strengths in the range of the autologous bone graft until 12 months of implantation. After 2 years, however, the strengths were significantly decreased. It is concluded that the new composites cannot yet be used for clinical application. An improvement in biocompatibility might be reached by a better coordination of the degradation times of the polymer and the ceramic component.     

Validation of a finite element model of a unilateral external fixator in a rabbit tibia defect model

In case of large segmental defects in load-bearing bones, an external fixator is used to provide mechanical stability to the defect site. The overall stiffness of the bone–fixator system is determined not only by the fixator design but also by the way the fixator is mounted to the bone. This stiffness is an important factor as it will influence the biomechanical environment to which tissue engineering scaffolds and regenerating tissues are exposed. A finite element (FE) model can be used to predict the system stiffness. The goal of this study is to develop and validate a 3D anatomical FE model of a bone–fixator system which includes a previously developed unilateral external fixator for a large segmental defect model in the rabbit tibia. It was hypothesized that the contact interfaces between bone and fixator screws play a major role for the prediction of the stiffness. In vitro mechanical testing was performed in order to measure the axial stiffness of cortical bone from mid-shaft rabbit tibiae and of the tibia–fixator system, as well as the bending stiffness of individual fixator screws, inserted in bone. μCT-based case-specific FE models of cortical bone and SCREW–BONE specimens were created to simulate the corresponding mechanical test set-ups. The Young's modulus of rabbit cortical bone as well as appropriate screw–bone contact settings were derived from those FE models. We then used the derived settings in an FE model of the tibia–fixator system. The difference between the FE predicted and measured axial stiffness of the tibia–fixator system was reduced from 117.93% to 7.85% by applying appropriate screw–bone contact settings. In conclusion, this study shows the importance of screw–bone contact settings for an accurate fixator stiffness prediction. The validated FE model can further be used as a tool for virtual mechanical testing in the design phase of new tissue engineering scaffolds and/or novel patient-specific external fixation devices.     

A biomechanical study comparing a raft of 3.5 mm cortical screws with 6.5 mm cancellous screws in depressed tibial plateau fractures

There has been a recent trend towards using a raft of small diameter 3.5mm cortical screws for supporting depressed tibial plateau fractures (Schatzker type III). Our aim was to compare the biomechanical properties of a raft of 3.5 mm cortical screws with that of 6.5 mm cancellous screws in a synthetic bone model. Ten rigid polyurethane foam (sawbone) blocks, with a density simulating osteoporotic bone and ten blocks with a density simulating normal density bone were obtained. A Schatzker type III fracture was created in each block. The fracture fragments were then elevated and supported using two 6.5 mm cancellous screws in ten blocks and four 3.5 mm cortical screws in the remaining. The fractures were loaded using a Lloyd testing machine. The mean force needed to produce a depression of 5 mm was 700.8 N with the four-screw construct and 512.4 N with the two-screw construct in the osteoporotic model. This difference was highly statistically significant (p = 0.009). The mean force required to produce the same depression was 1878.2 N with the two-screw construct and 1938.2 N with the four-screw construct in the non-osteoporotic model. Though the difference was not statistically significant (p = 0.42), an increased fragmentation of the synthetic bone fragments was noticed with the two-screw construct but not with the four-screw construct. A raft of four 3.5 mm cortical screws is biomechanically stronger than two 6.5 mm cancellous screws in resisting axial compression in osteoporotic bone.     

Biomechanical comparison between CentraLoc and Intrafix fixation of quadrupled semitendinosus-gracilis allografts in cadaveric tibiae with low bone mineral density

Supplementary or back-up tibial tunnel fixation of a quadruple semitendinosus-gracilis (STG) graft is often performed when the knee surgeon questions the integrity of intra-tunnel fixation. Back-up fixation devices such as staples however may contribute to increased knee pain and dysfunction. Both primary extra-tunnel and intra-tunnel fixation devices may provide sufficient quadruple STG graft fixation in a tibial tunnel to preclude the need for back-up fixation. This biomechanical study compared the fixation of quadruple STG allografts in standard drilled tunnels prepared in low apparent bone mineral density (BMD) cadaveric tibiae using either an Intrafix device with primary intra-tunnel fixation in a region of predominantly cancellous trabecular bone, or a CentraLoc device with primary extra-tunnel fixation in a region of predominantly cortical bone. The study hypothesis was that the CentraLoc device would display superior fixation in these low apparent BMD cadaveric tibiae. Matched pair tibiae and quadruple STG allografts were divided into two groups of seven specimens each. Extraction drilled tunnels matched allograft diameter. Constructs were pretensioned on a servo hydraulic device between 10 and 50 N for 10 cycles and isometric pretensioned at 50 N for 1 min prior to undergoing 500 loading cycles (50-250 N) and load to failure testing (20 mm/min). The CentraLoc group displayed superior load at failure (448.4+/-171 N vs. 338.4+/-119 N, P=0.04) and survived more loading cycles (410+/-154 cycles vs. 196+/-230 cycles, P=0.04) than the Intrafix group. Most CentraLoc group specimens (6/7, 85.7%) failed by device pullout with intact quadruple STG allograft strands while all Intrafix group specimens (7/7, 100%) failed by slippage of one or more strands (P=0.005).     

Early healing of nanothickness bioceramic coatings on dental implants. An experimental study in dogs

Thick bioceramic coatings like plasma sprayed hydroxyapatite have been shown to increase the overall tissue response and biomechanical fixation of dental implants. However, the presence and potential fracture of a bone-coating-metallic substrate interface at long times after implantation led these implants to fall from favor in clinical practice. The purpose of this study was to evaluate the biomechanical fixation and biological response of Ca- and P-based, 20-50 nm thickness bioceramic deposition on a previously alumina-blasted/acid-etched Ti-6Al-4V implant surface in a dog model. Cylindrical alumina-blasted/acid-etched (AB/AE) (Control, n = 16), and Nanothickness bioceramic coated AB/AE(Nano, n = 16) implant surfaces were surgically placed in dogs proximal tibia and remained for 2 and 4 weeks in vivo. Following euthanization, the implants-in-bone were mounted in epoxy and pullout at a 0.5 mm/min rate. Following mechanical testing, the specimens were decalcified and processed (Hematoxylin and Eosin) for standard transmitted light microscopy evaluation. Percent bone-to-implant contact (BIC) to the pulled out implant surface was determined through computer software. Statistical analyses were performed by one-way ANOVA at 95% level of significance and Tukey's post-hoc multiple comparisons. No significant differences in pullout force were observed (p > 0.88): 2W Control (212.08 +/- 42.96 N), 2W Nano (224.35 +/- 42.97 N), 4W Control (207.07 +/- 42.97 N), and 4W Nano (190.15 +/- 45.94 N). No significant differences in %BIC were observed (p > 0.94): 2W Control (72.66 +/- 8.51), 2W Nano (69.44 +/- 8.51), 4W Control (70.44 +/- 8.51), and 4W Nano (69.11 +/- 9.09). It is shown that 20-50 nm thickness bioceramic depositions onto previously alumina-blasted/acid-etched substrates did not improve the biomechanical fixation and the BIC at early implantation times, and studies concerning shorter and longer implantation times are recommended for confirmation or before a conclusion can be made.     

Conceptual finite element study for comparison among superior,anterior, and spiral clavicle plate fixations for midshaft clavicle fracture

Open reduction internal fixation technique has been generally accepted for treatment of midshaft clavicle fractures. Both superior and anterior clavicle plates have been reported in clinical or biomechanical researches, while presently the spiral clavicle plate design has been introduced improved biomechanical behavior over conventional designs. In order to objectively realize the multi-directional biomechanical performances among the three geometries for clavicle plate designs, a current conceptual finite element study has been conducted with identical cross-sectional features for clavicle plates. The conceptual superior, anterior, and spiral clavicle plate models were constructed for virtual reduction and fixation to an OTA 15-B1.3 midshaft transverse fracture of clavicle. Mechanical load cases including cantilever bending, axial compression, inferior bending, and axial torsion have been applied for confirming the multi-directional structural stability and implant safety in biomechanical perspective. Results revealed that the anterior clavicle plate model represented lowest plate stress under all loading cases. The superior clavicle plate model showed greater axial compressive stiffness, while the anterior clavicle plate model performed greater rigidity under cantilever bending load. Three model represented similar structural stiffness under axial torsion. Played as a transition structure between superior and anterior clavicle plate, the spiral clavicle plate model revealed comparable results with acceptable multi-directional biomechanical behavior. The concept of spiral clavicle plate design is worth considering in practical application in clinics. Implant safety should be further investigated by evidences in future mechanical tests and clinical observations.     

脊柱胸腰段骨折后路经伤椎单节段固定与常规短节段固定的力学性能比较

目的 应用三维有限元技术构建胸腰椎骨折经伤椎单节段固定及常规短节段固定模型,研究经伤椎单节段固定的生物力学特点,论证其在胸腰椎骨折治疗中应用的可行性。方法 选取青壮年健康男性志愿者,利用CT扫描数据建立脊柱T10~L2正常模型、T12骨折模型以及经伤椎单节段固定和短节段固定模型;分析在轴向压缩、前屈、后伸、侧屈及轴向旋转下各个节段的最大位移差及内固定物的应力情况。结果 骨折模型T10~11、T11~12、T12~L1的最大位移差较正常模型在大多数加载情况时明显增大,经短节段或者经伤椎单节段固定后,该值明显减小,两种固定方式无显著差异。内固定物应力方面：在轴向压缩及前屈时,经伤椎单节段固定模型中螺钉应力明显低于短节段固定;而在后伸、侧屈及轴向旋转时,螺钉应力无明显差异。对于固定棒,轴向压缩及前屈时,两种固定方式无差异;后伸及侧屈时经伤椎节段固定应力高于短节段固定,而旋转时则恰恰相反。结论 对于胸腰段单节段不完全骨折,经伤椎单节段固定可以提供与常规短节段固定相近的生物力学稳定性,是治疗胸腰椎不完全骨折的一种良好的选择。