骨愈灵对骨质疏松症大鼠骨代谢影响的研究

目的探讨骨愈灵对骨质疏松症大鼠骨代谢的影响。方法采用维甲酸灌饲造成大鼠骨质疏松症模型，使用骨愈灵胶囊进行治疗。结果使用骨愈灵治疗的大鼠胫骨骨小梁和股骨形态计量学各项指标均比模型组有显著性改善（Ｐ＜０．０５～０．０１）；治疗组大鼠股骨生物力学各检测参数亦显著好于模型组（Ｐ＜０．０５～０．００１）。结论骨愈灵治疗可改善维甲酸所致骨质疏松症大鼠的骨质丢失状态，提高骨的机械性能，避免或减少骨折的发生。

Three dimensional finite element analysis of anatomic distal radius Nitinol memory connector treating distal radius fracture

Objective: To study the memory biomechanical character of anatomic distal radius Nitinol memory connector (DRMC) in treating distal radius fracture. Methods: Establishing three dimensional model and finite element analysis, we calculated the stress in and around the fracture faces when distal radius fracture was fixated with DRMC. Results: Axial holding stress produced by holding part of DRMC on distal radius was 14.66 MPa. The maximum stress of holding part was 40-70 MPa, the minimum stress was 3-7 MPa,and the stress of compression part was 20-40 MPa. Conclusion: The distribution of stress produced by DRMC around the fracture line is reasonable, and axial holding stress can help stabilize fracture during earlier period. The existence of longitudal compression and memory effect can transfer fixated disused section into developed section and enhance fracture healing.

BIOMECHANICAL STUDY ON UNILATERAL SINGLE-PLANE EXTERNAL FIXER

Six tibias removed from 30-40 years old males, who died in an accident for in less than 12 hours, were osteotomized at one-third supra-medium segment. They were fixed by an unilateral adjustable external fixer (UAEF), to be used as a model of external fixation of tibial fracture (MEFTF). The compression. tension, torsion, antero-posterior and lateral bending strength, and the strength for vertically extracting the pins from the tibia were determined in the MEFTF. Within a certain range of load, the correlation of strain to stress was basically a linear relationship. These data provide a theoretical basis of biomechanics for the improvement of UAEF and for early exercises of fracture patients, such as extend-bending of the joint.raising the limb and walking with a walking stick.

Stress analysis of three-dimensional finite element model of malunion calcaneus during gait

Objective: To analyze the stress distribution of calcaneus with posterior articular facet compressed after fracture and talus during gait. Methods: A wedge under the posterior articular was transected from a normal finite element model of calcaneus and talus to simulate malformation of compression of the posterior facet after fracture of calcaneus. The model was used to simulate for three subphases of the stance during the gait(heel strike, midstance, push off) and calculate the finite element. The results were compared with normal situation. Results: The stress distribution within the bone in situation of malformation was obtained and regions of elevated stresses for three subphases were located. The results were significantly different from that of normal situation. Conclusion: The simulation of calcaneus and talus in malformation has important clinic implication and can provide an insight into the factors contributing to many clinic pathogenic changes after fracture of calcaneus.

A BIOMECHANICAL ANALYSIS OF UNILATERAL HOOKED-SULCATED EXTERNAL FIXATOR ON OSTEOMINED TIBIA

Four tibiae removed from 30-40 years males, who died of accidents in less than 12 hours, were os- teomized at medium part. Then these tibiae were fixed by an unilateral hooked-sulcated external fixator (UHSEF), and the bone-fixator system was used as a model of external fixation of tibial fracture. The axial compression, distraction, torsion, antero-posterior and lateral bending rigidly and the strain of the pins were determined in this system. Based on the results, we found that compared with the configuration of four paralled pins, the rigidity of the fan-like configuraton didn’t decrease significantly if the angle between lateral and medium pins was less than 45’. But the reverse was true when the frame separation increased from 5 to 8 cm. What’ more, the pin strain decreased if the rigidity of the system was improved. These data provided a theoretical basis of biomechanics for the improvement of UHSEF.

Comparative study of various internal fixation methods for treating patellar fractures by three-dimensional photoelasticity

Objective: To compare the biomechanical basis of 3 different internal fixation methods: nitinol patellar concentrator (NT-PC), tension band and wire circle in treating patellar fractures. Methods: The epoxy resin three dimensional photoelasticity patellar models were made by precise moulding, and were fixated by nitinol patellar concentrator (NT-PC), tension band and wire circle respectively. The patellar models with frozen stress stripes were put into the polarized light field and the stress distributions were compared. As for the model fixated by NT-PC, by dividing layer, photographing and tracing, we used the iterative method to calculate the stress value of every internal node of the epoxy resin patellar model, and the character of stress was analyzed. Results: An overall stress field was yielded when the patellar model was fixated by NT-PC, and the stripes were more than that of tension band model and wire circle model, which have only few stress stripes in the fixated layers. Further analysis indicated that there were continuous fixated stresses in the facies articularis and distal pole of patella, and the character of stresses produced by NT-PC were mainly in longitudinal direction, then in transverse direction. The shearing stresses were small. Conclusion: The initiative and continuous memorial stress of NT-PC and its overall stress distribution character are the essence of NT-PC distinguished with tension band and wire circle in treating patellar fractures. The stress character produced by NT-PC is good for the stability of fracture site and prompts fracture healing.

Mechanism of thoracolumbar burst fractures：a biomechanical study

OBJECTIVE: To investigate the mechanism associated with thoracolumbar burst fractures. METHODS: Stress distribution of the spine in the upright, flexion and extension positions was analyzed using a three-dimensional finite element model of the spinal motion segment. RESULTS: Stress concentration was noted at the pedicle and posterosuperior part of the vertebral body near the pedicle. CONCLUSION: Stress concentration of the spine may be implicated in the biomechanical mechanism underlying thoracolumbar burst fractures.

Relationship among bone mineral density,collagen composition,and biomechanical properties of callus in the healing of osteoporotic fracture

Objective： To study the change and relationship among bone mineral density （BMD）, collagen composition and biomechanical properties of the callus in the healing process of osteoporotic fracture. Methods： The osteoporotic rat model and fracture model were established through bilateral ovariectomy （OV＇X） and osteotomy of the middle shaft of the right hind tibiae, respectively. Ninety female SD rats were randomly divided into OVX group and sham group. With the samples of blood and callus, roentgenoraphic and histological observation were performed for the assessment of the healing progress of the fracture, and the serum concentration of TRAP-5b, proportion of type I collagen, BMD and biomechanical properties of the callus were measured. Results： The OVX group experienced a significant delay of fracture healing. The mean serum concentration of TRAP-5b of rats in the OVX group was much higher than that in the sham group after the operation （P 〈 0.05）, but the difference at the same time point after fracture was smaller than that before fracture （P 〈 0.05）. The BMD of the callus in both groups reached the peak value at the 6 th week after fracture while the proportion of the type I collagen and the biomechanical strength reached the peak at the 8th week. Conclusions. The deficiency of estrogen after the ovariectomy could induce the up-regulation of the osteoclasts activities, whereas the potency of further activation after fracture was depressed. Although the synthesis of collagen together with its mineralization determines the biomechanical properties of new bone, the accumulation of collagen could be assessed as an index in the prediction of biomechanical strength of bones independent of the bone mineral deposition.

A finite element analysis of the stress distribution to the mandible from impact forces with various orientations of third molars

Objective： To investigate the stress distribution to the mandible, with and without impacted third molars（IM3 s） at various orientations, resulting from a 2000-Newton impact force either from the anterior midline or from the body of the mandible. Materials and methods： A 3 D mandibular virtual model from a healthy dentate patient was created and the mechanical properties of the mandible were categorized to 9 levels based on the Hounsfield unit measured from computed tomography（CT） images. Von Mises stress distributions to the mandibular angle and condylar areas from static impact forces（Load I-front blow and Load II left blow） were evaluated using finite element analysis（FEA）. Six groups with IM3 were included： full horizontal bony, full vertical bony, full 450 mesioangular bony, partial horizontal bony, partial vertical, and partial 450 mesioangular bony impaction, and a baseline group with no third molars. Results： Von Mises stresses in the condyle and angle areas were higher for partially than for fully impacted third molars under both loading conditions, with partial horizontal IM3 showing the highest fracture risk. Stresses were higher on the contralateral than on the ipsilateral side. Under Load II, the angle area had the highest stress for various orientations of IM3 s. The condylar region had the highest stress when IM3 s were absent. Conclusions： High-impact forces are more likely to cause condylar rather than angular fracture when IM3 s are missing. The risk of mandibular fracture is higher for partially than fully impacted third molars, with the angulation of impaction having little effect on facture risk.

Biomechanical and clinical study on screw hook fixation after direct repair of lumbar spondylolysis

Objective： To evaluate the biomechanicai effect and clinical results of hook screw fixation after direct repair of lumbar spondylous defects in the pars interarticularis. Methods ： L2-L6 spines of 8 fresh-frozen and thawed calf cadavers were used for mechanical testing. Bilateral spondylous defects were created in the L4 vertebra. The intervertebrai rotation ranges between L4 and Ls were scanned and computerized in various states of motion, such as flexion/extension, lateral bending and torsional ioadings applied on the intact spine and the spondyious spine when the spondylous spine was fixed with modified Scott＇ s fixation, hook screw fixation and Buck ＇ s fixation sequentially and respectively. Between July 2002 and February 2004, 14 young male patients （aged 15-31 years） suffering from symptomatic lumbar spondyiolysis were treated with TSRH hook screw fixation after direct repair of the defects. MacNab criteria were used to assess their preand post-operative status. Results： Each fixation technique could significantly increase the intervertebral rotational stiffness and made the stiffness return to nearly the intact level. Hook screw technique provided more rotational stability than the others. Hook screw and Buck＇ s techniques provided more flexion/extension stability than modified Scott＇ s technique. Neither complication nor instrumental failure was observed in this study. The mean follow-up period was 21 months. All the patients except one acquired union during the follow-up period. Thirteen patients had a ＂ good ＂ or ＂excellent＂ result according to MacNab criteria. Conclusions ： Hook screw fixation shows biomechanicai advantages and is safe and effective for young patients with lumbar spondyiolysis.

Biomechanical comparison of locking plate and crossing metallic and absorbable screws fixations for intra-articular calcaneal fractures

The locking plate and percutaneous crossing metallic screws and crossing absorbable screws have been used clinically to treat intra-articular calcaneal fractures, but little is known about the biomechanical differences between them. This study compared the biomechanical stability of calcaneal fractures fixed using a locking plate and crossing screws. Three-dimensional finite-element models of intact and fractured calcanei were developed based on the CT images of a cadaveric sample. Surgeries were simulated on models of Sanders type III calcaneal fractures to produce accurate postoperative models fixed by the three implants. A vertical force was applied to the superior surface of the subtalar joint to simulate the stance phase of a walking gait. This model was validated by an in vitro experiment using the same calcaneal sample. The intact calcaneus showed greater stiffness than the fixation models. Of the three fixations, the locking plate produced the greatest stiffness and the highest von Mises stress peak. The micromotion of the fracture fixated with the locking plate was similar to that of the fracture fixated with the metallic screws but smaller than that fixated with the absorbable screws. Fixation with both plate and crossing screws can be used to treat intra-articular calcaneal fractures. In general, fixation with crossing metallic screws is preferable because it provides sufficient stability with less stress shielding.

Biomechanical properties of regenerated bone by mandibular distraction osteogenesis

To study the biomechanical properties of the new bone generated by mandibular distraction osteogenesis (DO). Methods: A total of 11 healthy adult goats were randomly divided into 2 groups, the experimental group (n=9) and the control group (n=2). For the goats in the experimental group, the bilateral mandibles were gradually lengthened for 10 mm with distraction appliances. Three goats were sacrificed respectively at 2, 4 and 8 weeks after completion of distraction. Compressive, three point bending and shearing tests were conducted on the standard regenerated bone samples and the whole unilateral mandibular specimens. For the goats in the control group, no operation was made and the whole unilateral mandible was taken as the test specimen.Results: The compressive strength and bending stiffness of the new bone reached the normal level at 4 and 8 weeks after completion of distraction, respectively. But the shearing strength remained significantly weaker than that of the controls at 8 weeks after distraction. Conclusions: The distraction appliance can be removed and the lengthened mandible should be exposed to adaptive functional exercise at 8 weeks after completion of distraction.

Study of the morphology and biomechanics of sacral fracture

Objective： To characteristics of sacral loads. observe the morphological fracture under different impact Method： Ten fresh pelvic specimens were loaded in dynamic or static state. A series of mechanical parameters including the pressure strain and velocity were recorded. Morphological characteristics were observed under scanning electron microscope. Results： The form of sacral fracture was related to the impact energy. Under low-energy impact loads, ilium fracture, acetabulum fracture and crista iliaca fracture were found. Under high-energy impact loads, three types of sacral fracture occurred according to the classification of Denis： sacral ala fracture, Type 1 fracture; sacral foramen cataclasm fracture, Type lI fracture; central vertebral canal fracture, Type m fracture. Nerve injury of one or two sides was involved in all three types of sacral fracture. The fracture mechanism of sacrum between the dynamic impact and static compression was significantly different.When the impact energy was above 25 J, sacral foramen cataclasm fracture occurred, involving nerve root injury. When it was below 20 J, ilium and sacral fracture was most likely to occur. When it was 20 - 25 J, Type l fracture would occur. While in the static test, most of the fracture belonged to ilium or acetabulum fracture. The cross section of sacrum was crackly and the bone board of Haversian system was brittle, which could lead to separation of bone boards and malposition of a few of cross bone boards. Conclusions： In dynamic state, sacrum fracture mostly belongs to Type I and Type lI, and usually involves the nerve roots. Sacrum fracture is relevant to the microstructures, the distribution of the bone trabecula, the osseous lacuna and the Haversian system of sacrum. The fracture of ilium and acetabulum more frequently appears in static state, with slight wound of peripheral tissues.

The biomechanics of point contact-dynamic compression plate and its effects on bone perfusion

Objective： To compare the mechanical properties of point contact-dynamic compression plate （PC-DCP） and its effects on cortical bone perfusion with that of dynamic compression plates （DCP） in goat tibiae. Methods： Twenty pairs of matched flesh goat tibiae were used. A transverse fracture model was established. The fractures with a 3ram interspace between the fracture ends were subject to fixations with the DCPs and the PC- DCPs respectively, then the four-points bending tests and the torsion tests were conducted to compare the mechanical properties of the PC-DCP with that of DCP. Another 13 sexually mature goats underwent fixations with the DCPs and the PC-DCPs, respectively, at the mid-shafts of the intact bilateral tibiae. Ischemic zones were observed at four time points （1 day, 2, 6, and 12 weeks after operation） using disuiphine blue staining technique. Remits： There were no significant differences in mechanical properties, such as bend- and torsionresistance, between the DCPs and the PC-DCPs. One day, 2, and 6 weeks after operation, on the side of DCP fixation, outer cortical bone ischemia under the plate persisted, and this condition did not reverse until 12 weeks after operation. However, on the side of PC-DCP fixation, cortical bone iscbemia occurred only in the periphery of the screw holes and at the contact sites of the PC NUTs 1 day after operation, and it disappeared at 2 weeks after operation. Conclusions： The PC-DCP has similar biomechanical properties of the DCP, but is less detrimental to local bone blood circulation than the conventional plates.

Porous Ti-10Mo alloy fabricated by powder metallurgy for promoting bone regeneration

Porous Ti-lOMo alloys were fabricated by powder metallurgy using a space-holder method. The pore characteristics, m icrostructure, mechanical properties, in vitro biocompatibility, and in vivo osseointegration of the fabricated alloys were systematically investigated. The results show that with different weight ratios of the space-holder (NH4- HC03) added, all of the porous Ti-10Mo alloys sintered at 1,300℃ exhibited a typical W idmanstatten microstructure. The porosity and average pore size of the porous structures can be controlled in the range of 50.8%-66.9% and 70.1 -381.4μm , respectively. The Ti-10Mo alloy with 63.4% porosity exhibited the most suitable mechanical properties for implant applications with an elastic modulus of 2.9 GPa and a compressive yield strength of 127.5 MPa. In vitro9 the alloyconditioned medium showed no deleterious effect on the cell proliferation. The cell viability in this medium was higher than that of the reference group, suggesting non-toxicity and good biological characteristics of the alloy specimens. In vivo, after eight weeks* implantation, new bone tissue formed surrounding the alloy implants, and no noticeable inflammation was observed at the implantation site. The bone bonding strength of the porous Ti-10Mo alloy increased over time from 46.6N at two weeks to 176.4 N at eight weeks. Suitable mechanical properties together with excellent biocompatibility in vitro and osteointegration in vivo make the porous Ti-10Mo fabricated by powder metallurgy an attractive orthopedic implant alloy.

A biomechanical investigation on the incorporation of cortical allograft in rabbit ulna defects

To explore the changes of biomechanical properties of cortical allograft in different mechanical environments. Methods: Cortical allograft was transplanted to each side of the midshaft diaphyseal ulna of each one of 40 rabbits. The left transplanted allograft underwent normal physiological load, while the right one underwent lower load. After animals were killed,specimens were taken for examination of bone mineral density, bone porosity and maximal three-point-bend breaking load. Results: The union strength of allograft-host bone junction was increased constantly; meanwhile, the internal creeping substitution led to an initial greater weakening of the cortical allograft itself and a later recovery of its strength. In comparison, the union strength of the normally loaded graft-host bone construct was significantly higher than that of the lower loaded side at the 8th and 16th week after transplantation. At the 16th week, there was greater bone strength in normally loaded graft than that in lower loaded graft. Conclusions: The internal repair can lead to initial greater weakening of cortical allograft and later gradual recovery of its strength. The effect of physiological load can accelerate the improvement of the biomechanical properties of allograft.

Three-dimensional finite element analysis of lumbar vertebra loaded by static stress and its biomechanical significance

Objective： To explore the mechanical behavior of lumbar spine loaded by stress and provide the mechanical basis for clinical analysis and judgement of lumbar spine fracture classification, mechanical distribution and static stress. Methods： By means of computer simulation method, the constructed lumbar spine three-dimensional model was introduced into three-dimensional finite element analysis by software Ansys 7.0. The lumbar spine mechanical behavior in different parts of the stress loading were calculated. Impact load is 0-8000 N. The peak value was 8000 N. The loading time is 0-40 minutes. The values of the main stress, stress distribution and the lumbar spine unit displacement in the direction of main stress were analyzed. Results： The lumbar spine model was divided into a total of 121 239 nodes, 112 491 units. It could objectively reflect the true anatomy of lumbar spine and its biomechanical behavior and obtain the end-plate images under different stress. The stress distribution on the lumbar intervertebral disc （L3-L4） under the axial, lateral flexion and extension stress, and the displacement trace of the corresponding processus articularis were analyzed. Conclusion： It is helpful to analyze the stress distribution of lumbar spine and units displacement in static stress loading in the clinical research of lumbar spine injury and the distribution of internal stress.

Biomechanical Effect of Chinese Immobilization Using Little Splint

Immobilization using little splint is an original innovation of Chinese people for the fracture fixation, which is simple to use and clinically effective. It was found that Chinese immobilization using little splint can make the non-invasive,uncovering, and trouble free healing of bone fracture via harmonious unity of the structure stability and the force balance, of the motion stability and the stress adaptability, of the constant and discontinuous physiological stress. The biomechanical effect of Chinese immobilization using little splint, including entirety, dynamic, and functional fixity, is the root cause of its inheritance and the use up to now, and also is a direction of today's fracture fixation towards personalization, individuality and entirety.