胸腰椎爆裂性骨折椎管内骨块形成机制的生物力学研究

Background Thoracolumbar burst fracture is a common clinical injury, and the fracture mechanism is still controversial. The aim of this research was to study the formation of intracanal fracture fragments in thoracolumbar burst fractures and to provide information for the prevention of thoracolumbar bursts fractures and reduction of damage to the nervous system.

Methods A nonlinear three-dimensional finite element model of T11–L3 segments was established, and the injury processes of thoracolumbar bursts were simulated. The intact finite element model and the finite element model after the superior articular were impacted by 100 J of energy in different directions. The distribution and variation of stress in the superior posterior region of the L1 vertebral body were analyzed. Abaqus 6.9 explicit dynamic solver was used as finite element software in calculations.

Results A three-dimensional nonlinear finite element model of the thoracolumbar spine was created. In the intact model, stress was concentrated in the superior posterior region of the L1 vertebral body. The stress peak was a maximum for the extension impact load and a minimum for the flexion impact load. The stress peak and contact force in the facet joint had close correlation with time. The stress peak disappeared after excision of the superior articular process.Conclusions The three-dimensional nonlinear finite element model was suitable for dynamic analysis. The contact force in the facet joint, which can be transferred to the superior posterior vertebral body, may explain the spinal canal fragment in thoracolumbar burst fractures.

     

Extremity and extremital replantation

<正>209202 Reconstructive osteotomy of calcaneus for malunited calcaneal fractures/Xin Jingyi(Dept Orthop,Tianjin Hosp,Tianjin 300211)…∥Chin J Orthop.-2009,29(3).-198~201Objective To investigate the feasibility of reconstructive osteotomy of calcaneus for malunited calcaneal fractures.Methods From August 2004 to May 2007,25 cases with 28 calcaneal malunion for 15. to 12 months(average 4.6 months) were treated by reconstructive osteotomy of calcaneus.According to Zwipp and Rammelt classification fro malunited calcaneal fractures.12 calcaneal were type Ⅲ,16 type Ⅳ.All patients underwent radiography including axial,lateral views and CT imaging for calcaneus,and three-dimensional CT imaging reconstruction for 12 cases.According to Essex-Lopresti and Sander classification,and combining with primary X-ray film,reconstructive osteotomy was performed through the primary fracture line.According to widening of the sustentaculum of talus and pitch of fracture,the osteotomy line was from superior anterolateral to inferior posteromedial.The posterior subtalar facet was reduced by elevating the fragment of the posterior subtalar facet upwards and backwards.The defect of calcaneus was filled with the bone graft resected from the extruding lateral wall of calcaneus,or iliac crest bone autografts.The calcaneus was fixed with plate and screw.Results Twenty-four cases with 26 feet were followed up for an average of 12 months (range,10-16 months.).Wound infection happened in 2 cases,which healed after the interfixed plate was removed.There were no screw breakage and displacement of the fracture.the average time for bone healing was 12 weeks (rage,10-14 weeks.)The postoperatively functional evaluation by Maryland for bone system revealed excellent result in 10 feet,good in 12 fair in 4.The rate of excellent and good results was 84%.     

An innovated treatment for intra-articular fracture of calcaneus.

An innovated composite treatment for intra-articular fracture of the calcaneus has been developed. A Steinmann's pin is introduced into the calcaneus percutaneously to release the impaction of the fragments and to lift the compressed subtalar joint facet, which forms a potential cavity in the calcaneal body facilitating restoration of Bohler's angle and correction of widening of the calcaneus by manual reduction. A new type external fixation device, the calcaneus fixation boot, is used to substitute for the traditional plaster immobilization. The boot can exert continuous centripetal pressure on both sides of the calcaneus to control transverse displacement and to maintain the normal height of the heel. The patient is allowed to do functional exercises 24 hours after reduction with the aid of the spring stepping roller, which not only helps dissipate swelling in the early stage but also remold the articular facet. Biomechanical determination showed that the power of triceps surae muscles returned to nearly normal in 4-5 weeks. The patients were allowed to bear weight with crutches in 6-7 weeks. In this series, 94 (87.8%) of 107 cases with an average follow-up period of 2 years and 9 months attained excellent and good results.

     

Effects of discectomy on the stress distribution in the lumbar spine.

The change of the stress distribution of the lumbar spine after discectomy was analysed by the three-dimensional finite element method. It was shown that the stress level in the posterior element was higher, but that in the anterior element was lower than before disc excision. The most significant change of the stress distribution was found in the trabecular bone of the vertebral body. It is considered that in discectomy the normal disc tissue should be preserved as much as possible to maintain good function of the spine.

     

Three-dimensional Finite Element Analysis of the Mechanical Stress on Root from Orthodontic Tooth Movement by Sliding Mechanics

In order to study mechanical stress on root from orthodontic tooth movement by sliding mechanics, a 3-dimensional finite element model incorporating all layers of a human mandibular dental arch with orthodontic appliance has been developed to simulate mechanical stress on root from the orthodontic tooth movement. Simulated orthodontic force of 2 N at 0, 30 and 45 degree from the horizontal axis was applied to the crown of the teeth. The finite element analysis showed when or- thodontic forces were applied to the tooth, the stress was mainly concentrated at the neck of the tooth decreasing uniformly to the apex and crown. The highest stress on the root was 0.621 N/mm2 for cer- vical margin of the canine, and 0.114 N/mm2 for apical region of the canine. The top of canine crown showed the largest amount of displacement (2.417 μm), while the lowest amount of displacement was located at the apical region of canine (0.043 μm). In conclusion, this model might enable one to simulate orthodontic tooth movements clinically. Sliding force at 2 N is ideal to ensure the bodily or- thodontic tooth movement. The highest stress concentration in the roots was always localized at the cervical margin when orthodontic force of 2 N at 0, 30 and 45 degree from the horizontal axis, so there may be the same risk of root resorption when orthodontic force of 2 N at 0, 30 and 45 degree was used in clinic cases.     

Comparisons in finite element analysis of minimally invasive,locking,and non-locking plates systems used in treating calcaneal fractures of Sanders type Ⅱ and type Ⅲ

Background Calcaneal fractures are relatively common but complex,while the treatment of these fractures is still controversial.The objective of this study was to compare the biomechanical stability of minimally invasive,locking,and non-locking plating systems used for fixing Sanders type Ⅱ and type Ⅲ calcaneal fractures.Finite element analysis was used for comparing the three types of plating systems.This study helped in guiding the clinical management of calcaneal fractures.Methods The CT data acquired from a volunteer was used to construct a finite element model of calcaneus.The fracture lines were made according to Sanders type Ⅱ （A,B,C） and type Ⅲ （AB,AC,BC） and six calcaneal fractures models were constructed accordingly.Three fixation methods used in clinical treatment were simulated by design tools （minimally invasive plating with percutaneous screws,Y-size non-locking plating,and locking plating） and then fixed to these fracture models with the help of clinical principles.The single minimally invasive plating fixation was also tested to compare the function of percutaneous screws.Then,the neutral force was applied on established methods.The displacement and presses distribution condition in various plating models were analyzed and compared.Results The levels of displacement and compressive press on the bone around fixation or strains on plating were within the physiological limit,indicating that the three methods were suitable for application.Compared with the locked and unlocked plates,the minimally invasive plating caused a relatively lower displacement without the high stress in bone or fixation.The minimum stress in fixation was observed in locking plate as the distribution of stress was concentrated in the anterior part of locking plate.Conclusions The minimally invasive plating method could be a better alternative method in treating Sanders type Ⅱ and type Ⅲ calcaneal fractures.The observed stiffness of locking plate was not obviously stronger than unlocked plate.     

A finite element analysis of the pelvic reconstruction using fibular transplantation fixed with four different rod-screw systems after typeⅠresection

Background The pelvis often needs to be reconstructed after bone tumor resection. A major challenge here for the orthopedic surgeons is to choose a method that gives the best performance which depends upon its biomechanical properties. In this study, a 3-dimensional finite element analysis （FEA） was used to analyze the biomechanical properties of reconstructed pelvis using fibula transplant fixed by four commonly used rod-screw systems.
Methods A total pelvic finite-element model including the lumbar-sacral spine and proximal femur was constructed based on the geometry of CT image from a healthy volunteer. Three-dimensional finite element models of different implants including fibula, rod and screw were simulated using ways of solid modeling. Then various reconstructed finite element models were assembled with different finite element implant model and type Ⅰ resected pelvic finite element model. The load of 500 N was imposed vertically onto the superior surface of L3 vertebral body, and the pelvis was fixed in bilateral leg standing positions. FEA was performed to account for the stress distribution on the bones and implants. The pelvis displacement of the different rod-screw fixation methods and the maximum equivalent stress （max EQV） on all nodes and element were figured out to evaluate the advantages and disadvantages of different reconstructive methods.
Results Stress concentration in the fibula transplant was extremely high in the reconstructed pelvis, but could be substantially decreased by internal fixation, which partially transferred the stress from the fibula to the rod-screw systems. High stress concentration was also found in the implants, especially in the connection sites between screw arid rod. Among the four methods of fixation, a double rod system with L5-S1 pedicle and ilium screws （L5-S1 HR） produced the best performance： least stress concentrations and least total displacement.
Conclusion According to the stability and stress concentration, the method of L5-S1 HR fixation     

Clinical significance of three dimensional finite element analysis on humerus fracture

Objective: To treat humerus fracture with three dimensional pattern and finite element analysis, providing mechanical basis for treating humerus fracture. Methods: Humerus pattern was established based on the CT images, and calculation was done by ANSYS5. 6 software. Three dimensional ten-node tetrahedron unit was selected and were divided into 2 729 nodes, 49 041 units. Distribution and amount of axial compression of humerus were analyzed when clip angle was 30°, 45°, 90° between fracture face and axial line with fixed X, Y, Z directions. Results: The distribution of stress was greatly different between fracture face and non fracture face. Stress in fracture part was fairly concentrated with incomplete symmetric distribution around the center of fracture face; Greater stress distributed in the regions 10 mm from fracture face, which was 2-3 times that of other stress regions. Conclusion: Required load must be estimated under various conditions as to select the suitable internal fixation implants dur     

THE EFFECT OF POSTERIOR ELEMENT RESECTION ON THE STRESS DISTRIBUTION IN THE LUMBAR SPINE

A three-dimenslonal finite element model of the lumbar motion segment was used to predict the stress distribution in lumbar spine with posterior element resection. It was shown that the stress level in all parts of the lumbar spine was elevated although the stress distribution remalned unchanged. The authors concluded that the posterior element resectlcal in lumbar surgery should he avoided as much as possible.