ABSTRACT
BACKGROUND:Vertebral compression fractures are the most common vertebral fractures in the elderly patients with osteoporosis, and the correlation between the compression of anterior border of vertebral body and adjacent vertebral refractures is not clear. OBJECTIVE:To establish a model of different compression of T12vertebral body with finite element method, and analyze the relationship between the compression of T12vertebral body and the stress of adjacent vertebral plate. METHODS:Based on thoracolumbar CT data of normal adult volunteers, MIMICS/3-matic was imported. Through image segmentation, repair and three-dimensional mesh of accessto thoracic and lumbar T11-L1data, grid assigned material properties was imported to ABAQUS so as to establish ligament, joint and other small features and obtain realistic three-dimensional finite element model. The six degrees of freedom, including anteflexion, posterior extension, left and right flexion, left and right rotation, were loaded, to verify the validity of the normal model. With the frontier of vertebral body compression to 90%, 80%, 70%…10% of the nine states, MISES stressesof the T11andL1segment intervertebral disc endplate were extracted; the relationship curve of compression state and endplate stress was obtained. RESULTS AND CONCLUSION:(1) The model was highly realistic and could reflect the actual stress state. (2) The stress value of T11vertebral body and L1vertebral body was positively correlated with the compression of T12vertebral body. Increased stress may lead to an increased likelihood of end plate fractures, which increases the risk of fractures in the adjacent vertebralbodies.
ABSTRACT
BACKGROUND: Vertebrae axial rotation is a basic deformity of scoliosis, the rotational degree of which is hard to measure due to the field limitation of posterior spinal instrumentation. Currently, vertebrae rotational degree is measured according to preoperative X-ray film or CT, while no reports concerning measuring vertebrae rotational degree during operation. OBJECTIVE: To explore the feasibility of measurement of vertebrae rotational degree with the entry point of pedicle screws.METHODS: Design of the path of pedicle screws on CT scans before surgery, a line bisection and perpendicular to another connecting bilateral entry point of pedicle screws, and the angle of vertebral rotation (EPPsag) was taken as the angle between this line and the saggital plane. The difference among vertebrae rotational degrees measured by conimeter, Ho's method and EPPsag was compared by Wilcoxon signed rank test. The intra-observer and inter-observer difference was analyzed with One-WayANOVA. Conimeter was used to measure vertebrae rotational degree of each vertebra in 9 lumbar specimens, and the results was compared to EPPsag.RESULTS AND CONCLUSION: There was no significant difference among EPPsag, actual rotational degree and measuring results of Ho's method (P>0.05). The One-Way ANOVA showed that the differences between intra-observer analysis and inter-observer analysis (P>0.05). The results demonstrated that EPPsag can exhibit vertebrae rotational degree accurately and repeatability. This anger can be obtained accurately with the instrument if the vertebrae rotational degree not exceeding 30°.
ABSTRACT
Objective To study the accuracy in placement pediele screws with different method in the selection of entrance point in surgery of scoliosis.Method 27 cases with Lenke Ⅰ type of Adolescent Idiopathic Seoliosis(AIS)from Mar 2006 to September 2008,were retrospectively analyzed.14 eases were randomly divided into standard group(group A)and the entrance point was the same one as described in literatures.13 cases were randomly divided into individually group(group B)and the entran~point wag designed by surgeons on CT scans before surgery.There was no statistical difference in the mean age at time of surgery,Cobb angle on coronal and saggital(T5T12)plane,flexibility and rotational degree of apical vertebra preoperatively between two groups.Result There was no statistical difference in the time of surgery,blood losing,fixation segments,correction rate in Cobb angle and rotational degree of apical vertebra between two groups.The accuracy in placement pedicle screws in individually group was higher than that in control group(P＜0.01).Conclusion The accuracy in placement pedicle screws in the surgery of scoliesis can be improved by individual selection of entrance point.
ABSTRACT
Objective To explore the indications of anterior and posterior approach operations for unstable thoraco-lumbar fractures coupled with neurologic deficits and prevention of intraoperative and postoperative complications. Methods We investigated 107 consecutive eases of thoraco-lumbar fractures coupled with spinal cord injury who had been operated on from January 2000 to December 2006.Their average age was 37.8(range.17 to 78) years old. They were 71 males and 36 females. Anterior approach was selected for 46 cases and posterior approach for 61 cases according to their McCormack grades. By the Frankle system for neurologie deficits, 7 cases were graded as A,16 as B,39 as C and 45 as D. Fracture height vecoveries before and after surgery were analyzed statistically. Kyphotic deformity was assessed on lateraJ radiographs using the Cobb method. Results The mean follow-up of 97 cases was 2.8(range,0.5 to 6) years. In both groups. All the cases gained at least 1 grade improvement except those with Frankle grade A. The mean kyphotic angles before operation, after operation and at the latest follow-up were 23.7°,10.6°and13.1°respectively, with significant differences(P＜0.01),in the anterior approach group, while 16.3°,8.4°and 11.7°respectively, with significant differences(P＜0.01),in the posterior approach group. Some complications, such as deficit of cutaneous nerve of thigh, appeared in the 2 groups. Conclusions In treatment of unstable thoraco-lumbar fractures coupled with neurologic deficits, the anterior approach may be better than the posterior approach. The posterior approach can be applied for the cases with less than 7 points in McCormack index. Correct selection of operative approach, careful operation and good rehabilitation after operation are necessary for the prevention of complications.
ABSTRACT
0.05). However,the accuracy in placement pedicle screws and derotation rate of apical vertebrae were much higher in the individually treated group than those in the standard group (P=0.001,0.02).[Conclusion]The accuracy in placement pedicle screws and correction effects on transverse plane of patients with Lenke Ⅰ AIS can be improved significantly by individual selection of entrance point.