Formative mechanism of intracanal fracture fragments in thoracolumbar burst fractures: a finite element study / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>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.</p><p><b>METHODS</b>A nonlinear three-dimensional finite element model of T11-3 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.</p><p><b>RESULTS</b>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.</p><p><b>CONCLUSIONS</b>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.</p>

Unilateral pedicle screw fixation through the pedicle of fractured vertebra in combination with the short segment of pedicle screw in the treatment of thoracolumbar fracture of mild to moderate instability / 中华外科杂志

<p><b>OBJECTIVE</b>To evaluate the efficacy of unilateral pedicle screw fixation through the pedicle of fractured vertebra in combination with the short segment of pedicle screw in the treatment of thoracolumbar fracture of mild to moderate instability.</p><p><b>METHODS</b>Twenty-six patients with single segment thoracolumbar fracture received unilateral pedicle screw fixation through the pedicle of fractured vertebra in combination with the short segment of pedicle screw from January 2008 to December 2009. There were 16 patients were male and 10 were female with an average age of 47.3 years (range from 39 to 60 years). Fracture severity score was constructed by using the load-sharing classification (4 points for 2 cases, 5 points for 14 cases, 6 points for 10 cases). By Frankel assessment system, 2 cases were in grade C, 3 in grade D, 21 in grade E. The assessment included anterior vertebral body height, the sagittal Cobb angle, the restoration of nervous function, visual analogue score (VAS) and Oswestry disability index (ODI).</p><p><b>RESULTS</b>The follow-up after the surgery was 13 - 26 months, with an average of 18.6 months. There were no fixation failure, defined as implant failure or ≥ 10° correction loss. The neurological status of 4 patients, who had an associated neurologic deficit preoperatively, was completely recovered. The Frankel grade of another case was re-rated D from the original C. The mean anterior vertebral body height increased from 57.0% ± 6.3% before the surgery to 93.1% ± 1.7% at the last follow-up(F = 455.276, P < 0.05). The sagittal Cobb angle decreased from 15.6° ± 4.7° before the surgery to 2.6° ± 5.2° at the last follow-up (F = 34.623, P < 0.05). VAS and ODI were 1.0 ± 0.7 and 17.0 ± 5.9 at the last follow-up.</p><p><b>CONCLUSION</b>Unilateral pedicle screw fixation through the pedicle of fractured vertebra combined with the short segment of pedicle screw is effective for thoracolumbar fracture with mild to moderate instability.</p>

Digital marker tracing combined with center-of-mass algorithm in measuring pelvic displacement / 第二军医大学学报

Objective: To evaluate the reliability of the digital marker tracing method combined with center-of-mass algorithm in measuring human pelvic displacement. Methods: Six cadaveric specimens of the third lumbar vertebra to the proximal 1/3 part of femur were used in present study. The specimens had no structural abnormality and all the soft tissues were dissected, reserving the hip joint capsules and the ligaments of the pelvic ring and floor. Markers with black dots against white back-ground were used to mark the key points of the pelvis. Axial loadings from the proximal lumbar (simulating the two-legged stance) were applied by MTS in the gradient of 0 N to 500 N. Images of the front and lateral views were obtained using two CCD cameras. Using Image J software, we calculated the vertical displacement of S1, (the first sacral vertebrae) in the front view and the micro-angular rotation of sacroiliac joint in the lateral view by measuring the marker's movement. Results: There was good correlation between the marked points before and after deformation of the pelvis, with the average correlation coefficient being 0. 983. Based on the 768 X 576 pixels, pixel size (mm) 0. 681 5 X 0. 681 5 image,the accuracy of the displacement was about 0. 018 pixels and the comparative error could reach 1. 11‰. The load-displacement curves obtained in this study accorded well with the clinical results. The pelvic load-displacement curve exhibited approximately a linear behavior; the sacroiliac joint load-angular rotation curve in the sagittal plane exhibited a non-linear behavior. Under a vertical load of 500 N,the average vertical displacement of S1, of the pelvis was (0. 835 6 ± 0. 283 0) mm and the average micro-angular rotation of sacroiliac joint in lateral view was (0. 584 ±0. 221). Conclusion: Digital marker tracing method combined with the center-of-mass algorithm is a simple, accurate method for measurement of pelvic displacement, which can be widely used in biomechanical research.

A finite element analysis of the pelvic reconstruction using fibular transplantation fixed with four different rod-screw systems after type I resection / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>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.</p><p><b>METHODS</b>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.</p><p><b>RESULTS</b>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 and 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.</p><p><b>CONCLUSION</b>According to the stability and stress concentration, the method of L5-S1 HR fixation combined with fibula transplantation is better than other fixation methods in pelvic reconstruction after type I resection.</p>

Analysis of the pelvic stability after type I resection of iliac tumor / 中华外科杂志

<p><b>OBJECTIVE</b>To analyze the pelvic stability after type I resection of iliac tumor.</p><p><b>METHODS</b>Six adult cadaveric specimens were tested. The iliac subtotal resection models were established according to Ennecking's type I resection. Markers were affixed to the key region of the pelves. Axial loading from the proximal lumbar was applied by MTS load cell in the gradient of 0-500 N in the double feet standing state. Images in front view were obtained using CCD camera. Based on Image J software, displacements of the first sacral vertebrae (S1) of the resected pelves and the intact pelves were calculated using digital marker tracing method with center-of-mass algorithm.</p><p><b>RESULTS</b>Serious instabilities were found in the resected pelves. S1 rotational movements around the normal side femoral head of the resected pelvis were found. The average vertical displacement of S1 of the resected pelvis was (7 +/- 3) mm under vertical load of 500 newtons, which were 8.3 times compared to the intact pelvis. The average angle of S1 rotation around the normal side femoral head of the resected pelvis was (4.0 +/- 1.8) degrees, which were 12.5 times compared to the intact pelvis.</p><p><b>CONCLUSIONS</b>Biomechanical model of type I resection of iliac tumor are established. Essential pelvic reconstruction must be introduced because of the serious instability of the bone defection after tumor resection.</p>

Tumor blood vessels formation in osteosarcoma: vasculogenesis mimicry / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Osteosarcoma is characterized by high neovascularization and a high propensity for metastasis through bloodstream. This study was to examine whether there is evidence for vasculogenic mimicry in osteosarcoma and to illustrate mechanism of tumor blood vessels formation in osteosarcoma.</p><p><b>METHODS</b>Osteosarcoma cell lines (U-2OS) were tested for their ability to form tubular networks in three-dimensional culture containing type I collagen. The structures of the tubular networks were observed with phase contrast microscope and transmission electron microscope (TEM). Morphometric studies using hematoxylin and eosin (HE) stain and CD31 immunohistochemical stain to show tumor-lined channels in human osteosarcoma were also performed.</p><p><b>RESULTS</b>Observation with light microscope and TEM showed that highly aggressive osteosarcoma cell lines (U-2OS) formed networks containing channels when grown in three-dimensional culture containing type I collagen, in the absence of endothelial cells or fibroblasts. Morphometric observation using HE stain and CD31 immunohistochemical stain showed that tumor cell-lined channels were also detected in vivo in osteosarcoma; by comparison, all vascular areas in the pedicle of osteochondroma or outside osteochondroma were endothelial-lined.</p><p><b>CONCLUSION</b>These observations strongly suggest that aggressive osteosarcoma cells may generate vascular channels that facilitate tumor perfusion independent of tumor angiogenesis and have the ability of vasculogenic mimicry.</p>