Biomechanics And Nail Road Of Expansion Pedicle Screw

At present, the pedicle screw fixation technology has a great development, been widely used in the treatment of spinal degenerative disease, fractures, deformity, bone metastases, and other diseases. However, a bone screw interface control of inadequate or excessive load after load when it could easily lead to the pedicle screw loosening or removal. Especially in patients with osteoporosis is more common in this phenomenon. Surgery is usually used for the renovation increase pedicle screw diameter, length, or in the original nails, filling in the bone adhesives, but that practice in the clinical application of this method in both its obvious limitations. To address this clinical problem, in accordance with principles of mechanical expansion designed expansion pedicle screw (expansive pedicle screw, EPS). EPS screw features without increasing the pedicle screw diameter of the circumstances, so that the screw diameter of vertebral body increased with the surrounding bone screws into contact angle increases, thereby increasing shear stress, enhance the ability of anti-pull-out , opened a field of spinal fixation a new way of thinking. On the expansion of this study conducted a series of screws and nails, biomechanical parameters of the test, its clinical application more fully basis.The subject of the following three areas of study: 1) This experiment will be used fresh Mavericks made lumbar spondylolisthesis model arch with two screws and two titanium rods fixed, fixed at both ends with PMMA samples will be embedded in special Fixture, MTS880 testing machine used to the frequency of 1 Hz to 1.2-12 KN 3000, the load cycle, then removed specimens in mechanical testing machine uplink axial pull out test to evaluate load conditions pedicle screw expansion the fixation strength. 2) EPS screw compared with the ordinary screw screw ordinary non-expansive remarkable features is its hollow structure, its strength may have a certain impact, the experimental use of vertebral total resection model test group EPS screw fatigue resistance . After the screw implanted in her neck because of the reasons for the stress concentration compared with other parts will face greater shear force, here is the possibility of greater fracture, the experimental use a special test fixture screw neck mechanical strength . 3) EPS screw implanted vertebral front will happen after the expansion of the late For screw removed when the expansion site for osteoporosis has been difficult to close, such as this will be a rotary screw may pedicle injury. The experimental use of fresh cadaver specimens in the spinal implant screw and spin after a screw (EPS rotary screw in a state of expansion) respectively Micro-CT canning and 3-D reconstruction, the site measured parameters.EPS before and after loading the largest axial screw insertion was significantly higher than that SINO and UPS screw (P <0.05). EPS before and after loading the largest axial screw pull out of the difference between the no statistical significance (P> 0.05), while SINO UPS screw and pull out of the largest in the axial load before and after the differences were statistically significant (P < 0.05).In the polyethylene material on the screw 100 million cycle fatigue test load after the completion of Duanwei EPS screw type, screw and universal type EPS SINO screws were no fatigue. In the mechanical strength tests, the fixed EPS screw placement in the suppository in the circumstances, the screw neck can bear the greatest shear stress compared with SINO screw there was no significant difference (P> 0.05), while Universal EPS screw-neck can withstand the maximum shear force and SINO screw compared statistically significant difference (P <0.05), but the upper body to withstand the load.Road screw nails in the test, the vertebral body were measured four parts of nail diameter: pedicle top, middle and bottom of the vertebral body and. The results suggested that, until the screw rotation expansion pedicle screw diameter of the largest expansion of the average increase of 1.11±0.13mm. EPS rotary screw after the screw in the various parts of nail diameter screw with SINO statistically significant difference (P <0.05), but EPS pedicle screw in the entire nail diameter than the width of the Chinese small pedicle .This study confirmed: expansion of pedicle screw fixation not only the initial strength compared with ordinary screw, and its load after a fixed strength is also higher than ordinary screw-expansion, the results further confirm that expansion in the pedicle screw fixation stability Sexual compared with ordinary screw-expansion has obvious advantages. In the test group of fatigue-resistant screws and screw neck mechanical strength of the experiment, in the implantation of the nail-core cases, EPS screws and screw compared to its general fatigue-resistant properties and the neck-bending strength has not decreased significantly , Has not confirmed its EPS screw hollow structure, fatigue-resistant properties and neck-bending strength decreased significantly. Screws, nails in the test, the expansion in the state of spin to the formation of the screw after screw diameter, and the people of lumbar pedicle significantly smaller than the width, so in the latter part of the EPS screws removed, as long as the proper operation will not damage Pedicle structure.