Specimens were prepared using 10 fresh human spine specimens, aged 78.1 ± 12.7 years, for a total of 28 vertebral bodies. The attached soft tissue is removed and released into a single vertebral body. Radiographs exclude congenital malformations and tumors. Using the surrounding quantitative, 960 people, 81 coffee 6 skill scan to measure the bone density of the cancellous bone of the vertebral body 150; 61, 80.28 vertebral cancellous bone average 3 cubits 0 pedicle screw 57 out 68, 818 placed in a constant Depth 45, does not penetrate the vertebral body leading edge cortex. The screw used has an outer diameter of 5.0 mm, an inner diameter of 53.0 mm, a pitch of 2.0 mm, and a threaded portion of 45 mm. The random anterior pedicle screw is placed in the formed channel with a syringe before random insertion. After mixing, it will gel out, 180.5. The film will confirm that the screw placement meets the requirements. The specimen was placed in a bone cement in a moisturizing 37-inch incubator before the 1516 biomechanical test, and the vertebral body was partially embedded in the bone cement and fixed on a special fixture.
The 1454 material testing machine was subjected to an axial pull-out test. Loaded at a constant speed along the longitudinal axis of the screw, the maximum allowable load of the test machine sensor can be loaded to a constant load speed of 4.0. The automatic recorder records the change curve of the screw pull-out distance and the loading force at different times, and can measure the large axial pull. The output Fmax, N and the energy absorption value when reaching Fmax 13 and the screw pull out a pitch 2.0mmftE2mm, Nm=Fmax can be read directly from the curve, and 21 is calculated according to the area under the load displacement curve.
Cyclic anti-flexion tests were performed on 12 lumbar vertebrae. The load was applied to the screw head perpendicular to the longitudinal axis of the screw by means of a 2 1454 material testing machine. The load was increased from 1 to 25 and then reduced to 10 at the beginning of the basic preload of 1 and repeated 100 times. Then adjust the negative load section 100 times. A total of 800 cycles of ladder load increase. Record the displacement of the screw head with special equipment and measuring instruments. If the looseness of the screw is specified to be shifted by 2.000 mm before the maximum load 2001 load cycle of 800 times, the maximum load at that time is recorded.
Because the data is non-normally distributed, the results of the paired data are out of the axial pull-out test, and the effect is significantly higher than that of the control side. On the control side, 8 was added to 2051750. After the bone density of the vertebral body, the measured Fmax was between 470N and 1910N. The median paw was added with spit, and the side 1 was 0.1441.702 as the median. Added 83.1 Jia 1 test, corpse 0.01. On the control side of the period of flexion test, the effect of the control side of the 831012 screw at the maximum load of 50200 inches began to appear loose displacement 彡 2.000, while adding 8,1 screws The middle looseness only accounts for 42. In the vertebral body where the screws on both sides are loose, the maximum load reached is 7, ±. 2 Control side and 16, ± 45.4 added 8; 4, 1 side. In the specimens with both sides of the screw capable of withstanding the maximum load and the 800-cycle flexion test, the displacement on the control side was 1.83, ±, 16, and the displacement of the addition, spit, and side was only 560 ±, 17 in total, in the cycle resistance In the flexion test, each screw with 8 must be able to withstand greater load strength than the control side screw, or only a small displacement 1 under the same load; the difference between the two is very significant. 05,5 check the maximum load of the specimen, the displacement control side is added, side discussion Many scholars have proved that the stability of the pedicle screw is significantly reduced in osteoporosis. 2. The bone screw interface is the key to the question. When the pedicle screw system is used in elderly or osteoporotic patients, the risk of postoperative screw loosening and slippage increases. A clinically available method for improving the stability of pedicle screws is to use a larger diameter screw. Increase the insertion depth. Adjust the placement angle. Adding bone cement is most commonly used for PMMA or special auxiliary equipment such as lamina hooks. Over-diameter pedicle screws increase the risk of nerve root injury and pedicle fracture. The maximum outer diameter of the screw should not exceed 80% of the transverse diameter of the pedicle. The insertion screw is too deep and can penetrate the vertebral body. The edge has the danger of damaging the important structure in front of the spine. In osteoporosis, increasing the diameter of the screw has little or no effect on improving its stability.
Adding ordinary bone cement such as PCT has been shown to significantly improve the stability of pedicle screws. 21 Mountain, etc. 4 found that PMMA was not added under pressure to repair the pedicle screws that had been removed, which could restore the stability of the reinserted screws; the pressure addition could increase the fixation strength of the screws by nearly double. However, the application of PMMA also has some high-heat accidents and overflows caused by polymerization. It can cause damage to nerve tissue adjacent to a small space. When it is left in the body for a long time, its toxicity and carcinogenesis can not be ignored. It is difficult to remove it during reoperation; Conductive, a layer of connective tissue between the bone tissue, can cause loosening under long-term load, and often lead to pedicle fracture.
In recent years, some scholars have tried to add other materials instead of PMMA to improve the stability of pedicle screws, such as coffee, 3 30, 17 17174, leg pairs 6, polyhexamethylene fumarate, etc. Effect. However, some materials are too brittle and the effect is not satisfactory. Some materials have obvious effects in the axial pull-out test, but have no obvious effect in the cyclic flexion test. Although the axial pull-out test has been adopted by most scholars, the maximum axial pull-out force can reflect the shear stress between the bone screws, but the pedicle screw is also affected by the lateral buckling moment and the rotational stress in the body. Out and looseness are the result of a combination of lateral load and axial pull. The mechanism called 21166 gamma plays an important role in the pedicle screw loosening. Therefore, we believe that the axial pull-out test is combined. The periodic flexion test was used to evaluate the stability of the pedicle screw.
In this test, we used a bioceramic 3, the main component of which is calcium phosphate, which was originally developed as a substitute for absorbable artificial bone. We have demonstrated in vitro biomechanical tests that the addition of 6 can significantly improve the stability of the pedicle screw, both in the axial pull-out test and the periodic flexion test. The increase in Fmax is slightly lower than in the axial pull-out test. Reported PMMA data 4A89.
The advantage of 813 is that it has good biocompatibility and osteoconductivity, can be slowly degraded in the body, and is eventually replaced by normal bone tissue; no toxicity; it can be coagulated at body temperature without generating high heat; it is very convenient to use, the same physiological The salt water is mixed into a toothpaste shape, and can be injected with a syringe and a thick needle. 1 We believe that for patients with moderate or elderly patients or those with mild osteoporosis, in order to prevent screw loosening, add such absorbable ceramics. Practical value. For patients with severe osteoporosis, comprehensive measures such as adding various bone cements and applying special equipment with laminar hooks should be adopted to improve the stability of the system.
At present, relevant animal experiments are underway to understand the shape metabolism of bone tissue and the effects of absorption process and speed on its biomechanical properties.
8 Zhu Qingan, Li Jiantie, Zhao Weidong, and so on. , biomechanical study of strengthening and repairing pedicle screws. Chinese Journal of Orthopaedics, 2000, 20283 286.9 Fan Shicai, Zhu Qing'an, Wang Bai, et al. Biomechanical effects of polymethyl methacrylate on pedicle screw fixation in osteoporosis. Chinese Journal of Orthopaedics, 20021 editor Yan Fuhong China Orthopedic Surgery magazine published a semi-monthly magazine in 2002, the news in order to provide the majority of orthopaedic professionals with practical and informative information and time-sensitive academic exchange field, China Orthopaedic Surgery magazine code 24097 from 2, At the same time of continuing to improve the quality of the publications in the past two years, the semi-monthly publication was published by the monthly magazine in the month of April, and the second edition of the second edition was published in two volumes. The page number and unit price of each issue were unchanged for the whole year of 140 yuan. Welcome to subscribe, welcome to the manuscript.
Please contact the Department of Orthopaedics, Shandong Tenth Hospital
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