| Part ? Effect of bone cement perfusion pressure of large inner diameter mode of Redesigned Bone-cement-Perfusion Pedicle Screw(RBPPS)Objectives: To determine whether or not the large inner diameter mode of RBPPS could significantly reduce the bone cement perfusion pressure during cement augmentation.Methods: According to the design of RBPPS, changing the hollow diameter and maintaining the remaining parameters unchanged, the experimental screw is divided into 3 groups: screw A group(1.5mm ID), screw B group(2.25 mm ID), screw C group(RBPPS group)(3.0mm ID). Two different methods were employed to examine the perfusion pressure in three group screws:(1) analytical model: Hagen-Poisseuille's flow through a tube was used to predict the pressure drop in the bone cement channel;(2) experiment: first a Newtonian silicone oil and then a PMMA bone cement was performed perfusion operation by using a cement pusher through the channel at a constant rate of 2ml/min, and the perfusion pressure was recorded.Results: Both the experimental and analytical findings confirmed that the hollow internal part of the screw is the “bottle neck” of the perfusion pressure and the RBPPS reduces the perfusion pressure significantly. Specifically, when the diameter is increased by 2 times, the perfusion pressure drops by about 59%.(p<0.05)Conclusion: The RBPPS effectively improved the application of bone cement augmentation with the ease of bone cement perfusion and, therefore, operational safety.Part ? Study of bone cement perfusion pressure in osteoporotic vertebral body of Redesigned Bone-cement-Perfusion Pedicle Screw(RBPPS)Objectives: To study the change of bone cement perfusion pressure of Redesigned Bone-cement-Perfusion Pedicle Screw(RBPPS) in osteoporotic vertebral body in vitro, to determine whether the design of large inner diameter can significantly reduce the perfusion pressure.Methods: Two groups of pedicle screws were randomly implanted in the two sides of the osteoporotic vertebral body:Control group(n=10) with inner diameter of 1.5mm and RBPPS group(n=10) with inner diameter of 3.0mm. Each screw was perfused with bone cement in the same time window to use the matching perfusion system in the material machine, simulating the clinical situation, with a constant rate of 2ml/min, in small strokes of 0.3 ml, a total of 1.8 ml and 6 strokes. Record the perfusion pressure and the amount of bone cement.Results: Bone cement perfusion was successfully completed in all vertebral specimens. The mean perfusion pressure of CPS group was 51 + 13.1N, and the maximum perfusion pressure was 82 N, often approaching the human physical limit and resulting in insufficient perfusion. The average pressure of RBPPS group was 29.4 + 4.7N, 41.8% lower than that of the CPS group, a highly significant result(P<0.001).Conclusion:(1) RBPPS and perfusion system can be effective perfusion of bone cement to osteoporotic vertebral body, and therefore, easy to operate.(2) RBPPS can significantly reduce the perfusion pressure in the osteoporotic vertebral body, and therefore, ease of bone cement perfusion.Part ? Study on the distribution of bone cement and biomechanics in osteoporotic vertebral body of Redesigned Bone-cement-Perfusion Pedicle Screw(RBPPS)Objectives: To evaluate the advantages of Redesigned Bone-cement-Perfusion Pedicle Screw(RBPPS) in the distribution of bone cement and the biomechanical stability in osteoporotic vertebral body.Methods: Five cadaveric spines(T12-L5) were separated into 30 vertebral bodies, which bone mineral density(BMD) was obtained using the dual-energy radiograph absorptiometry(DEXA) method. RBPPSs(a total of 30) were implanted in both sides of 15 vertebral bodies at random, one side of the two RBPPSs was selected to be augmented by perfusion 2ml PMMA randomly. The remaining 15 vertebral bodies were implanted with control pedicle screw(CPS) by the same method(a total of 30). The distribution of bone cement was examined by X-ray and CT scan. 9 vertebral bodies were randomly selected from each 15 vertebral bodies to perform the axial pullout strength test. According to whether or not augmented, the screws were divided into four groups: RBPPS non-augmented group, CPS non-augmented group, RBPPS PMMA-augmented group, CPS PMMA-augmented group(n=9). The remaining 6 vertebral bodies were divided into the same 4 groups(n=6) to perform the rotation-out torque test. The maximum axial pullout force and the maximum rotation-out torque were recorded respectively. The additional each 10 solid pedicle screws(SPS), no inner pin RBPPS, and the inner pin RBPPS are selected to perform static bending test.Results: A total of 60 pedicle screws were implanted in the 30 osteoporotic vertebral bodies, 1 of them broke through the lateral wall of the pedicle of the vertebral arch, 1 of which was broke out the lateral wall of the vertebral pedicle, 1 of which need to adjust the direction of hole Pilot. The perfusion system is simple and easy to operate, and no situation such as the return flow of bone cement causes the pollution of operation field. No leakage of bone cement was found by specimen observation, X-ray and CT examination. Bone cement was distributed at the distal end of the RBPPS with spherical morphology, most of which was distributed in the middle and anterior part of the vertebral body(three zones), which is far from the spinal canal. The average maximum pullout strength of the RBPPS PMMA-augmented group was 1361+59N, the CPS PMMA-augmented group was 1191+53N, and the RBPPS non-augmented group was 377 + 54 N, and the CPS non-augmented group was 373 + 21 N. The pullout strength of the RBPPS PMMA-augmented group was increased by 114%(P<0.05) than that of the CPS PMMA-augmented group. Compared with the RBPPS and CPS non-augmented group, The RBPPS and CPS PMMA-augmented group were increased by 361%, 319% respectively.(P<0.0001) The average maximum rotation-out torque of RBPPS PMMA-augmented group was 2.76+0.07 N·m, the CPS PMMA-augmented group was 1.88 + 0.06 N·m, and the RBPPS non-augmented was 0.82 + 0.07 N·m, and the CPS non-augmented was 0.81 + 0.07 N·m. Compared with the CPS PMMA-augmented group, the increase of rotation-out torque in the RBPPS PMMA-augmented group was 146%(P<0.0001). Compared with the non-augmented group, the RBPPS and CPS PMMA-augmented groups were increased by 337% and 232%, respectively.(P<0.0001) The maximum load of the inner pin RBPPS in the static bending test is slightly worse than that of SPS, and is higher than that of the inner pin RBPPS(P>0.05).Conclusion: RBPPS with large inner diameter and inclined side hole can be used for cement perfusion with higher viscosity, and can control the bone cement to be evenly distributed in the safety area of vertebral body. PMMA augmented RBPPS can significantly enhance the stability of the screw in the osteoporotic vertebral body, and provides a new choice for the clinical treatment of osteoporotic spinal diseases. |
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