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| LIU Da,KANG Xia,ZHENG Wei.Biomechanical comparison of expansive pedicle screw and PMMA-augmented pedicle screw in osteoporotic sheep lumbar vertebra[J].Chinese Journal of Spine and Spinal Cord,2014,(8):747-751. |
| Biomechanical comparison of expansive pedicle screw and PMMA-augmented pedicle screw in osteoporotic sheep lumbar vertebra |
| Received:May 12, 2014 Revised:July 02, 2014 |
| English Keywords:Osteoporosis Expansive pedicle screw Polymethylmethacrylate Biomechanics Stability |
| Fund:国家自然科学基金青年基金项目（编号：81301606），成都军区总医院院管课题资助项目（编号：2011YG-C07） |
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| English Abstract: |
| 【Abstract】 Objectives: To compare the biomechanical performance of expansive pedicle screw(EPS) and polymethylmethacrylate-augmented pedicle screw(PMMA-PS) in osteoporotic sheep lumbar vertebra. Methods: osteoporotic sheep model was established through bilateral ovariectomy combined with the intramuscular injection of methylprednisolone（0.45mg/kg/d）. The bone mineral density(BMD) of sheep lumbar was examined before the establishment of osteoporotic sheep model and one month after the injection of methylprednisolone, more than 25% decrease in BMD of lumbar spine was considered as the successful establishment of osteoporotic sheep. Six lumbar vertebrae(L1-L6) in each sheep were divided into three groups randomly(two vertebrae with four pedicles in each group) after the establishment of osteoporosis sheep. In CPS group, conventional pedicle screw(CPS) was inserted through the pilot hole into vertebral body without any augmentation. In PMMA-PS group, PMMA(1.0ml) was injected into the pilot hole prior to the insertion of CPS. In EPS group, EPS was inserted through pedicle into vertebral body. Four sheep were sacrificed and lumbar vertebrae(L1-L6) were harvested at the 6-week and 12-week post-operation, respectively. All the lumbar spines were disarticulated and dissected free of soft tissue, yielding individual vertebra. For two pedicle screws in each vertebra, one side was selected randomly for axial pullout tests. Once the specimen was tightly secured, each screw was pulled at a constant speed of 5mm/min by MTS 858 until purchase failure. The maximum pullout strength(Fmax) and the energy absorbed value(EAV) were recorded. Results: BMD value before and after the establishment of osteoporosis sheep was 1.14±0.10g/cm2 and 0.83±0.07g/cm2, respectively. There was a significant decrease on BMD(mean 27.2%, from 25.4% to 28.9%) between before and after the establishment of osteoporosis sheep(P<0.05), which demonstrated the successful establishment of osteoporosis sheep model. At 6-week post-operation, Fmax and EAV in both EPS group(1252.13±203.51N and 2.48±0.45J) and PMMA-PS group(1426.38±235.75N and 2.84±0.55J) were significantly higher than those(827.88±139.22N and 1.66±0.30J) in CPS group(P<0.05). At 12-week post-operation, Fmax and EAV in both EPS group(1518.88±256.81N and 3.09±0.59J) and PMMA-PS group(1426.38±235.75N and 2.95±0.60J) were significantly higher than those(906.63±152.50N and 1.80±0.35J) in CPS group(P<0.05). There were no significant differences on Fmax and EAV between PMMA-PS and EPS groups at both 6-week and 12-week post-operation(P>0.05). There were also no significant increments on Fmax and EAV in CPS and PMMA-PS groups at 12-week post-operation compared with those at the 6-week(P>0.05). In EPS group, however, there was a significant improvement on Fmax and EAV at the 12-week post-operation compared with those at the 6-week(P<0.05). Conclusions: Compared with CPS, EPS can markedly enhance screw stability in osteoporotic sheep lumbar vertebra with a similar effect to the traditional method of screw augmentation with PMMA in initial surgery in osteoporosis. |
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