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Pedicle screw fixation techniques are widely used in the treatment of degenerative diseases of the spine, spinal fractures, spinal deformity, spinal tuberculosis and other illnesses vertebral metastases. A pedicle screw fixed reliability depends on the maintenance of bone - the gripping force of the screws interface. However, in patients with osteoporosis (osteoporosis, OP), reduced bone mineral density (bone mineral density, BMD), trabecular thinning bone - screw interface connection is not solid, often makes patients facing a screw loose, fixed the risk of failure [1]. To strengthen the stability of the pedicle screw, nail tract addition of poly (methyl methacrylate) (polymethylmethacrylate, PMMA), calcium phosphate cement (Calcium phosphate cement, CPC), hydroxyapatite bone cement (Hyduoyapatite cement, HAC) Avoid adding complications caused by the biological material in order to simplify the process of surgery intensive operation, our group early research, design expandable pedicle screw [2,3] (expansive pedicle screw, EPS), and was the patent protection (Patent No.: CN2647255). Biomechanical in vitro tests and mechanical strength test, indicating that the EPS in strength no decline in the case, having a higher fixed reliability. But EPS osteoporosis conditions, whether it will achieve long-term stability and EPS stability mechanism remains unclear, and there are no reported EPS interface research. Objective: To observe the state of osteoporosis, EPS bones - the screw interface as well as EPS expansion gap within the histological explore its role in strengthening stability mechanism, to further provide a theoretical basis for clinical application. Methods: 1) to establish an animal model of osteoporosis sheep. Using the the bilateral oophorectomy method (ovariectomy, OVX) castration of sheep. Dual-energy X-ray absorptiometry method (dual energy X-ray absorptiometry, DEXA) determination castration before feeding sheep BMD were analyzed to determine the establishment of the animal model for the study of OP sheep. 2) EPS (micro-computed tomography, Micro-CT) in the the interface microstructure CT of OP sheep in vivo evaluation and organizational analysis. Implanted EPS, keeping the three months, six months later drawn. The latest Micro-CT technology and contains screws hard tissue sections, staining techniques, research in OP cancellous bone within the EPS the bone - the screw interface as well as EPS expansion gap the mechanics and histology. Results: 1) Micro-CT scanning and three-dimensional reconstruction of specimens found in the the EPS expansion section of bone - trabecular bone screw interface than the interface trabecular bushy, especially between the threads more obvious, and in EPS non-expansion segment trabecular bone - screw interface sparse, with the intensity of the surrounding bone. Take the same volume under the same boundary value EPS threaded adjacent ROIs (regeon of interest, ROI) \The scanned data is automatically displayed: EPS expansion segment ROI of tissue, bone mineral density (tissure mineral density TMD) and bone volume fraction (bone volume fraction BVF), bone surface area to volume ratio (bone surface / bone volume, BS / BV) three-dimensional parameters of the trabecular bone trabecular thickness (trabecular thickness, Tb.Th), trabecular bone gap (trabecular spacing, Tb.Sp), significantly better than non-expansion section of the Mann-Whitney nonparametric test, the difference statistically significant. 2) Slice microscope EPS bone - screw interface and expansion of the gap in trabecular bone closely with the EPS seamless contact interface without connective tissue layer. Newborn trabecular bone ingrowth after the expansion screw slits, and with the bone - screw interface oppressed densified cancellous phrenology continuation of the expansion has been extended to the central portion. Conclusions: 1) of EPS expansion section on the surrounding bone and continuous stress, so that it becomes more dense, and changes the local bone trabecular Ordering trend EPS in the state of osteoporosis in the early mechanical stability. 2) EPS formed bone nails, nail bone \EPS has a unique mechanical stability and biological stability, fixed for the need for spinal fusion in patients with osteoporosis, EPS is one of the best choices.
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