| Currently pedicle screw fixation technique has already been one of the nucleus techniques in spinal column surgery. The pedicle screw fixing stationary stability is decided by the holding force of the screw pass vs. the screw. At osteoporosis patients, bone trabecula became thin and split, bone mineral density (BMD) stepped - down, the holding force of the screw pass vs. the screw obviously decreased, and the pedicle screw loosed and drawn out could easily appear, which would result in internal fixation failure. How to raise the stability of the pedicle screw fixation in OP condition becomes a key point and difficult point in orthopedics clinical research. Study mainly at home and abroad currently is filling the bone cement materials into the nail pass so as to enhance pedicle screw stability. In clinical we usually use the polymethylmethacrylate (PMMA) bone cement to resolve this problem. Although PMMA can obviously enhance the stability of pedicle screw fixation, it can not absorb in the body, forming two interfaces between screw and bone, taking out the screw extremely difficult, its biocompatibility is bad, exothermic reaction etc. clinical doctors had a careful attitude towards its application. 45S5 bioactive glass is a kind of new bioactive material discovered by Professor Hench from United States in 1971. Studies showed that BG could bond to the bone, had good biocompatibility and biodegradability, could lead bone growth and induce bone regeneration. Bioactive glass had already been used in bone repair realm, and obtained good clinical effect. At home and abroad there is nobody got bioactive glass into pedicle screw fixation study.Objective: To evaluate the mechanical effect of pedicle screw augmentation using bioactive glass (BG) in osteoporosis sheep and observe the change of histology in the interface between bone and screw.Methods: 1. An OP sheep model was established. Osteoporosis sheep models were established by ovariectomy combined with methylprednisolone injection in 8 adult female sheep, the BMD of the lumber of the sheep before and 12 months after OVX was detected by dual energy X-ray absorptiometry (DXA), and the BMD changes were compared. 2. Took L1-L6 bilateral pedicles of each as object of study, all 12 pedicles were randomly divided into 3 groups. Group A: control group, the pedicles were implanted with pedicle screws without any transactions; Group B: PMMA group, the pedicles were implanted with pedicle screws after the augmentation with PMMA (about 0.5ml); Group C: BG group, the pedicles were implanted with pedicle screws after the augmentation with 45S5 bioglass (about 0.5g). Got materials after 3 months or 6 months feeding respectively, and axial pull-out-test was taken to evaluate the mechanical effect of pedicle screw augmentation in 3 groups. 3. Apply a 3D reconstruction technique of Micro-CT, fluorescence double label method and sclerous tissue section dye technique, to observe the bone growth and the change of histology in the interface of bone and screw.Result:1. The bone mineral density (BMD) of the lumbar of the sheep 12 months after OVX (0.828±0.032g/cm~2) was significance decreased by 22.70% compared with that before OVX (1.015±0.037 g/cm~2), and the OP sheep model was completed.2. The biomechanics result showed that the Fmax and E of BG group in 3 month and 6 month (1083.09±86.48N, 1175.20±134.84N respectively and 1.8741±0.1724.K 2.0375±0.2383J respectively ) was much higher than the Fmax and E of the control group in the same time stamp (871.76±79.03N,902.30±115.80 respectively and 1.3058±0.1492K 1.4440±0.1759J respectively), and was much lower than the Fmax and E of the PMMA group in the same time stamp (1411.58±171.54N, 1445.52±231.79N respectively and 2.8418±0.2435K 3.0986+0.1599J respectively), and significant difference was found in each group (P<0.05). The Fmax and E in the same group of different time stamp had no significant difference (P>0.05).3. The 3D reconstruction result of Micro-CT showed that the mass of the bone trabecular around the screw was much more and the structure was close-packed in BG group in 3 month and 3 month time stamp, and its bone substance surpassed the control group. The bone metrology result showed that the TMD, BVF, Tb.Th, Tb.N in BG group in 3 and 6 month stamp was much higher than that of the control group, and the BS/BV,Tb.Sp of the BG group was much lower than that of the control group, and significant difference was found (P< 0.05).4. The fluorescence result under fluorescence microscope showed that the distance of the yellow and green fluorescence band of BG group in 3 month stamp was much bigger than that of the control group and BG group in 6 month stamp. The mineralization apposition rate (MAR) of BG group in 3 month time stamp (11.94±1.26um/d ) was much higher than the MAR of the control group in the same time stamp (4.85±0.83 um/d), significant different was found (P<0.05), and the former was increased by 146.19% compared whit the latter. The MAR of BG group in 6 month time stamp (4.86±1.12um/d) had no significant difference compared whit the control group in the same time stamp(4.74±0.72um/d) (P> 0.05). The fluorescence results indicated that the bone in the BG group in 3 month time stamp had a rapid growth rate.5. Ponceau staining under microscope showed that the bone mass around the screw was much more and the bone trabecular was close-packed and wrapped the screws tightly in BG group of 3 month time stamp, the bone substance of the bone-screw interface surpassed the control group. In BG group of 6 month time stamp, the trabecular around the screw had a better bone structure and was thicker than that of the control group, the bone structure was close-packed and the trabecular wrapped the screws tightly, the bone substance of the interface surpassed the control group. In two time stamps, there were some BG found in the bone substance around the screw and combined with the bone well. In 6 month time stamp, the BG existed in the bone was much fewer, and had almost degradation completely.Conclusion: 1. BG could enhance the stability of pedicle screw fixation in OP condition, and it could maintain the stability over a long term. 2. The mechanics effect of BG in pedicle screw augmentation was not equal to PMMA. 3. The mechanism of pedicle screw augmentation with BG was that the BG could induce growth of the bone around the screw, improve the bone structure of screw- bone interface, and enhance the holding force of the interface vs. the screw. Therefore, BG can be one of materials choosing in pedicle screw augmentation through improving bone-screw interface intensity and enhancing the hoding force of pedicle screw under OP condition. |
