Background Posterior pedicle screw device is widely used in treatment of thoracolumbar burst fractures. As the clinical operation is not based upon quantitative data of adjustments, the results are not optimal. At pre...Background Posterior pedicle screw device is widely used in treatment of thoracolumbar burst fractures. As the clinical operation is not based upon quantitative data of adjustments, the results are not optimal. At present, no study has assessed the associations between the device adjustments and the restoration of stiffness. We investigated the biomechanical effects that adjustments of a pedicle screw device had on the burst fracture, and explored an optimal adjustment. Methods Burst fractures were produced at L1 vertebra in 24 fresh calf spines （T12-L3）. The specimens were divided into four groups at random. Pedicle screw devices were attached to T13 and L2. Four device adjustments, consisting of distraction and extension, were applied. Adjustment 1 was pure 6~ extension, adjustment 2 was pure 5 mm distraction, adjustment 3 was 6~ extension followed by 5 mm distraction, and adjustment 4 was 5 mm distraction followed by 6~ extension. The effect of each adjustment on the stiffness restoration, anatomical reduction, and neural decompression for the burst fractures was analyzed and evaluated. Results Pure extension （Group 1） produced the closest segment height and the least restoration of the canal to the intact. Pure distraction （Group 2） restored stiffness most, but with only 60% stiffness of the intact value, and lost the segmental angle most to the intact. The combination of extension-distraction （Group 3 and Group 4） produced the maximum reduction of the anatomy and restoration of the canal in the burst fracture, and the least stiffness restoration. The sequence of extension and distraction did not affect stiffness restoration, anatomical reduction, and neural decompression. Conclusions The device adjustments affected stiffness restoration, anatomical reduction, and neural decompression. The combined extension-distraction adjustment may be the most suitable considering the anatomical reduction and neural decompression, but the stiffness decreased the most; it should be considered to reconstruct L1 vertebra.展开更多
The discovery of the first miRNA, lin-4, in Caenorhabditis elegans initiated a new era of miRNA biology. Sincethen, thousands of miRNAs annotated, many of which have have been identified and been shown to play roles i...The discovery of the first miRNA, lin-4, in Caenorhabditis elegans initiated a new era of miRNA biology. Sincethen, thousands of miRNAs annotated, many of which have have been identified and been shown to play roles in a variety of biological processes, including development, differentiation, apoptosis, proliferation, and cell death） Furthermore, growing evidence indicates that miRNA deregulation is a critical cause of cancer formation. The biogenesis, function, and potential application of miRNAs have become active areas of research. With the development of molecular biological technologies, such as northern blotting with radio-labeled probes, cloning, quantitative PCR, serial analysis of gene expression （SAGE）-based techniques, bead-based profiling methods, and oligonucleotide microarrays,2 it is possible to conduct miRNA research precisely and comprehensively. BIOGENESIS OF MICRORNAS MicroRNAs are derived from introns or exons of protein- coding and non-coding genes,3＇4 and are either transcribed by polymerase II as a long primary transcript （primary miRNA） or originate from the introns of mRNAs. Primary miRNAs are further processed by the Drosha microprocessor complex, which recognizes stem-looped secondary structures within primary miRNAs, resulting in the excision and release of-70 nucleotide hairpin precursors termed pre-miRNAs （precursor microRNAs）.5 The mirtron subclass of miRNAs, which are encoded in the introns of genes, generate pre-miRNAs directly from byproducts of intron splicing and disbranching events in the nucleus with the assistance of a ＂debranching enzyme＂.6 After being exported from the nucleus by exportin-5, the pre-miRNAs are subsequently cleaved by Dicer to release a 22-nucleaotide miRNA-miRNA duplex. One strand of this duplex is incorporated into the RNA-induced silencing complex （miRISC）, and eventually serves as a mature microRNA, while the other strand is degraded. The ＂seed＂ region of the mature microRNA （nucleotides 2-8 at the 5＇ end） can bind partially or completely to the 3＇UTR of specific protein-coding gene mRNAs.7＇8 MicroRNAs regulate their targets by directly cleaving mRNAs or inhibiting protein synthesis, depending on the degree of complementarity with the 3＇UTRs of their targets.4展开更多
文摘Background Posterior pedicle screw device is widely used in treatment of thoracolumbar burst fractures. As the clinical operation is not based upon quantitative data of adjustments, the results are not optimal. At present, no study has assessed the associations between the device adjustments and the restoration of stiffness. We investigated the biomechanical effects that adjustments of a pedicle screw device had on the burst fracture, and explored an optimal adjustment. Methods Burst fractures were produced at L1 vertebra in 24 fresh calf spines （T12-L3）. The specimens were divided into four groups at random. Pedicle screw devices were attached to T13 and L2. Four device adjustments, consisting of distraction and extension, were applied. Adjustment 1 was pure 6~ extension, adjustment 2 was pure 5 mm distraction, adjustment 3 was 6~ extension followed by 5 mm distraction, and adjustment 4 was 5 mm distraction followed by 6~ extension. The effect of each adjustment on the stiffness restoration, anatomical reduction, and neural decompression for the burst fractures was analyzed and evaluated. Results Pure extension （Group 1） produced the closest segment height and the least restoration of the canal to the intact. Pure distraction （Group 2） restored stiffness most, but with only 60% stiffness of the intact value, and lost the segmental angle most to the intact. The combination of extension-distraction （Group 3 and Group 4） produced the maximum reduction of the anatomy and restoration of the canal in the burst fracture, and the least stiffness restoration. The sequence of extension and distraction did not affect stiffness restoration, anatomical reduction, and neural decompression. Conclusions The device adjustments affected stiffness restoration, anatomical reduction, and neural decompression. The combined extension-distraction adjustment may be the most suitable considering the anatomical reduction and neural decompression, but the stiffness decreased the most; it should be considered to reconstruct L1 vertebra.
基金This work was supported by the National Science Foundation of China （No. 30940034） and Shanghai Science Committee Foundation （No. STCSM 10411964700）.
文摘The discovery of the first miRNA, lin-4, in Caenorhabditis elegans initiated a new era of miRNA biology. Sincethen, thousands of miRNAs annotated, many of which have have been identified and been shown to play roles in a variety of biological processes, including development, differentiation, apoptosis, proliferation, and cell death） Furthermore, growing evidence indicates that miRNA deregulation is a critical cause of cancer formation. The biogenesis, function, and potential application of miRNAs have become active areas of research. With the development of molecular biological technologies, such as northern blotting with radio-labeled probes, cloning, quantitative PCR, serial analysis of gene expression （SAGE）-based techniques, bead-based profiling methods, and oligonucleotide microarrays,2 it is possible to conduct miRNA research precisely and comprehensively. BIOGENESIS OF MICRORNAS MicroRNAs are derived from introns or exons of protein- coding and non-coding genes,3＇4 and are either transcribed by polymerase II as a long primary transcript （primary miRNA） or originate from the introns of mRNAs. Primary miRNAs are further processed by the Drosha microprocessor complex, which recognizes stem-looped secondary structures within primary miRNAs, resulting in the excision and release of-70 nucleotide hairpin precursors termed pre-miRNAs （precursor microRNAs）.5 The mirtron subclass of miRNAs, which are encoded in the introns of genes, generate pre-miRNAs directly from byproducts of intron splicing and disbranching events in the nucleus with the assistance of a ＂debranching enzyme＂.6 After being exported from the nucleus by exportin-5, the pre-miRNAs are subsequently cleaved by Dicer to release a 22-nucleaotide miRNA-miRNA duplex. One strand of this duplex is incorporated into the RNA-induced silencing complex （miRISC）, and eventually serves as a mature microRNA, while the other strand is degraded. The ＂seed＂ region of the mature microRNA （nucleotides 2-8 at the 5＇ end） can bind partially or completely to the 3＇UTR of specific protein-coding gene mRNAs.7＇8 MicroRNAs regulate their targets by directly cleaving mRNAs or inhibiting protein synthesis, depending on the degree of complementarity with the 3＇UTRs of their targets.4
