[Comparative study of two elastic fixation systems in single-segment lumbar disc herniation surgery for nucleus pulposus extraction].

OBJECTIVE: To investigate the clinical application of two elastic pedicle internal fixation systems in single-segment lumbar disc herniation fenestration. METHODS: A retrospective analysis of 64 patients with lumbar intervertebral disc herniation treated by surgery from June 2019 to March 2021. According to the different elastic fixation systems placed during the operation, the patients were divided into ordinary pedicle screw elastic rod link group (elastic rod group) and a special elastic pedicle screw rigid rod fixed connection group (elastic screw group). There were 33 cases in the elastic rod group, including 18 males and 15 females, aged from 30 to 69 years old with an average of(49.18±10.23) years old;and 31 cases in the elastic screw group, including 16 males and 15 females, aged from 32 to 68 with an average of (49.81±9.24) years old. The operation time, intraoperative blood loss, postoperative wound drainage, and postoperative landing time of the two groups were recorded separately. The visual analogue scale (VAS), Japanese Orthopaedic Association (JOA) score, and Oswestry Disability Index (ODI) were compared before and 3, 12 months after operation. The height of the adjacent vertebral space on the lateral DR film before and 12 months after the operation was measured. The clinical efficacy was evaluated by Macnab standard. RESULTS: All the patients successfully completed the operation, and were followed up. The operation time, intraoperative blood loss, postoperative wound drainage and postoperative landing time in the elastic rod group were(63.73±12.01) min, (89.55±16.07) ml, (81.67±16.00) ml, (3.45±0.75) d , while in the elastic nail group was (62.96±11.54) min, (88.35±17.14) ml, (82.29±15.40) ml, (3.29±0.78) d, the difference was not statistically significant. The symptoms of low back pain and lower extremity numbness were significantly improved in all patients after operation. There was no significant difference in VAS, JOA score and ODI between the two groups before and after surgery (P>0.05). At 12 months after operation, there was no significant difference in the height of the adjacent vertebral space between the upper adjacent vertebral body and the same segment before operation(P>0.05), and there was no significant difference between the groups before and after the operation. According to Macnab criteria, the elastic rod group was excellent in 30 cases, good in 2 cases, fair in 1 case, while the elastic nail group was excellent in 29 cases, good in 2 cases, fair in 0 cases, and there was no significant difference(Z=-0.42, P=0.68). CONCLUSION: In fenestrated nucleus pulposus extraction for lumbar disc herniation, the two elastic pedicle internal fixation systems are equally effective and can be used. The elastic screw internal fixation system has certain advantages when the distance between the two vertebral bodies is short, and the elastic rod cannot be placed or is difficult to be placed, and it is more widely used.

Transport coefficients and entropy-scaling law in liquid iron up to Earth-core pressures.

Molecular dynamics simulations were applied to study the structural and transport properties, including the pair distribution function, the structure factor, the pair correlation entropy, self-diffusion coefficient, and viscosity, of liquid iron under high temperature and high pressure conditions. Our calculated results reproduced experimentally determined structure factors of liquid iron, and the calculated self-diffusion coefficients and viscosity agree well with previous simulation results. We show that there is a moderate increase of self-diffusion coefficients and viscosity along the melting curve up to the Earth-core pressure. Furthermore, the temperature dependencies of the pair correlation entropy, self-diffusion, and viscosity under high pressure condition have been investigated. Our results suggest that the temperature dependence of the pair correlation entropy is well described by T(-1) scaling, while the Arrhenius law well describes the temperature dependencies of self-diffusion coefficients and viscosity under high pressure. In particular, we find that the entropy-scaling laws, proposed by Rosenfeld [Phys. Rev. A 15, 2545 (1977)] and Dzugutov [Nature (London) 381, 137 (1996)] for self-diffusion coefficients and viscosity in liquid metals under ambient pressure, still hold well for liquid iron under high temperature and high pressure conditions. Using the entropy-scaling laws, we can obtain transport properties from structural properties under high pressure and high temperature conditions. The results provide a useful ingredient in understanding transport properties of planet's cores.

Isothermal crystallization of short polymer chains induced by the oriented slab and the stretched bundle of polymer: a molecular dynamics simulation.

Information on the interfacial interaction is vital in understanding the crystallization of short polymer chains around oriented nuclei. However, this interaction is difficult to observe at the atomic level. Molecular dynamics simulations are performed to investigate the structural formation of polymer chains induced by the highly oriented slab or the stretched bundle of polymer chains. The results show that the surface-induced crystallization of polymer chains is greatly influenced by the foreign surface on the crystal structure and the morphology of the polymers, hence providing molecular-level support for previous experimental observations [Lotz et al. Macromolecules 1993, 26, 5915 and Yan et al. Macromolecules 2009, 42, 9321]. The order parameter S and the configurations show that the ability of the polypropylene (PP) slab to induce the polyethylene (PE) melt crystallization is weaker than that of the PE slab and that the short PE chains display multiple orientations on the PP slab. In addition, the crystallization rate was found to be dependent on the lattice matching between the free chains and the substrates on the contact lattice planes.

Crystallization of alkane melts induced by carbon nanotubes and graphene nanosheets: a molecular dynamics simulation study.

The crystallization of alkane melts on carbon nanotubes (CNT) and the surface of graphene nanosheets (GNS) is investigated using molecular dynamics (MD) simulations. The crystallization process of the alkane melts is analyzed in terms of the bond-orientational order parameter, atomic radial distribution for the CNT/alkane, atomic longitudinal distribution for the GNS/alkane, and diffusion properties. The dimensional effects of the different carbon-based nanostructures on the crystallization of alkane melts are shown. It is found that one-dimensional CNT has a stronger ability to induce the crystallization of the polymer than that of two-dimensional GNS, which provides a support at molecular level for the experimental observation [Li et al., J. Am. Chem. Soc., 2006, 128, 1692 and Xu et al., Macromolecules, 2010, 43, 5000]. From the MD simulations, we also find that the crystallization of alkane molecules has been completed with the highly cooperative processes of adsorption and orientation.