Biomechanical Analysis of Different Internal Fixation Combined with Different Bone Grafting for Unstable Thoracolumbar Fractures in the Elderly.

This research was developed to accurately evaluate the unstable fractures of thoracolumbar before and after surgery and discuss the treatment timing and methods. Three-dimensional (3D) finite element method was adopted to construct the T12-L5 segment model of human body. The efficiency of percutaneous kyphoplasty (PKP) and percutaneous vertebroplasty (PVP), two commonly used internal fixation procedures, was retrospectively compared. A total of 150 patients with chest fracture who received PKP or PVP surgery in our hospital, and 104 patients with the same symptoms who received conservative treatment were collected and randomly rolled into PVP group (75 cases), PKP group (75 cases), and control group (104 cases). Visual analog scale (VAS) score and Oswestry disability index (ODI) of patients were collected before and after surgery and 2, 12, and 24 months after surgery. Then, the anterior and central height of the patient's cone and the kyphosis angle were calculated by X-ray. Lumbar minimally invasive fusion system and lumbar pedicle screw rod system were established by computer-aided design (CAD), and the biomechanical characteristics were analyzed. The results showed that there was no substantial difference in VAS score and ODI score between PKP and PVP (P > 0.05), but they were higher than those of the control group (P < 0.05). The anterior edge and middle height of vertebra in the two groups were higher than those in control group (P < 0.05), and the increase in PKP group was more substantial (P < 0.05). The kyphosis of the two groups was smaller than that of the control group (P < 0.05), and the decrease of the kyphosis of the PKP group was more substantial (P < 0.05). In summary, the thoracolumbar segment model established by 3D finite element method was an effective model, and it was verified on patients that both PKP and PVP could achieve relatively satisfactory efficacy. The implantation of the new internal fixation system had no obvious effect on the lumbar movement. This work provided a novel idea and method for the treatment of senile thoracolumbar unstable fracture, as well as experimental data of biomechanics for the operation of senile unstable fracture.

Soil water repellency of the artificial soil and natural soil in rocky slopes as affected by the drought stress and polyacrylamide.

Soil water repellency (SWR) causes reduced soil water storage, enhanced runoff and reduced ecosystem productivity. Therefore, characterization of SWR is a prerequisite for effective environmental management. SWR has been reported under different soils, land uses and regions of the world, particularly in forest land and after wildfires; however, the understanding of this variable in the artificial soil of rocky slope eco-engineering is still rather limited. This study presented the characterization of SWR in the artificial soil affected by the polyacrylamide (PAM) and drought stress. There were two molecular weights of PAM, and the CK was without PAM application. Three types of soil were studied: natural soil and two types of artificial soil which have been sprayed for 1y and 5y, respectively. The drought stress experiments had three drought gradients, lasted for three weeks. Water repellency index (WRI) and soil-water contact angle (ß) were determined using intrinsic sorptivity method by measuring the water sorptivity (SW) and ethanol sorptivity (SE) in all soil samples. The results showed that (1) Polyacrylamide treatments significantly increased SW by 3% to 38%, and reduced SE by 1% to 15%, WRI by 6% to 38%, ß by 3% to 23% compared to the control group. Polyacrylamide treatments also increased water-stable aggregates content and total porosity by 22% to 33%, 11% to 20% relative to the control, while PAM with a higher molecular weight performed best. (2) The interaction between PAM and drought stress had a significant effect on WRI and ß for all soil types (P<0.01) while it only had a significant effect on SW and SE for the artificial soil (P<0.01). (3) The artificial soil had a greater WRI and ß than the natural soil.