Viscoelastic properties of adjacent segments during prolonged flexion after anterior intervertebral fusion / 医用生物力学

Objective To analyze the viscoelastic properties of adjacent segments after anterior fusion under prolonged flexion, and further reveal the mechanism of accelerated adjacent segment degeneration after intervertebral fusion. Methods The same prolonged flexion lasted 30 minutes was applied on the two-level ovine lumbar specimen before and after anterior fusion respectively, and the moment relaxation and viscoelastic deformation of adjacent segments were measured. The moment relaxation curves from two groups were then fitted to obtain the quantitative viscoelastic results. Results After fusion，the initial and final moment in two groups significantly increased by 30.68% and 34.34%, and the viscoelastic deformation of the adjacent segments increased by 28.21%. The Prony model could perfectly fit the moment relaxation curves (R2=99.50%). The integral stiffness significantly increased by 47.82% and 31.14% for two groups, while the viscoelasticity significantly decreased by 27.19% and 28.16%, respectively(P<0.05). Conclusions After intervertebral fusion, to maintain the same posture with the same time, the joints should bear larger loads than before. The viscoelastic deformation of adjacent segments becomes larger, which increases the risk of instability or injury, and further leads to the accelerated degeneration of adjacent segments. The mechanism of quasi-static daily loading on adjacent segment degeneration should be focused in clinical research.

Load rate of facet joints at the adjacent segment increased after fusion / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>The cause of the adjacent segment degeneration (ASD) after fusion remains unknown. It is reported that adjacent facet joint stresses increase after anterior cervical discectomy and fusion. This increase of stress rate may lead to tissue injury. Thus far, the load rate of the adjacent segment facet joint after fusion remains unclear.</p><p><b>METHODS</b>Six C2-C7 cadaveric spine specimens were loaded under four motion modes: Flexion, extension, rotation, and lateral bending, with a pure moment using a 6° robot arm combined with an optical motion analysis system. The Tecscan pressure test system was used for testing facet joint pressure.</p><p><b>RESULTS</b>The contact mode of the facet joints and distributions of the force center during different motions were recorded. The adjacent segment facet joint forces increased faster after fusion, compared with intact conditions. While the magnitude of pressures increased, there was no difference in distribution modes before and after fusion. No pressures were detected during flexion. The average growth velocity during extension was the fastest and was significantly faster than lateral bending.</p><p><b>CONCLUSIONS</b>One of the reasons for cartilage injury was the increasing stress rate of loading. This implies that ASD after fusion may be related to habitual movement before and after fusion. More and faster extension is disadvantageous for the facet joints and should be reduced as much as possible.</p>

Numerical and experimental study on steady flow in the model of internal carotid artery siphon / 医用生物力学

Objective To investigate the hemodynamic factors in internal carotid arteries (ICA) with different shapes, and analyze the relationship between the arterial geometry and atherosclerotic stenosis to provide the hemodyanmic basis for the risk prediction and early diagnosis of ICA stenosis. Methods The flow field in the most two common types of ICAs, U and V-shaped ICA, were investigated by numerical simulation and particle image velocimetry (PIV) experiment under the condition of steady flow. Results At the upstream bend of ICA, the hemodynamic factors were monotonically associated with the curvature of the bend. As a result, the risk for stenosis here was smaller in the V-shaped ICA, as compared to U-shaped ICA. But at the downstream bend, such monotonic relationship didn’t exist due to the synergistic effect of the two bends. ConclusionsThe curvature of the artery is positively related to the risk for stenosis, but the synergistic effect of bends needs to be considered for studying arteries with the serial bends. The research on the synergistic effect may explain why the stenosis is frequently observed in arteries with multiple bends.

Real-time plantar pressure measurement for monitoring exercise load in daily life activities / 医用生物力学

Objective To monitor the exercise load in daily life activities, a reliable method to estimate the real-time plantar pressure based only on a few sensors was presented. Methods Pedar-X pressure insoles were applied to collect plantar pressures from 10 healthy young adults performing 5 typical motions (vertical jump-landing, level walking, level running, stair ascending and stair descending). Stepwise linear regression was performed to reconstruct a mathematic model of calculating the foot force for each style of the motion based on 99 individual pressure data. Then these models were validated by comparing the plantar pressures measured by Pedar-X system and the estimated values by these models when other 4 subjects conducted the same 5 motions and the continuous motion composed of the 5 motions. Results Regardless of the single motion or continuous motion, the foot force calculated by each model for each motion, as well as that calculated by level walking model for each motion were almost the same as the data measured by Pedar-X system. In addition, there was no significant difference between the estimated values by each motion model and level walking model. Conclusions The foot force in daily life activities can be monitored effectively by level walking model with only 5 pressure sensors placed under T1, M2, M3, HM and HL region of the foot.

Correlation study on bone density, microstructure and acoustic parameters of cancellous bone at different stages of decalcification / 医用生物力学

Objective To study changes and correlations in ultrasound acoustic parameters, bone density and microstructure of the cancellous bone at different stages of decalcification. Methods Fifteen defatted porcine cancellous bone specimens were decalcified at different decalcification stages, and the bone density, microstructure and acoustic parameters were measured by Micro CT and ultrasound system, respectively, before and after the decalcification. Correlations between acoustic parameters, bone density and microstructure were investigated. Results With the loss of calcium in bone specimens, BMD (bone mass density), BS/TV and BV/TV decreased continuously. Microstructure parameters SMI and BS/BV increased, while Tb.Th and Tb.N decreased with Tb. Sp increasing. Degree of anisotropy (DA) increased. Acoustic parameter SOS increased at first, and then decreased, with nBUA slightly decreasing. High correlation was found between acoustic parameters, BMD and bone microstructure parameters. Conclusions Ultrasound acoustic parameters are correlated with BMD and bone microstructure. This study may provide some reference information for the early diagnosis of osteoporosis based on ultrasound.

Effects of location training and orientation training on the visual-motor coordination under up-down reversed vision / 医用生物力学

Objective To compare the effects of location and orientation training on the improvement of visual motor coordination under up down reversed vision, provide reference for the preventation of space motion sickness and the design of adaptation training for sensory conflict. Method Sixteen subjects were instructed to complete the maze task wearing the up down reversing prism spectacle before and after the location training and the orientation training. Both trainings lasted 30 minutes respectively. The error rate and the executing time during the maze test were analyzed and compared. Results Both trainings significantly decreased the error rate and the executing time. In addition, the results of different training methods had significant difference, and the effects of the orientation training was better than that of the location training under up-down reversed vision. Conclusions Under the sensory conflict environment arising from the visual change, the adaptation induced by some task training could also be of benefit to some other task training so as to improve the ability of visual-motor coordination and the adaption to the sensory conflict. However, different trainings could have various degrees of improvement.

Chemical constituents from the seeds of Annona squamosa / 药学学报

<p><b>AIM</b>To study the antitumor active constituents of the seeds from Annona squamosa L. (Annonaceae).</p><p><b>METHODS</b>Various chromatographic techniques were used to isolate and purify the constituents. Their physico-chemical properties and spectral data were determined to elucidate the structures.</p><p><b>RESULTS</b>Eleven compounds were isolated and identified as annonaceous acetogenins: squamocenin (1), annotemoyin-2 (2), reticulatain-2 (3), squamocin-I (4), squamocin-B (5), squamocin (6), motrilin (7), squamostatin-D (8), squamostatin-E (9), cherimolin-1 (10), cherimolin-2 (11) from the ethyl alcohol extract of A. squamosa L.</p><p><b>CONCLUSION</b>Squamocenin (1) is a new acetogenin. Annotemoyin-2 (2) and reticulatain-2 (3) were isolated from this plant for the first time.</p>